i am trying to create an app to transmit beacons from android 5.0 devices but i get this error
{09-07 10:23:45.184 3057-3057/com.example.mohamed_pc.test2 E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.mohamed_pc.test2, PID: 3057
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.mohamed_pc.test2/com.example.mohamed_pc.test2.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.bluetooth.le.BluetoothLeAdvertiser android.bluetooth.BluetoothAdapter.getBluetoothLeAdvertiser()' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2416)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
at android.app.ActivityThread.-wrap11(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.bluetooth.le.BluetoothLeAdvertiser android.bluetooth.BluetoothAdapter.getBluetoothLeAdvertiser()' on a null object reference
at com.example.mohamed_pc.test2.MainActivity.onCreate(MainActivity.java:31)
at android.app.Activity.performCreate(Activity.java:6237)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1107)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2369)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
at android.app.ActivityThread.-wrap11(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616) }
The code is below
package com.example.mohamed_pc.test2;
import android.bluetooth.BluetoothAdapter;
import android.bluetooth.le.AdvertiseCallback;
import android.bluetooth.le.AdvertiseData;
import android.bluetooth.le.AdvertiseSettings;
import android.bluetooth.le.BluetoothLeAdvertiser;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.Button;
import java.nio.ByteBuffer;
import java.util.UUID;
public class MainActivity extends AppCompatActivity {
private BluetoothAdapter mBluetoothAdapter;
private BluetoothLeAdvertiser mBluetoothLeAdvertiser;
private AdvertiseData mAdvertiseData;
private AdvertiseSettings mAdvertiseSettings;
private AdvertiseCallback mAdvertiseCallback;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mBluetoothAdapter = BluetoothAdapter.getDefaultAdapter();
mBluetoothLeAdvertiser = mBluetoothAdapter.getBluetoothLeAdvertiser();
}
public void buttonOnClick(View v) {
// do something when the button is clicked
Button button=(Button) v;
((Button) v).setText("clicked");
setAdvertiseData();
setAdvertiseSettings();
mBluetoothLeAdvertiser.startAdvertising(mAdvertiseSettings, mAdvertiseData, mAdvertiseCallback);
}
protected void setAdvertiseData() {
AdvertiseData.Builder mBuilder = new AdvertiseData.Builder();
ByteBuffer mManufacturerData = ByteBuffer.allocate(24);
byte[] uuid = getIdAsByte(UUID.fromString("0CF052C297CA407C84F8B62AAC4E9020"));
mManufacturerData.put(0, (byte)0xBE); // Beacon Identifier
mManufacturerData.put(1, (byte)0xAC); // Beacon Identifier
for (int i=2; i<=17; i++) {
mManufacturerData.put(i, uuid[i-2]); // adding the UUID
}
mManufacturerData.put(18, (byte)0x00); // first byte of Major
mManufacturerData.put(19, (byte)0x09); // second byte of Major
mManufacturerData.put(20, (byte)0x00); // first minor
mManufacturerData.put(21, (byte)0x06); // second minor
mManufacturerData.put(22, (byte)0xB5); // txPower
mBuilder.addManufacturerData(224, mManufacturerData.array()); // using google's company ID
mAdvertiseData = mBuilder.build();
}
protected void setAdvertiseSettings() {
AdvertiseSettings.Builder mBuilder = new AdvertiseSettings.Builder();
mBuilder.setAdvertiseMode(AdvertiseSettings.ADVERTISE_MODE_LOW_POWER);
mBuilder.setConnectable(false);
mBuilder.setTimeout(0);
mBuilder.setTxPowerLevel(AdvertiseSettings.ADVERTISE_TX_POWER_MEDIUM);
mAdvertiseSettings = mBuilder.build();
}
public static byte[] getIdAsByte(java.util.UUID uuid)
{
ByteBuffer bb = ByteBuffer.wrap(new byte[16]);
bb.putLong(uuid.getMostSignificantBits());
bb.putLong(uuid.getLeastSignificantBits());
return bb.array();
}
}
mBluetoothAdapter = BluetoothAdapter.getDefaultAdapter();
is giving you null. Check permisses and if bluetooth is enabled
Changed the format:
UUID.fromString("0CF052C297CA407C84F8B62AAC4E9020")
By:
UUID.fromString("0CF052C2-97CA-407C-84F8-B62AAC4E9020");
Related
When starting my activity there is always an error message and the app does not open.
