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Google signin in android app

I'm a newbie in programming, trying to implement a Google Signin in my test app.
Folowing Google API documentation I've added all required dependencies at gradle files and registered my test app through OAuth...
Further I wrote a code as described in example provided by Google, but my app crashes at the begining, before any user's action in Virtual device, and does not even set up via APK file at the real device....
What am i doing wrong?
Main (single) activity code:
package ru.podgorny.carcall;
import android.accounts.Account;
import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.TextView;
import com.google.android.gms.auth.api.signin.GoogleSignIn;
import com.google.android.gms.auth.api.signin.GoogleSignInAccount;
import com.google.android.gms.auth.api.signin.GoogleSignInClient;
import com.google.android.gms.auth.api.signin.GoogleSignInOptions;
import com.google.android.gms.common.SignInButton;
import com.google.android.gms.common.api.ApiException;
import com.google.android.gms.tasks.Task;
public class MainActivity extends AppCompatActivity {
SignInButton signInButton;
public static final int RC_SIGN_IN = 07;
public static final String TAG = "MainActivity";
TextView tw1;
TextView tw2;
GoogleSignInOptions gso = new GoogleSignInOptions.Builder(GoogleSignInOptions.DEFAULT_SIGN_IN)
.requestEmail()
.requestProfile()
.build();
GoogleSignInClient mGSC = GoogleSignIn.getClient(this, gso);
#Override
protected void onCreate (Bundle savedInstanceState){
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
findViews();
}
private void findViews() {
signInButton = findViewById(R.id.idButtonGoogle);
tw1 = findViewById(R.id.textView1);
tw1 = findViewById(R.id.textView2);
}
public void onClick(View v) {
switch (v.getId()) {
case R.id.idButtonGoogle:
signIn();
break;
}
}
private void signIn() {
Intent signInIntent = mGSC.getSignInIntent();
startActivityForResult(signInIntent, RC_SIGN_IN);
}
#Override
public void onActivityResult(int requestCode, int resultCode, Intent data) {
super.onActivityResult(requestCode, resultCode, data);
// Result returned from launching the Intent from GoogleSignInClient.getSignInIntent(...);
if (requestCode == RC_SIGN_IN) {
// The Task returned from this call is always completed, no need to attach
// a listener.
Task<GoogleSignInAccount> task = GoogleSignIn.getSignedInAccountFromIntent(data);
handleSignInResult(task);
}
}
private void handleSignInResult(Task<GoogleSignInAccount> completedTask) {
try {
GoogleSignInAccount account = completedTask.getResult(ApiException.class);
updateUI(account);
} catch (ApiException e) {
Log.w(TAG, "signInResult:failed code=" + e.getStatusCode());
updateUI(null);
}
}
private void updateUI(GoogleSignInAccount account) {
tw1.setText("OK");
tw2.setText("Name: " + account.getGivenName() + ", Family name: " + account.getFamilyName() + ", Email: " + account.getEmail() + " image: " +
account.getPhotoUrl());
}
}
Activity.xml code:
<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="ru.podgorny.carcall.MainActivity"
>
<com.google.android.gms.common.SignInButton
android:id="#+id/idButtonGoogle"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:foregroundGravity="top"
android:onClick="onClick"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintTop_toTopOf="parent" />
<TextView
android:id="#+id/textView1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginTop="8dp"
android:text="TextView"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintTop_toBottomOf="#+id/idButtonGoogle" />
<TextView
android:id="#+id/textView2"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginTop="8dp"
android:text="TextView"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintTop_toBottomOf="#+id/textView1" />
</android.support.constraint.ConstraintLayout>
Manifest.xml by default:
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="ru.podgorny.carcall">
<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>
</application>
</manifest>
Console logs :
03-23 08:35:32.774 5682-5682/? E/libprocessgroup: failed to make and chown /acct/uid_10060: Read-only file system
03-23 08:35:32.774 5682-5682/? W/Zygote: createProcessGroup failed, kernel missing CONFIG_CGROUP_CPUACCT?
03-23 08:35:32.775 5682-5682/? I/art: Not late-enabling -Xcheck:jni (already on)
03-23 08:35:33.180 5682-5682/ru.podgorny.carcall I/InstantRun: starting instant run server: is main process
03-23 08:35:33.746 5682-5682/ru.podgorny.carcall D/AndroidRuntime: Shutting down VM
03-23 08:35:33.753 5682-5682/ru.podgorny.carcall E/AndroidRuntime: FATAL EXCEPTION: main
Process: ru.podgorny.carcall, PID: 5682
java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{ru.podgorny.carcall/ru.podgorny.carcall.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.os.Looper android.content.Context.getMainLooper()' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2236)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2387)
at android.app.ActivityThread.access$800(ActivityThread.java:151)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1303)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5254)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.os.Looper android.content.Context.getMainLooper()' on a null object reference
at android.content.ContextWrapper.getMainLooper(ContextWrapper.java:101)
at com.google.android.gms.common.api.GoogleApi.<init>(Unknown Source)
at com.google.android.gms.auth.api.signin.GoogleSignInClient.<init>(Unknown Source)
at com.google.android.gms.auth.api.signin.GoogleSignIn.getClient(Unknown Source)
at ru.podgorny.carcall.MainActivity.<init>(MainActivity.java:35)
at java.lang.reflect.Constructor.newInstance(Native Method)
at java.lang.Class.newInstance(Class.java:1606)
at android.app.Instrumentation.newActivity(Instrumentation.java:1066)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2226)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2387) 
at android.app.ActivityThread.access$800(ActivityThread.java:151) 
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1303) 
at android.os.Handler.dispatchMessage(Handler.java:102) 
at android.os.Looper.loop(Looper.java:135) 
at android.app.ActivityThread.main(ActivityThread.java:5254) 
at java.lang.reflect.Method.invoke(Native Method) 
at java.lang.reflect.Method.invoke(Method.java:372) 
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698) 
03-23 08:35:33.827 5682-5695/ru.podgorny.carcall I/art: Background sticky concurrent mark sweep GC freed 2567(255KB) AllocSpace objects, 0(0B) LOS objects, 30% free, 773KB/1117KB, paused 18.376ms total 73.744ms

