HarmonyOS 鸿蒙Next Canvas怎么手动触发onReady事件？

@Entry
@CustomDialog
export struct AudioRecorderDialog {
  controller: CustomDialogController
  private settings: RenderingContextSettings = new RenderingContextSettings(true)
  private context: CanvasRenderingContext2D = new CanvasRenderingContext2D(this.settings)
  @State @Watch(‘draw’) positionXY : number[] = [0, 0]; // 原始坐标点
  prePosition: number[] = []; // 上一次坐标点
  rectWidth: number = 100;
  rectHeight: number = 100;
  draw(){
    // console.log(‘demoTest :’ + ‘s’)
    if(this.prePosition.length) {
      this.context.clearRect(this.prePosition[0], this.prePosition[1], this.rectWidth, this.rectHeight);
    }
    this.context.fillRect(this.positionXY[0], this.positionXY[1], this.rectWidth, this.rectHeight)
  }
  build() {
    Column() {
      Button(‘点击重绘’).onClick((event: ClickEvent) => {
        const x = Math.floor(Math.random() * 51);
        const y = Math.floor(Math.random() * 51);
        this.prePosition = […this.positionXY];
        this.positionXY = [x, y];
      })
      Canvas(this.context)
        .width(‘100%’)
        .height(‘50%’)
        .backgroundColor(’#ffff00’)
        .margin({top: 50})
        .onReady(() => {
          this.draw()
        })
    }
  }
}