@Extend Decorator: Extension of Built-in Components

Apart from@Styles used to extend styles, ArkUI also provides @Extend, which allows you to add a new attribute feature to a built-in component.

NOTE Since API version 9, this decorator is supported in ArkTS widgets.

Rules of Use

Syntax

@Extend(UIComponentName) function functionName { ... }

Rules of Use

  • Unlike @Styles, @Extend can be defined only globally, that is, outside a component declaration.

NOTE This decorator can be used only in the current file and cannot be exported.

  • Unlike @Styles, @Extend can encapsulate private attributes and events of specified components and predefine @Extend decorated methods of the same component.

    // @Extend(Text) supports the private attribute fontColor of the <Text> component.
    @Extend(Text) function fancy () {
      .fontColor(Color.Red)
    }
    // superFancyText can call the predefined method fancy.
    @Extend(Text) function superFancyText(size:number) {
        .fontSize(size)
        .fancy()
    }
    
  • Unlike @Styles, @Extend decorated methods support parameters. You can pass in parameters when calling such methods. Regular TypeScript provisions for method parameters apply.

    // xxx.ets
    @Extend(Text) function fancy (fontSize: number) {
      .fontColor(Color.Red)
      .fontSize(fontSize)
    }
    
    @Entry
    @Component
    struct FancyUse {
      build() {
        Row({ space: 10 }) {
          Text('Fancy')
            .fancy(16)
          Text('Fancy')
            .fancy(24)
        }
      }
    }
    
  • A function can be passed as a parameter in an @Extend decorated method. The function is used as the handler of an event.

    @Extend(Text) function makeMeClick(onClick: () => void) {
      .backgroundColor(Color.Blue)
      .onClick(onClick)
    }
    
    @Entry
    @Component
    struct FancyUse {
      @State label: string = 'Hello World';
    
      onClickHandler() {
        this.label = 'Hello ArkUI';
      }
    
      build() {
        Row({ space: 10 }) {
          Text(`${this.label}`)
            .makeMeClick(() => {this.onClickHandler()})
        }
      }
    }
    
  • A state variable can be passed as a parameter in an @Extend decorated method. When the state variable changes, the UI is re-rendered.

    @Extend(Text) function fancy (fontSize: number) {
      .fontColor(Color.Red)
      .fontSize(fontSize)
    }
    
    @Entry
    @Component
    struct FancyUse {
      @State fontSizeValue: number = 20
      build() {
        Row({ space: 10 }) {
          Text('Fancy')
            .fancy(this.fontSizeValue)
            .onClick(() => {
              this.fontSizeValue = 30
            })
        }
      }
    }
    

Use Scenarios

The following example declares three <Text> components. The fontStyle, fontWeight, and backgroundColor styles are set for each <Text> component.

@Entry
@Component
struct FancyUse {
  @State label: string = 'Hello World'

  build() {
    Row({ space: 10 }) {
      Text(`${this.label}`)
        .fontStyle(FontStyle.Italic)
        .fontWeight(100)
        .backgroundColor(Color.Blue)
      Text(`${this.label}`)
        .fontStyle(FontStyle.Italic)
        .fontWeight(200)
        .backgroundColor(Color.Pink)
      Text(`${this.label}`)
        .fontStyle(FontStyle.Italic)
        .fontWeight(300)
        .backgroundColor(Color.Orange)
    }.margin('20%')
  }
}

@Extend combines and reuses styles. The following is an example:

@Extend(Text) function fancyText(weightValue: number, color: Color) {
  .fontStyle(FontStyle.Italic)
  .fontWeight(weightValue)
  .backgroundColor(color)
}

With the use of @Extend, the code readability is enhanced.

@Entry
@Component
struct FancyUse {
  @State label: string = 'Hello World'

  build() {
    Row({ space: 10 }) {
      Text(`${this.label}`)
        .fancyText(100, Color.Blue)
      Text(`${this.label}`)
        .fancyText(200, Color.Pink)
      Text(`${this.label}`)
        .fancyText(300, Color.Orange)
    }.margin('20%')
  }
}