Develop Reference

How to start game over activity? (android studio)

Goal
display Game over screen when health = 0;
Steps
create new activity (GameOver.class)
create layout for GameOver activity
create new activity in AndroidManifest.xml
<activity
android:name=".GameOver"
android:exported="false" />
when player dies new activity is called
if(player.heart == 0){
Intent gameOverIntent = new Intent(context, MainActivity.class);
context.startActivity(gameOverIntent);
}
Error
However I get this error...
Process: com.example.breakoutgame, PID: 21386
java.lang.NullPointerException: Attempt to invoke virtual method 'void android.graphics.Canvas.drawColor(int, android.graphics.PorterDuff$Mode)' on a null object reference
at android.view.SurfaceView.clearSurfaceViewPort(SurfaceView.java:665)
at android.view.SurfaceView.dispatchDraw(SurfaceView.java:610)
at android.view.View.draw(View.java:22353)
at android.view.SurfaceView.draw(SurfaceView.java:601)
at com.example.breakoutgame.Game.draw(Game.java:84)
at com.example.breakoutgame.GameLoop.run(GameLoop.java:57)
Maybe I missed some step?

I can not open a default camera after I resume the App in java

I am working on an App that use camera for face recognition. But i have some problem when i resume my app the the app always crash.
This is my code Onresume Activity:
#Override
public synchronized void onResume() {
// LOGGER.d("onResume " + this);
super.onResume();;
handlerThread = new HandlerThread("inference");
handlerThread.start();
handler = new Handler(handlerThread.getLooper());
}
This is my code in CameraActivity:
CameraActivity.java
And this is the class that i used for recognize the face that extends from cameraActivity:
Detector Activity
I forgot to show the erorr:
E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.samples.flironecamera, PID: 30923
java.lang.NullPointerException: Attempt to invoke virtual method 'void com.samples.flironecamera.tracking.MultiBoxTracker.trackResults(java.util.List, long)' on a null object reference
at com.samples.flironecamera.DetectorActivity.updateResults(DetectorActivity.java:728)
at com.samples.flironecamera.DetectorActivity.onRestart(DetectorActivity.java:761)
at android.app.Instrumentation.callActivityOnRestart(Instrumentation.java:1443)
at android.app.Activity.performRestart(Activity.java:8067)
at android.app.ActivityThread.performRestartActivity(ActivityThread.java:5188)
at android.app.servertransaction.TransactionExecutor.performLifecycleSequence(TransactionExecutor.java:243)
at android.app.servertransaction.TransactionExecutor.cycleToPath(TransactionExecutor.java:201)
at android.app.servertransaction.TransactionExecutor.executeLifecycleState(TransactionExecutor.java:173)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:97)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2270)
at android.os.Handler.dispatchMessage(Handler.java:107)
at android.os.Looper.loop(Looper.java:237)
at android.app.ActivityThread.main(ActivityThread.java:8125)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:496)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1100)
And Another Erorr
java.lang.RuntimeException: Unable to resume activity {com.samples.flironecamera/com.samples.flironecamera.DetectorActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.hardware.Camera.startPreview()' on a null object reference

java.lang.NullPointerException: Attempt to invoke virtual method FloatingActionButton.setImageResource(int)' on a null object reference

I am trying to change the image of a floating action button when the app detects an in coming phone call. Here is the java class
public class PhoneCallReceiver extends BroadcastReceiver {
Main2Activity main2Activity;
#Override
public void onReceive(Context context, Intent intent) {
String state= intent.getStringExtra(TelephonyManager.EXTRA_STATE);
if (state.equals(TelephonyManager.EXTRA_STATE_RINGING)) {
main2Activity=new Main2Activity();
main2Activity.pauseWorkout();
}
}
}
Inside the pauseWorkout method it contains a method call to another method that changes the image of the floating action button, and it is where the exception is pointing at. Here is the method:
public void showPlayButton() {
//CHANGING FLOATING ACTION BUTTON
startPauseFAB.setImageResource(R.drawable.play_white);
startPauseFAB.setBackgroundTintList(ColorStateList.valueOf(getResources().getColor(R.color.floating_action_button_color_play)));
startPauseFAB.setRippleColor(getResources().getColor(R.color.myGreen));
}
startPauseFAB.setImageResource(R.drawable.play_white); is where the problem is.
In the main2Activity the image changes from play to pause icons with no problem but when a call is ringing the app crushes. Here is how it is intitialized on onCreate:
startPauseFAB = (FloatingActionButton) findViewById(R.id.startAndPauseFAB);
And here is the xml for the floating action button:
<android.support.design.widget.FloatingActionButton
android:id="#+id/startAndPauseFAB"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="bottom"
android:layout_margin="16dp"
android:src="#drawable/play_white"
app:backgroundTint="#color/floating_action_button_color_play"
app:borderWidth="0dp"
app:elevation="8dp"
app:fabSize="normal" />
I tried to use the debugging tool at startPauseFAB.setImageResource(R.drawable.play_white); it says there is no value.
here is the error message :
E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.leonk.workouttimerv1, PID: 13567
java.lang.RuntimeException: Unable to start receiver com.example.leonk.workouttimerv1.classes.PhoneCallReceiver: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.design.widget.FloatingActionButton.setImageResource(int)' on a null object reference
at android.app.ActivityThread.handleReceiver(ActivityThread.java:2630)
at android.app.ActivityThread.access$1700(ActivityThread.java:151)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1387)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5268)
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:902)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:697)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.design.widget.FloatingActionButton.setImageResource(int)' on a null object reference
at com.example.leonk.workouttimerv1.Main2Activity.setFABButton(Main2Activity.java:1308)
at com.example.leonk.workouttimerv1.classes.PhoneCallReceiver.onReceive(PhoneCallReceiver.java:27)
at android.app.ActivityThread.handleReceiver(ActivityThread.java:2623)
at android.app.ActivityThread.access$1700(ActivityThread.java:151) 
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1387) 
at android.os.Handler.dispatchMessage(Handler.java:102) 
at android.os.Looper.loop(Looper.java:135) 
at android.app.ActivityThread.main(ActivityThread.java:5268) 
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:902) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:697) 
How can I solve this problem. I searched through similar questions but the solutions didn't help

