Can't toast on a thread that has not called Looper.prepare()

Question

I try to run a test for my android app but I get this trace. What does it mean?

java.lang.RuntimeException: Can't toast on a thread that has not called Looper.prepare() at android.widget.Toast$TN.<init>(Toast.java:390) at android.widget.Toast.<init>(Toast.java:114) at android.widget.Toast.makeText(Toast.java:277) at android.widget.Toast.makeText(Toast.java:267) at dev.android.gamex.CatchGame.onDraw(MainActivity.java:317) at dev.android.gamex.JamieTest.useAppContext(JamieTest.java:45) at java.lang.reflect.Method.invoke(Native Method) at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50) at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12) at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47) at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17) at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325) at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78) at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57) at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290) at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71) at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288) at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58) at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268) at org.junit.runners.ParentRunner.run(ParentRunner.java:363) at org.mockito.internal.runners.JUnit45AndHigherRunnerImpl.run(JUnit45AndHigherRunnerImpl.java:37) at org.mockito.runners.MockitoJUnitRunner.run(MockitoJUnitRunner.java:62) at org.junit.runners.Suite.runChild(Suite.java:128) at org.junit.runners.Suite.runChild(Suite.java:27) at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290) at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71) at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288) at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58) at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268) at org.junit.runners.ParentRunner.run(ParentRunner.java:363) at org.junit.runner.JUnitCore.run(JUnitCore.java:137) at org.junit.runner.JUnitCore.run(JUnitCore.java:115) at android.support.test.internal.runner.TestExecutor.execute(TestExecutor.java:58) at android.support.test.runner.AndroidJUnitRunner.onStart(AndroidJUnitRunner.java:375) at android.app.Instrumentation$InstrumentationThread.run(Instrumentation.java:2074)  Tests ran to completion. 

My test class

package dev.android.gamex;   import android.content.Context; import android.content.res.Resources; import android.graphics.Canvas; import android.graphics.drawable.Drawable; import android.support.test.InstrumentationRegistry; import android.widget.TextView;  import org.junit.Ignore; import org.junit.Test; import org.junit.runner.RunWith; import org.mockito.Mock; import org.mockito.runners.MockitoJUnitRunner;  import static junit.framework.Assert.assertEquals; import static junit.framework.Assert.assertTrue; import static org.hamcrest.CoreMatchers.is; import static org.hamcrest.MatcherAssert.assertThat; import static org.mockito.Mockito.mock; import static org.mockito.Mockito.when;  @RunWith(MockitoJUnitRunner.class) public class JamieTest {      private static final String FAKE_STRING = "HELLO WORLD";      private OnScoreListener onScoreListener = new OnScoreListener() {         @Override         public void onScore(int score) {         }     };      @Mock     Canvas can;      @Test     public void useAppContext() throws Exception {         Context appContext = InstrumentationRegistry.getTargetContext();         assertEquals("dev.android.gamex", appContext.getPackageName());         CatchGame cg = new CatchGame(appContext, 5, "Jamie", onScoreListener);         cg.initialize();         assertTrue(! cg.gameOver);         cg.onDraw(new Canvas());         assertTrue(! cg.paused);      } } 

The code I want to test is below.

