关于过去的问题How to get a ViewModel?,以及我找到的例子,它不能解决我的问题。我不允许在这里发表评论,所以我必须再问一次。我没有像在我找到的所有示例和文档中那样使用"of“方法的ViewModelProviders类,比如
model = ViewModelProviders.of(this).get(Something.class);
在Android Studio中,我没有找到要添加为依赖项的"android.arch.lifecycle:extensions“。当我搜索的时候,它显示“没有要显示的东西”。我在API 27。因此,为了尝试使用非弃用元素,我在片段中包含以下内容:
public class EventDetailsFragment extends Fragment
{
EventViewModel viewModel;
@Override
public void onActivityCreated (Bundle savedInstanceState)
{
super.onActivityCreated(savedInstanceState);
ViewModelProvider.Factory factory = ViewModelProvider.AndroidViewModelFactory.getInstance(getActivity().getApplication());
// HERE IS THE ISSUE: Seems not good practice to have to create a new ViewModelProvider every time this Fragment is created.
// Perhaps I should just create a singleton ViewModelProvider in the Activity or Application,
// so here could call getActivity().getViewModelProvider(this, factory).
ViewModelProvider viewModelProvider = new ViewModelProvider(this, factory);
viewModel = viewModelProvider.get(EventViewModel.class);
...
}
我该怎么办?
发布于 2018-08-16 06:20:50
打开app/build.gradle
,找到dependencies
块,并手动将生命周期依赖项添加到列表中:
dependencies {
implementation 'android.arch.lifecycle:extensions:1.1.1'
// ...
}
同步项目之后,您应该能够获得ViewModel的一个实例。
发布于 2018-08-16 07:52:33
如果你对安卓和Java有更好的了解,可以尝试学习一些MVVM
架构。将此代码放入某个baseFragment
方法中,然后执行:
abstract class BaseFragment extends Fragment() {
//kotlin
fun <T : ViewModel?> getViewModel(activity: FragmentActivity, modelClass: Class<T>): T {
return ViewModelProviders.of(this, ViewModelFactory(activity)).get(modelClass)
}
//bytecode to java is this :/
public final ViewModel obtainViewModel(@NotNull FragmentActivity activity, @NotNull Class modelClass) {
return ViewModelProviders.of((Fragment)this, (Factory)(new
ViewModelFactory((Activity)activity))).get(modelClass);
}
}
另外,不要将此代码放入onViewCreated
,而不是放入onActivityCreated
// kotlin
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
viewModel = obtainViewModel(requireActivity(), KebabFragmentViewModel::class.java)
}
// java bytecode
public void onViewCreated(@NotNull View view, @Nullable Bundle savedInstanceState) {
super.onViewCreated(view, savedInstanceState);
this.viewModel = (RollerFragmentViewModel)this.obtainViewModel(getFragmentActivity(), RollerFragmentViewModel.class);
}
现在,你需要在onViewCreated mby的viewModel place中观察一些东西,比如网络操作,或者需要更长时间的东西。
// kotlin
viewModel.list.observe(this, Observer { list ->
list?.let {
viewModel.myKebabAdapter.updateList(list)
}
})
//java
this.viewModel.getErrorMessage().observe((LifecycleOwner)this, (Observer)(new Observer() {
...
public final void onChanged(@Nullable List list) {
this.viewModel.myKebabAdapter.updateKebabList(list)
}
}
在viewModel中,你可以在activity/fragment
上观察到我们可爱的变量
// kotlin
var list: MutableLiveData<MutableList<User>> = MutableLiveData()
// java variable and getter
@NotNull
private MutableLiveData userList;
@NotNull
public final MutableLiveData getUserList() {
return this.userList;
}
现在您需要在dependencies{}
块中使用依赖项app/build.gradle
//lifecycle
implementation "android.arch.lifecycle:extensions:1.1.1"
implementation "android.arch.lifecycle:viewmodel:1.1.1"
// RxJava
implementation "io.reactivex.rxjava2:rxkotlin:2.2.0"
implementation "io.reactivex.rxjava2:rxandroid:2.0.0"
implementation "io.reactivex.rxjava2:rxjava:2.1.10"
找到一些博客教程如何正确地做到这一点。我个人不喜欢https://developer.android.com/,因为它过去很难理解。试试中号的。
总帐Java代码大部分都是反编译的,所以希望它能正常工作。
https://stackoverflow.com/questions/51867122
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