您正在呼叫 drawRect 两次（在使视图无效之前，以及在 onDraw 上）。另外，也无需存储对 Canvas 的引用。

You're calling to drawRect twice (before invalidating the view, and on onDraw). Also, there's no need to store a reference to Canvas.

将所需的颜色保留在变量中，对其进行更改并使视图无效。-

Keep the desired color in a variable, change it and invalidate the view.-

public class myView extends View {

    private Color color = Color.RED;

    Rect rects = new Rect(30,30,80,80); 

    @Override
    public void onDraw(Canvas canvas) {
         paint.setColor(color);
         canvas.drawRect(rects, paint);
    }

    void changeColor() {
        color = Color.BLUE
        invalidate();
    }
}