Since onDraw() will be called frequently, it is not recommended to create a new object instance in this method.

Your problem may be that you don’t know how to correctly obtain the size of the View. The obtained width and height are always 0.

I’m going to tell you the simplest way, so let’s use it as a starting point

Use view.post()

public class CustomView extends View { private Bitmap mBitmap; public CustomView(Context context) { super(context) ... this.post(new Runnable() { @Override public void run() { mBitmap = Bitmap.createBitmap(getWidth(), getHeight(), Bitmap.Config.ARGB_8888); } }); } }

You can use View.onLayout or ViewTreeObserver

Since you inherit ImageView, I think you will naturally use the setImageBitmap(), setImageDrawable and other methods of ImageView, so you can get the width and height in these methods or get the bitmap directly