Try this
GoogleSignInOptions gso ;
GoogleSignInClient mGSC ;
#Override
protected void onCreate (Bundle savedInstanceState){
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
gso = new GoogleSignInOptions.Builder(GoogleSignInOptions.DEFAULT_SIGN_IN)
.requestEmail()
.requestProfile()
.build();
mGSC = GoogleSignIn.getClient(this, gso);
findViews();
}

this android app works in API 22 emulator not but in API 16 emulator

I am a newbie to android development. I am making a simple app to open camera in sufaceView. I want to work this app from the android API level 16. I have written some code and that works in API level 22 emulator but not in API level 16 emulator (When I click on Start button, app crashes)
VideoServer.java
package com.example.admin2.cameraonsurfaceview;
import android.app.Activity;
import android.hardware.Camera;
import android.os.Bundle;
import android.util.Log;
import android.view.SurfaceHolder;
import android.view.SurfaceView;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
import android.widget.Toast;
public class VideoServer extends Activity implements SurfaceHolder.Callback {
TextView testView;
Camera camera;
SurfaceView surfaceView;
SurfaceHolder surfaceHolder;
private final String tag = "VideoServer";
Button start, stop;
/** Called when the activity is first created. */
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
start = (Button)findViewById(R.id.btn_start);
start.setOnClickListener(new Button.OnClickListener() {
public void onClick(View arg0) {
start_camera();
}
});
stop = (Button)findViewById(R.id.btn_stop);
stop.setOnClickListener(new Button.OnClickListener() {
public void onClick(View arg0) {
stop_camera();
}
});
surfaceView = (SurfaceView)findViewById(R.id.surfaceView1);
surfaceHolder = surfaceView.getHolder();
surfaceHolder.addCallback(this);
surfaceHolder.setType(SurfaceHolder.SURFACE_TYPE_PUSH_BUFFERS);
Toast.makeText(this, "Need your location!", Toast.LENGTH_SHORT).show();
}
private void start_camera() {
try{
camera = Camera.open();
}catch(RuntimeException e){
Log.e(tag, "init_camera: " + e);
return;
}
Camera.Parameters param;
param = camera.getParameters();
//modify parameter
param.setPreviewFrameRate(20);
param.setPreviewSize(176, 144);
camera.setParameters(param);
try {
camera.setPreviewDisplay(surfaceHolder);
camera.startPreview();
} catch (Exception e) {
Log.e(tag, "init_camera: " + e);
return;
}
}
private void stop_camera() {
camera.stopPreview();
camera.release();
}
public void surfaceChanged(SurfaceHolder arg0, int arg1, int arg2, int arg3) {
// TODO Auto-generated method stub
}
public void surfaceCreated(SurfaceHolder holder) {
// TODO Auto-generated method stub
}
public void surfaceDestroyed(SurfaceHolder holder) {
// TODO Auto-generated method stub
}
}
and the layout file look like
<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="com.example.admin2.cameraonsurfaceview.MainActivity">
<SurfaceView
android:id="#+id/surfaceView1"
android:layout_width="201dp"
android:layout_height="230dp"
tools:layout_constraintTop_creator="1"
tools:layout_constraintRight_creator="1"
android:layout_marginStart="52dp"
android:layout_marginEnd="52dp"
app:layout_constraintRight_toRightOf="parent"
android:layout_marginTop="25dp"
tools:layout_constraintLeft_creator="1"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintTop_toTopOf="parent"
android:layout_marginLeft="52dp"
android:layout_marginRight="52dp"
app:layout_constraintHorizontal_bias="0.0"
app:layout_constraintBottom_toBottomOf="parent"
android:layout_marginBottom="8dp"
app:layout_constraintVertical_bias="0.0" />
<Button
android:id="#+id/btn_start"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Start"
android:layout_marginTop="27dp"
app:layout_constraintTop_toBottomOf="#+id/surfaceView1"
android:layout_marginLeft="52dp"
app:layout_constraintLeft_toLeftOf="parent"
android:layout_marginStart="52dp" />
<Button
android:id="#+id/btn_stop"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Stop"
tools:layout_constraintRight_creator="1"
tools:layout_constraintBottom_creator="1"
app:layout_constraintBottom_toBottomOf="parent"
android:layout_marginEnd="52dp"
app:layout_constraintRight_toRightOf="parent"
android:layout_marginBottom="16dp"
android:layout_marginRight="131dp"
android:layout_marginTop="8dp"
app:layout_constraintTop_toBottomOf="#+id/surfaceView1"
app:layout_constraintVertical_bias="0.157" />
</android.support.constraint.ConstraintLayout>
My android manifest looks like
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.admin2.cameraonsurfaceview">
<uses-sdk android:minSdkVersion="16" android:targetSdkVersion="22" />
<uses-feature android:name="android.hardware.camera" />
<uses-permission android:name="android.permission.CAMERA" />
<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=".VideoServer">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
</application>
</manifest>
when I click on the start button, app stops and I get the following exception
10-05 15:39:48.174 2335-2335/com.example.admin2.cameraonsurfaceview E/AndroidRuntime: FATAL EXCEPTION: main
java.lang.NullPointerException
at com.example.admin2.cameraonsurfaceview.VideoServer.start_camera(VideoServer.java:61)
at com.example.admin2.cameraonsurfaceview.VideoServer.access$000(VideoServer.java:14)
at com.example.admin2.cameraonsurfaceview.VideoServer$1.onClick(VideoServer.java:34)
at android.view.View.performClick(View.java:4084)
at android.view.View$PerformClick.run(View.java:16966)
at android.os.Handler.handleCallback(Handler.java:615)
at android.os.Handler.dispatchMessage(Handler.java:92)
at android.os.Looper.loop(Looper.java:137)
at android.app.ActivityThread.main(ActivityThread.java:4745)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:511)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
at dalvik.system.NativeStart.main(Native Method)

Delete <uses-sdk android:minSdkVersion="16" android:targetSdkVersion="22" /> from your manifest.
Then check your version into build.gradle. Example:
android {
defaultConfig {
minSdkVersion 16 // here you need to change into 16 if you already didn't
targetSdkVersion 25
.
.
In order to work on API 16 you need to set minSdkVersion to 16. Then resync gradle and solve the problems that may appear with code that is not compatible with version 16.

Finally I fixed the issue myself.
The following line of code was causing the NullPointerException
camera = Camera.open();
I changed to
camera = Camera.open(1);
then it worked.