Error:
2022-05-11 23:18:12.470 17222-17222/com.example.myapplication E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.myapplication, PID: 17222
java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.myapplication/com.example.feuerwerkzndanlage.Biometric_Authentication}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.Context android.content.Context.getApplicationContext()' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3455)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3699)
at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:85)
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2135)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loop(Looper.java:236)
at android.app.ActivityThread.main(ActivityThread.java:8056)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:656)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:967)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.Context android.content.Context.getApplicationContext()' on a null object reference
at android.content.ContextWrapper.getApplicationContext(ContextWrapper.java:133)
at com.example.feuerwerkzndanlage.Biometric_Authentication.<init>(Biometric_Authentication.java:23)
at java.lang.Class.newInstance(Native Method)
at android.app.AppComponentFactory.instantiateActivity(AppComponentFactory.java:95)
at androidx.core.app.CoreComponentFactory.instantiateActivity(CoreComponentFactory.java:45)
at android.app.Instrumentation.newActivity(Instrumentation.java:1254)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3443)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3699)
at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:85)
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2135)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loop(Looper.java:236)
at android.app.ActivityThread.main(ActivityThread.java:8056)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:656)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:967)
Activity:
package com.example.feuerwerkzndanlage;
import android.annotation.SuppressLint;
import android.content.Context;
import android.os.Bundle;
import android.widget.Button;
import android.widget.TextView;
import android.widget.Toast;
import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;
import androidx.biometric.BiometricPrompt;
import androidx.core.content.ContextCompat;
import java.util.concurrent.Executor;
public class Biometric_Authentication extends AppCompatActivity {
private TextView authStatusTv;
private BiometricPrompt biometricPrompt;
private BiometricPrompt.PromptInfo promptInfo;
Context context = getApplicationContext();
CharSequence error_txt = "Indentifizierung Fehlgeschlagen: ";
CharSequence suceed_txt = "Indentifizierung Erfolgreich";
CharSequence failed_txt = "Indentifizierung Fehlgeschlagen";
int duration = Toast.LENGTH_SHORT;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_biometric_authentication);
authStatusTv = findViewById(R.id.authStatusTv);
Button btn_auth = findViewById(R.id.btn_auth);
Executor executor = ContextCompat.getMainExecutor(this);
biometricPrompt = new BiometricPrompt(Biometric_Authentication.this, executor, new BiometricPrompt.AuthenticationCallback() {
#SuppressLint("SetTextI18n")
#Override
public void onAuthenticationError(int errorCode, #NonNull CharSequence errString) {
super.onAuthenticationError(errorCode, errString);
authStatusTv.setText("Indentifizierung Fehlgeschlagen: " + errString);
Toast.makeText(context, error_txt, duration).show();
}
#SuppressLint("SetTextI18n")
#Override
public void onAuthenticationSucceeded(#NonNull BiometricPrompt.AuthenticationResult result) {
super.onAuthenticationSucceeded(result);
authStatusTv.setText("Indentifizierung Erfolgreich");
Toast.makeText(context, suceed_txt, duration).show();
}
#SuppressLint("SetTextI18n")
#Override
public void onAuthenticationFailed() {
super.onAuthenticationFailed();
authStatusTv.setText("Indentifizierung Fehlgeschlagen");
Toast.makeText(context, failed_txt, duration).show();
}
});
promptInfo = new BiometricPrompt.PromptInfo.Builder()
.setTitle("Biometrische Indentifizierung")
.setSubtitle("Login")
.setNegativeButtonText("Benutzer Passwort")
.build();
btn_auth.setOnClickListener(view -> biometricPrompt.authenticate(promptInfo));
}
}
Context context = getApplicationContext();
You can't do that at init time. You can't call any Context related functions, including getApplicationContect() until onCreate is called. This is because the framework hasn't fully initialized the activity before then. To make this work, you'd need to move this line into onCreate, and move any code that depends on this variable being set into onCreate or later as well.
This question already has answers here:
What is a NullPointerException, and how do I fix it?
(12 answers)
Closed 2 years ago.
