HarmonyOS 有封装好的Loading组件么，主要用在网络请求前显示、请求结束隐藏的场景中

参考示例：

Index.ets

import { GlobalContext } from './GlobalContext';
import { testPromptDialog } from './HttpUtil';

@Entry
@Component
struct Index {
  aboutToAppear(): void {
    GlobalContext.getContext().setObject('UIContext', this)
  }

  build() {
    Row() {
      Column() {
        Button("promptAction弹窗")
          .onClick(() => {
            testPromptDialog()
          })
      }
      .width('100%')
    }
    .height('100%')
  }
}

GlobalContext.ets

export class GlobalContext {
  private constructor() {
  }

  private static instance: GlobalContext;
  private _objects = new Map<string, Object>();

  public static getContext(): GlobalContext {
    if (!GlobalContext.instance) {
      GlobalContext.instance = new GlobalContext();
    }
    return GlobalContext.instance;
  }

  getObject(value: string): Object | undefined {
    return this._objects.get(value);
  }

  setObject(key: string, objectClass: Object): void {
    this._objects.set(key, objectClass);
  }
}

HttpUtil.ets

import { GlobalContext } from './GlobalContext';
import { promptAction } from '@kit.ArkUI';

let customDialogId: number = 0

@Builder
export function customDialogBuilder(content: String) {
  Column() {
    Text(Tip:
    $
    {
      content
    }
    )
    .
    fontSize(20).height("30%")
    Text('失败原因：失败原因!').fontSize(16).height("30%")
    Row() {
      Button("确认").onClick(() => {
        promptAction.closeCustomDialog(customDialogId)
      })
      Blank().width(50)
      Button("取消").onClick(() => {
        promptAction.closeCustomDialog(customDialogId)
      })
    }
    .margin({ top: 30 })
  }.height(200).padding(5)
}

export function testPromptDialog() {
  const that = GlobalContext.getContext().getObject('UIContext') as UIContext;
  if (that) {
    promptAction.openCustomDialog({
      builder: customDialogBuilder.bind(that, "网络请求失败！")
    }).then((dialogId: number) => {
      customDialogId = dialogId;
    })
  }
}