Android: Set alpha on button on click. Preferably xml only

Question

I want to introduce a 'down' style on some buttons. I've created a style, and a state list.

<selector xmlns:android="http://schemas.android.com/apk/res/android">

    <item android:drawable="@drawable/inactive_button_background" android:state_enabled="false"/>
    <item android:drawable="@drawable/active_button_background" android:state_enabled="true"/>
    <item android:drawable="@drawable/pressed_button_background" android:state_pressed="true"></item>
</selector>

The problem is that I want to be able to change just the alpha of the background when the button gets clicked (I will have variable backgrounds, so setting a sold color with alpha channel is not a solution).

And I want to do this from the declarative xml only (don't want to polute my code with layout stuff).

Problem is I don't know how to apply this alpha blending to the button from a xml drawable. I am pretty sure there's a way though.

Answer 1

I am bit late to answer this question but i just did this by changing the alpha value using View.onTouchListner

You can do this by implementing onTouch in this way

 @Override
public boolean onTouch(View v, MotionEvent event) {

    switch (event.getAction())
    {
        case MotionEvent.ACTION_DOWN:
            v.setAlpha(0.5f);
            break;
        case MotionEvent.ACTION_UP:
            v.setAlpha(1f);
        default : 
         v.setAlpha(1f)
    }
    return false;
}

I guess you cant change alpha value from drawable so you will have to do this in this way only.

Answer 2

This works perfectly

---

yourView.setOnTouchListener(new View.OnTouchListener() {
    @Override
    public boolean onTouch(View v, MotionEvent event) {
        switch (event.getAction()) {
            case MotionEvent.ACTION_DOWN: {
                v.setAlpha(0.5f);
                break;
            }
            case MotionEvent.ACTION_UP:
            case MotionEvent.ACTION_CANCEL: {
                v.setAlpha(1f);
                break;
            }
        }
        return false;
    }
});

Answer 3

Adding something to Michael answer, if you are looking for a "softer" click animation. I added this:

btn.setOnTouchListener(new View.OnTouchListener() {
        @Override
        public boolean onTouch(View v, MotionEvent motionEvent) {
            switch (motionEvent.getAction())
            {
                case MotionEvent.ACTION_DOWN:
                    v.animate().alpha(0.3f).setDuration(200).start();
                    break;
                case MotionEvent.ACTION_UP:
                    v.animate().alpha(1f).setDuration(200).start();
                default :
                    v.setAlpha(1f);
            }
            return false;
        }
    });
}

with lies on the same idea but with a animation