Android mvvm 实时数据未观察
Android mvvm livedata not observing
这是我第一次使用 MVVM architecture.I 我也在使用 LiveData。我只是在单击 View(MainActivity.class) 中的按钮后使用 Retrofit.So 从服务器检索数据 我调用 ViewModel class 的方法 (handleRetrofitcall()) 承担 Api 从 模型 class(Retrofit Handler.class)[=39= 调用的职责]。检索数据时模型 class 通知 ViewModel 数据（实际上是项目的大小）。我将大小设置为 LiveData 并尝试收听 it.Unfortunately 我不能't.For详细分析请看代码
型号...
改装Handler.class:
public class RetrofitHandler {
private ApiInterface apiInterface;
private SimpleViewModel viewModel;
public void getData(){
apiInterface= ApiClient.getClient().create(ApiInterface.class);
Call<Unknownapi> call=apiInterface.doGetListResources();
call.enqueue(new Callback<Unknownapi>() {
@Override
public void onResponse(Call<Unknownapi> call, Response<Unknownapi> response) {
List<Unknownapi.Data> list;
Unknownapi unknownapi=response.body();
list=unknownapi.getData();
viewModel=new SimpleViewModel();
viewModel.postValue(list.size());
Log.e("Size",Integer.toString(list.size()));
}
@Override
public void onFailure(Call<Unknownapi> call, Throwable t) {
}
});
}
}
ViewModel....
SimpleViewModel.class:
public class SimpleViewModel extends ViewModel {
private RetrofitHandler retrofitHandler;
private int size;
private MutableLiveData<Integer> mutablesize=new MutableLiveData<>();
public SimpleViewModel() {
super();
}
@Override
protected void onCleared() {
super.onCleared();
}
public void handleRetrofitcall(){
retrofitHandler=new RetrofitHandler();
retrofitHandler.getData();
}
public void postValue(int size){
this.size=size;
mutablesize.postValue(this.size);
Log.e("lk","f");
}
public MutableLiveData<Integer> getObject() {
return mutablesize;
}
}
查看.....
MainActivity.class:
public class MainActivity extends AppCompatActivity {
private TextView status;
private SimpleViewModel viewModel;
private Observer<Integer> observer;
private MutableLiveData<Integer> mutableLiveData;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
status=findViewById(R.id.status);
viewModel=ViewModelProviders.of(MainActivity.this).get(SimpleViewModel.class);
observer=new Observer<Integer>() {
@Override
public void onChanged(@Nullable Integer integer) {
Log.e("lk","f");
status.setText(Integer.toString(integer));
}
};
viewModel.getObject().observe(MainActivity.this,observer);
findViewById(R.id.retrofit).setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
viewModel.handleRetrofitcall();
}
});
}
@Override
protected void onDestroy() {
if (observer!=null){
viewModel.getObject().removeObserver(observer);
}
super.onDestroy();
}
}
您正在 RetrofitHandler 中创建一个新的 ViewModel，因此没有观察到该 ViewModel。与其让 RetrofitHandler 在内部依赖 ViewModel，不如自己处理 Retrofit 回调和那里的 post 数据可能更安全。
public void handleRetrofitcall(){
retrofitHandler=new RetrofitHandler();
retrofitHandler.getData(new Callback<List<Unknownapi.Data>> {
// add actual callback implementation here
); // add a callback here, so that the data is available in the view model. Then post the results from here.
}
编辑：更多说明。
在 Activity 中，您正确地创建了一个 ViewModel 并观察它（我们将其称为 ViewModel A）。 ViewModel A 然后创建一个 RetrofitHandler 并在该 Retrofithandler 上调用 getData。问题是 RetrofitHandler 正在 getData 中创建一个新的 ViewModel（我将其称为 ViewModel B）。
问题是结果正在 posted 到 ViewModel B，没有观察到任何东西，所以似乎没有任何效果。
避免此问题的简单方法是确保只有 Activity/Fragment 依赖（并创建）ViewModel。没有其他关于 ViewModel 的知识。
编辑 2：这是一个简单的实现。我没有测试过，但应该差不多是正确的。
// shouldn't know anything about the view model or the view
public class RetrofitHandler {
private ApiInterface apiInterface;
// this should probably pass in a different type of callback that doesn't require retrofit
public void getData(Callback<Unknownapi> callback) {
// only create the apiInterface once
if (apiInterface == null) {
apiInterface = ApiClient.getClient().create(ApiInterface.class);
}
// allow the calling function to handle the result
apiInterface.doGetListResources().enqueue(callback);
}
}
// shouldn't know how retrofit handler parses the data
public class SimpleViewModel extends ViewModel {
private RetrofitHandler retrofitHandler = new RetrofitHandler();
// store data in mutableSize, not with a backing field.
