HarmonyOS TextInput如何阻止其输入内容

可参考如下代码：

import { promptAction } from '@kit.ArkUI';

@Entry
@Component
struct Index {
  @State message: string = '';
  @State aa:boolean=false
  build() {

    Column(){
      TextInput({placeholder:"A"})
        .onChange((val:string)=>{
          this.message=val
          console.log(this.message+'cx')
          if(val!=''){
            this.aa=true
          }else {
            this.aa=false
          }
        })
      TextInput({placeholder:"B",})
        .focusable(this.aa)
        .onClick(()=>{
          if(!this.aa){
            promptAction.showToast({
              message:'请输入A'
            })
          }
        })
    }
    .height('100%')
    .width('100%')
  }
}