Hi currently i am working on project including parse server,and after adding parse library to my project ,when i run it it shows this error ( java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.myapplicationv/com.example.myapplicationv.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'java.io.File com.parse.ParsePlugins.getParseDir()' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2646)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2707)
at android.app.ActivityThread.-wrap12(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1460)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6077)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:866)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:756)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'java.io.File com.parse.ParsePlugins.getParseDir()' on a null object reference
at com.parse.Parse.getParseDir(Parse.java:509)
at com.parse.ParseCorePlugins.getCurrentUserController(ParseCorePlugins.java:130)
at com.parse.ParseUser.getCurrentUserController(ParseUser.java:55)
at com.parse.ParseUser.getCurrentUserAsync(ParseUser.java:883)
at com.parse.ParseObject.saveInBackground(ParseObject.java:1405)
at com.parse.ParseObject.saveInBackground(ParseObject.java:1529)
at com.example.myapplicationv.MainActivity.onCreate(MainActivity.java:22)
at android.app.Activity.performCreate(Activity.java:6662)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1118)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2599)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2707)
at android.app.ActivityThread.-wrap12(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1460)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6077)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:866)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:756)
)
this is MainActivity here
MainActivity
package com.example.myapplicationv;
import android.os.Bundle;
import android.util.Log;
import androidx.appcompat.app.AppCompatActivity;
import com.parse.ParseAnalytics;
import com.parse.ParseException;
import com.parse.ParseObject;
import com.parse.SaveCallback;
public class MainActivity extends AppCompatActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
ParseObject score = new ParseObject("Score");
score.put("username","Nalin");
score.put("score",200);
score.saveInBackground(new SaveCallback() {
#Override
public void done(ParseException e) {
if (e == null){
Log.i("success","we save the score");
}else{
e.printStackTrace();
}
}
});
ParseAnalytics.trackAppOpenedInBackground(getIntent());
}
}
StarterApplication
package com.example.myapplicationv;
import android.os.Bundle;
import androidx.appcompat.app.AppCompatActivity;
import com.parse.Parse;
import com.parse.ParseACL;
import com.parse.ParseUser;
public class StarterApplication extends AppCompatActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
//setContentView(R.layout.activity_starter_application);
Parse.enableLocalDatastore(this);
Parse.initialize(new Parse.Configuration.Builder(getApplicationContext())
.applicationId("myappID")
.clientKey("nV48GY6ZE5Lw")
.server("http://18.217.199.68/parse/")
.build()
);
ParseUser.enableAutomaticUser();
ParseACL defaultACL = new ParseACL();
defaultACL.setPublicReadAccess(true);
defaultACL.setPublicWriteAccess(true);
ParseACL.setDefaultACL(defaultACL, true);
}
}
You need to initialize the parser in the application class as explained in document here. Also should declare it in the Manifest file.
The problem that I encounter was that the Document that shows to Use a class App extending Application was never initialized even after adding the activity in Manifest(it gives a red line also).
So what I did was I saved the below code in the onCreate of my SplashActivity
Parse.initialize(new Parse.Configuration.Builder(this)
.applicationId(getString(R.string.back4app_app_id))
// if defined
.clientKey(getString(R.string.back4app_client_key))
.server(getString(R.string.back4app_server_url))
.enableLocalDataStore() // <--- This is important
.build());
Now After this I'm able to use it normally.
I am writing an app for my company but I cannot see my work since my emulator is not running.
Here is my code below. There are no errors. I am running this in android studio.
It runs on some apps but I tried inputting my code then it does not work.
