Java android覆盖按钮上的边框半径

下面是我在android中用来显示覆盖按钮的java代码。它显示了简单的长方体。我想在左上角和右上角添加边界半径。我搜索了很多，但在谷歌上找不到路。请告诉我如何添加半径

wm = (WindowManager) getSystemService(Context.WINDOW_SERVICE);

        overlayedButton = new Button(this);
        overlayedButton.setText("text here");
        overlayedButton.setBackgroundColor(Color.GRAY);
        overlayedButton.setTextColor(Color.WHITE);

        WindowManager.LayoutParams params = new WindowManager.LayoutParams(WindowManager.LayoutParams.WRAP_CONTENT, WindowManager.LayoutParams.WRAP_CONTENT, WindowManager.LayoutParams.TYPE_TOAST, WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE | WindowManager.LayoutParams.FLAG_NOT_TOUCH_MODAL, PixelFormat.TRANSLUCENT);
        params.gravity = Gravity.CENTER | Gravity.TOP;
        params.x = 0;
        params.y = 400;
        params.width = 920;
        params.height = 550;
        wm.addView(overlayedButton, params);

        topLeftView = new View(this);
        WindowManager.LayoutParams topLeftParams = new WindowManager.LayoutParams(WindowManager.LayoutParams.WRAP_CONTENT,  WindowManager.LayoutParams.WRAP_CONTENT, WindowManager.LayoutParams.TYPE_TOAST, WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE | WindowManager.LayoutParams.FLAG_NOT_TOUCH_MODAL, PixelFormat.TRANSLUCENT);
        topLeftParams.gravity = Gravity.CENTER | Gravity.CENTER;
        topLeftParams.x = 0;
        topLeftParams.y = 0;
        topLeftParams.width = 0;
        topLeftParams.height = 0;
        wm.addView(topLeftView, topLeftParams);

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您可以使用九块补丁图像作为叠加按钮的背景。欢迎使用StackOverflow！在发布问题之前，请阅读关于如何提问的用户指南（）谢谢