Switch activities in Android Activities

Switch activities in Android Activities - java

Whenever I try to click on a button and switch activities, it always gives me the error and stays on the same activity without doing anything:
W/EGL_emulation: eglSurfaceAttrib not implemented
W/OpenGLRenderer: Failed to set EGL_SWAP_BEHAVIOR on surface 0xa6d42940, error=EGL_SUCCESS
I thought that it was something in my manifest file, but I can't find anything. I've tried changing many things around and inserting different filters and such and nothing solves this problem.
My code is:
AndroidManifest.xml
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.robertmonks.mytestapp" >
<application
android:allowBackup="true"
android:icon="#mipmap/ic_launcher"
android:label="#string/app_name"
android:supportsRtl="true"
android:theme="#style/AppTheme" >
<activity
android:name="Main_Activity"
android:label="#string/app_name"
android:theme="#style/AppTheme.NoActionBar" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<activity
android:name="Login_Activity"
android:label="#string/title_activity_login_"
android:theme="#style/AppTheme.NoActionBar" >
</activity>
<activity
android:name="Register_Activity"
android:label="#string/title_activity_register_"
android:theme="#style/AppTheme.NoActionBar" >
</activity>
</application>
</manifest>
Main_Activity
package com.example.robertmonks.mytestapp;
import android.app.AlertDialog;
import android.os.Bundle;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.Snackbar;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.View;
import android.app.AlertDialog;
public class Main_Activity extends AppCompatActivity {
android.widget.Button logoutButton;
android.widget.EditText password;
android.widget.EditText username;
#Override
protected void onCreate( Bundle savedInstanceState )
{
super.onCreate(savedInstanceState);
setContentView(R.layout.content_login_);
password = (android.widget.EditText) findViewById( R.id.etPassword );
username = (android.widget.EditText) findViewById( R.id.etEmailAddress );
logoutButton = (android.widget.Button) findViewById( R.id.blogin);
logoutButton.setOnClickListener(new android.widget.Button.OnClickListener() {
#Override
public void onClick(View v) {
if (v.getId() == R.id.blogin) {
logoutButtonClicked();//move action to new method to keep code clean
}
}
});
}
private void logoutButtonClicked()
{
android.content.Intent loginintent = new android.content.Intent(Main_Activity.this, Login_Activity.class);
Main_Activity.this.startActivity(loginintent);
android.util.Log.d("Logout", "Attempted");
}
}
Login_Activity
package com.example.robertmonks.mytestapp;
import android.app.AlertDialog;
import android.os.Bundle;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.Snackbar;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.View;
import android.app.AlertDialog;
public class Login_Activity extends AppCompatActivity {
android.widget.Button loginButton;
android.widget.Button registerButton;
android.widget.EditText password;
android.widget.EditText username;
#Override
protected void onCreate( Bundle savedInstanceState )
{
super.onCreate(savedInstanceState);
setContentView(R.layout.content_login_);
password = (android.widget.EditText) findViewById( R.id.etPassword );
username = (android.widget.EditText) findViewById( R.id.etEmailAddress );
loginButton = (android.widget.Button) findViewById( R.id.blogin);
registerButton = (android.widget.Button) findViewById( R.id.bregister);
loginButton.setOnClickListener(new android.widget.Button.OnClickListener(){
#Override
public void onClick(View v) {
if(v.getId() == R.id.blogin) {
loginButtonClicked();//move action to new method to keep code clean
}
if(v.getId() == R.id.bregister) {
registerButtonClicked();
}
}
});
registerButton.setOnClickListener(new android.widget.Button.OnClickListener(){
#Override
public void onClick(View v) {
if(v.getId() == R.id.bregister) {
registerButtonClicked();
}
}
});
}
private void loginButtonClicked()
{
//startActivity(Main_Activity.class);
android.util.Log.d("Login", "Attempted");
}
private void registerButtonClicked()
{
android.content.Intent registerintent = new android.content.Intent(Login_Activity.this, Register_Activity.class);
Login_Activity.this.startActivity(registerintent);
android.util.Log.d("New User", "Attempted");
}
}
Registration_Activity
package com.example.robertmonks.mytestapp;
import android.os.Bundle;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.Snackbar;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.View;
public class Register_Activity extends AppCompatActivity {
android.widget.Button createAccountButton;
android.widget.Button LoginPageButton;
android.widget.EditText password1;
android.widget.EditText password2;
android.widget.EditText FirstName;
android.widget.EditText LastName;
android.widget.EditText EmailAddress;
#Override
protected void onCreate( Bundle savedInstanceState )
{
super.onCreate(savedInstanceState);
setContentView(R.layout.content_login_);
password1 = (android.widget.EditText) findViewById( R.id.etFirstPassword );
password2 = (android.widget.EditText) findViewById( R.id.etSecondPassword );
FirstName = (android.widget.EditText) findViewById( R.id.etFirstName );
LastName = (android.widget.EditText) findViewById( R.id.etLastName );
createAccountButton = (android.widget.Button) findViewById( R.id.blogin);
LoginPageButton = (android.widget.Button) findViewById( R.id.bregister);
EmailAddress = (android.widget.EditText) findViewById( R.id.etEmailAddress);
createAccountButton.setOnClickListener(new android.widget.Button.OnClickListener(){
#Override
public void onClick(View v) {
if(v.getId() == R.id.blogin) {
createAccountButtonClicked();//move action to new method to keep code clean
}
}
});
LoginPageButton.setOnClickListener(new android.widget.Button.OnClickListener() {
#Override
public void onClick(View v) {
if (v.getId() == R.id.bregister) {
LoginPageButtonClicked();
}
}
});
}
private void createAccountButtonClicked()
{
android.util.Log.d("Create Account", "Attempted");
}
private void LoginPageButtonClicked()
{
android.util.Log.d("Login Page", "Attempted");
android.content.Intent loginintent = new android.content.Intent(this, Login_Activity.class);
startActivity(loginintent);
}
}

