自定义View画一个圆

public class CustomViews extends View  implements Runnable{

    private Context mcontext;
    private int screenWidth;
    private int screenHeight;
    private int radial = 50;
    private Paint mpaint;

    public CustomViews(Context context) {
        super(context);
        init();
    }


    public CustomViews(Context context, AttributeSet attrs) {
        super(context, attrs);
        mcontext = context;
        init();
    }

    public CustomViews(Context context,  AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
    }

    private void init() {
        mpaint = new Paint();
        //设置画笔为抗锯齿
        mpaint.setAntiAlias(true);
        //设置颜色为红色
        mpaint.setColor(Color.RED);
        //填充
        mpaint.setStyle(Paint.Style.STROKE);
        mpaint.setStrokeWidth(20);
        //获取屏幕的宽高
        WindowManager wm  = (WindowManager) mcontext.getSystemService(Context.WINDOW_SERVICE);
        Display display = wm.getDefaultDisplay();
        screenWidth = display.getWidth();
        screenHeight = display.getHeight();
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        canvas.drawCircle(screenWidth/2,screenHeight/2,radial,mpaint);
    }

    @Override
    public void run() {
        /*while (true){
            if(radial<=170){
                radial+=20;
                postInvalidate();
            }else{
                radial=50;
            }
            try {
                Thread.sleep(200);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }*/
    }
}

MainActivity

 customViews = findViewById(R.id.cv);
        new Thread(customViews).start();