ViewOverlay: When, How and for What Purpose?

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[code]public ViewOverlay getOverlay() {
    if (mOverlay == null) {
        mOverlay = new ViewOverlay(mContext, this);
    }
    return mOverlay;
}

public ViewGroupOverlay getOverlay() {
    if (mOverlay == null) {
        mOverlay = new ViewGroupOverlay(mContext, this);
    }
    return (ViewGroupOverlay) mOverlay;
}

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[code]int[] parentLocation = new int[2];
int[] hostViewLocation = new int[2];
parent.getLocationOnScreen(parentLocation);
mHostView.getLocationOnScreen(hostViewLocation);
child.offsetLeftAndRight(parentLocation[0] - hostViewLocation[0]);
child.offsetTopAndBottom(parentLocation[1] - hostViewLocation[1]);

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[code]@Override
public void invalidate(Rect dirty) {
    super.invalidate(dirty);
    if (mHostView != null) {
        mHostView.invalidate(dirty);
    }
}

@Override
public void invalidate(int l, int t, int r, int b) {
    super.invalidate(l, t, r, b);
    if (mHostView != null) {
        mHostView.invalidate(l, t, r, b);
    }
}

@Override
public void invalidate() {
    super.invalidate();
    if (mHostView != null) {
        mHostView.invalidate();
    }
}

[...]

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[code]<RelativeLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent">

<Button
android:id="@+id/button"
android:text="Click me even if I'm a pirate"
android:background="@drawable/badged"
android:layout_width="250dp"
android:layout_height="250dp"
android:textColor="#FFF"
android:fontFamily="sans-serif-condensed"
android:layout_centerHorizontal="true"/>

</RelativeLayout>

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[code]class BannerDrawable extends Drawable {

private static final double SQRT_2 = Math.sqrt(2);
private final Rect mTextBounds;
private Paint mPaintFill;
private Paint mPaintText;
private String mMessage = "I'M A PIRATE BANNER";
private int mBannerWidth = 50;
private int mTextSize;

public BannerDrawable() {
  initPaintFill();
  initPaintText();
  mTextBounds = new Rect();
}

private void initPaintFill() {
  mPaintFill = new Paint(ANTI_ALIAS_FLAG);
  mPaintFill.setStyle(Paint.Style.FILL);
  mPaintFill.setColor(getResources().getColor(R.color.banner));
}

private void initPaintText() {
  mPaintText = new Paint(ANTI_ALIAS_FLAG);
  mPaintText.setStyle(Paint.Style.FILL);
  mPaintText.setColor(Color.WHITE);
  mPaintText.setTextSize(20);
  mPaintText.setShadowLayer(4.0f, 2.0f, 2.0f, Color.BLACK);
}

@Override
public void draw(Canvas canvas) {
  Rect bounds = getBounds();
            if (bounds.isEmpty()) {
                bounds = canvas.getClipBounds();
            }
            float width = bounds.width();

            adaptTextSize((int) (width * 0.9), (int) (mBannerWidth * 0.9));

            float bannerHyp = (float) (mBannerWidth * SQRT_2);

            canvas.translate(0, bounds.centerY() - mBannerWidth);
            canvas.rotate(45, bounds.centerX(), bounds.centerY() - mBannerWidth);
            canvas.drawRect(bounds.left - bannerHyp, bounds.top, bounds.right + bannerHyp, bounds.top + mBannerWidth, mPaintFill);

            canvas.drawText(mMessage, bounds.centerX() - mTextBounds.centerX(), mBannerWidth / 2 + mTextBounds.height() / 2, mPaintText);
}

private void adaptTextSize(float width, int height) {
  if (mTextSize > 0) {
      mPaintText.setTextSize(mTextSize);
      return;
  }
  int textSize = 10;
  int textHeight;
  int textWidth;
  boolean stop = false;
  while (!stop) {
      mTextSize = textSize++;
      mPaintText.setTextSize(mTextSize);
      mPaintText.getTextBounds(mMessage, 0, mMessage.length(), mTextBounds);

      textHeight = mTextBounds.height();
      textWidth = mTextBounds.width();

      stop = textHeight >= height || textWidth >= width;
  }
}

@Override
public void setAlpha(int alpha) {
}

@Override
public void setColorFilter(ColorFilter cf) {
}

@Override
public int getOpacity() {
  return PixelFormat.OPAQUE;
}
}

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[code]final View button = findViewById(R.id.button);
final ViewOverlay overlay = button.getOverlay();
final BannerDrawable bannerDrawable = new BannerDrawable();
button.post(new Runnable() {
  @Override
  public void run() {
      //top right square
      bannerDrawable.setBounds(button.getWidth() / 2, 0, button.getWidth(), button.getHeight() / 2);
      overlay.add(bannerDrawable);
  }
});

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[code]for(int i=0; i<10; i++) {
final Button button = new Button(this);
[... customize the button ...]

buttons.addView(button, params);

button.setOnClickListener(new View.OnClickListener() {
  @Override
  public void onClick(View v) {
      Toast.makeText(AnimActivity.this, "You click on a button", Toast.LENGTH_SHORT).show();
  }
});
button.setOnLongClickListener(new View.OnLongClickListener() {
  @Override
  public boolean onLongClick(View v) {
      animatedDelete(button);
      return true;
  }
});
}

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[code]private void animatedDelete(final Button button) {
final ViewGroupOverlay viewGroupOverlay = ((ViewGroup) findViewById(android.R.id.content)).getOverlay();
viewGroupOverlay.add(button);
AnimatorSet set = new AnimatorSet();
set.playTogether(
      ObjectAnimator.ofFloat(button, "scaleX", 1, 3f),
      ObjectAnimator.ofFloat(button, "scaleY", 1, 3f),
      ObjectAnimator.ofFloat(button, "alpha", 1, 0.0f)
);
set.start();
set.addListener(new AnimatorListenerAdapter() {
  @Override
  public void onAnimationEnd(Animator animation) {
      viewGroupOverlay.remove(button);
  }
});
}