Communication Between the TaskPool Task and Host Thread

When a task needs to do more than just return a final result—such as periodically updating the host thread on its status, reporting data changes, or returning large volumes of data in segments (for example, fetching large datasets from a database)—you can use the approach described in this topic.

The following example uses multiple image loading tasks that provide real-time updates to illustrate the process.

Implement a method to receive messages sent by the task.

// TaskSendDataUsage.ets
export function notice(data: number): void {
  console.info("Child thread task completed. Total images loaded:", data)
}

Add sendData() to the task to enable the child thread to send messages to the host thread.

// IconItemSource.ets
export class IconItemSource {
  image: string | Resource = '';
  text: string | Resource = '';

  constructor(image: string | Resource = '', text: string | Resource = '') {
    this.image = image;
    this.text = text;
  }
}

// TaskSendDataUsage.ets
import { taskpool } from '@kit.ArkTS';
import { IconItemSource } from './IconItemSource';

// Use sendData to notify the host thread of information in real time.
@Concurrent
export function loadPictureSendData(count: number): IconItemSource[] {
  let iconItemSourceList: IconItemSource[] = [];
  // Add six IconItem data records.
  for (let index = 0; index < count; index++) {
    const numStart: number = index * 6;
    // Use six images in the loop.
    iconItemSourceList.push(new IconItemSource('$media:startIcon', `item${numStart + 1}`));
    iconItemSourceList.push(new IconItemSource('$media:background', `item${numStart + 2}`));
    iconItemSourceList.push(new IconItemSource('$media:foreground', `item${numStart + 3}`));
    iconItemSourceList.push(new IconItemSource('$media:startIcon', `item${numStart + 4}`));
    iconItemSourceList.push(new IconItemSource('$media:background', `item${numStart + 5}`));
    iconItemSourceList.push(new IconItemSource('$media:foreground', `item${numStart + 6}`));

    taskpool.Task.sendData(iconItemSourceList.length);
  }
  return iconItemSourceList;
}

In the host thread, use onReceiveData() to receive messages.

This allows the host thread to receive data sent by the task through notice().

// Index.ets
import { taskpool } from '@kit.ArkTS';
import { IconItemSource } from './IconItemSource';
import { loadPictureSendData, notice } from './TaskSendDataUsage';

@Entry
@Component
struct Index {
  @State message: string = 'Hello World';

  build() {
    Row() {
      Column() {
        Text(this.message)
          .fontSize(50)
          .fontWeight(FontWeight.Bold)
          .onClick(async () => {
            let iconItemSourceList: IconItemSource[] = [];
            let loadPictureTask: taskpool.Task = new taskpool.Task(loadPictureSendData, 30);
            // Use notice to receive messages from the task.
            loadPictureTask.onReceiveData(notice);
            iconItemSourceList = await taskpool.execute(loadPictureTask) as IconItemSource[];
            console.info("The length of iconItemSourceList is " + iconItemSourceList.length);
          })
      }
      .width('100%')
    }
    .height('100%')
  }
}

目录

Communication Between the TaskPool Task and Host Thread