HarmonyOS 如何设置应用内悬浮窗，通过创建子窗口方式，但是子窗口加载的页面都是空白

请参考以下demo：

//FloatWindow.ets
// 引入window类
import window from '@ohos.window';
import { BusinessError } from '@ohos.base';
import router from '@ohos.router';

@Entry
@Component
struct FloatWindow {
  // 定义windowClass变量，用来接收创建的悬浮窗
  // 自定义创建悬浮窗方法
  createFloatWindow() {
    // 窗口类型设置为window.WindowType.TYPE_FLOAT
    let windowStage = AppStorage.get("windowStage") as window.WindowStage;

    // let config:window.Configuration = {name: "floatWindow", windowType: window.WindowType.TYPE_FLOAT, ctx: getContext(this)};
    // 创建悬浮窗
    windowStage.createSubWindow("floatWindow", (err, win) => {

      if (err.code) {
        console.error('Failed to create the floatWindow. Cause: ' + JSON.stringify(err));
        return;
      }
      console.info('Succeeded in creating the floatWindow. Data: ' + JSON.stringify(win));

      // 设置悬浮窗位置
      win.moveWindowTo(300, 300, (err) => {
        if (err.code) {
          console.error('Failed to move the window. Cause:' + JSON.stringify(err));
          return;
        }
        console.info('Succeeded in moving the window.');
      });
      // 设置悬浮窗大小
      win.resize(700, 200, (err) => {
        if (err.code) {
          console.error('Failed to change the window size. Cause:' + JSON.stringify(err));
          return;
        }
        console.info('Succeeded in changing the window size.');
      });
      // 为悬浮窗加载页面内容，这里可以设置在main_pages.json中配置的页面
      win.setUIContent("pages/FloatContent", (err: BusinessError) => {
        if (err.code) {
          console.error('Failed to load the content. Cause:' + JSON.stringify(err));
          return;
        }
        win.setWindowBackgroundColor("#00000000")
        console.info('Succeeded in loading the content.');
        // 显示悬浮窗。
        win.showWindow((err: BusinessError) => {
          if (err.code) {
            console.error('Failed to show the window. Cause: ' + JSON.stringify(err));
            return;
          }
          console.info('Succeeded in showing the window.');
        });
      });
    });
  }
}