How to "hollow" View on Android
Various View shapes can be realized by using canvas provided by Android API level 1. Isn't the general usage such as generating a View such as a circle or a rectangle or cutting a Bitmap? So this time, I would like to introduce how to ** hollow out the View **.
First of all, how to draw View
public class CanvasView extends View {
private Paint paint = new Paint();
public CanvasView(Context context) {
super(context);
}
public CanvasView(Context context, @Nullable AttributeSet attrs) {
super(context, attrs);
}
public CanvasView(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
}
@Override
public void draw(Canvas canvas) {
super.draw(canvas);
paint.setStyle(Paint.Style.FILL);
canvas.drawCircle(getRootView().getWidth() / 2, getRootView().getHeight() / 2, 50, paint);
}
}
How to hollow out View
public class CanvasView extends View {
private Paint backgroundPaint = new Paint();
private Paint paint = new Paint();
public CanvasView(Context context) {
super(context);
}
public CanvasView(Context context, @Nullable AttributeSet attrs) {
super(context, attrs);
}
public CanvasView(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
}
@Override
public void draw(Canvas canvas) {
super.draw(canvas);
setLayerType(View.LAYER_TYPE_HARDWARE, null);
//Draw the whole
backgroundPaint.setColor(ContextCompat.getColor(getContext(), android.R.color.background_dark));
canvas.drawRect(0, 0, canvas.getWidth(), canvas.getHeight(), backgroundPaint);
//Hollow out a circle from the whole background
paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.CLEAR));
canvas.drawCircle(getWidth() / 2, getHeight() / 2, 250, paint);
}
}
Finally
I created a library using the method introduced here. If you like it, I would be grateful if you could give it a star.
https://github.com/TakuSemba/Spotlight
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