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

Exception or error:

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.

How to solve:

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.


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() {
    // ...
}

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()

###

In kotlin put your code inside this:

runOnUiThread { 
    Log.i(TAG, "runOnUiThread")
    Toast.makeText(MainActivity.this, "Play", Toast.LENGTH_SHORT).show()
}

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