For all the buttons, try changing the onclicklistener.
e.g. For the register button,
registerButton.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
// Perform action on click
}
});
I hope this helps. Cheers :)

Your code looks ok... i think problem is your emulator configuration.
only on emulators that have the Use Host GPU setting ticked. Try turning that off, you'll no longer see those warnings (and the emulator will run horribly, horribly slowly..)
Tools > Android > AVD Manager > Edit the virtual device and the Use Host GPU setting is found there.
for more detail.. click

Related

Android Studio App crashes after adding code for Bluetooth Connection

Im currently working at an app for controlling an arduino via bluetooth. I added some Activitys for menus and so on. Yesterday I added a new Activity for connecting my device to the bluetooth module.
Is it even possible to connect to the device in one activity and actually controlling (sending letters) it in another Activity?
With that said the app crashes every time I try to open the activity with the bluetooth code in it. Every other Activity works without any problem.
I hope somebody can help.
Here is my Code:
MainActivity.java (the activity which will control the module):
package com.car.bluetooth.bluetoothcar;
import android.bluetooth.BluetoothAdapter;
import android.content.Intent;
import android.os.Bundle;
import com.google.android.material.floatingactionbutton.FloatingActionButton;
import com.google.android.material.snackbar.Snackbar;
import androidx.appcompat.app.AppCompatActivity;
import androidx.appcompat.widget.Toolbar;
import android.view.View;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.CheckBox;
import android.widget.SeekBar;
import android.widget.TextView;
import android.widget.Toast;
public class MainActivity extends AppCompatActivity {
#Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_main, menu);
return true;
}
#Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
//MENÜPUNKTE
if (id == R.id.action_settings) {
Intent settingsintent = new Intent(MainActivity.this,
settingsactivity.class);
startActivity(settingsintent);
return false;
}
if (id == R.id.action_connect) {
Intent connectintent = new Intent(MainActivity.this,
connectactivity.class);
startActivity(connectintent);
return false;
}
return super.onOptionsItemSelected(item);
}
//SeekBars
private SeekBar seekBarGas;
private TextView textViewGas;
private SeekBar seekBarSteering;
private TextView textViewSteering;
private CheckBox backwards_checkBox;
boolean rückwärts_var = false;
boolean safeMode;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
BluetoothAdapter btAdapter = BluetoothAdapter.getDefaultAdapter();
seekBarGas = (SeekBar) findViewById(R.id.seekBarGas);
textViewGas = (TextView) findViewById(R.id.textViewGas);
seekBarGas.setOnSeekBarChangeListener(new SeekBar.OnSeekBarChangeListener() {
#Override
public void onProgressChanged(SeekBar seekBar, int progress, boolean fromUser) {
textViewGas.setText(progress + " / " + seekBarGas.getMax());
}
#Override
public void onStartTrackingTouch(SeekBar seekBar) {
}
#Override
public void onStopTrackingTouch(SeekBar seekBar) {
seekBarGas.setProgress(0);
}
});
seekBarSteering = (SeekBar) findViewById(R.id.seekBarSteering);
textViewSteering = (TextView) findViewById(R.id.textViewSteering);
seekBarSteering.setOnSeekBarChangeListener(new SeekBar.OnSeekBarChangeListener() {
#Override
public void onProgressChanged(SeekBar seekBar, int progress, boolean fromUser) {
textViewSteering.setText(progress + " / " + seekBarSteering.getMax());
}
#Override
public void onStartTrackingTouch(SeekBar seekBar) {
}
#Override
public void onStopTrackingTouch(SeekBar seekBar) {
seekBarSteering.setProgress(3);
}
});
//GET DATA Settings
Intent safeMode_Intent = getIntent();
safeMode = safeMode_Intent.getBooleanExtra("safeMode", false);
//Rückwärts
CheckBox backwards_checkBox=(CheckBox)findViewById(R.id.backwards_checkBox);
backwards_checkBox.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
// TODO Auto-generated method stub
if (((CheckBox)v).isChecked()) {
Toast.makeText(getApplicationContext(), "Rückwärts", Toast.LENGTH_SHORT).show();
rückwärts_var = true;
if (safeMode == true) {
seekBarGas.setMax(2);
}
}
else{
Toast.makeText(getApplicationContext(), "Vorwärts", Toast.LENGTH_SHORT).show();
rückwärts_var = false;
if (safeMode == true){
seekBarGas.setMax(5);
}
}
}
});
//Bluetooth
if (btAdapter == null){
Toast.makeText(getApplicationContext(), "Bluetooth wird auf diesem Gerät nicht unterstützt", Toast.LENGTH_LONG).show();
}
}
}
BT_Classic.java (the activity which connects to the module) :
package com.car.bluetooth.bluetoothcar;
import androidx.appcompat.app.AppCompatActivity;
import android.bluetooth.BluetoothAdapter;
import android.bluetooth.BluetoothDevice;
import android.content.Intent;
import android.content.IntentFilter;
import android.os.Bundle;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.ListView;
import android.widget.TextView;
import android.widget.Toast;
import java.util.ArrayList;
import java.util.Set;
public class BT_Classic extends AppCompatActivity {
private Button pairedButton;
private Button discoveredButton;
private Button btonButton;
