Canvas绘制内容如何动态更新

@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%') 
  } 
}