Custom Event Dispatch

When handling a touch event, ArkUI performs a touch test on the touch point and the component area before the event is triggered – to determine the components targeted by the event – and dispatches the event based on the test result. You can use onChildTouchTest on a parent node to specify how to perform the touch test on child nodes and thereby exert an impact on touch event dispatch. For details about the impact, see TouchTestStrategy.

NOTE

• This feature is supported since API version 11. Updates will be marked with a superscript to indicate their earliest API version.

• With use of onChildTouchTest, the onClick, rotation, and pinch gesture events may receive no response due to the touch target not being hit.

onChildTouchTest

onChildTouchTest(event: (value: Array<TouchTestInfo>) => TouchResult): T

Called to specify how to perform the touch test on the children of this component.

Atomic service API: This API can be used in atomic services since API version 12.

System capability: SystemCapability.ArkUI.ArkUI.Full

Parameters

Return value

NOTE

The array of child components contains only components for which id is set.

TouchTestInfo

Provides information about the coordinate system, ID, and size of the component where the current touch point is located.

Atomic service API: This API can be used in atomic services since API version 12.

System capability: SystemCapability.ArkUI.ArkUI.Full

TouchResult

Defines the custom event dispatch result. You can influence event dispatch by returning specific results.

Atomic service API: This API can be used in atomic services since API version 12.

System capability: SystemCapability.ArkUI.ArkUI.Full

TouchTestStrategy

Enumerates the event dispatch strategies.

Atomic service API: This API can be used in atomic services since API version 12.

System capability: SystemCapability.ArkUI.ArkUI.Full

Example

Example 1: Setting the Event Dispatch Strategy to FORWARD_COMPETITION

In this example, dragging the blank area below the list allows the list to scroll, and clicking the button will trigger its onClick event.

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

@Entry
@Component
struct ListExample {
  private arr: number[] = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12]
  @State text: string = 'Button'

  build() {
    Column() {
      List({ space: 12, initialIndex: 0 }) {
        ForEach(this.arr, (item: number) => {
          ListItem() {
            Text('Item ' + item)
              .width('100%')
              .height(56)
              .fontSize(16)
              .textAlign(TextAlign.Start)
          }.borderRadius(24)
          .backgroundColor(Color.White)
          .padding({ left: 12, right: 12 })
        }, (item: string) => item)
      }
      .listDirection(Axis.Vertical)
      .scrollBar(BarState.Off)
      .edgeEffect(EdgeEffect.Spring)
      .onScrollIndex((start: number, end: number) => {
        console.info('first' + start)
        console.info('last' + end)
      })
      .onDidScroll((scrollOffset: number, scrollState: ScrollState) => {
        console.info(`onScroll scrollState = ScrollState` + scrollState + `, scrollOffset = ` + scrollOffset)
      })
      .width('100%')
      .height('65%')
      .id('MyList')

      Button(this.text)
        .width(312)
        .height(40)
        .id('Mybutton')
        .fontSize(16)
        .fontWeight(FontWeight.Medium)
        .margin({ top: 80 })
        .onClick(() => {
          this.text = 'click the button'
          promptAction.showToast({ message: 'you click the button.', duration: 3000 })
        })
    }
    .width('100%')
    .height('100%')
    .backgroundColor(0xF1F3F5)
    .justifyContent(FlexAlign.End)
    .padding({ left: 12, right: 12, bottom: 24 })
    .onChildTouchTest((touchinfo) => {
      for (let info of touchinfo) {
        if (info.id == 'MyList') {
          return { id: info.id, strategy: TouchTestStrategy.FORWARD_COMPETITION }
        }
      }
      return { strategy: TouchTestStrategy.DEFAULT }
    })
  }
}

Example 2: Setting the Event Dispatch Strategy to FORWARD

In this example, dragging the blank area below the list allows the list to scroll, but clicking the button will not trigger its onClick event.

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

@Entry
@Component
struct ListExample {
  private arr: number[] = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12]
  @State text: string = 'Button'

  build() {
    Column() {
      List({ space: 12, initialIndex: 0 }) {
        ForEach(this.arr, (item: number) => {
          ListItem() {
            Text('Item ' + item)
              .width('100%')
              .height(56)
              .fontSize(16)
              .textAlign(TextAlign.Start)
          }.borderRadius(24)
          .backgroundColor(Color.White)
          .padding({ left: 12, right: 12 })
        }, (item: string) => item)
      }
      .listDirection(Axis.Vertical)
      .scrollBar(BarState.Off)
      .edgeEffect(EdgeEffect.Spring)
      .onScrollIndex((start: number, end: number) => {
        console.info('first' + start)
        console.info('last' + end)
      })
      .onDidScroll((scrollOffset: number, scrollState: ScrollState) => {
        console.info(`onScroll scrollState = ScrollState` + scrollState + `, scrollOffset = ` + scrollOffset)
      })
      .width('100%')
      .height('65%')
      .id('MyList')

      Button(this.text)
        .width(312)
        .height(40)
        .id('Mybutton')
        .fontSize(16)
        .fontWeight(FontWeight.Medium)
        .margin({ top: 80 })
        .onClick(() => {
          this.text = 'click the button'
          promptAction.showToast({ message: 'you click the button.', duration: 3000 })
        })
    }
    .width('100%')
    .height('100%')
    .backgroundColor(0xF1F3F5)
    .justifyContent(FlexAlign.End)
    .padding({ left: 12, right: 12, bottom: 24 })
    .onChildTouchTest((touchinfo) => {
      for (let info of touchinfo) {
        if (info.id == 'MyList') {
          return { id: info.id, strategy: TouchTestStrategy.FORWARD }
        }
      }
      return { strategy: TouchTestStrategy.DEFAULT }
    })
  }
}

Example 3: Setting the Event Dispatch Strategy to DEFAULT

In this example, dragging the blank area below the list will not scroll the list, and clicking the button will trigger its onClick event.

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

@Entry
@Component
struct ListExample {
  private arr: number[] = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12]
  @State text: string = 'Button'

  build() {
    Column() {
      List({ space: 12, initialIndex: 0 }) {
        ForEach(this.arr, (item: number) => {
          ListItem() {
            Text('Item ' + item)
              .width('100%')
              .height(56)
              .fontSize(16)
              .textAlign(TextAlign.Start)
          }.borderRadius(24)
          .backgroundColor(Color.White)
          .padding({ left: 12, right: 12 })
        }, (item: string) => item)
      }
      .listDirection(Axis.Vertical)
      .scrollBar(BarState.Off)
      .edgeEffect(EdgeEffect.Spring)
      .onScrollIndex((start: number, end: number) => {
        console.info('first' + start)
        console.info('last' + end)
      })
      .onDidScroll((scrollOffset: number, scrollState: ScrollState) => {
        console.info(`onScroll scrollState = ScrollState` + scrollState + `, scrollOffset = ` + scrollOffset)
      })
      .width('100%')
      .height('65%')
      .id('MyList')

      Button(this.text)
        .width(312)
        .height(40)
        .id('Mybutton')
        .fontSize(16)
        .fontWeight(FontWeight.Medium)
        .margin({ top: 80 })
        .onClick(() => {
          this.text = 'click the button'
          promptAction.showToast({ message: 'you click the button.', duration: 3000 })
        })
    }
    .width('100%')
    .height('100%')
    .backgroundColor(0xF1F3F5)
    .justifyContent(FlexAlign.End)
    .padding({ left: 12, right: 12, bottom: 24 })
    .onChildTouchTest((touchinfo) => {
      return { strategy: TouchTestStrategy.DEFAULT }
    })
  }
}

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