Please Help
package com.example.tankoverfill;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
public class MainActivity extends AppCompatActivity {
Button calc;
TextView tv_heightfills = findViewById(R.id.tv_heightfills);
TextView tv_timefills = findViewById(R.id.tv_timefills);
EditText flow, areas, heights, densities, heightones, cvs;
int x1,y1,w1,a1, x2,y2,w2,a2,g;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
flow = findViewById(R.id.flow);
areas = findViewById(R.id.areas);
heights = findViewById(R.id.heights);
densities = findViewById(R.id.densities);
heightones = findViewById(R.id.heightones);
cvs = findViewById(R.id.cvs);
calc = findViewById(R.id.calc);
calc.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
x1 = Integer.parseInt(flow.getText().toString());
y1 = Integer.parseInt(cvs.getText().toString());
w1 = Integer.parseInt(densities.getText().toString());
g = (int) 9.8;
a1 = (x1 / (y1*w1*g));
tv_heightfills.setText(a1);
}
});
calc.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
x2 = Integer.parseInt(areas.getText().toString());
y2 = Integer.parseInt(cvs.getText().toString());
w2 = Integer.parseInt(densities.getText().toString());
g = (int) 9.8;
a2 = (x1 / (y1*w1*g));
tv_timefills.setText(a2);
}
});
}
}
D/AndroidRuntime: Shutting down VM E/AndroidRuntime: FATAL EXCEPTION:
main
Process: com.example.tankoverfill, PID: 10137
java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.tankoverfill/com.example.tankoverfill.MainActivity}:
java.lang.NullPointerException: Attempt to invoke virtual method
'android.view.Window$Callback android.view.Window.getCallback()' on a
null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2843)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3048)
at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78)
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1808)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loop(Looper.java:193)
at android.app.ActivityThread.main(ActivityThread.java:6669)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.Window$Callback
android.view.Window.getCallback()' on a null object reference
at android.support.v7.app.AppCompatDelegateImpl.(AppCompatDelegateImpl.java:249)
at android.support.v7.app.AppCompatDelegate.create(AppCompatDelegate.java:182)
at android.support.v7.app.AppCompatActivity.getDelegate(AppCompatActivity.java:520)
at android.support.v7.app.AppCompatActivity.findViewById(AppCompatActivity.java:191)
at com.example.tankoverfill.MainActivity.(MainActivity.java:15)
at java.lang.Class.newInstance(Native Method)
at android.app.AppComponentFactory.instantiateActivity(AppComponentFactory.java:69)
at android.support.v4.app.CoreComponentFactory.instantiateActivity(CoreComponentFactory.java:43)
at android.app.Instrumentation.newActivity(Instrumentation.java:1215)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2831)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3048)
at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78)
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1808)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loop(Looper.java:193)
at android.app.ActivityThread.main(ActivityThread.java:6669)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)
I/Process: Sending signal. PID: 10137 SIG: 9 Application terminated.
Hello two of the errors you have in your code are:
first error that you must link the two textview to xml inside onCreate() method
error
TextView tv_heightfills = findViewById(R.id.tv_heightfills);
TextView tv_timefills = findViewById(R.id.tv_timefills);
correct
TextView tv_heightfills;
TextView tv_timefills;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
tv_heightfills = findViewById(R.id.tv_heightfills);
tv_timefills = findViewById(R.id.tv_timefills);
....
}
Second error is setting int value to the textview setText() method
so it should be:
tv_heightfills.setText(String.valueOf(a1));
same for
tv_timefills.setText(String.valueOf(a2));
I'm new to programming and have been assigned to code a simple music player, there were slides to help guide and I have slightly altered them (can't use the exact same variables).
So now it's error free but when I click on the play button it crashes, no idea why. Here's my code for the page where I select the library:
package sg.edu.tp.project1;
import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import sg.edu.tp.project1.util.AppUtil;
public class myMusic extends AppCompatActivity {
private String[] Musicsong = new String[6];
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_my_music);
//store values in array of the first song
Musicsong[0] = "s1001";
Musicsong[1] = "The Way You Look Tonight";
Musicsong[2] = "ed sheeran";
Musicsong[3] = "a5b8972e764025020625bbf9c1c2bbb06e394a60?cid=null";
Musicsong[4] = "4.39";
Musicsong[5] = "music to play";
}
public void sendDataToActiviy(String[] song)
{
//1.create intent and specify destination
Intent intent = new Intent(this, PlayMusicActivity.class);
//2.store song info in intent to send to destination
intent.putExtra("id", song[0]);
intent.putExtra("title",song[1]);
intent.putExtra("artist",song[2]);
intent.putExtra("fileLink",song[3]);
intent.putExtra("coverArt",song[5]);
//3. launch desntination activiy
startActivity(intent);
}
public void handleSelection(View view)
{
// 1. get id of selected song
String resourceId = AppUtil.getResourceId(this, view);
//2. Search for the selected song based on the ID so that
// all infomation of the song can be retreived
String[] selectedSong =searchById(resourceId);
//3.popup to show tittle of song
AppUtil.popMessage(this, "Streaming song:" + selectedSong[1]);
//4. send song data to player screen
sendDataToActiviy(selectedSong);
}
private Object[] songs = {Musicsong};
public String[] searchById(String id) {
//temporary empty array
String[] song = null;
//for loop to get song
for (int index = 0; index < songs.length; index++) {
//3. store each song item to song array.