private MutableLiveData<Integer> mutableSize = new MutableLiveData<>();
public void handleRetrofitCall() {
// handle the data parsing here
retrofitHandler.getData(new Callback<Unknownapi>() {
@Override
public void onResponse(Call<Unknownapi> call, Response<Unknownapi> response) {
Unknownapi unknownapi = response.body();
int listSize = unknownapi.getData().size;
// set the value of the LiveData. Observers will be notified
mutableSize.setValue(listSize); // Note that we're using setValue because retrofit callbacks come back on the main thread.
Log.e("Size", Integer.toString(listSize));
}
@Override
public void onFailure(Call<Unknownapi> call, Throwable t) {
// error handling should be added here
}
});
}
// this should probably return an immutable copy of the object
public MutableLiveData<Integer> getObject() {
return mutableSize;
}
}
public class MainActivity extends AppCompatActivity {
private TextView status;
// initialize the view model only once
private SimpleViewModel viewModel = ViewModelProviders.of(MainActivity.this).get(SimpleViewModel.class);
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
status = findViewById(R.id.status);
// observe the view model's changes
viewModel.getObject().observe(this, new Observer<Integer>() {
@Override
public void onChanged(@Nullable Integer integer) {
// you should handle possibility of interger being null
Log.e("lk","f");
status.setText(Integer.toString(integer));
}
});
findViewById(R.id.retrofit).setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
// call the view model's function
viewModel.handleRetrofitCall();
}
});
}
}
这是我第一次使用 MVVM architecture.I 我也在使用 LiveData。我只是在单击 View(MainActivity.class) 中的按钮后使用 Retrofit.So 从服务器检索数据 我调用 ViewModel class 的方法 (handleRetrofitcall()) 承担 Api 从 模型 class(Retrofit Handler.class)[=39= 调用的职责]。检索数据时模型 class 通知 ViewModel 数据（实际上是项目的大小）。我将大小设置为 LiveData 并尝试收听 it.Unfortunately 我不能't.For详细分析请看代码
型号...
改装Handler.class:
public class RetrofitHandler {
private ApiInterface apiInterface;
private SimpleViewModel viewModel;
public void getData(){
apiInterface= ApiClient.getClient().create(ApiInterface.class);
Call<Unknownapi> call=apiInterface.doGetListResources();
call.enqueue(new Callback<Unknownapi>() {
@Override
public void onResponse(Call<Unknownapi> call, Response<Unknownapi> response) {
List<Unknownapi.Data> list;
Unknownapi unknownapi=response.body();
list=unknownapi.getData();
viewModel=new SimpleViewModel();
viewModel.postValue(list.size());
Log.e("Size",Integer.toString(list.size()));
}
@Override
public void onFailure(Call<Unknownapi> call, Throwable t) {
}
});
}
}
ViewModel....
SimpleViewModel.class:
public class SimpleViewModel extends ViewModel {
private RetrofitHandler retrofitHandler;
private int size;
private MutableLiveData<Integer> mutablesize=new MutableLiveData<>();
public SimpleViewModel() {
super();
}
@Override
protected void onCleared() {
super.onCleared();
}
public void handleRetrofitcall(){
retrofitHandler=new RetrofitHandler();
retrofitHandler.getData();
}
public void postValue(int size){
this.size=size;
mutablesize.postValue(this.size);
Log.e("lk","f");
}
public MutableLiveData<Integer> getObject() {
return mutablesize;
}
}
查看.....