Error with facebook activity in android studio

I'm trying to develop basic facebook activty and The app will get username and display it in screen but I'm facing a kind of FATAL EXCEPTION: main error I have provided my complete set of codes starting with manifest file, class file, xml file and the Logcat error,your help is highly required
The below provided code is my manifest file
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.world.trialwithmugaputhagam">
<uses-permission android:name="android.permission.INTERNET" />
<application
android:name=".MyApplicatioon"
android:allowBackup="true"
android:icon="#mipmap/ic_launcher"
android:label="#string/app_name"
android:supportsRtl="true"
android:theme="#style/AppTheme">
<meta-data
android:name="com.facebook.sdk.ApplicationId"
android:value="#string/app_id" />
<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="com.facebook.FacebookActivity"
android:configChanges="keyboard|keyboardHidden|screenLayout|screenSize|orientation"
android:label="#string/app_name"
android:theme="#android:style/Theme.Translucent.NoTitleBar" />
<activity android:name=".MainFragment" />
</application>
The below code is the class file I have used.In below code I have also assigned mTextDetails but when I hover the cursor it say the value is not assigned
import android.os.Bundle;
import android.app.Fragment;
import android.content.Intent;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;
import com.facebook.AccessToken;
import com.facebook.CallbackManager;
import com.facebook.FacebookCallback;
import com.facebook.FacebookException;
import com.facebook.FacebookSdk;
import com.facebook.Profile;
import com.facebook.login.LoginResult;
import com.facebook.login.widget.LoginButton;
public class MainActivity extends Fragment {
private TextView mTextDetails;
private CallbackManager mcallbackManager;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
FacebookSdk.sdkInitialize(getActivity().getApplicationContext());
mcallbackManager=CallbackManager.Factory.create();
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
return inflater.inflate(R.layout.activity_main,container,false);
}
private FacebookCallback<LoginResult> mcallback = new FacebookCallback<LoginResult>() {
#Override
public void onSuccess(LoginResult loginResult) {
AccessToken accessToken = loginResult.getAccessToken();
Profile profile = Profile.getCurrentProfile();
if (profile != null){
mTextDetails.setText("Welcome "+ profile.getName());
}
}
#Override
public void onCancel() {
}
#Override
public void onError(FacebookException error) {
}
};
#Override
public void onViewCreated(View view, Bundle savedInstanceState) {
super.onViewCreated(view, savedInstanceState);
LoginButton loginButton = (LoginButton) view.findViewById(R.id.login_button);
loginButton. setReadPermissions("user_friends");
loginButton. setFragment(this);
loginButton.registerCallback(mcallbackManager, mcallback);
}
#Override
public void onActivityResult(int requestCode, int resultCode, Intent data) {
super.onActivityResult(requestCode, resultCode, data);
mcallbackManager.onActivityResult(requestCode, resultCode, data);
}}
The below code is my XML file
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="#dimen/activity_vertical_margin"
android:paddingLeft="#dimen/activity_horizontal_margin"
android:paddingRight="#dimen/activity_horizontal_margin"
android:paddingTop="#dimen/activity_vertical_margin"
tools:context="com.example.world.trialwithmugaputhagam.MainActivity">
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="#string/Welcome"
android:id="#+id/text_details"
android:layout_centerHorizontal="true"
android:layout_centerVertical="true"
android:layout_above="#+id/login_button"/>
<com.facebook.login.widget.LoginButton
android:id="#+id/login_button"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center_horizontal"
android:layout_marginTop="30dp"
android:layout_marginBottom="30dp"
android:layout_centerInParent="true"/></RelativeLayout>
Logcat error Sorry about the wrong alignment.
FATAL EXCEPTION: main
java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.world.trialwithmugaputhagam/com.example.world.trialwithmugaputhagam.MainActivity}: java.lang.ClassCastException: com.example.world.trialwithmugaputhagam.MainActivity cannot be cast to android.app.Activity
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2137)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2261)
at android.app.ActivityThread.access$600(ActivityThread.java:141)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1256)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:137)
at android.app.ActivityThread.main(ActivityThread.java:5103)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:525)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.ClassCastException: com.example.world.trialwithmugaputhagam.MainActivity cannot be cast to android.app.Activity
at android.app.Instrumentation.newActivity(Instrumentation.java:1061)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2128)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2261) 
at android.app.ActivityThread.access$600(ActivityThread.java:141) 
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1256) 
at android.os.Handler.dispatchMessage(Handler.java:99) 
at android.os.Looper.loop(Looper.java:137) 
at android.app.ActivityThread.main(ActivityThread.java:5103) 
at java.lang.reflect.Method.invokeNative(Native Method) 
at java.lang.reflect.Method.invoke(Method.java:525) 
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553) 
at dalvik.system.NativeStart.main(Native Method)

Because you are extending MainActivity from Fragment. Thus, your MainActivity is not actually an Activity but a Fragment. Extend it from Activity or subclasses of Activity.
Like this:
MainActivity extends AppCompatActivity
Edit 1: (Based on comments):
You haven't initialized mTextDetails;
try to do like this in Activity's onCreate:
mTextDetails = (TextView)findViewById(R.id.text_view_id);