song = (String[]) songs[index];
//4. match song id to see if its the one i want
if (song[0].equals(id)) {
return song;
}
}
//if song not found in array empty array will be returned
return song;
}
}
This part where the player is:
package sg.edu.tp.project1;
import android.media.AudioManager;
import android.media.MediaPlayer;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.ImageView;
import android.widget.TextView;
import java.io.IOException;
import sg.edu.tp.project1.util.AppUtil;
public class PlayMusicActivity extends AppCompatActivity
{
//streaming website
private static final String BASE_URL = "https://p.scdn.co/mp3-preview/";
private String songId ="";
private String title = "";
private String artist = "";
private String fileLink = "";
private String coverArt = "";
private String url = "";
//builtin media player
private MediaPlayer player = null;
//position of song in playback
private int musicPosition = 0;
//button variable to link to play btn
private Button btnPlayPause = null;
private String[] Musicsong = {
"s1001",
"The Way You Look Tonight",
"ed sheeran",
"a5b8972e764025020625bbf9c1c2bbb06e394a60?cid=null",
"4.39",
"music to play"};
private Object[] songs = {Musicsong};
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_play_music);
btnPlayPause = (Button) findViewById(R.id.btnPlayPause);
retrieveData();
displaySong(title,artist,coverArt);
}
private void retrieveData() {
Bundle songData = this.getIntent().getExtras();
songId = songData.getString("id");
title = songData.getString("title");
artist = songData.getString("artist");
fileLink = songData.getString("fileLink");
coverArt = songData.getString("coverArt");
url = BASE_URL + fileLink;
}
private void displaySong(String title, String artist, String coverArt)
{
//retrieve song title
TextView txtTitle = (TextView) findViewById(R.id.txtSongTitle);
//set text of song title
txtTitle.setText(title);
//retrieve artist
TextView txtArtist = (TextView) findViewById(R.id.txtArtist);
//set text of artist
txtArtist.setText(artist);
//get id of coverart
int imageId = AppUtil.getImageIdFromDrawable(this,coverArt);
//retrieve coverart
ImageView ivCoverArt = (ImageView) findViewById(R.id.imgCoverArt);
ivCoverArt.setImageResource(imageId);
}
public void playOrPauseMusic(View view)
{// start player
player.start();
//2.
btnPlayPause.setText("PAUSE");
//3.set the heading title of played song
setTitle("Now Playing:" + title + "-" + artist);
}
private void preparePlayer() { //create a new player
player = new MediaPlayer();
try {
//set stream type to music
player.setAudioStreamType(AudioManager.STREAM_MUSIC);
//set source of music
player.setDataSource(url);
//prepare player for playback
player.prepare();
} catch (IOException e) {
e.printStackTrace();
}
}}
Logs:
08-10 16:04:02.478 2567-2567/sg.edu.tp.project1 I/art: Not late-enabling -Xcheck:jni (already on)
08-10 16:04:02.478 2567-2567/sg.edu.tp.project1 W/art: Unexpected CPU variant for X86 using defaults: x86
08-10 16:04:02.535 2567-2567/sg.edu.tp.project1 W/System: ClassLoader referenced unknown path: /data/app/sg.edu.tp.project1-2/lib/x86
08-10 16:04:02.539 2567-2567/sg.edu.tp.project1 I/InstantRun: Starting Instant Run Server for sg.edu.tp.project1
08-10 16:04:02.913 2567-2567/sg.edu.tp.project1 W/art: Before Android 4.1, method android.graphics.PorterDuffColorFilter android.support.graphics.drawable.VectorDrawableCompat.updateTintFilter(android.graphics.PorterDuffColorFilter, android.content.res.ColorStateList, android.graphics.PorterDuff$Mode) would have incorrectly overridden the package-private method in android.graphics.drawable.Drawable
08-10 16:04:03.399 2567-2632/sg.edu.tp.project1 I/OpenGLRenderer: Initialized EGL, version 1.4
08-10 16:04:03.400 2567-2632/sg.edu.tp.project1 D/OpenGLRenderer: Swap behavior 1
08-10 16:04:03.400 2567-2632/sg.edu.tp.project1 W/OpenGLRenderer: Failed to choose config with EGL_SWAP_BEHAVIOR_PRESERVED, retrying without...