private Button btoffButton;
ListView list;
private static final int REQUEST_ENABLED = 0;
private static final int REQUEST_DISCOVERABLE = 0;
BluetoothAdapter btAdapter = BluetoothAdapter.getDefaultAdapter();
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_bt__classic);
pairedButton = (Button) findViewById(R.id.pairedButton);
discoveredButton = (Button) findViewById(R.id.discoveredButton);
list = (ListView) findViewById(R.id.list) ;
//Pairing Button
pairedButton.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
Set<BluetoothDevice> pairedDevices = btAdapter.getBondedDevices();
ArrayList<String> devices = new ArrayList<String>();
for (BluetoothDevice bt : pairedDevices){
devices.add(bt.getName());
}
ArrayAdapter arrayAdapter = new ArrayAdapter(BT_Classic.this, android.R.layout.simple_list_item_1, devices);
list.setAdapter(arrayAdapter);
}
});
discoveredButton.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
if(!btAdapter.isDiscovering()){
Intent bton = new Intent(BluetoothAdapter.ACTION_REQUEST_DISCOVERABLE);
startActivityForResult(bton, REQUEST_DISCOVERABLE);
}
}
});
btonButton.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
Intent bton = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE);
startActivityForResult(bton, REQUEST_ENABLED);
}
});
btoffButton.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
btAdapter.disable();
}
});
}
}
AndroidManifest.xml
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.car.bluetooth.bluetoothcar">
<uses-feature android:name="android.hardware.bluetooth" />
<uses-permission android:name="android.permission.BLUETOOTH" />
<uses-permission android:name="android.permission.BLUETOOTH_ADMIN" />
<application
android:allowBackup="true"
android:icon="#mipmap/ic_launcher"
android:label="#string/app_name"
android:roundIcon="#mipmap/ic_launcher_round"
android:supportsRtl="true"
android:theme="#style/AppTheme">
<activity
android:name=".MainActivity"
android:label="Bluetooth Car"
android:screenOrientation="landscape"
android:theme="#style/AppTheme.NoActionBar">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<activity
android:name=".connectactivity"
android:label="Connect"
android:screenOrientation="landscape" />
<activity
android:name=".settingsactivity"
android:label="Settings"
android:screenOrientation="landscape" />
<activity
android:name=".BT_LE"
android:label="Connect Bluetooth Low Energy"
android:screenOrientation="landscape"/>
<activity
android:name=".BT_Classic"
android:label="Connect Bluetooth Classic"
android:screenOrientation="landscape"
></activity>
</application>
build.gradle (Module:app) :
apply plugin: 'com.android.application'
android {
compileSdkVersion 28
defaultConfig {
applicationId "com.car.bluetooth.bluetoothcar"
minSdkVersion '16'
targetSdkVersion 28
versionCode 1
versionName "1.0"
testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
}
buildTypes {
release {
minifyEnabled false
proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
}
}
}
dependencies {
implementation fileTree(dir: 'libs', include: ['*.jar'])
implementation 'androidx.appcompat:appcompat:1.0.0-beta01'
implementation 'android.arch.navigation:navigation-fragment:1.0.0-alpha05'
implementation 'android.arch.navigation:navigation-ui:1.0.0-alpha05'
implementation 'androidx.constraintlayout:constraintlayout:1.1.2'
implementation 'com.google.android.material:material:1.0.0-beta01'
testImplementation 'junit:junit:4.12'
androidTestImplementation 'androidx.test:runner:1.1.0-alpha4'
androidTestImplementation 'androidx.test.espresso:espresso-core:3.1.0-alpha4'
}
Crashlog:
2018-09-12 17:25:36.957 10178-10178/com.car.bluetooth.bluetoothcar
E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.car.bluetooth.bluetoothcar, PID: 10178
java.lang.RuntimeException: Unable to start activity
ComponentInfo{com.car.bluetooth.bluetoothcar/com.car.bluetooth.bluetoothcar.BT_Classic}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
at
android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2830)
at
android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2909)
at android.app.ActivityThread.-wrap11(Unknown Source:0)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1606)
at android.os.Handler.dispatchMessage(Handler.java:105)
at android.os.Looper.loop(Looper.java:164)
at android.app.ActivityThread.main(ActivityThread.java:6592)
at java.lang.reflect.Method.invoke(Native Method)
at
com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:769)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
at com.car.bluetooth.bluetoothcar.BT_Classic.onCreate(BT_Classic.java:78)
at android.app.Activity.performCreate(Activity.java:6984)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1235)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2783)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2909) 
at android.app.ActivityThread.-wrap11(Unknown Source:0) 
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1606) 
at android.os.Handler.dispatchMessage(Handler.java:105) 
at android.os.Looper.loop(Looper.java:164) 
at android.app.ActivityThread.main(ActivityThread.java:6592) 
at java.lang.reflect.Method.invoke(Native Method) 
at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:769)

