视图模型不断创建实时数据的实例 [英] View Model keeps creating instance of Live Data

问题描述

我在活动的 onCreate 方法中创建了 View Model 的实例.

I created the instance of View Model in onCreate method of an activity.

    ticketViewModel = ViewModelProviders.of(this).get(TicketViewModel.class);

然后我有一个方法，AddTicket，它使用 viewModel 来点击服务，并在来自 viewModel 的响应中关闭加载动画.

Then i have a method, AddTicket, which uses viewModel to hit a service and on response from viewModel i dismiss loading animation.

 public void addTicket(View view){

     ticketViewModel.AddTicket(id).observe(this, response ->{
                        dismissLoadingAnimation();
    } 

现在添加工单后，用户可以再次按下添加工单按钮，addTicket()方法将再次被调用.

Now after adding a ticket, user can repress the Add Ticket button, and the addTicket() method will be called again.

但是这次在 ViewModel 中定义的 observer 被调用了 2 次，导致 2 次网络调用和 2 次 dismissLoadingAnimation 执行.

but this time observer defined in ViewModel gets called 2 times, resulting in 2 network calls, and 2 dismissLoadingAnimation execution.

如果我一直按 addTicket 按钮，ViewModel 中定义的执行观察者的数量会增加.

And if i keep pressing addTicket button, the number of executing observer defined inside ViewModel keep increases.

这是我的视图模型代码.

public class TicketViewModel extends AndroidViewModel implements IServiceResponse {

    MutableLiveData<String> mObservableResponse = new MutableLiveData<String>();


    public MutableLiveData AddTicket(String id){

        JsonObject jsonObject= new JsonObject();
        jsonObject.addProperty("id",  id);

        NetworkUtility networkUtility= new NetworkUtility(this, ADD_TICKET);
        networkUtility.hitService(URL, jsonObject, RequestMethods.POST);

        return mObservableResponse;
    }


     @Override
        public void onServiceResponse(String response, String callType){

        if(serviceTag.equalsIgnoreCase(ADD_TICKET)){    
             mObservableResponse.setValue("success");
        }
    }

}

推荐答案

• Viewmodel 的目的是公开 observables (Livedata)
• View(Activity/Fragment) 的目的是获取这些可观察对象并观察它们
• 每当这些 observables(Livedata) 发生变化时，该变化就会自动发布到活动订阅的所有者 (Activity/Fragment)，因此您无需在 onPause/onStop 中删除它们，因为它不是强制性的

我可以建议对您的代码进行一些更改以解决上述指针的问题

I can suggest few changes to your code to solve the problem with the above mentioned pointers

视图模型

public class TicketViewModel extends AndroidViewModel implements IServiceResponse {

    MutableLiveData<String> mObservableResponse = new MutableLiveData<String>();

   public LiveData<String> getResponseLiveData(){
        return mObservableResponse;
        }

    public void AddTicket(String id){

        JsonObject jsonObject= new JsonObject();
        jsonObject.addProperty("id",  id);

        NetworkUtility networkUtility= new NetworkUtility(this, ADD_TICKET);
        networkUtility.hitService(URL, jsonObject, RequestMethods.POST);

    }


     @Override
        public void onServiceResponse(String response, String callType){

        if(serviceTag.equalsIgnoreCase(ADD_TICKET)){    
             mObservableResponse.setValue("success");
        }
    }

}

查看

    onCreate(){
    ticketViewModel = ViewModelProviders.of(this).get(TicketViewModel.class);
    observeForResponse();
    }

    private void observeForResponse(){
       ticketViewModel.getResponseLiveData().observe(this, response ->{
                            //do what has to be updated in UI
    }
    }

public void addTicket(View view){
     ticketViewModel.AddTicket(id);
    }

希望这对您有所帮助:)

Hope this is of help :)

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