【每日学点 HarmonyOS Next 知识】防截屏、作用域问题、观察器问题、对话框关闭、判断对象包含某个字段

2025-03-15
北京
本文字数：2612 字
阅读完需：约 9 分钟

1、HarmonyOS 防截屏功能如何实现？

防截屏功能如何实现

参考 demo：

aboutToDisappear(): void {  let windowClass: window.Window | undefined = undefined;  window.getLastWindow(getContext(this)).then((win) => {  this.window = win})window.getLastWindow(getContext(this), (err: BusinessError, data) => {  const errCode: number = err.code;  if (errCode) {    console.error('Failed to obtain the top window. Cause: ' + JSON.stringify(err));    return;  }  windowClass = data;  console.info('Succeeded in obtaining the top window. Data: ' + JSON.stringify(data));  setWindowPrivacyMode(windowClass, true)});}

export function setWindowPrivacyMode(windowClass: window.Window, isPrivacyMode: boolean) {  // try {  windowClass.setWindowPrivacyMode(isPrivacyMode    /*, (err: BusinessError) => {    if (err) {      console.error('Failed to set the window to the privacy mode. Cause:'+ JSON.stringify(err));      return;    }    console.info('Succeeded in setting the window to the privacy mode.');  }*/  );  console.info(`setWindowPrivacyMode 已执行`);  // } catch (exception) {  //   console.error('Failed to set the window to the privacy mode. Cause:'+ JSON.stringify(exception));  // }}

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2、HarmonyOS 作用域问题？

使用 CustomDialog，点击确定后，调用当前页面的方法，提示不可调用，是作用域的问题么？![[Pasted image 20250222233839.png]]

这是 this 指向问题，自定义弹窗这里使用“confirm：this.onConfirm”，this 指向调用者“自定义弹窗”。这会将 onConfirm()方法传给自定义弹窗调用，调用者是自定义弹窗。然而自定义弹窗代码中没有 jumpToMainPage()这个方法，所以报错“is not callable”，建议改写成如下的方法调用形式：

confirm:()=>{  this.onConfirm()}

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3、HarmonyOS @Watch 可以观察到 @Consume 装饰的状态变量更改吗？

@Watch 可以观察到 @Consume 装饰的状态变量更改吗

参考 demo：

@Componentstruct CompD {  @Consume @Watch('onChange') selectedDate: Date;
  onChange() {    console.info("值改变了！！！")  }
  build() {    Column() {      Button(`child increase the day by 1`)        .onClick(() => {          this.selectedDate.setDate(this.selectedDate.getDate() + 1)        })      Button('child update the new date')        .margin(10)        .onClick(() => {          this.selectedDate = new Date('2023-09-09')        })      DatePicker({        start: new Date('1970-1-1'),        end: new Date('2100-1-1'),        selected: this.selectedDate      })    }  }}
@Entry@Componentstruct CompA {  @Provide selectedDate: Date = new Date('2021-08-08')
  build() {    Column() {      Button('parent increase the day by 1')        .margin(10)        .onClick(() => {          this.selectedDate.setDate(this.selectedDate.getDate() + 1)        })      Button('parent update the new date')        .margin(10)        .onClick(() => {          this.selectedDate = new Date('2023-07-07')        })      DatePicker({        start: new Date('1970-1-1'),        end: new Date('2100-1-1'),        selected: this.selectedDate      })      CompD()    }  }}

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4、HarmonyOS 自定义 Dialog this.controller.close() 关闭失败或 undefined？

请参考 demo：

@CustomDialogstruct CustomDialogExample {  controller?: CustomDialogController  cancel: () => void = () => {  }  confirm: () => void = () => {  }
  build() {    Column() {      Text('可展示在主窗口外的弹窗')        .fontSize(30)        .height(100)      Button('点我关闭弹窗')        .onClick(() => {          if (this.controller != undefined) {            this.controller.close()            console.log('关闭成功')          } else {            console.log('关闭失败')          }        })        .margin(20)    }  }}
@Entry@Componentstruct CustomDialogUser {  dialogController: CustomDialogController | null = new CustomDialogController({    builder: CustomDialogExample({      cancel: () => {        this.onCancel()      },      confirm: () => {        this.onAccept()      }    }),    cancel: this.existApp,    autoCancel: true,    alignment: DialogAlignment.Center,    offset: { dx: 0, dy: -20 },    gridCount: 4,    showInSubWindow: true,    isModal: true,    customStyle: false,    cornerRadius: 10,  })
  // 在自定义组件即将析构销毁时将dialogControlle置空  aboutToDisappear() {    this.dialogController = null // 将dialogController置空  }
  onCancel() {    console.info('Callback when the first button is clicked')  }
  onAccept() {    console.info('Callback when the second button is clicked')  }
  existApp() {    console.info('Click the callback in the blank area')  }
  build() {    Column() {      Button('click me')        .onClick(() => {          if (this.dialogController != null) {            this.dialogController.open()          }        }).backgroundColor(0x317aff)    }.width('100%').margin({ top: 5 })  }}

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5、HarmonyOS 如何判断 object 中是否包含这个 key？

res 是接口请求返回的 object，需要判断是否包含 ad_4 这个 key。

参考以下代码：

let jsonobject:Record<string,Object> = JSON.parse(JSON.stringify(res)) as Record<string,Object>;Object.keys(jsonobject).forEach(key => {  if (key != undefined && key === 'ad_4'){    let ob4: CarouselInfo1[] = res[key] as CarouselInfo1[];    for (let index = 0; index < ob4.length; index++) {      this.rechargeCarouseInfo.push(ob4[index])    }  }});

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