Android App crashed when moving from one activity to another

Right now I have two activities, activity_bustracking and activity_main
When the button in the main activity is pressed it is supposed to move to the bustracking activity; however, right now it when I click the button the application crashes with the error:
05-28 16:34:32.680 26130-26130/com.example.robertloggia.test1 D/ViewRootImpl﹕ ViewPostImeInputStage ACTION_DOWN
05-28 16:34:32.770 26130-26130/com.example.robertloggia.test1 D/AndroidRuntime﹕ Shutting down VM
05-28 16:34:32.770 26130-26130/com.example.robertloggia.test1 E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: com.example.robertloggia.test1, PID: 26130
java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String android.content.Context.getPackageName()' on a null object reference
at android.content.ComponentName.<init>(ComponentName.java:77)
at android.content.Intent.<init>(Intent.java:4562)
at com.example.robertloggia.test1.MainActivity$1.onClick(MainActivity.java:67)
at android.view.View.performClick(View.java:5162)
at android.view.View$PerformClick.run(View.java:20873)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:145)
at android.app.ActivityThread.main(ActivityThread.java:5835)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1388)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1183)
My MainActivity.class looks like:
package com.example.robertloggia.test1;
import android.app.Activity;
import android.content.Intent;
import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.view.View.OnClickListener;
//import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.Spinner;
import android.widget.Toast;
import android.content.Context;
import android.location.Location;
import android.location.LocationListener;
import android.location.LocationManager;
import android.widget.TextView;
public class MainActivity extends Activity implements LocationListener{
//GPS Specific variables
protected LocationManager locationManager;
protected LocationListener locationListener;
protected Context context;
TextView txtLat;
String lat;
String provider;
protected String latitude,longitude;
boolean gps_enabled, network_enabled;
Spinner routeChoice;
Button btnSubmit;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
routeChoice = (Spinner) findViewById(R.id.route_choices);
btnSubmit = (Button) findViewById(R.id.btn_submit);
txtLat = (TextView) findViewById(R.id.textView1);
locationManager = (LocationManager) getSystemService(Context.LOCATION_SERVICE);
//get location and make sure it is enabled
locationManager.requestLocationUpdates(LocationManager.GPS_PROVIDER, 0, 0, this);
if(!locationManager.isProviderEnabled(LocationManager.GPS_PROVIDER) && !locationManager.isProviderEnabled(LocationManager.NETWORK_PROVIDER)) {
Toast.makeText(MainActivity.this, "Please enable GPS", Toast.LENGTH_LONG).show();
}
addListenerOnButton();
}
public void addListenerOnButton() {
btnSubmit.setOnClickListener(new OnClickListener() {
#Override
public void onClick(View v) {
// Toast.makeText(MainActivity.this,
// "OnClickListener : " +
// "\nSpinner 1 : " + String.valueOf(routeChoice.getSelectedItem()),
// Toast.LENGTH_SHORT).show();
Intent intent = new Intent(context, BusTrackingActivity.class);
startActivity(intent);
}
});
}
/*
* METHODS FOR GETTING LOCATION
*/
#Override
public void onLocationChanged(Location location) {
txtLat = (TextView) findViewById(R.id.textView1);
txtLat.setText("Latitude:" + location.getLatitude() + ", Longitude:" + location.getLongitude());
}
#Override
public void onProviderDisabled(String provider) {
Log.d("Latitude", "disable");
}
#Override
public void onProviderEnabled(String provider) {
Log.d("Latitude", "enable");
}
#Override
public void onStatusChanged(String provider, int status, Bundle extras) {
Log.d("Latitude", "status");
}
}
My BusTrackingActivity.class looks like:
package com.example.robertloggia.test1;
import android.app.Activity;
import android.os.Bundle;
import android.widget.Button;
/**
* Created by RobertLoggia on 5/28/15.
*/
public class BusTrackingActivity extends Activity {
Button button;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_bustracking);
}
}
My activity_main.xml:
<ImageView
android:layout_width="330dp"
android:layout_height="200.5dp"
android:layout_marginTop="110dp"
android:id="#+id/imageView"
android:src="#drawable/ripta_logo"
android:layout_gravity="center_horizontal"
android:contentDescription="#string/logo" />
<Spinner
android:layout_width="290dp"
android:layout_height="50dp"
android:id="#+id/route_choices"
android:entries="#array/route_array"
android:prompt="#string/route_prompt"
android:layout_gravity="center_vertical"
android:layout_below="#+id/imageView" />
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="#string/submit_text"
android:id="#+id/btn_submit"
android:layout_gravity="center_vertical"
android:layout_alignBottom="#+id/route_choices"
android:layout_toRightOf="#id/route_choices"/>
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Please make sure GPS is enabled"
android:id="#+id/textView1"
android:layout_below="#+id/route_choices"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true" />
activity_bustracking.xml:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical" android:layout_width="match_parent"
android:layout_height="match_parent">
</LinearLayout>
And my android manifest looks like:
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.robertloggia.test1" >
<uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />
<uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION" />
<uses-permission android:name="android.permission.INTERNET" />
<application
android:allowBackup="true"
android:icon="#mipmap/ic_launcher"
android:label="#string/app_name"
android:theme="#style/AppTheme" >
<activity
android:name=".MainActivity"
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:label="#string/app_name"
android:name=".BusTrackingActivity" >
</activity>
</application>
</manifest>