In the phoneCallReceiver java class in the onReceive method I add the method call context.sendBroadCast with an intent as follows
public class PhoneCallReceiver extends BroadcastReceiver {
#Override
public void onReceive(Context context, Intent intent) {
String state= intent.getStringExtra(TelephonyManager.EXTRA_STATE);
if (state.equals(TelephonyManager.EXTRA_STATE_RINGING)) {
context.sendBroadcast(new Intent("PHONE_RING"));
}
}
}
Then on the mainActivity create an object of the phoneCallReceiver class and override the onReceive method then call the activity method to change the image like :
PhoneCallReceiver phoneCallReceiver=new PhoneCallReceiver(){
#Override
public void onReceive(Context context, Intent intent) {
pauseWorkout();
}
};
Then on onCreate register the receiver like so:
registerReceiver(phoneCallReceiver,new IntentFilter("PHONE_RING"));
Then destroy :
#Override
protected void onDestroy() {
super.onDestroy();
unregisterReceiver(phoneCallReceiver);
}
Solution I got it here : Thanks everyone who commented you helped a lot
Blockquote

Android activity class gives NullPointerException [duplicate]

This question already has answers here:
What is a NullPointerException, and how do I fix it?
(12 answers)
Closed 6 years ago.
My problem is that one specific activity in my app can't be launched for some reason, and it throws:
java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.Class java.lang.Object.getClass()' on a null object reference
All other launching code that looks like this work fine, the problem is ONLY when I'm launching Player1. The class surely exists, and I can't understand what is the problem.
I'm launching an activity called Player1 from an activity called ChooseLevel. When some button is pressed, the call is:
Intent intent = new Intent(ChooseLevel.this, Player1.class);
Bundle b = new Bundle();
b.putInt("game_level", 1);
intent.putExtras(b);
startActivity(intent);
finish();
The logs show that the error is in: Player1.onCreate(Player1.java:50)
The code in line Player1:50 is:
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_player1);
changeIndex = 0;
cards = new ArrayList<Card>(8);
score = (TextView) findViewById(R.id.score_text);
message = (TextView) findViewById(R.id.msg_text);
timer = (TextView) findViewById(R.id.timer);
timer.setText(String.valueOf(definitions.TIMER_START)); # LINE 50
Bundle b = getIntent().getExtras();
...
}
When this launching code runs, I get this in my logs:
33:04.338 18302-18302/com... D/AndroidRuntime: Shutting down VM
01-18 10:33:04.338 18302-18302/com... E/AndroidRuntime: FATAL EXCEPTION: main
Process: com..., PID: 18302
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.../com....Player1}: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.Class java.lang.Object.getClass()' on a null object reference
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.Class java.lang.Object.getClass()' on a null object reference
at com....Player1.onCreate(Player1.java:50)
EDIT:
I found my answer, it had to do with some object that I had in my Player1.onCreate() method. In a wierd way, android-studio raised the exception regarding getClass(). If someone knows why this happend, please share :)

use context,getApplicationContext()orgetActivity()`
Intent intent = new Intent(context, Player1.class);
Bundle b = new Bundle();
b.putInt("game_level", 1);
intent.putExtras(b);
startActivity(intent);
finish();

How i can open browser onPostExecute

Here is the code
Intent browserIntent = new Intent(Intent.ACTION_VIEW, Uri.parse(this.redirectUrl+"?username="+getValue(loginString)+"&password="+getValue(pwdString)));
startActivity(browserIntent);
I have this error :
10-17 15:30:35.288 5467-5467/com.example.android.navigationdrawerexample W/dalvikvm﹕ threadid=1: thread exiting with uncaught exception (group=0x40cd7930)
10-17 15:30:35.298 5467-5467/com.example.android.navigationdrawerexample E/AndroidRuntime﹕ FATAL EXCEPTION: main
java.lang.IllegalStateException: Fragment PlanetFragment{41b91f78} not attached to Activity
at this line :
startActivity(browserIntent);
This and this DOESN'T work for me.
What i can do ?

Why don't you just call getActivity() from Fragment and then call startActivity() like getActivity().startActivity(intent);

From the exception, it looks like you're calling this method on a Fragment that is not (yet?) attached to an Activity. From the source of the Fragment class:
public void startActivity(Intent intent, Bundle options) {
if (mActivity == null) {
throw new IllegalStateException("Fragment " + this + " not attached to Activity");
}
...
To fix this, just change the place where this method is called, i.e. after onAttach() and before onDetach().