btonButton and btoffButton are not initialized and equals null.
You should initialize them with findViewById() like you do with pairedButton
btonButton = (Button) findViewById(R.id.put_here_btn_on_id);
btoffButton = (Button) findViewById(R.id.put_here_btn_off_id);

btonButton and btoffButton have not been initialised yet and then you are calling setonClickListener this causes NPE
Inside onCreate initialise like this:
btonButton = (Button) findViewById(R.id.btonButton);
btoffButton = (Button) findViewById(R.id.btoffButton);

Repetadly getting same bug

I've almost built one chat app with the login functionality using Firebase. But when I clear/delete all users from Firebase, uninstall app from my device and run the app from fresh and when it install and open app, it directly login it means it redirect to MainActivty instead of StartActivity where user can login or signup. I also faced this problem before and somehow I solved it, but again I improve the project, made some other classes and now again I'm facing the same problem.
Note:
When this things happens (automatically login), in my firebase database, it creates one ID automatically in under "Users" section. Actually it should happen only when user Singup.
I implemented the Facebook login button just before an hour, but this is not the issue, I'm sure about that, so please ignore Facebook login related stuff, this issue is getting before I implemented Facebook login button.
I tell you my app structure flow: When user first time install the app, it must redirect to StartActivity. If user already installed the app and login already, but not logout and simply closes the app and again open, it can login directly, it means it will redirect to MainActivity, no need to enter thr crendetials again.
Basically, my launcher activity is MainActivity, so if new user installed the app, it redirects from MainActivity to StartActivity (which is for login/singup).
LapitChat is a application class.
I'm attaching MainActivity.java, StartActivity.java, LapitChat.java, and AndroidManifest.xml
MainActivity.java
package com.jimmytrivedi.lapitchat;
import android.content.Intent;
import android.os.Bundle;
import android.support.design.widget.TabLayout;
import android.support.v4.view.ViewPager;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.Menu;
import android.view.MenuItem;
import com.facebook.login.LoginManager;
import com.google.firebase.auth.FirebaseAuth;
import com.google.firebase.auth.FirebaseUser;
import com.google.firebase.database.DatabaseReference;
import com.google.firebase.database.FirebaseDatabase;
import com.google.firebase.database.ServerValue;
public class MainActivity extends AppCompatActivity {
private FirebaseAuth mAuth;
private FirebaseUser currentUser;
private Toolbar toolbar;
private ViewPager viewPager;
private SectionsPagerAdapter sectionsPagerAdapter;
private TabLayout tabLayout;
private DatabaseReference UserDatabaseReference;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mAuth = FirebaseAuth.getInstance();
currentUser = mAuth.getCurrentUser();
if (currentUser == null) {
sendTostart();
} else {
UserDatabaseReference = FirebaseDatabase.getInstance().getReference().child("Users").child(mAuth.getCurrentUser().getUid());
UserDatabaseReference.child("Online").setValue("true");
}
viewPager = findViewById(R.id.viewPager);
sectionsPagerAdapter = new SectionsPagerAdapter(getSupportFragmentManager());
viewPager.setAdapter(sectionsPagerAdapter);
toolbar = findViewById(R.id.mainToolbar);
setSupportActionBar(toolbar);
getSupportActionBar().setTitle("Home");
tabLayout = findViewById(R.id.tabLayout);
tabLayout.setupWithViewPager(viewPager);
}
#Override
protected void onPause() {
super.onPause();
if (currentUser != null) {
UserDatabaseReference.child("Online").setValue(ServerValue.TIMESTAMP);
}
}
private void sendTostart() {
startActivity(new Intent(MainActivity.this, StartActivity.class));
finish();
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
super.onCreateOptionsMenu(menu);
getMenuInflater().inflate(R.menu.main_menu, menu);
return true;
}
#Override
public boolean onOptionsItemSelected(MenuItem item) {
super.onOptionsItemSelected(item);
if (item.getItemId() == R.id.logout) {
FirebaseAuth.getInstance().signOut();
LoginManager.getInstance().logOut();
sendTostart();
}
if (item.getItemId() == R.id.settings) {
startActivity(new Intent(MainActivity.this, SettingsActivity.class));
}
if (item.getItemId() == R.id.allUsers) {
startActivity(new Intent(MainActivity.this, UsersActivity.class));
}
return true;
}
}
StartActivity.java
package com.jimmytrivedi.lapitchat;
import android.content.Intent;
import android.os.Bundle;
import android.support.annotation.NonNull;
import android.support.v7.app.AppCompatActivity;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.Toast;
import com.facebook.AccessToken;
import com.facebook.CallbackManager;
import com.facebook.FacebookCallback;
import com.facebook.FacebookException;
import com.facebook.login.LoginResult;
import com.facebook.login.widget.LoginButton;
import com.google.android.gms.tasks.OnCompleteListener;
import com.google.android.gms.tasks.Task;
import com.google.firebase.auth.AuthCredential;
import com.google.firebase.auth.AuthResult;
import com.google.firebase.auth.FacebookAuthProvider;
import com.google.firebase.auth.FirebaseAuth;
import com.google.firebase.auth.FirebaseUser;
public class StartActivity extends AppCompatActivity {
private Button signup, exist;
private CallbackManager mCallbackManager;
private FirebaseAuth mAuth;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_start);
mAuth = FirebaseAuth.getInstance();
signup = findViewById(R.id.signup);
exist = findViewById(R.id.exist);
signup.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
startActivity(new Intent(StartActivity.this, RegisterActivity.class));
}
});
exist.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
