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[英]As ViewModelProviders.of() is deprecated, how should I create object of ViewModel?
[英]How do I get a ViewModel without ViewModelProviders class?
与过去的问题有关如何获取ViewModel? ,我发现的例子,它并没有解决我的情况。 我没有在那里发表评论的许可,所以我不得不再问一遍。 我没有ViewModelProviders类,我想在我找到的所有示例和文档中使用“of”方法,比如
model = ViewModelProviders.of(this).get(Something.class);
在Android Studio中,我没有找到“android.arch.lifecycle:extensions”作为依赖项添加。 当我搜索时,它说“无需显示”。 我在API 27.所以,尝试使用非弃用元素,我在片段中有这个:
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?
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的实例。
如果您对Android和Java有更好的了解,请尝试学习一些MVVM
架构。 将此代码放入一些baseFragment
方法,然后进行:
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);
}
}
也不要将此代码放入onViewCreated
而不是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);
}
现在你需要观察者从onViewCreated mby中的viewModel位置获取某些可能的网络操作或者可能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中你得到了我们可爱的变量来观察activity/fragment
// kotlin
var list: MutableLiveData<MutableList<User>> = MutableLiveData()
// java variable and getter
@NotNull
private MutableLiveData userList;
@NotNull
public final MutableLiveData getUserList() {
return this.userList;
}
现在你需要dependencies{}
app/build.gradle
dependencies{}
依赖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/过去很难遵循。 试试中等。
GL。 Java代码主要是反编译的,所以希望它能运行。
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