harmony(鸿蒙)EventHub

  • 2022-08-09
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EventHub

The EventHub module provides APIs to subscribe to, unsubscribe from, and trigger events.

NOTE

The initial APIs of this module are supported since API version 9. Newly added APIs will be marked with a superscript to indicate their earliest API version. The APIs of this module can be used only in the stage model.

Usage

Before using any APIs in the EventHub, you must obtain an EventHub instance through the member variable context of the Ability instance.

import Ability from '@ohos.application.Ability';
export default class MainAbility extends Ability {
    func1(){
        console.log("func1 is called");
    }
    onForeground() {
        this.context.eventHub.on("123", this.func1);
    }
}

EventHub.on

on(event: string, callback: Function): void;

Subscribes to an event.

System capability: SystemCapability.Ability.AbilityRuntime.Core

Parameters

Name Type Mandatory Description
event string Yes Event name.
callback Function Yes Callback invoked when the event is triggered.

Example

  import Ability from '@ohos.application.Ability';
  
  export default class MainAbility extends Ability {
      onForeground() {
          this.context.eventHub.on("123", this.func1);
          this.context.eventHub.on("123", () => {
              console.log("call anonymous func 1");
          });
          // Result
          // func1 is called
          // call anonymous func 1
          this.context.eventHub.emit("123"); 
      }
      func1() {
          console.log("func1 is called");
      }
  }

EventHub.off

off(event: string, callback?: Function): void;

Unsubscribes from an event. If callback is specified, this API unsubscribes from the specified callback. If callback is not specified, this API unsubscribes from all callbacks in the event.

System capability: SystemCapability.Ability.AbilityRuntime.Core

Parameters

Name Type Mandatory Description
event string Yes Event name.
callback Function No Callback for the event. If callback is unspecified, all callbacks of the event are unsubscribed.

Example

  import Ability from '@ohos.application.Ability';
  
  export default class MainAbility extends Ability {
      onForeground() {
          this.context.eventHub.on("123", this.func1);
          this.context.eventHub.off("123", this.func1); // Unsubscribe from func1.
          this.context.eventHub.on("123", this.func1);
          this.context.eventHub.on("123", this.func2);
          this.context.eventHub.off("123"); // Unsubscribe from func1 and func2.
      }
      func1() {
          console.log("func1 is called");
      }
      func2() {
          console.log("func2 is called");
      }
  }

EventHub.emit

emit(event: string, …args: Object[]): void;

Triggers an event.

System capability: SystemCapability.Ability.AbilityRuntime.Core

Parameters

Name Type Mandatory Description
event string Yes Event name.
…args Object[] Yes Variable parameters, which are passed to the callback when the event is triggered.

Example

  import Ability from '@ohos.application.Ability';
  
  export default class MainAbility extends Ability {
      onForeground() {
          this.context.eventHub.on("123", this.func1);
          // Result
          // func1 is called,undefined,undefined
          this.context.eventHub.emit("123");
          // Result
          // func1 is called,1,undefined
          this.context.eventHub.emit("123", 1);
          // Result
          // func1 is called,1,2
          this.context.eventHub.emit("123", 1, 2);
      }
      func1(a, b) {
          console.log("func1 is called," + a + "," + b);
      }
  }

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