startActivity(new Intent(StartActivity.this, LoginActivity.class));
}
});
// Initialize Facebook Login button
mCallbackManager = CallbackManager.Factory.create();
LoginButton loginButton = findViewById(R.id.login_button);
loginButton.setReadPermissions("email", "public_profile");
loginButton.registerCallback(mCallbackManager, new FacebookCallback<LoginResult>() {
#Override
public void onSuccess(LoginResult loginResult) {
Log.d("wihddiewd", "facebook:onSuccess:" + loginResult);
handleFacebookAccessToken(loginResult.getAccessToken());
}
#Override
public void onCancel() {
Log.d("wihddiewd", "facebook:onCancel");
}
#Override
public void onError(FacebookException error) {
Log.d("wihddiewd", "facebook:onError", error);
}
});
}
#Override
public void onStart() {
super.onStart();
FirebaseUser currentUser = mAuth.getCurrentUser();
if (currentUser != null) {
updateUI();
}
}
private void updateUI() {
startActivity(new Intent(StartActivity.this, MainActivity.class));
}
#Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
super.onActivityResult(requestCode, resultCode, data);
// Pass the activity result back to the Facebook SDK
mCallbackManager.onActivityResult(requestCode, resultCode, data);
}
private void handleFacebookAccessToken(AccessToken token) {
Log.d("wihddiewd", "handleFacebookAccessToken:" + token);
AuthCredential credential = FacebookAuthProvider.getCredential(token.getToken());
mAuth.signInWithCredential(credential)
.addOnCompleteListener(this, new OnCompleteListener<AuthResult>() {
#Override
public void onComplete(#NonNull Task<AuthResult> task) {
if (task.isSuccessful()) {
Log.d("wihddiewd", "signInWithCredential:success");
FirebaseUser user = mAuth.getCurrentUser();
updateUI();
} else {
Log.w("wihddiewd", "signInWithCredential:failure", task.getException());
Toast.makeText(StartActivity.this, "Authentication failed.",
Toast.LENGTH_SHORT).show();
}
}
});
}
}
LapitChat.java
package com.jimmytrivedi.lapitchat;
import android.app.Application;
import android.support.annotation.NonNull;
import com.google.firebase.auth.FirebaseAuth;
import com.google.firebase.database.DataSnapshot;
import com.google.firebase.database.DatabaseError;
import com.google.firebase.database.DatabaseReference;
import com.google.firebase.database.FirebaseDatabase;
import com.google.firebase.database.ServerValue;
import com.google.firebase.database.ValueEventListener;
import com.squareup.picasso.OkHttp3Downloader;
import com.squareup.picasso.Picasso;
public class LapitChat extends Application {
private DatabaseReference UserDatabaseReference;
private FirebaseAuth mAuth;
#Override
public void onCreate() {
super.onCreate();
FirebaseDatabase.getInstance().setPersistenceEnabled(true);
Picasso.Builder builder = new Picasso.Builder(this);
builder.downloader(new OkHttp3Downloader(this, Integer.MAX_VALUE));
Picasso built = builder.build();
built.setIndicatorsEnabled(true);
built.setLoggingEnabled(true);
Picasso.setSingletonInstance(built);
mAuth = FirebaseAuth.getInstance();
if (mAuth.getCurrentUser() != null) {
UserDatabaseReference = FirebaseDatabase.getInstance().getReference().child("Users").child(mAuth.getCurrentUser().getUid());
UserDatabaseReference.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(#NonNull DataSnapshot dataSnapshot) {
if (dataSnapshot != null) {
UserDatabaseReference.child("Online").onDisconnect().setValue(ServerValue.TIMESTAMP);
}
}
#Override
public void onCancelled(#NonNull DatabaseError databaseError) {
}
});
}
}
}
AndroidManifest.xml
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.jimmytrivedi.lapitchat">
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
<uses-permission android:name="android.permission.INTERNET" />
<application
android:name=".LapitChat"
android:allowBackup="true"
android:icon="#mipmap/ic_launcher"
android:label="#string/app_name"
android:roundIcon="#mipmap/ic_launcher_round"
android:supportsRtl="true"
android:theme="#style/AppTheme">
<service android:name=".FirebaseMessagingService">
<intent-filter>
<action android:name="com.google.firebase.MESSAGING_EVENT" />
</intent-filter>
</service>
<activity android:name=".MainActivity">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<activity android:name=".StartActivity" />
<activity
android:name=".RegisterActivity"
android:parentActivityName=".StartActivity" />
<activity
android:name=".LoginActivity"
android:parentActivityName=".StartActivity" />
<activity
android:name=".SettingsActivity"
android:parentActivityName=".MainActivity" />
<activity
android:name=".StatusActivity"
android:parentActivityName=".SettingsActivity" />
<activity
android:name="com.theartofdev.edmodo.cropper.CropImageActivity"
android:theme="#style/Base.Theme.AppCompat" /> <!-- optional (needed if default theme has no action bar) -->
<activity
android:name=".UsersActivity"
android:parentActivityName=".MainActivity" />
<activity android:name=".ProfileActivity">
<intent-filter>
<action android:name="com.jimmytrivedi.lapitchat_TARGET_NOTIFICATION" />
<category android:name="android.intent.category.DEFAULT" />
</intent-filter>
</activity>
<activity
android:name=".ChatActivity"
android:parentActivityName=".MainActivity" />
<meta-data android:name="com.facebook.sdk.ApplicationId"
android:value="#string/facebook_app_id"/>
<activity android:name="com.facebook.FacebookActivity"
android:configChanges=
"keyboard|keyboardHidden|screenLayout|screenSize|orientation"
android:label="#string/app_name" />
<activity
android:name="com.facebook.CustomTabActivity"
android:exported="true">
<intent-filter>
<action android:name="android.intent.action.VIEW" />
<category android:name="android.intent.category.DEFAULT" />
<category android:name="android.intent.category.BROWSABLE" />
<data android:scheme="#string/fb_login_protocol_scheme" />
</intent-filter>
</activity>
</application>
</manifest>
Thanks for reading and waiting for your help. Thank you so much!

