Develop Reference

OnClickListener on Bitmap animations in Android Studio throws NullPointerException [duplicate]

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What is a NullPointerException, and how do I fix it?
(12 answers)
findViewByID returns null
(33 answers)
Closed 1 year ago.
I made a simple screen with two flying bird animations using SurfaceView and Bitmap. I'm now trying to add an OnClickListener to each animation, I want different sounds to be played depending on which animation is clicked using SoundPool but for now, I have just added a toast message to see if the OnClickListener works.
Im not sure how to go about this, the method I am currently trying is that I have added two different ImageButtons in the XML file and attach those ImageButtons to my Bitmaps.
I have added all the code but I think the problem lies in the draw() method.
Heres the Error I get
java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ImageButton.setImageBitmap(android.graphics.Bitmap)' on a null object reference
The error message links to the following line of code
imgBtnPurple.setImageBitmap(resizedPurpleBird);
Code
public class PlayActivity extends AppCompatActivity {
surfaceView view;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
view = new surfaceView(this);
setContentView(view);
private class Anim extends Thread {
int counter = 0;
int counter2 = 0;
#Override
public void run() {
long last_updated_time = 0;
long delay = 150;
int[] purple_bird = {
R.drawable.bird1,
R.drawable.bird2
};
int[] red_bird = {
R.drawable.red1,
R.drawable.red2,
R.drawable.red3,
R.drawable.red4,
R.drawable.red5,
R.drawable.red6,
R.drawable.red7,
R.drawable.red8,
R.drawable.red9,
R.drawable.red10
};
while (true) {
boolean playing = true;
if (playing) {
long current_time = System.currentTimeMillis();
if (current_time > last_updated_time + delay) {
if (counter >= 2) {
counter = 0;
}
if (counter2 >= 4) {
counter2 = 0;
}
draw(purple_bird[counter], red_bird[counter2]);
last_updated_time = current_time;
counter++;
counter2++;
}
}
}
}
private void draw(int red_bird, int purple_bird) {
SurfaceHolder holder = getHolder();
Canvas canvas = holder.lockCanvas();
if (canvas != null) {
canvas.drawColor(Color.WHITE);
Paint paint = new Paint();
Bitmap purpleBird = BitmapFactory.decodeResource(getContext().getResources(), purple_bird);
Bitmap redBird = BitmapFactory.decodeResource(getContext().getResources(), red_bird);
Bitmap resizedRedBird = Bitmap.createScaledBitmap(redBird, (int) (redBird.getWidth() * 0.1), (int) (redBird.getHeight() * 0.1), true);
Bitmap resizedPurpleBird = Bitmap.createScaledBitmap(purpleBird, (int) (purpleBird.getWidth() * 0.4), (int) (purpleBird.getHeight() * 0.4), true);
canvas.drawBitmap(resizedRedBird, 100, 100, paint);
canvas.drawBitmap(resizedPurpleBird, 100, 600, paint);
holder.unlockCanvasAndPost(canvas);
ImageButton imgBtnPurple = (ImageButton) findViewById(R.id.imageBtnPurple);
imgBtnPurple.setImageBitmap(resizedPurpleBird);
imgBtnPurple.setOnClickListener(new OnClickListener() {
#Override
public void onClick(View v) {
Toast.makeText(getApplicationContext(),"Hello Purple Bird", Toast.LENGTH_SHORT).show();
}
});
ImageButton imgBtnRed = (ImageButton) findViewById(R.id.imageBtnRed);
imgBtnRed.setImageBitmap(resizedRedBird);
imgBtnRed.setOnClickListener(new OnClickListener() {
#Override
public void onClick(View v) {
Toast.makeText(getApplicationContext(),"Hello Red Bird",Toast.LENGTH_SHORT).show();
}
});
}
}
}
}
}
Layout Code
<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.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=".PlayActivity">
<ImageButton
android:id="#+id/imageBtnPurple"
android:layout_width="58dp"
android:layout_height="49dp"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.155"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintVertical_bias="0.143"
app:srcCompat="#drawable/bird1" />
<ImageButton
android:id="#+id/imageBtnRed"
android:layout_width="54dp"
android:layout_height="45dp"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="#+id/imageBtnPurple"
app:layout_constraintHorizontal_bias="0.0"
app:layout_constraintStart_toStartOf="#+id/imageBtnPurple"
app:layout_constraintTop_toBottomOf="#+id/imageBtnPurple"
app:layout_constraintVertical_bias="0.332"
app:srcCompat="#drawable/red1" />
</androidx.constraintlayout.widget.ConstraintLayout>