The problem is that you never assign context to this.
However, there is no reason to save off a Context in an Activity, just use MainActivity.this instead of context:
#Override
public void onClick(View v) {
// Toast.makeText(MainActivity.this,
// "OnClickListener : " +
// "\nSpinner 1 : " + String.valueOf(routeChoice.getSelectedItem()),
// Toast.LENGTH_SHORT).show();
Intent intent = new Intent(MainActivity.this, BusTrackingActivity.class);
startActivity(intent);
}

When you are starting the new intent in this line:
Intent intent = new Intent(context, BusTrackingActivity.class);
The context object has not been initiated yet. You declared it earlier:
protected Context context;
Inside your onCreate() method, use this code:
context = this;

context in MainActivity is null.Either initialize it or use MainActivity.this in place of context.

Add the line of code from the 67th line in the MainActivity, as this is the line with the error.
However without this, I am guessing something went wrong with the button listener.
This being said, try removing all of this:
public void addListenerOnButton() {
btnSubmit.setOnClickListener(new OnClickListener() {
#Override
public void onClick(View v) {
Intent intent = new Intent(context, BusTrackingActivity.class);
startActivity(intent);
}
});
}
Listeners are better put in the method they are used, or in this case on create. This can be done by putting this line of code:
btnSubmit.setOnClickListener(new OnClickListener() {
#Override
public void onClick(View v) {
Intent intent = new Intent(context, BusTrackingActivity.class);
startActivity(intent);
}
});
Really though, if this doesn't work I just need to like of code at the error. If you click the first blue thing in the logcat (the rest will be grey), I can help more.

this could be because of using card view in first activity or that activity on which your app got crashed while running.
used this code to implement card view in dependencies
implementation 'androidx.cardview:cardview:1.0.0'

