我需要从承诺中返回Observable,但是当我试图学习angular时,我被语法所困扰。所以这就是事情:
我有一个以下函数getCountries(这是由另一个实用程序订阅),我需要调用它来检索国家/地区列表。' lang'尚未定义。我补充说,只是为了完成我的api的网址。
getCountries(): Observable<Country[]> {
if (this.countries) {
return Observable.of(this.countries);
} else if (this.countriesObservable) {
return this.countriesObservable;
} else {
//lang is not defined yet it has to be retrieved from storage
this.countriesObservable = this.http.get(AppSettings.API_URL + '?locale=' + lang).map(json => {
delete this.countriesObservable; // when the cached countries is available we don't need reference anymore
this.countries = json as Country[];
this.countries = this.countries.sort(function (a, b) { return (a.Name > b.Name) ? 1 : ((b.Name > a.Name) ? -1 : 0); });
return this.countries;
}).share();
return this.countriesObservable;
}
}
由于api需要语言(lang),并且此信息存储在存储中,可以从存储中检索,如下所示:
this.storage.get(AppSettings.STORAGE_KEYS.LANGUAGE_APP).then(language=>{
//here I can use language
});
现在我被困的地方是在从上述承诺中检索语言信息后如何拨打我的api。我需要确保函数(getCountries)仍然返回它最初返回的observable。 谢谢你的帮助。
有些人建议将它们包装在Observable.fromPromise中,我做了同样的事情,但这打破了代码。我必须遗漏一些我知道的东西。这就是:它是否错过了返回的东西,发布我的堆栈跟踪后代码:
getCountries(): Observable<Country[]> {
if (this.countries) {
return Observable.of(this.countries);
} else if (this.countriesObservable) {
return this.countriesObservable;
} else {
Observable.fromPromise(this.storage.get(AppSettings.STORAGE_KEYS.LANGUAGE_APP)).subscribe(language=>{
//here I can use language
this.countriesObservable = this.http.get(AppSettings.API_URL + '?locale=' + language).map(json => {
delete this.countriesObservable;
this.countries = json as Country[];
this.countries = this.countries.sort(function (a, b) { return (a.Name > b.Name) ? 1 : ((b.Name > a.Name) ? -1 : 0); });
return this.countries;
}).share();
return this.countriesObservable;
});
}
}
Error: Uncaught (in promise): TypeError: Cannot read property 'subscribe' of undefined
TypeError: Cannot read property 'subscribe' of undefined
at http://localhost:8100/build/main.js:71:33
at new t (http://localhost:8100/build/polyfills.js:3:20886)
at UtilsProvider.webpackJsonp.10.UtilsProvider.getCountryById (http://localhost:8100/build/main.js:70:16)
at MyApp.webpackJsonp.851.MyApp.updateUserInfo (http://localhost:8100/build/main.js:10067:47)
at http://localhost:8100/build/main.js:9774:23
at SafeSubscriber.schedulerFn [as _next] (http://localhost:8100/build/vendor.js:4004:36)
at SafeSubscriber.__tryOrUnsub (http://localhost:8100/build/vendor.js:16987:16)
at SafeSubscriber.next (http://localhost:8100/build/vendor.js:16934:22)
at Subscriber._next (http://localhost:8100/build/vendor.js:16874:26)
at Subscriber.next (http://localhost:8100/build/vendor.js:16838:18)
at c (http://localhost:8100/build/polyfills.js:3:19132)
at c (http://localhost:8100/build/polyfills.js:3:18841)
at http://localhost:8100/build/polyfills.js:3:19613
at t.invokeTask (http://localhost:8100/build/polyfills.js:3:15040)
at Object.onInvokeTask (http://localhost:8100/build/vendor.js:4238:33)
at t.invokeTask (http://localhost:8100/build/polyfills.js:3:14961)
at r.runTask (http://localhost:8100/build/polyfills.js:3:10214)
at o (http://localhost:8100/build/polyfills.js:3:7274)
at e.invokeTask [as invoke] (http://localhost:8100/build/polyfills.js:3:16203)
at p (http://localhost:8100/build/polyfills.js:2:26993)
答案 0 :(得分:1)
任何承诺都可以(轻松)转为使用Observable.fromPromise()
Observable.fromPromise(this.storage.get(AppSettings.STORAGE_KEYS.LANGUAGE_APP))
.subscribe((language) => {
//here you can use language
});
答案 1 :(得分:1)
只需使用Observable.fromPromise。所以在你的情况下,它将是
getCountries(): Observable<Country[]> {
if (this.countries) {
return Observable.of(this.countries);
} else if (this.countriesObservable) {
return this.countriesObservable;
} else {
return Observable.fromPromise(this.storage.get(AppSettings.STORAGE_KEYS.LANGUAGE_APP)).mergeMap(language=>{
//here I can use language
this.countriesObservable = this.http.get(AppSettings.API_URL + '?locale=' + language).map(json => {
delete this.countriesObservable; // when the cached countries is available we don't need the reference anymore
this.countries = json as Country[];
this.countries = this.countries.sort(function (a, b) { return (a.Name > b.Name) ? 1 : ((b.Name > a.Name) ? -1 : 0); });
return this.countries;
}).share();
return this.countriesObservable;
});
}
}