[英]Android ViewModel's LiveData not updating the UI
我有以下片段:
今天_training_fragment.xml
<?xml version="1.0" encoding="utf-8"?>
<layout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto">
<data>
<import type="android.view.View" />
<variable
name="viewmodel"
type="com.myapp.viewmodel.CurrentTrainingSessionViewModel" />
</data>
<LinearLayout
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".fragments.CurrentProgramFragment"
android:id="@+id/todays_training_fragment"
>
<TextView
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="@{String.valueOf(viewmodel.activeProgramId)}" />
</LinearLayout>
</layout>
TodaysTrainingFragment.java
public class TodaysTrainingFragment extends Fragment {
CurrentTrainingSessionViewModel viewModel;
private TodaysTrainingFragmentBinding binding;
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
binding = DataBindingUtil
.inflate(inflater, R.layout.todays_training_fragment, container, false);
binding.setLifecycleOwner(this);
viewModel =
ViewModelProviders
.of(this)
.get(CurrentTrainingSessionViewModel.class);
return binding.getRoot();
}
@Override
public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
super.onViewCreated(view, savedInstanceState);
binding.setViewmodel(viewModel);
binding.getViewmodel().setActiveProgramId(12342); // <-- I'm expecting the layout to show this value
binding.setLifecycleOwner(this);
}
}
CurrentTrainingSessionViewModel.java
public class CurrentTrainingSessionViewModel extends ViewModel {
private MutableLiveData<Long> activeProgramId = new MutableLiveData<>(0L);
public long getActiveProgramId() {
return activeProgramId.getValue();
}
public void setActiveProgramId(long id) {
activeProgramId.postValue(id);
}
}
我希望我的布局在文本視圖中顯示 0,因為它是 activeProgramId 的初始值,然后在隨后更改時將顯示的值更新為 12342。 但是,該值保持為 0 並且不會更新。 我究竟做錯了什么?
不確定你為什么要這樣做兩次:binding.setLifecycleOwner(this); 在更新 ViewModel 中的 LiveData 后立即重置它可能是罪魁禍首,因此請嘗試將其從 onViewCreated 中刪除。
另一件要嘗試的事情是在不使用 DataBindingUtil 的情況下膨脹數據綁定,試試這個:TodaysTrainingFragmentBinding.inflate(inflater)
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