Android application crashed

I'm doing an app for Android. I have a main activity (not the default MainActivity.java, other activity named HotelPresentacion.java that has 3 buttons for insert/check registers or exit the app).
If I touch the Registrar button, supposedly I can register, but the app stops unexpectedly. If I touch the Registros button I can visualize the registers of my app, but when I touch one register (a short touch or long short) for only visualize or edit the app again stops unexpectedly.
I modified my androidmanifest.xml to set HotelPresentacion.java as my default starting activity.
This is the code of the HotelPresentacion.java
package com.example.lab007;
import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
public class HotelPresentacion extends Activity{
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_hotel_presentacion);
}
public void onReservar(View v){
Intent i=new Intent(HotelPresentacion.this, ReservacionFormulario.class);
startActivity(i);
}
public void onVer(View v){
Intent i=new Intent(HotelPresentacion.this, MainActivity.class);
startActivity(i);
}
public void onSalir(View v){
finish();
}
}
My androidmanifest.xml
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.lab007"
android:versionCode="1"
android:versionName="1.0" >
<uses-sdk
android:minSdkVersion="8"
android:targetSdkVersion="21" />
<application
android:allowBackup="true"
android:icon="#drawable/ic_launcher"
android:label="#string/app_name"
android:theme="#style/AppTheme" >
<activity
android:name=".HotelPresentacion"
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="com.example.lab007.ReservacionFormulario"
android:label="#string/app_name" >
</activity>
<activity
android:name="com.example.lab007.MainActivity"
android:label="#string/app_name" >
</activity>
</application>
</manifest>
LOGCAT
10-25 11:16:38.880: E/AndroidRuntime(4247): FATAL EXCEPTION: main
10-25 11:16:38.880: E/AndroidRuntime(4247): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.lab007/com.example.lab007.ReservacionFormulario}: java.lang.RuntimeException: Your content must have a ListView whose id attribute is 'android.R.id.list'
10-25 11:16:38.880: E/AndroidRuntime(4247): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1651)
10-25 11:16:38.880: E/AndroidRuntime(4247): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1667)
10-25 11:16:38.880: E/AndroidRuntime(4247): at android.app.ActivityThread.access$1500(ActivityThread.java:117)
10-25 11:16:38.880: E/AndroidRuntime(4247): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:935)
10-25 11:16:38.880: E/AndroidRuntime(4247): at android.os.Handler.dispatchMessage(Handler.java:99)
10-25 11:16:38.880: E/AndroidRuntime(4247): at android.os.Looper.loop(Looper.java:130)
10-25 11:16:38.880: E/AndroidRuntime(4247): at android.app.ActivityThread.main(ActivityThread.java:3687)
10-25 11:16:38.880: E/AndroidRuntime(4247): at java.lang.reflect.Method.invokeNative(Native Method)
10-25 11:16:38.880: E/AndroidRuntime(4247): at java.lang.reflect.Method.invoke(Method.java:507)
10-25 11:16:38.880: E/AndroidRuntime(4247): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:867)
10-25 11:16:38.880: E/AndroidRuntime(4247): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:625)
10-25 11:16:38.880: E/AndroidRuntime(4247): at dalvik.system.NativeStart.main(Native Method)
10-25 11:16:38.880: E/AndroidRuntime(4247): Caused by: java.lang.RuntimeException: Your content must have a ListView whose id attribute is 'android.R.id.list'
10-25 11:16:38.880: E/AndroidRuntime(4247): at android.app.ListActivity.onContentChanged(ListActivity.java:243)
10-25 11:16:38.880: E/AndroidRuntime(4247): at com.android.internal.policy.impl.PhoneWindow.setContentView(PhoneWindow.java:212)
10-25 11:16:38.880: E/AndroidRuntime(4247): at android.app.Activity.setContentView(Activity.java:1657)
10-25 11:16:38.880: E/AndroidRuntime(4247): at com.example.lab007.ReservacionFormulario.onCreate(ReservacionFormulario.java:39)
10-25 11:16:38.880: E/AndroidRuntime(4247): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
