HarmonyOS 如何实现清除canvas内容，重新绘制？

@Entry  
@Component  
struct CanvasDemo {  
  private settings: RenderingContextSettings = new RenderingContextSettings(true)  
  private context: CanvasRenderingContext2D = new CanvasRenderingContext2D(this.settings)  
  @State @Watch('draw')content: string = ""  
  draw() {  
    this.context.clearRect(0, 0, 200, 200) // 清理画布内容  
    this.context.fillText(this.content, 50, 50) // 重新填充  
  }  
  build() {  
    Column() {  
      Canvas(this.context)  
        .width('100%')  
        .height('25%')  
        .backgroundColor('#F5DC62')  
        .onReady(() => {  
          //可以在这里绘制内容。  
          this.context.font = '55px sans-serif'  
          this.context.fillText(this.content, 50, 50)  
        })  
      TextInput({  
        text:$$this.content  
      })  
    }  
    .borderColor('#31525B')  
    .borderWidth(12)  
    .width('100%')  
    .height('100%')  
  }  
}
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