Layout Constraints

Layout constraints refer to constraints on the aspect ratio and display priority of components.

NOTE

The APIs of this module are supported since API version 7. Updates will be marked with a superscript to indicate their earliest API version.

aspectRatio

aspectRatio(value: number)

Sets the aspect ratio of the component, which can be obtained using the following formula: width/height. - If only width and aspectRatio are set, the height is calculated using the following formula: width/aspectRatio. - If only height and aspectRatio are set, the width is calculated using the following formula: height x aspectRatio. - If width, height, and aspectRatio are all set, the explicitly set height is ignored, and the effective height is calculated using the following formula: width/aspectRatio.

After aspectRatio is set, the width and height of the component are constrained by the size of the parent component’s content area.

Widget capability: This API can be used in ArkTS widgets since API version 9.

Atomic service API: This API can be used in atomic services since API version 11.

System capability: SystemCapability.ArkUI.ArkUI.Full

Parameters

displayPriority

displayPriority(value: number)

Sets the display priority for the component in the layout container.

Widget capability: This API can be used in ArkTS widgets since API version 9.

Atomic service API: This API can be used in atomic services since API version 11.

System capability: SystemCapability.ArkUI.ArkUI.Full

Parameters

Example

Example 1: Setting the Component Aspect Ratio

This example illustrates how to use the aspectRatio attribute to set different aspect ratios for a component.

// xxx.ets
@Entry
@Component
struct AspectRatioExample {
  private children: string[] = ['1', '2', '3', '4', '5', '6']

  build() {
    Column({ space: 20 }) {
      Text('using container: row').fontSize(14).fontColor(0xCCCCCC).width('100%')
      Row({ space: 10 }) {
        ForEach(this.children, (item:string) => {
          // Component width = Component height x 1.5 = 90
          Text(item)
            .backgroundColor(0xbbb2cb)
            .fontSize(20)
            .aspectRatio(1.5)
            .height(60)
          // Component height = Component width/1.5 = 60/1.5 = 40
          Text(item)
            .backgroundColor(0xbbb2cb)
            .fontSize(20)
            .aspectRatio(1.5)
            .width(60)
        }, (item:string) => item)
      }
      .size({ width: "100%", height: 100 })
      .backgroundColor(0xd2cab3)
      .clip(true)

      // Grid child component width/height = 3/2
      Text('using container: grid').fontSize(14).fontColor(0xCCCCCC).width('100%')
      Grid() {
        ForEach(this.children, (item:string) => {
          GridItem() {
            Text(item)
              .backgroundColor(0xbbb2cb)
              .fontSize(40)
              .width('100%')
              .aspectRatio(1.5)
          }
        }, (item:string) => item)
      }
      .columnsTemplate('1fr 1fr 1fr')
      .columnsGap(10)
      .rowsGap(10)
      .size({ width: "100%", height: 165 })
      .backgroundColor(0xd2cab3)
    }.padding(10)
  }
}

Figure 1 Portrait display

Figure 2 Landscape display

Example 2: Setting the Component Display Priority

This example shows how to use displayPriority to assign display priorities to child components.

class ContainerInfo {
  label: string = '';
  size: string = '';
}

class ChildInfo {
  text: string = '';
  priority: number = 0;
}

@Entry
@Component
struct DisplayPriorityExample {
  // Display the container size.
  private container: ContainerInfo[] = [
    { label: 'Big container', size: '90%' },
    { label: 'Middle container', size: '50%' },
    { label: 'Small container', size: '30%' }
  ]
  private children: ChildInfo[] = [
    { text: '1\n(priority:2)', priority: 2 },
    { text: '2\n(priority:1)', priority: 1 },
    { text: '3\n(priority:3)', priority: 3 },
    { text: '4\n(priority:1)', priority: 1 },
    { text: '5\n(priority:2)', priority: 2 }
  ]
  @State currentIndex: number = 0;

  build() {
    Column({ space: 10 }) {
      // Switch the size of the parent container.
      Button(this.container[this.currentIndex].label).backgroundColor(0x317aff)
        .onClick(() => {
          this.currentIndex = (this.currentIndex + 1) % this.container.length;
        })
      // Set the width for the parent flex container through variables.
      Flex({ justifyContent: FlexAlign.SpaceBetween }) {
        ForEach(this.children, (item:ChildInfo) => {
          // Bind the display priority to the child component through displayPriority.
          Text(item.text)
            .width(120)
            .height(60)
            .fontSize(24)
            .textAlign(TextAlign.Center)
            .backgroundColor(0xbbb2cb)
            .displayPriority(item.priority)
        }, (item:ChildInfo) => item.text)
      }
      .width(this.container[this.currentIndex].size)
      .backgroundColor(0xd2cab3)
    }.width("100%").margin({ top: 50 })
  }
}

Landscape display in containers of different sizes

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