package dev.android.gamex;  import android.content.Context; import android.graphics.Bitmap; import android.graphics.BitmapFactory; import android.graphics.Canvas; import android.graphics.Color; import android.graphics.drawable.Drawable; import android.os.Bundle; import android.os.Handler; import android.support.v4.view.MotionEventCompat; import android.support.v7.app.AppCompatActivity; import android.view.Menu; import android.view.MenuItem; import android.view.MotionEvent; import android.view.View; import android.view.Window; import android.widget.ArrayAdapter; import android.widget.Button; import android.widget.LinearLayout; import android.widget.Spinner; import android.widget.TextView; import android.widget.Toast;  import java.util.Random;  public class MainActivity extends AppCompatActivity {     CatchGame cg;     public TextView textView;     public LinearLayout mainLayout;     String[] spinnerValue = {"Rookie", "Advanced", "Expert", "Master"};     // start app     @Override     public void onCreate(Bundle savedInstanceState) {         super.onCreate(savedInstanceState);         mainLayout = new LinearLayout(this);         mainLayout.setOrientation(LinearLayout.VERTICAL);          LinearLayout menuLayout = new LinearLayout(this);         menuLayout.setBackgroundColor(Color.parseColor("#FFFFFF"));          textView = new TextView(this);         textView.setVisibility(View.VISIBLE);         String str = "Score: 0";         textView.setText(str);         menuLayout.addView(textView);          Button button = new Button(this);         button.setText("Pause");         button.setOnClickListener(new View.OnClickListener() {             @Override             public void onClick(View v) {                 togglePausePlay();             }         });         menuLayout.addView(button);           Spinner spinner2 =new Spinner(this);         ArrayAdapter<String> adapter = new ArrayAdapter<>(MainActivity.this, android.R.layout.simple_list_item_1, spinnerValue);         spinner2.setAdapter(adapter);         menuLayout.addView(spinner2);          mainLayout.addView(menuLayout);          cg = new CatchGame(this, 5, "Jamie", onScoreListener);         cg.setBackground(getResources().getDrawable(R.drawable.bg_land_mdpi));         mainLayout.addView(cg);         getWindow().requestFeature(Window.FEATURE_ACTION_BAR);         getSupportActionBar().hide();         setContentView(mainLayout);     }      private void togglePausePlay() {         if (cg.paused) {             // play             //  getSupportActionBar().hide();             Toast.makeText(MainActivity.this, "Play", Toast.LENGTH_SHORT).show();         } else {             // pause             //    getSupportActionBar().show();             Toast.makeText(MainActivity.this, "Pause", Toast.LENGTH_SHORT).show();         }          cg.paused = !cg.paused;     }      private OnScoreListener onScoreListener = new OnScoreListener() {         @Override         public void onScore(int score) {             textView.setText("Score: " + score);         }     };      @Override     public boolean onCreateOptionsMenu(Menu menu) {         // Inflate the menu; this adds items to the action bar if it is present.         getMenuInflater().inflate(R.menu.main_menu, menu);         return true;     }      // method called when top right menu is tapped     @Override     public boolean onOptionsItemSelected(MenuItem item) {         super.onOptionsItemSelected(item);         int difficulty = cg.NBRSTEPS;         String name = cg.heroName;          switch (item.getItemId()) {             case R.id.item11:                 cg = new CatchGame(this, 3, name, onScoreListener);                 setContentView(cg);                 mainLayout.addView(cg);                 getWindow().requestFeature(Window.FEATURE_ACTION_BAR);                 getSupportActionBar().hide();                 setContentView(mainLayout);                 return true;             case R.id.item12:                 cg = new CatchGame(this, 5, name, onScoreListener);                 setContentView(cg);                 mainLayout.addView(cg);                 getWindow().requestFeature(Window.FEATURE_ACTION_BAR);                 getSupportActionBar().hide();                 setContentView(mainLayout);                 return true;             case R.id.item13:                 cg = new CatchGame(this, 7, name, onScoreListener);                 setContentView(cg);                 mainLayout.addView(cg);                 getWindow().requestFeature(Window.FEATURE_ACTION_BAR);                 getSupportActionBar().hide();                 setContentView(mainLayout);                 return true;             case R.id.item14:                 cg = new CatchGame(this, 9, name, onScoreListener);                 setContentView(cg);                 mainLayout.addView(cg);                 getWindow().requestFeature(Window.FEATURE_ACTION_BAR);                 getSupportActionBar().hide();                 setContentView(mainLayout);                 return true;             case R.id.item15:                 cg = new CatchGame(this, 11, name, onScoreListener);                 setContentView(cg);                 mainLayout.addView(cg);                 