mSubscription.unsubscribe onCreate 是否与 Activity 中的 onDestroy 一样工作？

Question

1. rxjava mSubscription.unsubscribe onCreate 的工作方式是否与 Activity 中的 onDestroy 相同？

2. 它是否会以相同的方式工作并取消订阅以通过将其放在 onCreate 中作为 subscription.subscribeOn().observeOn().subscribe().unsubscribe 来防止内存泄漏 因为不断调用 Activity 来填充下一个片段并弹回堆栈。如果 mSubscription.unsubscribe 在 Activity 的 onDestroy 中完成，它会给出一个 RunTimeException: Unable to destroy Activity because of NullPointerException

3. 我是否遗漏了一些生命周期问题？

谢谢！

    private ViewPager viewPager;
    private TabLayout tabLayout;
    private int mPosition;
    private String id;
    private Subscription mSubscription;
    private Context mContext;
    private RealmResults<Experience> realmResults; 
    private String animateExtraColumnName, tag;
    private Boolean automaticUpdate, animateResults;


    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_employment);

        User currentUser = AppDelegate.getCurrentUser();
        assert currentUser != null;
        mEmployee = getRealm().where(Employee.class).equalTo("user.id", currentUser.getId()).findFirst();


            //Server returns Experience's ID
            if (employeeExperience == null) {

                AccessToken accessToken = currentUser.getAccessTokenAsTokenType(AppDelegate.getContext(), "Bearer");
               employeeExperienceAPIOAuth2Call apiCall = new employeeExperienceAPIOAuth2Call(AppDelegate.getContext(), accessToken);

                Observable<ResponseEmployeeExperience> postEmployeeExperienceObservable = apiCall.postEmployeeExperiencesRX();

                mSubscription = postEmployeeExperienceObservable
                        .subscribeOn(Schedulers.io())
                        .observeOn(AndroidSchedulers.mainThread())
                        .subscribe((data) -> {
                            Log.d(TAG, "onCreate: Subscribe ");
                         employeeExperience = data.getEmployeeExperience();
                            Log.d(TAG, "onCreate: employeeExperience.getId()");

                            getRealm().beginTransaction();
                            getRealm().copyToRealmOrUpdate(employeeExperience);
                            // This adds the new employeeExperience object into the EmployeeExperiences RealmList
                            employee.employeeExperiences.add(employeeExperience);
                            getRealm().commitTransaction();
                            getRealm().close();

                            //unsubscribe here because the activity doesnt close itself to begin with?
                            mSubscription.unsubscribe();
                            Log.d(TAG, "onCreate: Unsubscribe: ");

                            // prepare data needed by our fragment
                            FragmentAddOrUpdateEmploymentHistory addEmploymentHistoryFragment = new FragmentAddOrUpdateEmploymentHistory();

                            FragmentManager fm = getSupportFragmentManager();
                            fm.beginTransaction().replace(R.id.edit_frame_layout, addEmploymentHistoryFragment, "EDIT_FRAGMENT").commit();

                        }, (error) -> {
                            // TODO do whatever error handling we need to do here
                            Log.d(TAG, "onCreate: postEmployeeExp error");
                            error.printStackTrace();
                        });
            }

        } else if (employee.getEmployeeExperiences() != null) {
            employeeExperience = getRealm().where(employeeExperience.class).equalTo("id", id).findFirst();

            FragmentAddOrUpdateEmploymentHistory addEmploymentHistoryFragment = new FragmentAddOrUpdateEmploymentHistory();

            FragmentManager fm = getSupportFragmentManager();
            fm.beginTransaction().replace(R.id.edit_frame_layout, addEmploymentHistoryFragment, "EDIT_FRAGMENT").commit();
        }

        ImageButton checkButton = (ImageButton) findViewById(R.id.edit_toolbar_check);
        checkButton.setOnClickListener(this);

        ImageButton crossButton = (ImageButton) findViewById(R.id.edit_toolbar_cross);
        crossButton.setOnClickListener(this);

