HarmonyOS/OpenHarmony应用开发-ArkTS语言渲染控制LazyForEach数据懒加载

LazyForEach(
    dataSource: IDataSource,             // 需要进行数据迭代的数据源 
    itemGenerator: (item: any) => void,  // 子组件生成函数
    keyGenerator?: (item: any) => string // (可选) .键值生成函数
): void
interface IDataSource {
    totalCount(): number;                                             // Get total count of data
    getData(index: number): any;                                      // Get single data by index
    registerDataChangeListener(listener: DataChangeListener): void;   // Register listener to listening data changes
    unregisterDataChangeListener(listener: DataChangeListener): void; // Unregister listener
}
interface DataChangeListener {
    onDataReloaded(): void;                      // Called while data reloaded
    onDataAdd(index: number): void;            // Called while single data added
    onDataMove(from: number, to: number): void; // Called while single data moved
    onDataDelete(index: number): void;          // Called while single data deleted
    onDataChange(index: number): void;          // Called while single data changed
.}

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interface IDataSource {
    totalCount(): number;
    getData(index: number): any; 
    registerDataChangeListener(listener: DataChangeListener): void;
    unregisterDataChangeListener(listener: DataChangeListener): void;
}

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LazyForEach(dataSource, 
  item => Text(`${item.i}. item.data.label`),
  item => item.data.id.toString())

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// Basic implementation of IDataSource to handle data listener
class BasicDataSource implements IDataSource {
  private listeners: DataChangeListener[] = [];

  public totalCount(): number {
    return 0;
  }

  public getData(index: number): any {
    return undefined;
  }

  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: string[] = ['/path/image0', '/path/image1', '/path/image2', '/path/image3'];

  public totalCount(): number {
    return this.dataArray.length;
  }

  public getData(index: number): any {
    return this.dataArray[index];
  }

  public addData(index: number, data: string): void {
    this.dataArray.splice(index, 0, data);
    this.notifyDataAdd(index);
  }

  public pushData(data: string): void {
    this.dataArray.push(data);
    this.notifyDataAdd(this.dataArray.length - 1);
  }
}

@Entry
@Component
struct MyComponent {
  private data: MyDataSource = new MyDataSource();

  build() {
    List({ space: 3 }) {
      LazyForEach(this.data, (item: string) => {
        ListItem() {
          Row() {
            Image(item).width('30%').height(50)
            Text(item).fontSize(20).margin({ left: 10 })
          }.margin({ left: 10, right: 10 })
        }
        .onClick(() => {
          this.data.pushData('/path/image' + this.data.totalCount());
        })
      }, item => item)
    }
  }
}

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