@Builder

ArkUI提供了一种更轻量的UI元素复用机制 @Builder，可以将重复使用的UI元素抽象成一个方法，在 build 方法里调用。

@Entry
@Component
struct Parent {
  label: string = `Parent`

  @Builder componentBuilder() {
    Text(`${this.label}`)
  }

  build() {
    Column() {
      this.componentBuilder()
    }
  }
}

效果图

@Builder function overBuilder() {} // 全局定义

@Component
struct Child {
  @Builder doNothingBuilder() {}; // 组件内定义

  build(){
     Column(){
          overBuilder() // 组件内使用全局Builder
          this.doNothingBuilder() // 使用组件内Builder
      }
  }
}

@BuilderParam装饰器

@BuilderParm可接收组件，类似vue的slot

尾随闭包

@Component
struct QfBlackButton {
  @BuilderParam DefaultContent: () => void 

  build() {
      Row() {
        this.DefaultContent()
      }
  }
}

// 父组件调用
QfBlackButton() {
  Text('21312321)
} 

注意！！！@BuilderParam装饰的方法，默认值只能是被@Builder装饰的方法

@Component
struct Child {
  @Builder customBuilder() {}
  // 使用父组件@Builder装饰的方法初始化子组件@BuilderParam
  @BuilderParam customBuilderParam: () => void = this.customBuilder;
   
   @BuilderParam textBuilderParam: () => void;
  build() {
    Column() {
      this.customBuilderParam()
    }
  }
}

@Entry
@Component
struct Parent {
  @Builder componentBuilder() {
    Text(`Parent builder `)
  }

@Builder textBuilder() {
    Text(`Text  builder `)
  }

  build() {
    Column() {
     // 传入多个组件时最好具名传入
      Child({ customBuilderParam: this.componentBuilder, textBuilderParam: this.textBuilder()   })
    }
  }
}

@BuilderParam接收@Builder后this指针问题
官网中有一段话叫:

需注意this指向正确。
以下示例中，Parent组件在调用this.componentBuilder()时，this指向其所属组件，即“Parent”。@Builder componentBuilder()通过this.componentBuilder的形式传给子组件@BuilderParam customBuilderParam，this指向在Child的label，即“Child”。@Builder componentBuilder()通过():void=>{this.componentBuilder()}的形式传给子组件@BuilderParam customChangeThisBuilderParam，因为箭头函数的this指向的是宿主对象，所以label的值为“Parent”。

@Component
struct Child {
  label: string = `Child`
  @Builder customBuilder() {}
  @Builder customChangeThisBuilder() {}
  @BuilderParam customBuilderParam: () => void = this.customBuilder;
  @BuilderParam customChangeThisBuilderParam: () => void = this.customChangeThisBuilder;

  build() {
    Column() {
      this.customBuilderParam()
      this.customChangeThisBuilderParam()
    }
  }
}

@Entry
@Component
struct Parent {
  label: string = `Parent`

  @Builder componentBuilder() {
    Text(`${this.label}`)
  }

  build() {
    Column() {
      this.componentBuilder()
      Child({ customBuilderParam: this.componentBuilder, customChangeThisBuilderParam: ():void=>{this.componentBuilder()} })
    }
  }
}

也就是说在父组件定义的Builder函数内如果想继续使用父组件的this需要这样给子组件传

// 使用箭头函数传入这样this会存在定义的上下文中
Child({ customChangeThisBuilderParam: ():void=>{this.componentBuilder()} })