This is happening because from Android 6.0 (API level 23) the automatic backup is set by default to true. So to solve this, you need to add the following lines of code, in your AndroidManifest.xml file:
android:allowBackup="false"
android:fullBackupContent="false"
See here more informations.

avoid of send null from destroyed activity to restarted service

I want to programing app for data track in background , so I use service .
I want to write a program that monitors all data sent and received by the device, and when the total volume of received or received messages reaches a specified value, the Internet device is turned off.
So I used the following code to monitor the data:
 
mStartRX = TrafficStats.getTotalRxBytes ();
mStartTX = TrafficStats.getTotalTxBytes ();
And I used the services to work on the background in the background.
To specify the download or upload limit from the user with edittext, I requested this limit in mainactivity and send this value to the service.
The problem is when: When I destroy the program, I will restart the service and get the NULL value and the program crashes.
My application code:
Main Activity :
package ir.alexandre9009.service;
import android.app.AlertDialog;
import android.content.Context;
import android.net.TrafficStats;
import android.os.Bundle;
import android.app.Activity;
import android.content.Intent;
import android.os.Handler;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
public class MainActivity extends Activity {
public static Handler mHandler = new Handler();
public static long UPP;
public static long DLL;
Button startService,stopService;
public Context context=this;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
if (FirstService.mStartRX == TrafficStats.UNSUPPORTED || FirstService.mStartTX == TrafficStats.UNSUPPORTED) {
AlertDialog.Builder alert = new AlertDialog.Builder(this);
alert.setTitle("Uh Oh!");
alert.setMessage("Your device does not support traffic stat monitoring.");
alert.show();
} else {
mHandler.postDelayed(mRunnable, 1000);
}
startService=(Button)findViewById(R.id.startService);
stopService=(Button)findViewById(R.id.stopService);
startService.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
EditText UP = (EditText) findViewById(R.id.UP);
String UPPP = UP.getText().toString();
UPP=Long.parseLong(UPPP);
EditText DL = (EditText) findViewById(R.id.DL);
String DLLL = DL.getText().toString();
DLL=Long.parseLong(DLLL);
Intent intent = new Intent(getApplicationContext(), FirstService.class);
String myString = DLLL;
intent.putExtra("StringName", myString);
startService(intent);
}
});
stopService.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
stopService(new Intent(getBaseContext(),FirstService.class));
}
});
}
public final Runnable mRunnable = new Runnable() {
public void run() {
TextView RX = (TextView)findViewById(R.id.RX);
TextView TX = (TextView)findViewById(R.id.TX);
RX.setText(Long.toString(FirstService.rxBytes));
TX.setText(Long.toString(FirstService.txBytes));
mHandler.postDelayed(mRunnable, 1000);
}
};
}
Service :
package ir.alexandre9009.service;
import android.app.AlertDialog;
import android.app.Service;
import android.content.Context;
import android.content.Intent;
import android.net.TrafficStats;
import android.net.wifi.WifiManager;
import android.os.Handler;
import android.os.IBinder;
import android.widget.TextView;
import android.widget.Toast;
public class FirstService extends Service{
public static long mStartRX ;
public static long mStartTX ;
public static long rxBytes ;
public static long txBytes ;
public long dl=MainActivity.DLL;
Context context=this;
private final Runnable mRunnable = new Runnable() {
public void run() {
rxBytes = (TrafficStats.getTotalRxBytes()- mStartRX)/1048576;
txBytes = (TrafficStats.getTotalTxBytes()- mStartTX)/1048576;
if (rxBytes==2) {
stopService(new Intent(getBaseContext(),FirstService.class));
Intent i = new Intent(context,MainActivity.class);
context.startActivity(i);
// WifiManager wifiManager = (WifiManager)getApplicationContext().getSystemService(Context.WIFI_SERVICE);
// wifiManager.setWifiEnabled(false);
//معرفی توست برای نمایش یک پیام کوتاه به کاربر در هنگام خاموش کردن وای فای
Toast.makeText(FirstService.this, "هشدار", Toast.LENGTH_LONG).show();
}
mHandler.postDelayed(mRunnable, 1000);
}
};
private Handler mHandler = new Handler();
#Override
public IBinder onBind(Intent arg0) {
return null;
}
#Override
public int onStartCommand(Intent intent, int flags, int startId) {
Toast.makeText(this,"staart",Toast.LENGTH_LONG).show();
mStartTX=0;
mStartRX=0;
mStartRX = TrafficStats.getTotalRxBytes();
mStartTX = TrafficStats.getTotalTxBytes();
mHandler.postDelayed(mRunnable, 1000);
return Service.START_STICKY;
}
#Override
public void onDestroy() {
TrafficStats.clearThreadStatsTag();
Toast.makeText(this,"FirstService Stoped",Toast.LENGTH_LONG).show();
mStartTX=0;
mStartRX=0;
super.onDestroy();
}
}
AndroidManifest :
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="ir.alexandre9009.service">
<uses-permission android:name="android.permission.ACCESS_WIFI_STATE" />
<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.CHANGE_WIFI_STATE"/>
<uses-permission android:name="android.permission.UPDATE_DEVICE_STATS" />
<uses-permission android:name="android.permission.WAKE_LOCK" />
<application
android:allowBackup="true"
android:icon="#mipmap/ic_launcher"
android:label="#string/app_name"
android:roundIcon="#mipmap/ic_launcher_round"
android:supportsRtl="true"
android:theme="#style/AppTheme">
<activity android:name=".MainActivity">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<service android:name=".FirstService"
>
</service>
</application>
</manifest>
please help me ...

The problem is with this line
public long dl=MainActivity.DLL;
You're referring to a variable in the Activity, surly when the Activity is destroyed, this variable is no longer in scope, thus you get Null Exception.
You must get this value using the intent.
The other problem is that you can't prevent any service from being killed by the system except foreground services which need to show a notification to the user. But this is not suitable for your situation.
Therefore, the best approach for you is to check whether intent is null or not. If it is not null, you get the value and save it into Preferences or Database or somewhere, if it is null, you retrieve the value from where you stored it before.

