# 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.


## Attributes

| Name             | Type  | Description                                      |
| --------------- | ------ | ---------------------------------------- |
| aspectRatio     | number | Aspect ratio of the component, which can be obtained using the following formula: Width/Height.<br>Since API version 9, this API is supported in ArkTS widgets.|
| displayPriority | number | Display priority for the component in the layout container. When the space of the parent container is insufficient, the component with a lower priority is hidden.<br>The digits after the decimal point are not counted in determining the display priority. That is, numbers in the [x, x + 1) range are considered to represent the same priority. For example, **1.0** and **1.9** represent the same priority.<br>Since API version 9, this API is supported in ArkTS widgets.<br>**NOTE**<br>This attribute is valid only for the **\<Row>**, **\<Column>**, and **\<Flex>** (single-row) container components.|

## Example

### Example 1

```ts
// 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) => {
          // 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 => 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) => {
          GridItem() {
            Text(item)
              .backgroundColor(0xbbb2cb)
              .fontSize(40)
              .width('100%')
              .aspectRatio(1.5)
          }
        }, item => item)
      }
      .columnsTemplate('1fr 1fr 1fr')
      .columnsGap(10)
      .rowsGap(10)
      .size({ width: "100%", height: 165 })
      .backgroundColor(0xd2cab3)
    }.padding(10)
  }
}
```

**Figure 1** Portrait display

![en-us_image_0000001256978379](figures/en-us_image_0000001256978379.gif)

**Figure 2** Landscape display

![en-us_image_0000001212218476](figures/en-us_image_0000001212218476.gif)

### Example 2

```ts
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) => {
          // 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 => item.text)
      }
      .width(this.container[this.currentIndex].size)
      .backgroundColor(0xd2cab3)
    }.width("100%").margin({ top: 50 })
  }
}

```

Landscape display in containers of different sizes

![en-us_image_0000001212058504](figures/en-us_image_0000001212058504.gif)