@BuilderParam装饰器：引用@Builder函数

装饰器使用说明

初始化@BuilderParam装饰的方法

@BuilderParam装饰的方法只能被自定义构建函数（@Builder装饰的方法）初始化。如果在API 11中和@Require结合使用，则必须父组件构造传参。

• 使用所属自定义组件的自定义构建函数或者全局的自定义构建函数，在本地初始化@BuilderParam。

  已复制
  @Builder function overBuilder() {}
  
  @Component
  struct Child {
    @Builder doNothingBuilder() {};
  
    // 使用自定义组件的自定义构建函数初始化@BuilderParam
    @BuilderParam customBuilderParam: () => void = this.doNothingBuilder;
    // 使用全局自定义构建函数初始化@BuilderParam
    @BuilderParam customOverBuilderParam: () => void = overBuilder;
    build(){}
  }

• 用父组件自定义构建函数初始化子组件@BuilderParam装饰的方法。

  已复制
  @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;
  
    build() {
      Column() {
        this.customBuilderParam()
      }
    }
  }
  
  @Entry
  @Component
  struct Parent {
    @Builder componentBuilder() {
      Text(`Parent builder `)
    }
  
    build() {
      Column() {
        Child({ customBuilderParam: this.componentBuilder })
      }
    }
  }

  图1 示例效果图

  

• 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”。

  已复制
  复制
  @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()} })
      }
    }
  }

图2 示例效果图

使用场景

参数初始化组件

@BuilderParam装饰的方法可以是有参数和无参数的两种形式，需与指向的@Builder方法类型匹配。@BuilderParam装饰的方法类型需要和@Builder方法类型一致。

已复制
class Tmp{
  label:string = ''
}
@Builder function overBuilder($$ : Tmp) {
  Text($$.label)
    .width(400)
    .height(50)
    .backgroundColor(Color.Green)
}

@Component
struct Child {
  label: string = 'Child'
  @Builder customBuilder() {}
  // 无参数类型，指向的componentBuilder也是无参数类型
  @BuilderParam customBuilderParam: () => void = this.customBuilder;
  // 有参数类型，指向的overBuilder也是有参数类型的方法
  @BuilderParam customOverBuilderParam: ($$ : Tmp) => void = overBuilder;

  build() {
    Column() {
      this.customBuilderParam()
      this.customOverBuilderParam({label: 'global Builder label' } )
    }
  }
}

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

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

  build() {
    Column() {
      this.componentBuilder()
      Child({ customBuilderParam: this.componentBuilder, customOverBuilderParam: overBuilder })
    }
  }
}

图3 示例效果图

尾随闭包初始化组件

在自定义组件中使用@BuilderParam装饰的属性时也可通过尾随闭包进行初始化。在初始化自定义组件时，组件后紧跟一个大括号“{}”形成尾随闭包场景。

开发者可以将尾随闭包内的内容看做@Builder装饰的函数传给@BuilderParam。示例如下：

已复制
@Component
struct CustomContainer {
  @Prop header: string = '';
  @Builder closerBuilder(){}
  // 使用父组件的尾随闭包{}(@Builder装饰的方法)初始化子组件@BuilderParam
  @BuilderParam closer: () => void = this.closerBuilder

  build() {
    Column() {
      Text(this.header)
        .fontSize(30)
      this.closer()
    }
  }
}

@Builder function specificParam(label1: string, label2: string) {
  Column() {
    Text(label1)
      .fontSize(30)
    Text(label2)
      .fontSize(30)
  }
}

@Entry
@Component
struct CustomContainerUser {
  @State text: string = 'header';

  build() {
    Column() {
      // 创建CustomContainer，在创建CustomContainer时，通过其后紧跟一个大括号“{}”形成尾随闭包
      // 作为传递给子组件CustomContainer @BuilderParam closer: () => void的参数
      CustomContainer({ header: this.text }) {
        Column() {
          specificParam('testA', 'testB')
        }.backgroundColor(Color.Yellow)
        .onClick(() => {
          this.text = 'changeHeader';
        })
      }
    }
  }
}

图4 示例效果图