Android 按键按下实现阴影效果

final Button btn_gallery=(Button)findViewById(R.id.btn_gallery);
btn_gallery.setOnClickListener(new View.OnClickListener(){
    @Override
    public void onClick(View v){
        Intent intentgallery=new Intent(Intent.ACTION_GET_CONTENT);
        intentgallery.setType("image/*") ;
        startActivityForResult(intentgallery,GALLERY_REQUEST_CODE);
    }
});
btn_gallery.setOnTouchListener(new View.OnTouchListener() {
    @Override
    public boolean onTouch(View view, MotionEvent motionEvent) {
        int action = motionEvent.getAction();
        switch (action){
            case MotionEvent.ACTION_DOWN:
                btn_gallery.setBackgroundResource(R.drawable.galleryyy);
                break;
            case MotionEvent.ACTION_UP:
            case MotionEvent.ACTION_CANCEL:
                btn_gallery.setBackgroundResource(R.drawable.galleryy);
                break;
        }

        return false;
    }
});

galleryyy 

galleryy (有白边的)