Animation doesn't end - Android

In my app, I have a button to show a drop-down menu, inside of that menu we have some options, one of this is "flip A coin",
the purpose of this option is to flip a coin easy animation, that animation appears inside a textView, and show a head-side or a tail-side of a coin instead of the text in the textView.
I have two problems:
The animation doesn't work how I want, it should appear in 1 second a coin instead of the text inside the textView, it stays there and after 2 seconds he disappears, but after the disappearance, the coin image come back inside the textView, it shouldn't reappear.
This is not a real question for a problem but more an optional question like "you know how to do that?". I 'don't know how to create a flip animation with a coin multiple rotations.
XML drop down menu:
<item
android:id="#+id/flipacoin"
android:title="#string/flipACoin" />
<item
android:id="#+id/rolladice"
android:title="#string/rollADice" />
<item
android:id="#+id/imagebackground"
android:title="#string/changeImage" />
JAVA code that calls the animation function:
#Override
public boolean onMenuItemClick(MenuItem item) {
switch (item.getItemId()){
case R.id.flipacoin:
flipACoin();
return true;
case R.id.rolladice:
Toast.makeText(this,"TODO roll a dice",Toast.LENGTH_SHORT).show();
return true;
case R.id.imagebackground:
Toast.makeText(this,"TODO image background",Toast.LENGTH_SHORT).show();
return true;
default:
return false;
}
}
JAVA animation function:
public void flipACoin(){
coin.setText(null); //this is for remove the text inside the textView
coin.setBackground(RANDOM.nextFloat() > 0.5f ? getResources().getDrawable(R.drawable.tails) : getResources().getDrawable(R.drawable.heads));
Animation fadeIn = new AlphaAnimation(0, 1);
fadeIn.setInterpolator(new DecelerateInterpolator());
fadeIn.setDuration(1000);
Animation fadeOut = new AlphaAnimation(1, 0);
fadeOut.setInterpolator(new AccelerateInterpolator());
fadeOut.setStartOffset(2000);
fadeOut.setDuration(1000);
AnimationSet animation = new AnimationSet(false);
animation.addAnimation(fadeIn);
animation.addAnimation(fadeOut);
coin.setAnimation(animation);
}

When You set background at the beginning it just stays after animation. To set back text and background to null You can add Animation listener. Below is sample application which does it:
public class MainActivity extends AppCompatActivity
{
TextView coin;
Random RANDOM;
#Override
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
RANDOM = new Random();
coin = findViewById(R.id.coin);
(findViewById(R.id.click)).setOnClickListener(new View.OnClickListener()
{
#Override
public void onClick(View view)
{
flipACoin();
}
});
}
public void flipACoin()
{
coin.setText(null);
coin.setBackground(ResourcesCompat.getDrawable(getResources(),
RANDOM.nextFloat() > 0.5f ? R.drawable.ic_launcher_background : R.drawable.ic_launcher_foreground,
null
));
Animation fadeIn = new AlphaAnimation(0, 1);
fadeIn.setInterpolator(new DecelerateInterpolator());
fadeIn.setDuration(1000);
Animation fadeOut = new AlphaAnimation(1, 0);
fadeOut.setInterpolator(new AccelerateInterpolator());
fadeOut.setStartOffset(2000);
fadeOut.setDuration(1000);
AnimationSet animation = new AnimationSet(false);
animation.addAnimation(fadeIn);
animation.addAnimation(fadeOut);
// listener, it will execute function when animation starts/ends/repeats
animation.setAnimationListener(new Animation.AnimationListener()
{
#Override
public void onAnimationStart(Animation animation)
{
Log.d("MyTag", "onAnimationStart:");
}
#Override
public void onAnimationEnd(Animation animation) // when animation ends, set text and background to null
{
Log.d("MyTag", "onAnimationEnd:");
coin.setBackground(null);
coin.setText("Default");
}
#Override
public void onAnimationRepeat(Animation animation)
{
Log.d("MyTag", "onAnimationRepeat:");
}
});
coin.setAnimation(animation);
}
}
activity_main.xml:
<?xml version="1.0" encoding="utf-8"?>
<androidx.appcompat.widget.LinearLayoutCompat xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
>
<Button
android:id="#+id/click"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="click"
/>
<TextView
android:id="#+id/coin"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Default"
/>
</androidx.appcompat.widget.LinearLayoutCompat>