getWindow().requestFeature(Window.FEATURE_ACTION_BAR);                 getSupportActionBar().hide();                 setContentView(mainLayout);                 return true;             case R.id.item21:                 cg = new CatchGame(this, difficulty, "Jamie", onScoreListener);                 setContentView(cg);                 mainLayout.addView(cg);                 getWindow().requestFeature(Window.FEATURE_ACTION_BAR);                 getSupportActionBar().hide();                 setContentView(mainLayout);                 return true;             case R.id.item22:                 cg = new CatchGame(this, difficulty, "Spaceship", onScoreListener);                 setContentView(cg);                 //mainLayout.addView(cg);                 //getWindow().requestFeature(Window.FEATURE_ACTION_BAR);                 getSupportActionBar().hide();                 //setContentView(mainLayout);                 return true;             default:                 cg.paused = true;                 return super.onOptionsItemSelected(item);         }     }  }  interface OnScoreListener {     void onScore(int score); }  class CatchGame extends View {     int NBRSTEPS; // number of discrete positions in the x-dimension; must be uneven     String heroName;     int screenW;     int screenH;     int[] x; // x-coordinates for falling objects     int[] y; // y-coordinates for falling objects     int[] hero_positions; // x-coordinates for hero     Random random = new Random();     int ballW; // width of each falling object     int ballH; // height of ditto     float dY; //vertical speed     Bitmap falling, hero, jamie2, jamieleft, jamieright;     int heroXCoord;     int heroYCoord;     int xsteps;     int score;     int offset;     boolean gameOver; // default value is false     boolean toastDisplayed;     boolean paused = false;      OnScoreListener onScoreListener;      // constructor, load images and get sizes     public CatchGame(Context context, int difficulty, String name, OnScoreListener onScoreListener) {         super(context);         NBRSTEPS = difficulty;         heroName = name;         this.onScoreListener = onScoreListener;          x = new int[NBRSTEPS];         y = new int[NBRSTEPS];         hero_positions = new int[NBRSTEPS];         int resourceIdFalling = 0;         int resourceIdHero = 0;         if (heroName.equals("Jamie")) {             resourceIdFalling = R.mipmap.falling_object2;             resourceIdHero = R.drawable.left_side_hdpi;             setBackground(getResources().getDrawable(R.mipmap.background));         }         if (heroName.equals("Spaceship")) {             resourceIdFalling = R.mipmap.falling_object;             resourceIdHero = R.mipmap.ufo;             setBackground(getResources().getDrawable(R.mipmap.space));         }         falling = BitmapFactory.decodeResource(getResources(), resourceIdFalling); //load a falling image         hero = BitmapFactory.decodeResource(getResources(), resourceIdHero); //load a hero image         jamieleft = BitmapFactory.decodeResource(getResources(), R.drawable.left_side_hdpi); //load a hero image         jamieright = BitmapFactory.decodeResource(getResources(), R.drawable.right_side_hdpi); //load a hero image          ballW = falling.getWidth();         ballH = falling.getHeight();     }      public CatchGame(Context context, int difficulty, String name, OnScoreListener onScoreListener, Drawable background) {         this(context, difficulty, name, onScoreListener);         this.setBackground(background);     }      // set coordinates, etc.     void initialize() {         if (!gameOver) { // run only once, when the game is first started             int maxOffset = (NBRSTEPS - 1) / 2;             for (int i = 0; i < x.length; i++) {                 int origin = (screenW / 2) + xsteps * (i - maxOffset);                 x[i] = origin - (ballW / 2);                 hero_positions[i] = origin - hero.getWidth();             }             int heroWidth = hero.getWidth();             int heroHeight = hero.getHeight();              hero = Bitmap.createScaledBitmap(hero, heroWidth * 2, heroHeight * 2, true);             hero = Bitmap.createScaledBitmap(hero, heroWidth * 2, heroHeight * 2, true);             jamieleft = Bitmap.createScaledBitmap(jamieleft, jamieleft.getWidth()* 2, jamieright.getWidth() * 2, true);             jamieright = Bitmap.createScaledBitmap(jamieright, jamieright.getWidth()* 2, jamieright.getWidth() * 2, true);              heroYCoord = screenH - 2 * heroHeight; // bottom of screen          }         for (int i = 0; i < y.length; i++) {             y[i] = -random.nextInt(1000); // place items randomly in vertical direction         }          offset = (NBRSTEPS - 1) / 2; // place hero at centre of the screen         heroXCoord = hero_positions[offset];          // initialize or reset global attributes         dY = 2.0f;         score = 0;         gameOver = false;         toastDisplayed = false;     }      // method called when the screen opens     @Override     public void onSizeChanged(int w, int h, int oldw, int oldh) {         super.onSizeChanged(w, h, oldw, oldh);         screenW = w;         screenH = h;         xsteps = w / NBRSTEPS;         initialize();     }      // method called when the "game over" toast has finished displaying     void restart(Canvas canvas) {          toastDisplayed = true;         initialize();         draw(canvas);     }      // update the canvas in order to display the game action     @Override     public void onDraw(Canvas canvas) {         if (toastDisplayed) {             restart(canvas);             return;         }         super.onDraw(canvas);          int heroHeight = hero.getHeight();         int heroWidth = hero.getWidth();         int heroCentre = heroXCoord + heroWidth / 2;          Context context = this.getContext();          // compute locations of falling objects         for (int i = 0; i < y.length; i++) {             if (!paused) {                 y[i] += (int) dY;             }             // if falling object hits bottom of screen             if (y[i] > (screenH - ballH) && !gameOver) {                 dY = 0;                 gameOver = true;                 paused = true;                 int duration = Toast.LENGTH_SHORT;                  final Toast toast = Toast.makeText(context, "GAME OVER!\nScore: " + score, duration);                 toast.show();                 Handler handler = new Handler();                 handler.postDelayed(new Runnable() {                     @Override                     public void run() {                         toast.cancel();                         toastDisplayed = true;                     }                 }, 3000);                 //Vibrator v = (Vibrator) context.getSystemService(context.VIBRATOR_SERVICE);                 // Vibrate for 3000 milliseconds                 //v.vibrate(3000);              }             // if the hero catches a falling object             if (x[i] < heroCentre && x[i] + ballW > heroCentre &&                     y[i] > screenH - ballH - heroHeight) {                  y[i] = -random.nextInt(1000); // reset to new vertical position                 score += 1;                 onScoreListener.onScore(score);             }          }          canvas.save(); //Save the position of the canvas.          for (int i = 0; i < y.length; i++) {             canvas.drawBitmap(falling, x[i], y[i], null); //Draw the falling on the canvas.         }         canvas.drawBitmap(hero, heroXCoord, heroYCoord, null); //Draw the hero on the canvas.          canvas.restore();         //Call the next frame.         invalidate();     }      // event listener for when the user touches the screen     @Override     public boolean onTouchEvent(MotionEvent event) {         if (paused) {             paused = false;         }         int action = MotionEventCompat.getActionMasked(event);         if (action != MotionEvent.ACTION_DOWN || gameOver) { // non-touchdown event or gameover             return true; // do nothing         }         int coordX = (int) event.getX();         int xCentre = (screenW / 2) - (hero.getWidth() / 2);         int maxOffset = hero_positions.length - 1; // can't move outside right edge of screen         int minOffset = 0; // ditto left edge of screen          if (coordX < xCentre && offset > minOffset) { // touch event left of the centre of screen             offset--; // move hero to the left              if(coordX < heroXCoord)// + heroWidth / 2)                 hero = Bitmap.createScaledBitmap(jamieleft, jamieleft.getWidth() , jamieleft.getHeight() , true);          }         if (coordX > xCentre && offset < maxOffset) { // touch event right of the centre of screen             offset++; // move hero to the right              if(coordX > heroXCoord)                 hero  = Bitmap.createScaledBitmap(jamieright, jamieright.getWidth() , jamieright.getHeight() , true);          }         heroXCoord = hero_positions[offset];          return true;     } } 

The repository is available online.

Answer 1

You CANNOT show a Toast on non-UI thread. You need to call Toast.makeText() (and most other functions dealing with the UI) from within the main thread.

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You could use Activity#runOnUiThread():

runOnUiThread(new Runnable() {       public void run() {          final Toast toast = Toast.makeText(context, "GAME OVER!\nScore: " + score, duration);          toast.show();       }  }); 

If you want execute a instrumentation test on main thread, add @UiThreadTest annotation:

@Test @UiThreadTest public void useAppContext() {     // ... } 

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P.s: There are also many other ways with explain (using Handler, Looper, Observable..) in these posts: Android: Toast in a thread and Can't create handler inside thread that has not called Looper.prepare()

Answer 2

One cannot show a Toast from a non UI Thread. So you can do the following from the worker thread and it doesn't require Activity or Context

JAVA

 new Handler(Looper.getMainLooper()).post(new Runnable() { @Override public void run() {     Toast toast = Toast.makeText(mContext, "Toast", Toast.LENGTH_SHORT);     toast.show(); } }); 

KOTLIN

Handler(Looper.getMainLooper()).post {     Toast.makeText(mContext, "Toast", Toast.LENGTH_SHORT).show() }