HarmonyOS 如何实现一个悬浮球/悬浮窗，悬浮在所有页面之上？

onWindowStageCreate(windowStage: window.WindowStage): void {  
  // Main window is created, set main page for this ability  
  hilog.info(0x0000, 'testTag', '%{public}s', 'Ability onWindowStageCreate');  
  
  windowStage.loadContent('pages/Page', (err, data) => {  
  if (err.code) {  
  hilog.error(0x0000, 'testTag', 'Failed to load the content. Cause: %{public}s', JSON.stringify(err) ?? '');  
  return;  
}  
// 保存窗口管理器  
AppStorage.setOrCreate("windowStage", windowStage);  
hilog.info(0x0000, 'testTag', 'Succeeded in loading the content. Data: %{public}s', JSON.stringify(data) ?? '');  
});  
}

this.windowStage.createSubWindow("mySubWindow", (err, windowClass) => {  
  if (err.code > 0) {  
    console.error("failed to create subWindow Cause:" + err.message)  
    return;  
  }  
  try {  
    // 设置子窗口加载页  
    windowClass.setUIContent("pages/MySubWindow", () => {  
      windowClass.setWindowBackgroundColor("#00000000")  
    });  
    // 设置子窗口左上角坐标  
    windowClass.moveWindowTo(0, 200)  
    // 设置子窗口大小  
    windowClass.resize(vp2px(75), vp2px(75))  
    // 展示子窗口  
    windowClass.showWindow();  
    // 设置子窗口全屏化布局不避让安全区  
    windowClass.setWindowLayoutFullScreen(true);  
  } catch (err) {  
    console.error("failed to create subWindow Cause:" + err)  
  }  
})

.gesture(  
  // 声明该组合手势的类型为Sequence类型  
  PanGesture(this.panOption)  
    .onActionStart((event: GestureEvent) => {  
      console.info('Pan start');  
    })// 发生拖拽时，获取到触摸点的位置，并将位置信息传递给windowPosition  
    .onActionUpdate((event: GestureEvent) => {  
      this.windowPosition.x += event.offsetX;  
      this.windowPosition.y += event.offsetY;  
  
      this.subWindow.moveWindowTo(this.windowPosition.x, this.windowPosition.y)  
    })  
    .onActionEnd((event: GestureEvent) => {  
      // 贴边判断  
      if (event.offsetX > 0) {  
        this.windowPosition.x = display.getDefaultDisplaySync().width - this.subWindow.getWindowProperties()  
          .windowRect  
          .width;  
      } else if (event.offsetX < 0) {  
        this.windowPosition.x = 0;  
      }  
      this.subWindow.moveWindowTo(this.windowPosition.x, this.windowPosition.y)  
      console.info('Pan end');  
    })  
)