[英]Angular 2 service: Why the private member is undefined?
Trying to figure out why If I set a private member of a service, when I get back to that service I will find out that the member is undefined. 试图弄清原因如果我设置服务的私有成员,当我返回该服务时,我会发现该成员是未定义的。
getResult (): Observable<result[]> {
return this.http.get(this.url)
.map(this.extractData)
.catch(this.handleError);
}
private extractData(res: Response) {
let body = res.json();
// save the data in the service
this.data = body;
return body || { };
}
From another function in the service, when I try to read this.data it is undefined. 从服务中的另一个功能,当我尝试读取this.data时,它是未定义的。 Why?
为什么?
getData() {
this.data // undefeind !!!!
}
From a component there is a call to the service to getData onInit: 从组件可以调用该服务以调用getData onInit:
this.myService.getResult()
.subscribe(res => {this.data= res;
},
error => {
console.log("error on getData function: " + error);
}
);
If you want to access this
within the passed method you need to bind this
如果要在传递的方法中访问
this
方法,则需要绑定this
.map(this.extractData.bind(this))
bind(this)
is IMHO more convenient for this use case than () => {}
because it works, no matter how many parameters need to be passed. 在此用例中,
bind(this)
比() => {}
更方便,因为不管需要传递多少参数,它都可以工作。 With arrow functions all parameters need to be repeated twice. 使用箭头功能时,所有参数都需要重复两次。
@Gunther's solution works. @Gunther的解决方案有效。 Another way to solve is to wrap in arrow functions.
解决的另一种方法是包装箭头函数。
getResult (): Observable<result[]> {
return this.http.get(this.url)
.map((res)=>this.extractData(res))
.catch((err)=>this.handleError(err));
}
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