作用：当子组件多处使用时，给某处的子组件添加特定功能

一、初始化

1、只能被@Builder装饰的方法初始化
2、使用所属自定义组件的@builder方法初始化
3、使用父组件的@builder方法初始化 - 把父组件的@builder传过去，参数名和子组件的@builderParam同名

@Component
struct Child {
  @Builder childBuilder() {}
  @BuilderParam childBuilderParam: () => void = this.childBuilder // 必须用childBuilder初始化下，否则预览出不来

  build() {
    Column() {
      Text('我是子组件')
        .fontColor(Color.White)
      this.childBuilderParam()
    }
  }
}

@Entry
@Component
struct Index7 {

  @Builder parentBuilder() {
    Text('我是父组件定制的的 builder')

  }

  build() {
    Column() {
      Row() {
        Child({childBuilderParam: this.parentBuilder}) // 添加独特功能
      }
      .padding(10)
      .backgroundColor(Color.Brown)

      Row() {
        Child()
      }
      .padding(10)
      .backgroundColor(Color.Green)

    }
  }
}

二、this指向

@Component
struct Child1 {
  label: string = '我是子组件的label'
  @Builder childBuilder() {}
  @BuilderParam childBuilderParam: () => void = this.childBuilder
  @BuilderParam childChangeThisBuilderParam: () => void = this.childBuilder

  build() {
    Column() {
      this.childBuilderParam()
      this.childChangeThisBuilderParam()
    }
  }
}

@Entry
@Component
struct Index7_1 {
  label: string = '我是父组件的label'

  @Builder parentBuilder() {
    Text(this.label)

  }

  build() {
    Column() {
      this.parentBuilder() // this指向父组件


      Child1({
        childBuilderParam: this.parentBuilder, // this.parentBuilder传入到child中指向child
        childChangeThisBuilderParam: (): void => this.parentBuilder(), // 箭头函数的this指向宿主对象，即父组件
      })

    }
  }
}

三、带参数

class Tmp {
  label: string = ''
}
// 全局builder
@Builder function globalBuilder($$: Tmp) {
  Text($$.label)
}

// Child1中
...
// 有参数
@BuilderParam childHasParamsBuilderParam: ($$: Tmp) => void = globalBuilder
build() {
  Column() {
	  ...
	  this.childHasParamsBuilderParam({label: '我是一个有参数的BuilderParam'})
  }
}
// 父组件中
...
Child1({
  ...
  childHasParamsBuilderParam: globalBuilder
})

四、尾随闭包的形式

@Component
struct Child2 {
  @Builder childBuilder() {}
  // 尾随闭包的形式传入时子组件内只能有一个BuilderParam
  @BuilderParam childBuilderParam: () => void = this.childBuilder

  build() {
    Column() {
      Text('我是子组件2')
      this.childBuilderParam()
    }
    .margin({top: 30})
  }
}
// 父组件中
...
Child2() {
   Column() {
     globalBuilder({label: '我是通过尾随闭包传入的'})
   }
}

注意：
尾随闭包的形式子组件内只能有一个 @BuilderParam