10-25 11:16:38.880: E/AndroidRuntime(4247): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1615)
10-25 11:16:38.880: E/AndroidRuntime(4247): ... 11 more
The class ReservacionFormulario.java
package com.example.lab007;
import android.app.Activity;
import android.app.AlertDialog;
import android.app.ListActivity;
import android.content.DialogInterface;
import android.content.Intent;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;
import android.widget.CheckBox;
import android.widget.DatePicker;
import android.widget.EditText;
import android.widget.LinearLayout;
import android.widget.Spinner;
import android.widget.Toast;
public class ReservacionFormulario extends ListActivity{
private ComplejoDBAdapter dbAdapterComplejo;
private ComplejoSpinnerAdapter complejoSpinnerAdapter;
private int modo ;
private long id ;
private Reservacion reserva = new Reservacion(this);
private EditText nombre;
private EditText apellidos;
//private DatePicker fechaInicio;
//private DatePicker fechaFin;
private Spinner complejo ;
private Button boton_guardar;
private Button boton_cancelar;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_reservacion_formulario);
Intent intent = getIntent();
Bundle extra = intent.getExtras();
if (extra == null) return;
nombre = (EditText) findViewById(R.id.nombre);
apellidos = (EditText) findViewById(R.id.apellidos);
//fechaInicio = (DatePicker) findViewById(R.id.);
//fechaInicio = (DatePicker) findViewById(R.id.);
complejo = (Spinner) findViewById(R.id.complejo);
boton_guardar = (Button) findViewById(R.id.boton_guardar);
boton_cancelar = (Button) findViewById(R.id.boton_cancelar);
complejoSpinnerAdapter = new ComplejoSpinnerAdapter(this, Complejo.getAll(this, null));
complejo.setAdapter(complejoSpinnerAdapter);
if (extra.containsKey(ReservacionDBAdapter.C_COL_ID)){
id = extra.getLong(ReservacionDBAdapter.C_COL_ID);
consultar(id);
}
establecerModo(extra.getInt(ReservacionActivity.C_MODO));
boton_guardar.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v){
guardar();
}
});
boton_cancelar.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v){
cancelar();
}
});
}
private void establecerModo(int m)
{
this.modo = m ;
if (modo == ReservacionActivity.C_VISUALIZAR){
this.setTitle(nombre.getText().toString());
this.setEdicion(false);
}
else if (modo == ReservacionActivity.C_CREAR){
this.setTitle("Nuevo reservacion");
this.setEdicion(true);
}
else if (modo == ReservacionActivity.C_EDITAR){
this.setTitle("Editar reservacion");
this.setEdicion(true);
}
}
private void consultar(long id){
reserva = Reservacion.find(this, id);
nombre.setText(reserva.getNombre());
apellidos.setText(reserva.getApellidos());
complejo.setSelection(complejoSpinnerAdapter.getPositionById(reserva.getComplejoId()));
}
private void setEdicion(boolean opcion){
nombre.setEnabled(opcion);
apellidos.setEnabled(opcion);
complejo.setEnabled(opcion);
// Controlamos visibilidad de botonera
LinearLayout v = (LinearLayout) findViewById(R.id.botonera);
if (opcion)
v.setVisibility(View.VISIBLE);
else
v.setVisibility(View.GONE);
}
private void guardar(){
/*verificar si funciona*/
try{
if(nombre.length()<=0){
reserva.setNombre(nombre.getText().toString());
}
}catch(Exception e){
}
reserva.setApellidos(apellidos.getText().toString());
reserva.setComplejoId(complejo.getSelectedItemId());
reserva.save();
if (modo == ReservacionActivity.C_CREAR){
Toast.makeText(ReservacionFormulario.this, "Creado", Toast.LENGTH_SHORT).show();
}
else if (modo == ReservacionActivity.C_EDITAR){
Toast.makeText(ReservacionFormulario.this, "Modificado", Toast.LENGTH_SHORT).show();
}
setResult(RESULT_OK);
finish();
}
private void cancelar(){
setResult(RESULT_CANCELED, null);
finish();
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
menu.clear();
if (modo == ReservacionActivity.C_VISUALIZAR)
getMenuInflater().inflate(R.menu.reservacion_formulario_ver, menu);
else
getMenuInflater().inflate(R.menu.reservacion_formulario_editar, menu);
return true;
}
#Override
