Screenshot Prevention, Scope Issues, Observer Problems, Dialog Closure, Object Field Check

[Daily HarmonyOS Next Knowledge] Screenshot Prevention, Scope Issues, Observer Problems, Dialog Closure, Object Field Check

1. How to Implement Screenshot Prevention in HarmonyOS?

Reference 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) {
  windowClass.setWindowPrivacyMode(isPrivacyMode);
  console.info(`setWindowPrivacyMode 已执行`);
}

2. HarmonyOS Scope Issues

When using CustomDialog, calling the current page's method after clicking "Confirm" prompts it as non-callable. Is this a scope issue?

This is a this binding issue. If using confirm: this.onConfirm in the custom dialog, this refers to the dialog itself. Since the dialog has no jumpToMainPage() method, it errors with "is not callable". Suggest rewriting as:

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

3. Can @Watch Observe Changes in @Consume-Decorated State Variables in HarmonyOS?

Reference demo:

@Component
struct 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
@Component
struct 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()
    }
  }
}

4. HarmonyOS Custom Dialog this.controller.close() Fails or Returns undefined

Reference demo:

@CustomDialog
struct 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
@Component
struct 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,
  })

  aboutToDisappear() {
    this.dialogController = null 
  }

  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 })
  }
}

5. How to Check if an Object Contains a Key in HarmonyOS?

To check if res (an object returned by an API) contains the key ad_4:

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])
    }
  }
});