Event and Notification Development

How do I encapsulate a commonEvent utility class? (API version 9)

Symptom

A commonEvent utility class needs to be encapsulated for the following purpose: Register a custom callback function when creating a subscriber, and then call the custom callback function when receiving an event notification.

Solution

import commonEvent from '@ohos.commonEventManager';

export class SubscribeEvent {
  private static subscriber = null
  // Custom callback function variable
  private static callback = null
  /**
   * Create a subscriber.
   * @param subscribeInfo Indicates the event to subscribe to.
   * @callback Indicates the custom callback.
   */
  static createSubscriber(subscribeInfo, callback:(a,b)=>void) {
    this.callback = callback
    commonEvent.createSubscriber(subscribeInfo, (err, subscriber) => {
      if (err) {
        console.error('CreateSubscriberCallBack err = ' + JSON.stringify(err))
      } else {
        this.subscriber = subscriber;
        this.subscribe(this.subscriber)
        console.info('Create subscriber succeed')
      }
    })
  }

  /**
   * Subscribe to a common event.
   * @param subscriber Indicates the subscriber.
   */
  private static subscribe(subscriber) {
    if (subscriber != null) {
      commonEvent.subscribe(subscriber, (err, data) => {
        if (err) {
          console.error('subscribe err = ' + JSON.stringify(err))
        } else {
          console.info('SubscribeCallBack data= ' + JSON.stringify(data))
          this.callback('hello callback', data)
        }
      })
    } else {
      console.info("Need create subscriber")
    }
  }
}

@Entry
@Component
struct Faq10_1 {
  @State message: string = ''

  build() {
    Row() {
      Column() {
        Text('Subscribe:' + this.message)
          .fontSize(30)
          .fontWeight(FontWeight.Bold)
          .onClick(() => {
            let subscribeInfo = {
              events: ["myEvent"]
            };
            let callback = (a,b) => {
              this.message = a
            }
            SubscribeEvent.createSubscriber(subscribeInfo,callback)
          })
        Text('Publish')
          .fontSize(30)
          .fontWeight(FontWeight.Bold)
          .onClick(() => {
            // Properties of a common event
            let options = {
              code: 0,    // Result code of the common event.
              data: "initial data",// Result data of the common event.
              isOrdered: true  // The common event is an ordered one.
            }
            // Callback for common event publication
            function publishCB(err) {
              if (err) {
                console.error(`publish failed, code is ${err.code}, message is ${err.message}`);
              } else {
                console.info("publish");
              }
            }
            // Publish a common event.
            try {
              commonEvent.publish("myEvent", options, publishCB);
            } catch (err) {
              console.error(`publish failed, code is ${err.code}, message is ${err.message}`);
            }
          })
      }
      .width('100%')
    }
    .height('100%')
  }
}

Reference

@ohos.commonEventManager (Common Event)

How do I make events be transferred in only one UIAbility instance? (API version 9)

Symptom

Events need to be subscribed to and triggered only in one UIAbility instance.

Solution

You can call the EventHub module in UIAbility to subscribe to events. EventHub provides an event center that allows you to subscribe to, unsubscribe from, and trigger events.

Example

import UIAbility from '@ohos.app.ability.UIAbility';
 export default class EntryAbility extends UIAbility {
    onCreate() {
        this.context.eventHub.on('myEvent', this.eventFunc);
    }

    onDestroy() {
        // Result
        // eventFunc is called,undefined,undefined
        this.context.eventHub.emit('myEvent');
        // Result
        // eventFunc is called,1,undefined
        this.context.eventHub.emit('myEvent', 1);
        // Result
        // eventFunc is called,1,2
        this.context.eventHub.emit('myEvent', 1, 2);
    }

     eventFunc(argOne, argTwo) {
        console.log('eventFunc is called, ${argOne}, ${argTwo}');
    }}

Reference

Using EventHub for Data Synchronization.

How do I implement a click-to-open-application feature in the notification? (API version 9)

Solution

Configure the wantAgent property in the NotificationRequest parameter of the Notification.publish API.

Example

import notificationManager from '@ohos.notificationManager';
import WantAgent from '@ohos.app.ability.wantAgent';

async function publishNotification() {
  let wantAgentInfo = {
    wants: [
      {
        bundleName: "com.example.webuseragent", // Bundle name of your application
        abilityName: "EntryAbility",
      }
    ],
    operationType: WantAgent.OperationType.START_ABILITIES,
    requestCode: 1,
  }
  const wantAgent = await WantAgent.getWantAgent(wantAgentInfo)
  let contentType = notificationManager.ContentType.NOTIFICATION_CONTENT_BASIC_TEXT;
  await notificationManager.publish({
    content: {
      contentType: contentType,
      normal: {
        title: "Test title",
        text: "Test content",
      }
    },
    id: 1,
    wantAgent: wantAgent
  })
}

Reference

Notification and WantAgent

What should I do if calling notificationManager.publish fails? (API version 9)

Symptom

After a notification is published, no error log is displayed, and no notification is displayed in the notification bar.

Solution

When publishing a notification, you need to enable the notification feature of the corresponding application in the system settings of a real device so that the published notification can be viewed in the notification bar.

To enable this feature manually, go to Settings > Notifications & status bar. Tap the target application and turn on Allow notifications.

You can also call the notificationManager.requestEnableNotification() API to display a dialog box (only once) to prompt the user to enable the feature.