如何優雅地取消Retrofit請求?

在實際開發中,頁面關閉,取消請求是很常見的需求,這裏分享一種簡單的實現方法。 個人思路是把網絡請求和上下文的生命週期綁定。這裏用用到了Rxjava的Subject,Subject 既是 Observable 又是 Observer(Subscriber)。既能夠發消息也能夠接收消息。java

我首先定義了幾個枚舉,對應上下文的生命週期。後端

public enum ActivityLifeCycleEvent {
    CREATE,START,RESUME,PAUSE,STOP,DESTROY
}
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Fragment爲例,在BaseFragment中,相應的生命週期回調中發射消息。bash

import rx.subjects.PublishSubject;

public abstract class BaseFragment extends Fragment {

    protected final PublishSubject<ActivityLifeCycleEvent> lifecycleSubject = PublishSubject.create();



    @Override
    public void onActivityCreated(@Nullable Bundle savedInstanceState) {
        // TODO Auto-generated method stub
        super.onActivityCreated(savedInstanceState);
    }

    @Override
    public void onPause() {
        super.onPause();
        lifecycleSubject.onNext(ActivityLifeCycleEvent.PAUSE);
    }

    @Override
    public void onStop() {
        super.onStop();
        lifecycleSubject.onNext(ActivityLifeCycleEvent.STOP);
    }


    @Override
    public void onResume() {
        super.onResume();
        lifecycleSubject.onNext(ActivityLifeCycleEvent.RESUME);
    }


    @Override
    public void onDestroy() {
        super.onDestroy();
        lifecycleSubject.onNext(ActivityLifeCycleEvent.DESTROY);
    }

}

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通常狀況下咱們會使用Retrofit+Rxjava來進行網絡請求,好比像下面這樣:網絡

@Multipart
@POST(Urls.TIMER_GETUSERDETAIL_RX)
Observable<Results<User>> getUser(@PartMap Map<String, RequestBody> map);
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具體請求的時候多是下面這樣ide

ApiService.instancce()
  .getUser(p.build())
  .takeUntil(bindLifeCycle(lifecycleSubject,ActivityLifeCycleEvent.DESTROY))
  .subscribe({
      ……
  })
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注意:下面這句話ui

.takeUntil(RxUtils.bindLifeCycle(lifecycleSubject, ActivityLifeCycleEvent.DESTROY))
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takeUntil一旦響應是成功它將自動終止源Observable因而中止向後端發送數據。若是不是則繼續發送請求。這裏若是收到ActivityLifeCycleEvent.DESTROY消息,就會中止向後端發送數據。spa

public static Observable<ActivityLifeCycleEvent> bindLifeCycle(PublishSubject<ActivityLifeCycleEvent> lifecycleSubject, ActivityLifeCycleEvent bindEvent) {
        return  lifecycleSubject.takeFirst(activityLifeCycleEvent -> activityLifeCycleEvent.equals(bindEvent));
    }
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嗯,就這麼多。下面就是愉快地使用吧~code

本方法只是取消了接受網絡數據以後的後續操做,並非真正中止了當前的請求哦~server

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