    }

    @Override
    protected void onStart() {
        super.onStart();
    }

    @Override
    public void onClick(View view) {

        Fragment editFragments = getSupportFragmentManager().findFragmentByTag("EDIT_FRAGMENT");

        switch (view.getId()) {

            case R.id.edit_toolbar_check:
                if (editFragments instanceof FragmentEditDate) {
                    Log.d(TAG, "onClick: editdate ");
                    getSupportFragmentManager().popBackStack();
                } else if (editFragments instanceof FragmentSalary){
                    Log.d(TAG, "onClick: salary ");
                    getSupportFragmentManager().popBackStack();
                } else if (editFragments instanceof FragmentAddOrUpdateEmploymentHistory) {
                    Log.d(TAG, "onClick: employmenthistory ");
                    finish();
                } else if (editFragments instanceof FragmentSingleChoice) {
                    Log.d(TAG, "singlechoice  " );
                    getSupportFragmentManager().popBackStack();
                }
                else if (editFragments instanceof FragmentMultipleChoice) {
                    Log.d(TAG, "multiplechoice  " );
                    getSupportFragmentManager().popBackStack();
                }
                break;


            case R.id.edit_toolbar_cross:
                if (editFragments instanceof FragmentAddOrUpdateEmploymentHistory) {

                            getRealm().beginTransaction();
                            employeeExperience.DELETE();
                            getRealm().commitTransaction();
                            getRealm().close();
                        }
                        finish();
                    } else {
                        finish();

                    }
                } else {
                    getSupportFragmentManager().popBackStack(); }
                break;

        }
    }

Answer 1

简而言之 - 一旦您订阅了 Observable，您就可以接收并响应来自它的通知（onNext、onError、onComplete）。同样在大多数情况下（对于冷 Observables），这实际上是Observable 开始发射项目的触发点。

Unsubscribing 来自 Observable 意味着您不再有兴趣接收任何进一步的通知。当您不再想接收任何东西时，您需要unsubscribe，类似于如何在Activity 的onDestroy() 方法中释放任何资源。当然，与活动生命周期的平行只是为了比较 - 订阅/取消订阅过程是完全独立的。

您可以详细了解subscribing 和unsubscribing 的含义 [这里][1] [1]：http://reactivex.io/documentation/contract.html

也就是说，对您的代码的具体建议很少：

您目前在 Android 的主线程上执行的操作过多。我建议将所有与真实相关的东西作为 RX 链的一部分移动，而不是在 subscribe(...) 的 onNext() 处理程序中。这样它将在io 线程上执行。比如：

...
mSubscription = postEmployeeExperienceObservable
            .subscribeOn(Schedulers.io())
            .doOnNext(data -> saveDataToRealm(data))
            .observeOn(AndroidSchedulers.mainThread())
            .subscribe((data) -> {
                // prepare data needed by our fragment
                FragmentAddOrUpdateEmploymentHistory addEmploymentHistoryFragment = new FragmentAddOrUpdateEmploymentHistory();

                FragmentManager fm = getSupportFragmentManager();
                fm.beginTransaction().replace(R.id.edit_frame_layout, addEmploymentHistoryFragment, "EDIT_FRAGMENT").commit();

            }, (error) -> {
                // TODO do whatever error handling we need to do here
                Log.d(TAG, "onCreate: postEmployeeExp error");
                error.printStackTrace();
            });
}

private Data saveDataToRealm(Data data) {
    employeeExperience = data.getEmployeeExperience();
    Log.d(TAG, "onCreate: employeeExperience.getId()");

    getRealm().beginTransaction();
    getRealm().copyToRealmOrUpdate(employeeExperience);
    // This adds the new employeeExperience object into the EmployeeExperiences RealmList
    employee.employeeExperiences.add(employeeExperience);
    getRealm().commitTransaction();
    getRealm().close();
}

就取消订阅而言——如果你真的想在onNext() 事件中unsubscribe，更好的策略是通过Subscriber<Data> 订阅，然后使用它的unsubscribe() 方法。换句话说 - 你不会打电话给mSubscription.unsubscribe()，而是this.unsubscribe()。

mSubscription = postEmployeeExperienceObservable
            .subscribeOn(Schedulers.io())
            .doOnNext(data -> saveDataToRealm(data))
            .observeOn(AndroidSchedulers.mainThread())
            .subscribe(new Subscriber<Data>() {

                @Override
                public void onCompleted() {

                }

                @Override
                public void onError(Throwable e) {

                }

                @Override
                public void onNext(Data data) {
                    ...
                    this.unsubscribe();
                }
            });

说了这么多，我认为你真的不需要从 onNext() 方法中 unsubscribe ，而是你可以在 onDestroy() 中这样做，当然检查之前是否创建了订阅：

@Override
protected void onDestroy() {
    super.onDestroy();
    if (mSubscription != null) {
        mSubscription.unsubscribe();
    }
}