MainActivity.class:
public class MainActivity extends AppCompatActivity {
private TextView status;
private SimpleViewModel viewModel;
private Observer<Integer> observer;
private MutableLiveData<Integer> mutableLiveData;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
status=findViewById(R.id.status);
viewModel=ViewModelProviders.of(MainActivity.this).get(SimpleViewModel.class);
observer=new Observer<Integer>() {
@Override
public void onChanged(@Nullable Integer integer) {
Log.e("lk","f");
status.setText(Integer.toString(integer));
}
};
viewModel.getObject().observe(MainActivity.this,observer);
findViewById(R.id.retrofit).setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
viewModel.handleRetrofitcall();
}
});
}
@Override
protected void onDestroy() {
if (observer!=null){
viewModel.getObject().removeObserver(observer);
}
super.onDestroy();
}
}
您正在 RetrofitHandler 中创建一个新的 ViewModel，因此没有观察到该 ViewModel。与其让 RetrofitHandler 在内部依赖 ViewModel，不如自己处理 Retrofit 回调和那里的 post 数据可能更安全。
public void handleRetrofitcall(){
retrofitHandler=new RetrofitHandler();
retrofitHandler.getData(new Callback<List<Unknownapi.Data>> {
// add actual callback implementation here
); // add a callback here, so that the data is available in the view model. Then post the results from here.
}
编辑：更多说明。
在 Activity 中，您正确地创建了一个 ViewModel 并观察它（我们将其称为 ViewModel A）。 ViewModel A 然后创建一个 RetrofitHandler 并在该 Retrofithandler 上调用 getData。问题是 RetrofitHandler 正在 getData 中创建一个新的 ViewModel（我将其称为 ViewModel B）。
问题是结果正在 posted 到 ViewModel B，没有观察到任何东西，所以似乎没有任何效果。
避免此问题的简单方法是确保只有 Activity/Fragment 依赖（并创建）ViewModel。没有其他关于 ViewModel 的知识。
编辑 2：这是一个简单的实现。我没有测试过，但应该差不多是正确的。
// shouldn't know anything about the view model or the view
public class RetrofitHandler {
private ApiInterface apiInterface;
// this should probably pass in a different type of callback that doesn't require retrofit
public void getData(Callback<Unknownapi> callback) {
// only create the apiInterface once
if (apiInterface == null) {
apiInterface = ApiClient.getClient().create(ApiInterface.class);
}
// allow the calling function to handle the result
apiInterface.doGetListResources().enqueue(callback);
}
}
// shouldn't know how retrofit handler parses the data
public class SimpleViewModel extends ViewModel {
private RetrofitHandler retrofitHandler = new RetrofitHandler();
// store data in mutableSize, not with a backing field.
private MutableLiveData<Integer> mutableSize = new MutableLiveData<>();
public void handleRetrofitCall() {
// handle the data parsing here
retrofitHandler.getData(new Callback<Unknownapi>() {
@Override
public void onResponse(Call<Unknownapi> call, Response<Unknownapi> response) {
Unknownapi unknownapi = response.body();
int listSize = unknownapi.getData().size;
// set the value of the LiveData. Observers will be notified
mutableSize.setValue(listSize); // Note that we're using setValue because retrofit callbacks come back on the main thread.
Log.e("Size", Integer.toString(listSize));
}
@Override
public void onFailure(Call<Unknownapi> call, Throwable t) {
// error handling should be added here
}
});
}
// this should probably return an immutable copy of the object
public MutableLiveData<Integer> getObject() {
return mutableSize;
}
}
public class MainActivity extends AppCompatActivity {
private TextView status;
// initialize the view model only once
private SimpleViewModel viewModel = ViewModelProviders.of(MainActivity.this).get(SimpleViewModel.class);
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
status = findViewById(R.id.status);
// observe the view model's changes
viewModel.getObject().observe(this, new Observer<Integer>() {
@Override
public void onChanged(@Nullable Integer integer) {
// you should handle possibility of interger being null
Log.e("lk","f");
status.setText(Integer.toString(integer));
}
});
findViewById(R.id.retrofit).setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
// call the view model's function
viewModel.handleRetrofitCall();
}
});
}
}