08-10 16:04:03.400 2567-2632/sg.edu.tp.project1 D/OpenGLRenderer: Swap behavior 0
08-10 16:04:03.490 2567-2567/sg.edu.tp.project1 W/art: Before Android 4.1, method int android.support.v7.widget.ListViewCompat.lookForSelectablePosition(int, boolean) would have incorrectly overridden the package-private method in android.widget.ListView
08-10 16:04:14.759 2567-2632/sg.edu.tp.project1 D/OpenGLRenderer: endAllActiveAnimators on 0x8d2e9b00 (RippleDrawable) with handle 0x8d2ff830
08-10 16:04:27.207 2567-2570/sg.edu.tp.project1 I/art: Do partial code cache collection, code=29KB, data=27KB
08-10 16:04:27.207 2567-2570/sg.edu.tp.project1 I/art: After code cache collection, code=29KB, data=27KB
08-10 16:04:27.207 2567-2570/sg.edu.tp.project1 I/art: Increasing code cache capacity to 128KB
08-10 16:04:27.463 2567-2632/sg.edu.tp.project1 D/OpenGLRenderer: endAllActiveAnimators on 0x8c313a00 (RippleDrawable) with handle 0x8d2ff420
08-10 16:04:29.695 2567-2567/sg.edu.tp.project1 D/AndroidRuntime: Shutting down VM
Beginning of crash:
08-10 16:04:29.696 2567-2567/sg.edu.tp.project1 E/AndroidRuntime: FATAL EXCEPTION: main
Process: sg.edu.tp.project1, PID: 2567
java.lang.IllegalStateException: Could not execute method for android:onClick
at android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:293)
at android.view.View.performClick(View.java:5637)
at android.view.View$PerformClick.run(View.java:22429)
at android.os.Handler.handleCallback(Handler.java:751)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6119)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)
Caused by: java.lang.reflect.InvocationTargetException
at java.lang.reflect.Method.invoke(Native Method)
at android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:288)
at android.view.View.performClick(View.java:5637)
at android.view.View$PerformClick.run(View.java:22429)
at android.os.Handler.handleCallback(Handler.java:751)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6119)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.media.MediaPlayer.start()' on a null object reference
at sg.edu.tp.project1.PlayMusicActivity.playOrPauseMusic(PlayMusicActivity.java:106)
at java.lang.reflect.Method.invoke(Native Method)
at android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:288)
at android.view.View.performClick(View.java:5637)
at android.view.View$PerformClick.run(View.java:22429)
at android.os.Handler.handleCallback(Handler.java:751)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6119)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)
The exception message is very clear:
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.media.MediaPlayer.start()' on a null object reference
at sg.edu.tp.project1.PlayMusicActivity.playOrPauseMusic(PlayMusicActivity.java:106)
So your player field is null because you've never called PlayMusicActivity's preparePlayer() before.
I am a beginner and i am trying to learn how to use APIs on android. I am doing a bitcoin price app to learn APIs. But i have a few problems.I created a progressbar and a price TextView in mainactivity.xml . I set progressbar visible and textview invisible by default.My thought is very simple, i created a new AsyncTask class and after background things are done , i will set the progressbar invisible and the textview visible in the onPostExecute() to show price. But it didn't work. The progressbar keeps spinning, it doesn't show the price i dont understand why it doesn't work.
