HarmonyOS Canvas如何触发重绘

Canvas(this.renderContext)
  .expandSafeArea([SafeAreaType.SYSTEM], [SafeAreaEdge.TOP, SafeAreaEdge.BOTTOM])
  .width('100%')
  .height('100%')
  .backgroundColor(Color.White)
  .padding(this.calcPadding(this.isValidate))
  .onReady(() => {
    this.renderContext.....
  })

Canvas组件在onReady中可以进行初次绘制，后续用户交互以后，比如移动、点击、缩放等操作之后，我需要将Canvas组件进行重新绘制，请问该如何触发？或者有其他解决方案也可以

HarmonyOS

Excelsior_abit

2天前

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回答 1

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回答 1

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zxjiu

canvas不会根据数据变化自行重绘，需要调用canvas的clearRect方法清空画布后再重新绘制。同时，需要使用@watch监听更新的那个变量，在更新后触发方法重新绘制canvas画布。可以参考一下代码实现：

@Entry
@CustomDialog
export struct AudioRecorderDialog {
  controller: CustomDialogController
  @State @Watch('draw') volumeList: number[] = [1, 1, 1, 1, 1, 1, 1, 1, 1, 1];
  private settings: RenderingContextSettings = new RenderingContextSettings(true)
  private context: CanvasRenderingContext2D = new CanvasRenderingContext2D(this.settings)
  private timer: number = 0;

  aboutToAppear() {
    this.volumeList.fill(Math.floor(Math.random() * 100) + 1);
  }

  aboutToDisappear() {
    clearInterval(this.timer);
  }

  build() {
    Column() {
      Canvas(this.context).width('100%').height('50%').backgroundColor('#ffff00').onReady(() => {
        this.draw()
      })
      Text(this.volumeList.toString()).onClick(() => {
        this.timer = setInterval(() => {
          let tem = Math.floor(Math.random() * 100) + 1;
          this.volumeList.shift();
          this.volumeList.push(tem)
          console.error('licheeng', '点击执行 ' + this.volumeList);
        }, 1000)
      }).height(50)
    }
  }

  draw() {
    console.log('demoTest :' +
      's')
  }
}