Android Studio app crashes

I have a problem with my application I am making on Android Studio. I don't know why, but after the splash screen, the application crashes. I want the activity "Accueil" to open after the splash screen. It worked fine last week and now it doesn't anymore. I didn't touch anything. I show you the manifest, and the .java files.
Splashscreen.java:
import android.app.Activity;
import android.content.Intent;
import android.graphics.PixelFormat;
import android.os.Bundle;
import android.view.Window;
import android.view.animation.Animation;
import android.view.animation.AnimationUtils;
import android.widget.ImageView;
import android.widget.LinearLayout;
public class Splashscreen extends Activity {
public void onAttachedToWindow() {
super.onAttachedToWindow();
Window window = getWindow();
window.setFormat(PixelFormat.RGBA_8888);
}
Thread splashTread;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_splashscreen);
StartAnimations();
Thread loading = new Thread() {
public void run() {
try {
sleep(5000);
Intent main = new Intent(Splashscreen.this,Menu.class);
startActivity(main);
finish();
} catch (Exception e) {
e.printStackTrace();
} finally {
finish();
}
}
};
loading.start();
}
private void StartAnimations() {
Animation anim = AnimationUtils.loadAnimation(this, R.anim.alpha);
anim.reset();
LinearLayout l = (LinearLayout) findViewById(R.id.lin_lay);
l.clearAnimation();
l.startAnimation(anim);
anim = AnimationUtils.loadAnimation(this, R.anim.rotate);
anim.reset();
ImageView iv = (ImageView) findViewById(R.id.splash);
iv.clearAnimation();
iv.startAnimation(anim);
splashTread = new Thread() {
#Override
public void run() {
try {
int waited = 0;
while (waited < 3500) {
sleep(100);
waited += 100;
}
Intent intent = new Intent(Splashscreen.this,Menu.class);
startActivity(intent);
finish();
} catch (InterruptedException e) {
}
}
};
}
}
Android Manifest:
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.thibaudmangeot.erdfapplicationsecurite">
<application
android:allowBackup="true"
android:icon="#mipmap/ic_launcher"
android:label="#string/app_name"
android:theme="#style/AppTheme">
<activity android:name=".Splashscreen"
android:label="#string/app_name">
<intent-filter>
<action android:name="android.intent.action.MAIN"/>
<category android:name="android.intent.category.LAUNCHER"/>
</intent-filter>
</activity>
<activity android:name=".Accueil"
android:label="#string/title_activity_accueil"/>
</application>
</manifest>
Accueil.java:
package com.example.thibaudmangeot.erdfapplicationsecurite;
import android.content.Intent;
import android.os.Bundle;
import android.support.v7.app.ActionBarActivity;
import android.widget.Button;
import android.view.View;
public class Accueil extends ActionBarActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_accueil);
Button buttonfis = (Button) findViewById(R.id.buttonfis);
buttonfis.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
goTosignin();
}
});
}
private void goTosignin() {
Intent intent = new Intent(this, Menu.class);
startActivity(intent);
}
}

Do this
Intent main = new Intent(Splashscreen.this, Accueil.class);
startActivity(main);
finish();
Instead of
Intent main = new Intent(Splashscreen.this, Menu.class);
startActivity(main);
finish();
You have not even mentioned Menu activity in your manifest.

This is your error:
Intent main = new Intent(Splashscreen.this,Menu.class);
it should be:
Intent main = new Intent(Splashscreen.this, Accueil.class);

I think your application is crashing maybe because of two reasons
There is no Activity named "Menu"
Menu Activity is not mentioned in manifest file
If you want to open "Accueil" activity then write your intent in following fashion.
Intent openAccueil = new Intent(Splashscreen.this,Menu.class);
startActivity(openAccueil);

