HarmonyOS 为什么@Link的属性变更不会触发UI刷新？

子组件@Link content，定义BuilderParams buildContent()，并在build里调用。

父组件@State content，buildContent的实现，赋给子组件。

//这个是子组件。

@Component  
export struct BaseDialog {  
  @Link title?:string | Resource  
  @Link content?:string | Resource//TODO 这里是关键  
  @Link buttons?:ButtonParams[]  
  
  refreshContent(content?:string | Resource) {  
    Logger.debug(TAG, "refreshContent(" + content + ") old=" + this.content)  
    this.content = content  
  }  
  
  @BuilderParam buildContent:($$:BaseDialog, content?:string | Resource)=>void  
  build() {  
    Column() {  
      this.buildContent(this, this.content)//TODO 这里是关键，为什么这里加了content，content变化为什么不会重新触发buildContent  
      )  
    }  
  }  
}1.
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//这是父组件。

@CustomDialog  
export struct SendEmailDialog {  
  controller: CustomDialogController  
  @State title?: string|Resource = $r('app.string.send_email_title')  
  @State content?: string = ""//TODO 这里是关键  
  @State buttons?: ButtonParams[] = []  
  @State email?:string = ""  
  
  build() {  
    BaseDialog({  
      title:this.title,  
      content:this.content,  
      buildContent: overrideBuildContent,  
      buttons:this.buttons  
    })  
  }  
}1.
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这是父组件文件中的一个builder函数（并不在父组件的struct里，在文件头部定义）。

@Builder  
function createDocTypeText($$:BaseDialog, text:string, selected:boolean, docType:string) {  
  Text(text)  
    .fontSize(18)  
    .fontWeight(FontWeight.Normal)  
    .fontColor(selected? $r('app.color.tag_selected') : $r('app.color.tag_unselected'))  
    .textAlign(TextAlign.Start)  
    .height($r('app.float.spacing_24'))  
    .borderColor(selected? $r('app.color.tag_selected') : $r('app.color.tag_unselected'))  
    .borderWidth(1)  
    .borderRadius(4)  
    .margin({right:$r("app.float.spacing_6")})  
    .padding({left:$r("app.float.spacing_8"), right:$r("app.float.spacing_8"), top:0, bottom:0})  
    .onClick((event)=>{  
      let params = SendEmailDialog.parse($$.content as string)  
      if (params) {  
        params.docType = docType  
        $$.refreshContent(SendEmailDialog.stringify(params))//TODO 这里是关键，更改了content为什么不会触发更新？  
        Logger.debug(TAG, "DocTypeText.onClick() result:" + $$.content)  
      }  
    })  
}1.
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