The API i am using
MainActivity
import android.os.AsyncTask;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.util.Log;
import android.view.View;
import android.widget.ProgressBar;
import android.widget.TextView;
import org.json.JSONObject;
import org.json.JSONTokener;
import java.net.URL;
import java.net.HttpURLConnection;
import java.io.InputStreamReader;
import java.io.BufferedReader;
public class MainActivity extends AppCompatActivity {
public static String line;
public static ProgressBar progressBar;
static String API_URL="https://api.coindesk.com/v1/bpi/currentprice/try.json";
static TextView priceTextView;
static TextView timeTextView;
static int priceInt;
#Override
protected void onCreate( Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
priceTextView=(TextView)findViewById(R.id.priceText);
timeTextView=(TextView)findViewById(R.id.timeText);
progressBar=(ProgressBar)findViewById(R.id.progressBar);
retrievePriceTask retrievePriceTask=new retrievePriceTask();
retrievePriceTask.execute();
}
}
class retrievePriceTask extends AsyncTask <Void,Void,String>{
#Override
protected void onPreExecute() {
MainActivity.progressBar.setVisibility(View.VISIBLE);
MainActivity.priceTextView.setVisibility(View.INVISIBLE);
}
#Override
protected String doInBackground(Void... urls) {
try {
URL url = new URL(MainActivity.API_URL);
HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();
try {
BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(urlConnection.getInputStream()));
StringBuilder stringBuilder = new StringBuilder();
while ((MainActivity.line = bufferedReader.readLine()) != null) {
stringBuilder.append(MainActivity.line).append("\n");
}
bufferedReader.close();
return stringBuilder.toString();
}
finally{
urlConnection.disconnect();
}
}
catch(Exception e) {
Log.e("ERROR", e.getMessage(), e);
return null;
}
}
#Override
protected void onPostExecute(String s) {
MainActivity.priceTextView.setVisibility(View.VISIBLE);
MainActivity.progressBar.setVisibility(View.INVISIBLE);
try{
JSONObject jsonObject=(JSONObject)new JSONTokener(MainActivity.line).nextValue();
MainActivity.priceInt=jsonObject.getJSONObject("bpi").getJSONObject("TRY").getInt("rate");
MainActivity.priceTextView.setText(MainActivity.priceInt);
}
catch (Exception e){
e.printStackTrace();
}
}
}
My Logcat
07-16 10:20:08.884 2269-2269/zaaa.trinki E/AndroidRuntime: FATAL EXCEPTION: main
Process: zaaa.trinki, PID: 2269
java.lang.RuntimeException: Unable to start activity ComponentInfo{zaaa.trinki/zaaa.trinki.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ProgressBar.setVisibility(int)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2298)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
at android.app.ActivityThread.access$800(ActivityThread.java:144)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5221)
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:899)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ProgressBar.setVisibility(int)' on a null object reference
at zaaa.trinki.retrievePriceTask.onPreExecute(MainActivity.java:94)
at android.os.AsyncTask.executeOnExecutor(AsyncTask.java:587)
at android.os.AsyncTask.execute(AsyncTask.java:535)
at zaaa.trinki.MainActivity.onCreate(MainActivity.java:55)
at android.app.Activity.performCreate(Activity.java:5933)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1105)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2251)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
at android.app.ActivityThread.access$800(ActivityThread.java:144)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5221)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
07-16 10:37:42.062 16262-16262/zaaa.trinki E/AndroidRuntime: FATAL EXCEPTION: main
Process: zaaa.trinki, PID: 16262
java.lang.RuntimeException: Unable to start activity ComponentInfo{zaaa.trinki/zaaa.trinki.MainActivity}: android.content.res.Resources$NotFoundException: String resource ID #0x0
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2298)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
at android.app.ActivityThread.access$800(ActivityThread.java:144)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5221)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
Caused by: android.content.res.Resources$NotFoundException: String resource ID #0x0
at android.content.res.Resources.getText(Resources.java:274)
at android.support.v7.widget.ResourcesWrapper.getText(ResourcesWrapper.java:52)
at android.widget.TextView.setText(TextView.java:4122)
at zaaa.trinki.MainActivity.onCreate(MainActivity.java:63)
at android.app.Activity.performCreate(Activity.java:5933)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1105)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2251)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
at android.app.ActivityThread.access$800(ActivityThread.java:144)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5221)
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:899)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
Use a ProgressDialog instead of a ProgressBar:
ProgressDialog myProgressDialog = ProgressDialog.show(Context CONTEXT, String TITLE, String MESSAGE, boolean INDETERMINATE, boolean CANCELABLE);
myProgressDialog.setProgressStyle(ProgressDialog.STYLE_SPINNER);
and in your onPostExecute() just put myProgressDialog.dismiss()