Android Could execute method of the activity

I'm building a simple paint app and encountering this error given by the logcat:
I'm using the following code:
This SaveDrawing.java serves as the main activity
package com.example.SaveDrawing;
import com.example.SaveDrawing.drawings.DrawingActivity;
import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
public class SaveDrawing extends Activity {
/** Called when the activity is first created. */
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
}
public void onClick(View view){
switch (view.getId()){
case R.id.drawBtn:
//Intent drawIntent = new Intent(this, DrawingActivity.class);
//startActivity( drawIntent);
//Toast.makeText(getBaseContext(), "This is the Toast message", Toast.LENGTH_SHORT).show();
Intent nextActivity = new Intent(SaveDrawing.this, DrawingActivity.class);
startActivity(nextActivity);
break;
}
}
}
Then the next activity after clicking the button is DrawingActivity.java
package com.example.SaveDrawing.drawings;
import android.app.Activity;
import android.app.AlertDialog;
import android.content.Context;
import android.content.DialogInterface;
import android.content.Intent;
import android.graphics.Bitmap;
import android.graphics.Paint;
import android.graphics.Path;
import android.os.AsyncTask;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.view.MotionEvent;
import android.view.View;
import android.widget.Button;
import java.io.File;
import java.io.FileOutputStream;
import com.example.SaveDrawing.R;
import com.example.SaveDrawing.R.id;
import com.example.SaveDrawing.R.layout;
public class DrawingActivity extends Activity implements View.OnTouchListener{
private DrawingSurface drawingSurface;
private DrawingPath currentDrawingPath;
private Paint currentPaint;
private Button redoBtn;
private Button undoBtn;
private static File APP_FILE_PATH = new File("/sdcard/TutorialForAndroidDrawings");
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.drawing_activity);
setCurrentPaint();
drawingSurface = (DrawingSurface) findViewById(R.id.drawingSurface);
drawingSurface.setOnTouchListener(this);
redoBtn = (Button) findViewById(R.id.redoBtn);
undoBtn = (Button) findViewById(R.id.undoBtn);
redoBtn.setEnabled(false);
undoBtn.setEnabled(false);
}
private void setCurrentPaint(){
currentPaint = new Paint();
currentPaint.setDither(true);
currentPaint.setColor(0xFFFFFF00);
currentPaint.setStyle(Paint.Style.STROKE);
currentPaint.setStrokeJoin(Paint.Join.ROUND);
currentPaint.setStrokeCap(Paint.Cap.ROUND);
currentPaint.setStrokeWidth(3);
}
public boolean onTouch(View view, MotionEvent motionEvent) {
if(motionEvent.getAction() == MotionEvent.ACTION_DOWN){
currentDrawingPath = new DrawingPath();
currentDrawingPath.paint = currentPaint;
currentDrawingPath.path = new Path();
currentDrawingPath.path.moveTo(motionEvent.getX(), motionEvent.getY());
currentDrawingPath.path.lineTo(motionEvent.getX(), motionEvent.getY());
}else if(motionEvent.getAction() == MotionEvent.ACTION_MOVE){
currentDrawingPath.path.lineTo(motionEvent.getX(), motionEvent.getY());
}else if(motionEvent.getAction() == MotionEvent.ACTION_UP){
currentDrawingPath.path.lineTo(motionEvent.getX(), motionEvent.getY());
drawingSurface.addDrawingPath(currentDrawingPath);
undoBtn.setEnabled(true);
redoBtn.setEnabled(false);
}
return true;
}
public void onClick(View view){
switch (view.getId()){
case R.id.colorRedBtn:
currentPaint = new Paint();
currentPaint.setDither(true);
currentPaint.setColor(0xFFFF0000);
currentPaint.setStyle(Paint.Style.STROKE);
currentPaint.setStrokeJoin(Paint.Join.ROUND);
currentPaint.setStrokeCap(Paint.Cap.ROUND);
currentPaint.setStrokeWidth(3);
break;
case R.id.colorBlueBtn:
currentPaint = new Paint();
currentPaint.setDither(true);
currentPaint.setColor(0xFF00FF00);
currentPaint.setStyle(Paint.Style.STROKE);
currentPaint.setStrokeJoin(Paint.Join.ROUND);
currentPaint.setStrokeCap(Paint.Cap.ROUND);
currentPaint.setStrokeWidth(3);
break;
case R.id.colorGreenBtn:
currentPaint = new Paint();
currentPaint.setDither(true);
currentPaint.setColor(0xFF0000FF);
currentPaint.setStyle(Paint.Style.STROKE);
currentPaint.setStrokeJoin(Paint.Join.ROUND);
currentPaint.setStrokeCap(Paint.Cap.ROUND);
currentPaint.setStrokeWidth(3);
break;
case R.id.undoBtn:
drawingSurface.undo();
if( drawingSurface.hasMoreUndo() == false ){
undoBtn.setEnabled( false );
}
redoBtn.setEnabled( true );
break;
case R.id.redoBtn:
drawingSurface.redo();
if( drawingSurface.hasMoreRedo() == false ){
redoBtn.setEnabled( false );
}
undoBtn.setEnabled( true );
break;
case R.id.saveBtn:
final Activity currentActivity = this;
Handler saveHandler = new Handler(){
#Override
public void handleMessage(Message msg) {
final AlertDialog alertDialog = new AlertDialog.Builder(currentActivity).create();
alertDialog.setTitle("Saved 1");
alertDialog.setMessage("Your drawing had been saved :)");
alertDialog.setButton("OK", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int which) {
return;
}
});
alertDialog.show();
}
} ;
new ExportBitmapToFile(this,saveHandler, drawingSurface.getBitmap()).execute();
break;
}
}
private class ExportBitmapToFile extends AsyncTask<Intent,Void,Boolean> {
private Context mContext;
private Handler mHandler;
private Bitmap nBitmap;
public ExportBitmapToFile(Context context,Handler handler,Bitmap bitmap) {
mContext = context;
nBitmap = bitmap;
mHandler = handler;
}
#Override
protected Boolean doInBackground(Intent... arg0) {
try {
if (!APP_FILE_PATH.exists()) {
APP_FILE_PATH.mkdirs();
}
final FileOutputStream out = new FileOutputStream(new File(APP_FILE_PATH + "/myAwesomeDrawing.png"));
nBitmap.compress(Bitmap.CompressFormat.PNG, 90, out);
out.flush();
out.close();
return true;
}catch (Exception e) {
e.printStackTrace();
}
//mHandler.post(completeRunnable);
return false;
}
#Override
protected void onPostExecute(Boolean bool) {
super.onPostExecute(bool);
if ( bool ){
mHandler.sendEmptyMessage(1);
}
}
}
}
AndroidManifest.xml
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.SaveDrawing"
android:versionCode="1"
android:versionName="1.0">
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
<uses-sdk android:minSdkVersion="8" />
<application android:icon="#drawable/icon" android:label="#string/app_name">
<activity android:name=".SaveDrawing"
android:label="#string/app_name">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<activity android:name=".DrawingActivity" android:screenOrientation="landscape" ></activity>
<activity android:name=".drawings.DrawingActivity"/>
</application>
</manifest>
I have the following in my explorer. I'm not so sure if I got a wrong file structure.
Anyone can help me? I'm kinda new to java and android programming. Many thanks!!! :)

remove <activity android:name=".DrawingActivity" android:screenOrientation="landscape" ></activity> from your manifest as there is no such activity. there is only DrawingActivity in your project structure. Then clean build Run.
Also another possible problem could having an Activity Class name SaveDrawing in the package. You should try to rename the package, update relevant changes to the manifest and try running the app again..

You probably forgot to declare DrawingActivity in your manifest.xml

This is because you attempt to launch com.example.SaveDrawing.drawings/com.example.SaveDrawing.drawings.DrawingActivity,
but actual activity you launch in code is com.example.SaveDrawing/com.example.SaveDrawing.drawings.DrawingActivity
Please change
Intent nextActivity = new Intent(SaveDrawing.this, DrawingActivity.class);
to
Intent nextActivity = new Intent();
nextActivity.setClassName ("com.example.SaveDrawing.drawings", "com.example.SaveDrawing.drawings.DrawingActivity");
It might work.

We Keep Coding

Java is a programming language and computing platform first released by Sun Microsystems in 1995.

Switch activities in Android Activities - java

For all the buttons, try changing the onclicklistener. e.g. For the register button, registerButton.setOnClickListener(new View.OnClickListener() { public void onClick(View v) { // Perform action on click } }); I hope this helps. Cheers :)

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avoid of send null from destroyed activity to restarted service

Android Studio app crashes

Android Could execute method of the activity

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