HarmonyOS鸿蒙Next中List中的图片闪烁

若仅靠LazyForEach的刷新机制，当item变化时若想更新子组件，需要将原来的子组件全部销毁再重新构建，在子组件结构较为复杂的情况下，靠改变键值去刷新渲染性能较低。因此框架提供了@Observed与@ObjectLink机制进行深度观测，可以做到仅刷新使用了该属性的组件，提高渲染性能,避免更新listitem时图片闪烁问题

参考： https://developer.huawei.com/consumer/cn/doc/harmonyos-guides-V5/arkts-rendering-control-lazyforeach-V5

改变数据子属性

可参考如下demo：

class BasicDataSource implements IDataSource {

  private listeners: DataChangeListener[] = [];

  private originDataArray: StringData[] = [];

  public totalCount(): number {

    return 0;

  }

  public getData(index: number): StringData {

    return this.originDataArray[index];

  }

  registerDataChangeListener(listener: DataChangeListener): void {

    if (this.listeners.indexOf(listener) < 0) {

      console.info('add listener');

      this.listeners.push(listener);

    }

  }

  unregisterDataChangeListener(listener: DataChangeListener): void {

    const pos = this.listeners.indexOf(listener);

    if (pos >= 0) {

      console.info('remove listener');

      this.listeners.splice(pos, 1);

    }

  }

  notifyDataReload(): void {

    this.listeners.forEach(listener => {

      listener.onDataReloaded();

    })

  }

  notifyDataAdd(index: number): void {

    this.listeners.forEach(listener => {

      listener.onDataAdd(index);

    })

  }

  notifyDataChange(index: number): void {

    this.listeners.forEach(listener => {

      listener.onDataChange(index);

    })

  }

  notifyDataDelete(index: number): void {

    this.listeners.forEach(listener => {

      listener.onDataDelete(index);

    })

  }

  notifyDataMove(from: number, to: number): void {

    this.listeners.forEach(listener => {

      listener.onDataMove(from, to);

    })

  }

}

class MyDataSource extends BasicDataSource {

  private dataArray: StringData[] = [];

  public totalCount(): number {

    return this.dataArray.length;

  }

  public getData(index: number): StringData {

    return this.dataArray[index];

  }

  public addData(index: number, data: StringData): void {

    this.dataArray.splice(index, 0, data);

    this.notifyDataAdd(index);

  }

  public pushData(data: StringData): void {

    this.dataArray.push(data);

    this.notifyDataAdd(this.dataArray.length - 1);

  }

}

[@Observed](/user/Observed)

class StringData {

  message: string;

  constructor(message: string) {

    this.message = message;

  }

}

@Entry
@Component
struct MyComponent {

  private moved: number[] = [];

  @State data: MyDataSource = new MyDataSource();

  aboutToAppear() {

    for (let i = 0; i <= 20; i++) {

      this.data.pushData(new StringData(`Hello ${i}`));

    }

  }

  build() {

    List({ space: 3 }) {

      LazyForEach(this.data, (item: StringData, index: number) => {

        ListItem() {

          ChildComponent({data: item})

        }
        .onClick(() => {

          item.message += '0';

        })

      }, (item: StringData, index: number) => index.toString())

    }.cachedCount(5)

  }

}

@Component
struct ChildComponent {

  [@ObjectLink](/user/ObjectLink) data: StringData

  build() {

    Row() {

      Image($r("app.media.startIcon"))
        .width(100)
        .height(100)

      Text(this.data.message).fontSize(50)
        .onAppear(() => {

          console.info("appear:" + this.data.message)

        })

    }.margin({ left: 10, right: 10 })

  }

}