public boolean onMenuItemSelected(int featureId, MenuItem item) {
switch (item.getItemId()){
case R.id.menu_eliminar:
borrar(id);
return true;
case R.id.menu_cancelar:
cancelar();
return true;
case R.id.menu_guardar:
guardar();
return true;
case R.id.menu_editar:
establecerModo(ReservacionActivity.C_EDITAR);
return true;
}
return super.onMenuItemSelected(featureId, item);
}
private void borrar(final long id){
AlertDialog.Builder dialogEliminar = new AlertDialog.Builder(this);
dialogEliminar.setIcon(android.R.drawable.ic_dialog_alert);
dialogEliminar.setTitle("Eliminar");
dialogEliminar.setMessage("¿Desea eliminar?");
dialogEliminar.setCancelable(false);
dialogEliminar.setPositiveButton(getResources().getString(android.R.string.ok), new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int boton) {
reserva.delete();
Toast.makeText(ReservacionFormulario.this, "Eliminado", Toast.LENGTH_SHORT).show();
setResult(RESULT_OK);
finish();
}
});
dialogEliminar.setNegativeButton(android.R.string.no, null);
dialogEliminar.show();
}
}
The activity_reservacion_formulario.xml
<?xml version="1.0" encoding="utf-8"?>
<ScrollView xmlns:android="http://schemas.android.com/apk/res/android"
android:id="#+id/ScrollView1"
android:layout_width="match_parent"
android:layout_height="match_parent" >
<RelativeLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
android:padding="10dp" >
<!-- Nombre -->
<TextView
android:id="#+id/label_nombre"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Nombre" />
<EditText
android:id="#+id/nombre"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_alignParentLeft="true"
android:layout_below="#+id/label_nombre"
android:maxLength="40"
android:ems="10" />
<!-- Apellidos -->
<TextView
android:id="#+id/label_apellidos"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_below="#+id/nombre"
android:maxLength="60"
android:text="Apellidos" />
<EditText
android:id="#+id/apellidos"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_alignParentLeft="true"
android:layout_below="#+id/label_apellidos"
android:ems="10" />
<!-- Fecha de Inicio -->
<!-- <TextView
android:id="#+id/label_fechainicio"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_below="#+id/apellidos"
android:text="Fecha de Inicio" />
<DatePicker
android:id="#+id/datePickerInicio"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_below="#+id/label_fechainicio" /> -->
<!-- Fecha de Fin -->
<!-- <TextView
android:id="#+id/label_fechafin"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_below="#+id/datePickerInicio"
android:text="Fecha de Fin" />
<DatePicker
android:id="#+id/datePickerFin"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_below="#+id/label_fechafin" /> -->
<!-- Spinner -->
<TextView
android:id="#+id/label_complejo"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_below="#+id/datePickerFin"
android:text="Complejo" />
<Spinner
android:id="#+id/complejo"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_below="#+id/label_complejo" />
<TextView
android:id="#+id/label_ciudad"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Complejo"
android:layout_below="#+id/complejo" />
<LinearLayout
android:id="#+id/botonera"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_marginTop="20dp"
android:gravity="center"
android:layout_below="#+id/datePickerFin"
android:orientation="horizontal" >
<Button
android:id="#+id/boton_cancelar"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Cancelar" />
<Button
android:id="#+id/boton_guardar"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Guardar" />
</LinearLayout>
</RelativeLayout>
</ScrollView>
This is the entire project:
Project
I'll appreciante any help for solve my problem. Thanks

Replace
public class ReservacionFormulario extends ListActivity{
with
public class ReservacionFormulario extends Activity{
As you have extended the ListActivity so Android is searching for the a ListView with Id list, but In your XML there is no any such type of ListView.

From the crash log i guess its.
Change ListActivity to Activity