@Extend Decorator: Extension of Built-in Components

Apart from @Styles used to reuse 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.

This decorator can be used in atomic services since API version 11.

How to Use

Syntax

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

Rules of Use

Unlike @Styles, @Extend can encapsulate private attributes, private events, and custom global methods of specified components.

// @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
        })
    }
  }
}

Constraints

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.

To the export the decorator, you are advised to use AttributeModifier.

[Negative Example]

@Entry
@Component
struct FancyUse {
  // Incorrect format. @Extend can be defined only globally, but not inside a component.
  @Extend(Text) function fancy (fontSize: number) {
    .fontSize(fontSize)
  }

  build() {
    Row({ space: 10 }) {
      Text('Fancy')
        .fancy(16)
    }
  }
}

[Positive Example]

// Correct format.
@Extend(Text) function fancy (fontSize: number) {
  .fontSize(fontSize)
}

@Entry
@Component
struct FancyUse {

  build() {
    Row({ space: 10 }) {
      Text('Fancy')
        .fancy(16)
    }
  }
}

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%')
  }
}