javascript - 正确使用 Promise.resolve().then() 错误 : Uncaught (in promise): TypeError: Cannot read property

Question

这个问题已经有答案了:

How to access the correct `this` inside a callback (15 个回答)

去年已关闭。

我有这个代码:

export class Page {
  constructor(public modalController: ModalController) { }

  private async openModal(value) {    
    const modal = await this.modalController.create({
      component: AnotherPage,
      componentProps: {
        "paramID": 123,
        "paramTitle": "Test Title",
        "takenPhoto": "null"
      }
    });

    return await modal.present();
  }

  public async takePicture() {
    this.openModel(null); // here's OK
    Promise.resolve(this.someMethod()).then(this.openModal); // ERROR!!
  }

}

关于方法takePicture我想在执行 Promise.resolve 后打开一个模式。第一次执行时一切正常，但第二次执行时出现错误。

错误:

ERROR Error: Uncaught (in promise): TypeError: Cannot read property 'modalController' of undefined
TypeError: Cannot read property 'modalController' of undefined
    at tab2.page.ts:25
    at Generator.next (<anonymous>)
    at tslib.es6.js:73
    at new ZoneAwarePromise (zone-evergreen.js:876)
    at Module.__awaiter (tslib.es6.js:69)
    at openModal (tab2.page.ts:22)
    at ZoneDelegate.invoke (zone-evergreen.js:359)
    at Object.onInvoke (core.js:34201)
    at ZoneDelegate.invoke (zone-evergreen.js:358)
    at Zone.run (zone-evergreen.js:124)
    at resolvePromise (zone-evergreen.js:797)
    at resolvePromise (zone-evergreen.js:754)
    at zone-evergreen.js:858
    at ZoneDelegate.invokeTask (zone-evergreen.js:391)
    at Object.onInvokeTask (core.js:34182)
    at ZoneDelegate.invokeTask (zone-evergreen.js:390)
    at Zone.runTask (zone-evergreen.js:168)
    at drainMicroTaskQueue (zone-evergreen.js:559)

Answer 1

export class Page {
  constructor(public modalController: ModalController) { }

  private async openModal(value) {    
    const modal = await this.modalController.create({
      component: AnotherPage,
      componentProps: {
        "paramID": 123,
        "paramTitle": "Test Title",
        "takenPhoto": "null"
      }
    });

    return modal.present();
  }

  public async takePicture() {
    await this.openModel(null); // Need to await a promise
    const data = await this.someMethod()
    await this.openModal(data);
  }

}