Android Studio change background color multiple times with 1 button click

I am brand new to Android Studio and am trying to figure out how to change the background color of my start up app.
The moment the app loads, I see a button on the screen, and when I click, it goes to the color red.
What I want is when you click the button, it goes from red to green to blue than back to red.
However, I keep getting these errors:
Error:Execution failed for task ':app:compileDebugJavaWithJavac'.
Compilation failed; see the compiler error output for details.
Error:(72, 9) error: class, interface, or enum expected
Main Activity XML File:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
android:id="#+id/layout">
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Change Color"
android:onClick="onChangeColor"/>
</LinearLayout>
Test Activity Java Code:
private int colorIndex = 1;
public void onChangeColor(View view) {
int color;
if(colorIndex==0) {
color = Color.RED;
colorIndex = 1;
}else if(colorIndex==1) {
color = Color.GREEN;
colorIndex = 2;
}else {
//colorIndex = 2
color = Color.BLUE;
colorIndex = 0;
}
View layout = findViewById(R.id.layout);
layout.setBackgroundColor(color);
}
public class TestActivity extends AppCompatActivity {
View view;
//declare a string variable in java a class
//private var colour = "green";
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
View layout = findViewById(R.id.layout);
layout.setBackgroundColor(Color.RED);
view= this.getWindow().getDecorView();
view.setBackgroundResource(R.color.gray);
}
public void goRed(View v)
{
//if (colour == "green"){
view.setBackgroundResource(R.color.red);
//colour = "red";
//}
}
}

To give you a excellent help, it will be necessary to see you code.
Any way if i andersted you right maybe this will help you :
On your xml layout:
<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
android:id="#+id/layout">
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Change Color"
android:onClick="onChangeColor"/>
</LinearLayout>
On your activity :
private int colorIndex = 1;
public void onChangeColor(View view) {
int color;
if(colorIndex==0) {
color = Color.RED;
colorIndex = 1;
}else if(colorIndex==1) {
color = Color.GREEN;
colorIndex = 2;
}else {
//colorIndex = 2
color = Color.BLUE;
colorIndex = 0;
}
View layout = findViewById(R.id.layout);
layout.setBackgroundColor(color);
}
On you onCreate in the activity
View layout = findViewById(R.id.layout);
layout.setBackgroundColor(Color.RED);

If I understood correctly what you want is, to transition over a series of colours over time, and each colour lasting for some 1-2 seconds. You can use Android's default CountDownTimer.
Keep Your xml layout same.
In your Activity:
public class TestActivity extends AppCompatActivity {
LinearLayout layout;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
layout = (LinearLayout)findViewById(R.id.layout);
layout.setBackgroundColor(Color.RED);
}
public void onChangeColor(View view) {
// start your timer on button click
new CountDownTimer(3000, 1000) {
public void onTick(long millisUntilFinished) {
changeBackground(3-millisUntilFinished/1000);
}
}.start();
}
private void changeBackground(int colorIndex){
int color;
if(colorIndex==1) {
color = Color.GREEN;
}else if(colorIndex==2) {
color = Color.BLUE;
}else {
color = Color.RED;
}
layout.setBackgroundColor(color);
}
}
Hope this might help. If I misunderstood something please comment.
Edit: I typecasted View to LinearLayout

How to change textView (digitalClock) color on touch(screen)

I'm making an app that just displays a clock, but I want is so that everytime a user touches the screen it changes the color of the text (from a list of preselected colors in a colors.xml file) but I haven't got a clue where to start. Can someone point me in the right direction?
Here's the main activity:
public class MainActivity extends Activity {
private static final Random RANDOM = new Random();
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
getWindow().addFlags(WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON);
setContentView(R.layout.activity_main);
Handler handler = new RandomMoveHandler((TextView) findViewById(R.id.digitalClock1));
handler.sendEmptyMessage(0);
}
// Make the handler subclass static because of this: http://stackoverflow.com/a/11408340/111777
private static class RandomMoveHandler extends Handler {
private final WeakReference<TextView> textViewWeakReference;
private RandomMoveHandler(TextView textView) {
this.textViewWeakReference = new WeakReference<TextView>(textView);
}
#Override
public void handleMessage(Message msg) {
TextView textView = textViewWeakReference.get();
if (textView == null) {
Log.i(TAG, "WeakReference is gone so giving up.");
return;
}
int x = RANDOM.nextInt(350 - 100);
int y = RANDOM.nextInt(800 - 100);
Log.i(TAG, String.format("Moving text view to (%d, %d)", x, y));
textView.setX(x);
textView.setY(y);
//change the text position here
this.sendEmptyMessageDelayed(0, 30000);
}
}
private static final String TAG = MainActivity.class.getSimpleName();
}
and here's the layout xml:
<AbsoluteLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
tools:context=".MainActivity"
android:background="#color/black" >
<DigitalClock
android:id="#+id/digitalClock1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="DigitalClock"
android:textColor="#color/ics_blue"
android:textSize="28sp" />

I haven't making deal with DigitalClock but I think, at first, you should reference DigitalClock variable, not TextView. And second, to intercept touch event you need to override onTouckEvent method of your activity, it will callback everytime user touches the screen.

