HarmonyOS 状态绑定写法

可以使用@watch来监听messageCode、mobile的状态改变并返回false或者true，参考示例：

@Entry
@Component
struct Index65 {
  @State message: string = '点击改变';
  @State @Watch('isOk') messageCode: string = '012';
  @State @Watch('isOk') mobile: string = '1';
  @State result: boolean = false
  build() {
    Column() {
      Text('hello World')
        .id('Index65HelloWorld')
        .fontSize(50)
        .fontWeight(FontWeight.Bold)
        .alignRules({
          center: { anchor: '__container__', align: VerticalAlign.Center },
          middle: { anchor: '__container__', align: HorizontalAlign.Center }
        })
        .backgroundColor(this.isOk() ? '#00cab7' : '#f3f3f3')
      Text('绿色')
        .id('Index65HelloWorld')
        .fontSize(50)
        .fontWeight(FontWeight.Bold)
        .alignRules({
          center: { anchor: '__container__', align: VerticalAlign.Center },
          middle: { anchor: '__container__', align: HorizontalAlign.Center }
        })
        .onClick(() => {
          this.messageCode = '0123'
          this.mobile = '0123456789!'
        })
      Text('灰色')
        .id('Index65HelloWorld')
        .fontSize(50)
        .fontWeight(FontWeight.Bold)
        .alignRules({
          center: { anchor: '__container__', align: VerticalAlign.Center },
          middle: { anchor: '__container__', align: HorizontalAlign.Center }
        })
        .onClick(() => {
          this.messageCode = '012'
          this.mobile = '1'
        })
    }
    .height('100%')
    .width('100%')
  }

  isOk(): boolean {
    if (this.messageCode.length >= 4 && this.mobile.length === 11) {
      return true
    } else {
      return false
    }
  }
}