问题
I want to change a drawable's alpha value when it is pressed. So I create two drawables and put them in a StateListDrawable and set the alpha value for the pressed state. But it just doesn't work.
StateListDrawable content = new StateListDrawable();
Drawable contentSelected = this.getResources().getDrawable(
R.drawable.content_background);
contentSelected.mutate().setAlpha(100);
Drawable contentNormal = this.getResources().getDrawable(R.drawable.content_background);
content.addState(new int[] { android.R.attr.state_pressed }, contentSelected);
content.addState(new int[] { android.R.attr.state_enabled }, contentNormal);
ImageButton button = (ImageButton) view.findViewById(R.id.content_thumbnail);
button.setImageDrawable(content);
Update:
My final solution is to create a subclass of BitmapDrawable like this,
and change the alpha value in the onStateChange()
method.
public AlphaAnimatedDrawable(Resources res, Bitmap bitmap) {
super(res, bitmap);
this.setState(new int[] { android.R.attr.state_pressed, android.R.attr.state_selected,
android.R.attr.state_enabled });
}
private static final int PRESSED_ALPHA = 180;
private static final int REGULAR_ALPHA = 255;
@Override
protected boolean onStateChange(int[] states) {
for (int state : states) {
if (state == android.R.attr.state_pressed) {
setAlpha(PRESSED_ALPHA);
} else if (state == android.R.attr.state_selected) {
setAlpha(REGULAR_ALPHA);
} else if (state == android.R.attr.state_enabled) {
setAlpha(REGULAR_ALPHA);
}
}
return true;
}
回答1:
This worked for me
StateListDrawable drawable = new StateListDrawable();
Bitmap enabledBitmap = ((BitmapDrawable)mIcon).getBitmap();
// Setting alpha directly just didn't work, so we draw a new bitmap!
Bitmap disabledBitmap = Bitmap.createBitmap(
mIcon.getIntrinsicWidth(),
mIcon.getIntrinsicHeight(), Config.ARGB_8888);
Canvas canvas = new Canvas(disabledBitmap);
Paint paint = new Paint();
paint.setAlpha(126);
canvas.drawBitmap(enabledBitmap, 0, 0, paint);
BitmapDrawable disabled = new BitmapDrawable(mContext.getResources(), disabledBitmap);
drawable.addState(new int[] { -android.R.attr.state_enabled}, disabled);
drawable.addState(StateSet.WILD_CARD, mIcon);
来源:https://stackoverflow.com/questions/6705304/how-to-set-alpha-value-for-drawable-in-a-statelistdrawable