You should follow these steps
Use a TimerTask to.continusly show the time
Implement a touchlistener on that clock view
like this
view.setOnTouchListener
Make an array Colors like this
int[] colr={Color.BLACK,Color.BLUE};
and use random index in your touch event andset it as your color of the view

Android Button Doesn't Respond After Animation

I have a basic animation of a button after it is pressed currently in my application. After the button finishes animating, I can no longer click on it. It doesn't even press with an orange highlight.
Any help?
Here's my code:
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
animation = new AnimationSet(true);
animation.setFillAfter(true);
Animation translate = new TranslateAnimation(Animation.RELATIVE_TO_SELF, 0.0f, Animation.RELATIVE_TO_SELF, 0.0f, Animation.RELATIVE_TO_SELF, 0.0f, Animation.RELATIVE_TO_SELF, 5.0f);
translate.setDuration(500);
animation.addAnimation(translate);
LayoutAnimationController controller = new LayoutAnimationController(animation, 0.25f);
generate = (Button)findViewById(R.id.Button01);
generate.setOnClickListener(new View.OnClickListener(){
public void onClick(View v){
keyFromTop();
}
});
}
public void keyFromTop(){
generate.setAnimation(animation);
}

Animations affect only the drawing of widgets, which means after the animation is done, your button is still at its previous location. You need to manually update the layout parameters of your button if you want to move it to the new location. Also, your AnimationSet and your AnimationController are useless.

If you want to be able to click the button after the animation is complete, you have to manually move the component.
Here's an example of a translate animation applied to a button:
public class Test2XAnimation extends Activity {
private RelativeLayout buttonContainer;
private Button button;
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
button = (Button) this.findViewById(R.id.button1);
buttonContainer = (RelativeLayout) button.getParent();
}
public void startTapped(View view) {
animateButton(200, 100);
}
public void buttonTapped(View view) {
Toast.makeText(this, "tap", Toast.LENGTH_SHORT).show();
}
private RelativeLayout.LayoutParams params;
private CharSequence title;
private void animateButton(final int translateX, final int translateY) {
TranslateAnimation translate = new TranslateAnimation(0, translateX, 0,
translateY);
translate.setDuration(1500);
translate.setAnimationListener(new AnimationListener() {
public void onAnimationEnd(Animation animation) {
buttonContainer.removeView(button);
button = new Button(Test2XAnimation.this);
button.setText(title);
button.setOnClickListener(new OnClickListener() {
public void onClick(View v) {
buttonTapped(button);
}
});
params.leftMargin = translateX + params.leftMargin;
params.topMargin = translateY + params.topMargin;
params.rightMargin = 0 + params.rightMargin;
params.bottomMargin = 0 + params.bottomMargin;
button.setLayoutParams(params);
buttonContainer.addView(button);
}
public void onAnimationRepeat(Animation animation) {
}
public void onAnimationStart(Animation animation) {
params = (RelativeLayout.LayoutParams) button.getLayoutParams();
title = button.getText();
}
});
button.startAnimation(translate);
}
}
The method startTapped() is triggered when a user clicks a button in the UI. The other button moves by (200,100). At the end, I remove the old one and create a new one, thenaI add it to the parent view. You can see that buttonTapped() is called after the animation.
A suggestion: you can use NineOldAndroids project if you want to support both the new and the old way of animating a component, then you can check the OS version and run this code only on Gingerbread and lower versions.

I really struggled with shuffling layout params to make the "real" button match up to its animated location. I finally succeeded by using this approach. I extended ImageButton and overrode getHitRect:
#Override
public void getHitRect(Rect outRect) {
Rect curr = new Rect();
super.getHitRect(curr);
outRect.bottom = curr.bottom + 75;
outRect.top = curr.top + 75;
outRect.left = curr.left;
outRect.right = curr.right;
}
Then, I could use this button in the troublesome view:
<com.sample.YPlus75ImageButton a:id="#+id/....
It's worth noting that all of this changes for 3.0.