Angular 2 value from service not available outside

问题:

In my component I have a save function like below:

save() {
    var result;
    //For updating task
    if (this.task.AllTaskId) {
        if (this.task.AssignedToCode == null) {
            this.task.AssignedToCode = "All";
        }
        this.task.CreatedDate = new Date();

        this.task.CreatedBy = this.empcode;
        result = this._tasksService.updateTask(this.task).subscribe(
            res => {
                this._router.navigate(['/regtask'])
            }
        )
    }
    //For Adding new task
    else {
        if (this.task.AssignedToCode == null) {
            this.task.AssignedToCode = "All";
        }
        this.task.CreatedDate = new Date();
        this._tasksService.addTask(this.task)
            .subscribe((ntask) => {
                this.emitntask.emit(ntask);
                this._router.navigate(['/regtask']);
                this.temp = ntask.allTaskId;
                console.log(this.temp);
            })
        debugger;
        console.log(this.temp);
    }

    this.compform.reset();
}

If you look at the else condition of the save function, When I log the value temp in the .subscribe() function, it shows me the value in my log but when I try to log the same value outside the .subscribe() function, it shows me an undefined value like below:

Can anyone suggest me what to do and why 'this.temp' gets unavailable while it is available to me in .subscribe function?

回答1:

Because it's asynchronous code. The second console.log(this.temp) actually occurs before the first one, because that one is wrapped in a subscribe() call that only executes after addTask completes (returns a value). The second one just executes immediately.

回答2:

That's because the callback you pass to subscribe() is run ASYNCHRONOUSLY.

Try running the following code:

// Some observable that takes a little while to complete (could be an HTTP request).
const obs = Observable.interval(200).first();

// Some callback that you want to execute when the obs emits/completes.
const callback = (val) => console.log('callback');

// Subscribe and log to console right after subscribing.
obs.subscribe(callback);
console.log('after subscribe');

You will see this in the console:

"after subscribe"
"callback"

The callback is run AFTER the code that comes right after obs.subscribe().