当存在多个片段实例时将视图模型注入片段

Question

我正在为 Android 应用程序使用 Toothpick 依赖项注入框架，当后台堆栈上存在同一片段的多个实例时，我无法将 android 视图模型注入片段。我希望每个片段实例都有自己的视图模型实例，但问题是只创建了一个视图模型并在所有片段实例之间共享。

我创建了一个演示该问题的示例项目。单个 activity 包含具有 android 视图模型的单个片段。此 activity 的多个实例已创建并放置在 activity 后栈中。

这是我的 Activity:

class MainActivity : FragmentActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.my_layout)
    }
}

它包含此布局：

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical" android:layout_width="match_parent"
    android:layout_height="match_parent">

    <fragment
        android:id="@+id/main_fragment"
        android:name="no.knowit.android.tptest.MainFragment"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />

</FrameLayout>

主要片段：

class MainFragment : Fragment() {

    companion object {
        const val TAG = "MainFragment"
    }

    @Inject
    lateinit var viewModel: MainViewModel

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        openScope()
    }

    override fun onCreateView(
        inflater: LayoutInflater,
        container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {

        val v =  inflater.inflate(R.layout.main_fragment_layout, container, false)
        v.findViewById<Button>(R.id.spawn_button).setOnClickListener {
            Log.i(TAG, "spawn")
            val i = Intent(context, MainActivity::class.java)
            startActivity(i)
        }
        return v
    }

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)
        Log.i(TAG, "fragment  " + System.identityHashCode(this))
        Log.i(TAG, "viewModel " + System.identityHashCode(viewModel))
        Log.i(TAG, "liveData  " + System.identityHashCode(viewModel.myLiveData))
    }

    protected fun openScope() {
        val scope = KTP.openScopes(ApplicationScope::class.java)
            .openSubScope(ViewModelScope::class.java)
        installViewModelBindings(scope)

        scope.closeOnViewModelCleared(this)
            .openSubScope(activity!!)
            .closeOnDestroy(activity!!)
            .openSubScope(this)
            .closeOnDestroy(this)

        scope.inject(this)
    }

    private fun installViewModelBindings(scope: Scope) {
        scope.installViewModelBinding<MainViewModel>(this)
    }
}

主视图模型：

class MainViewModel : ViewModel() {

    @Inject
    lateinit var myLiveData: MyLiveData
}

我的直播数据：

class MyLiveData @Inject constructor(): LiveData<Int>() {
}

输出：

2020-02-18 09:12:56.325 23253-23253/no.knowit.android.tptest I/MainFragment: fragment  45659892
2020-02-18 09:12:56.326 23253-23253/no.knowit.android.tptest I/MainFragment: viewModel 236316818
2020-02-18 09:12:56.326 23253-23253/no.knowit.android.tptest I/MainFragment: liveData  241221950
2020-02-18 09:13:03.472 23253-23253/no.knowit.android.tptest I/MainFragment: spawn
2020-02-18 09:13:03.632 23253-23253/no.knowit.android.tptest I/MainFragment: fragment  8599012
2020-02-18 09:13:03.632 23253-23253/no.knowit.android.tptest I/MainFragment: viewModel 236316818
2020-02-18 09:13:03.632 23253-23253/no.knowit.android.tptest I/MainFragment: liveData  241221950
2020-02-18 09:13:05.194 23253-23253/no.knowit.android.tptest I/MainFragment: spawn
2020-02-18 09:13:05.289 23253-23253/no.knowit.android.tptest I/MainFragment: fragment  130024810
2020-02-18 09:13:05.289 23253-23253/no.knowit.android.tptest I/MainFragment: viewModel 236316818
2020-02-18 09:13:05.289 23253-23253/no.knowit.android.tptest I/MainFragment: liveData  241221950
2020-02-18 09:13:06.436 23253-23253/no.knowit.android.tptest I/MainFragment: spawn

如您所见，创建了新片段，但共享相同的视图模型和实时数据。我想为每个片段创建一个新的 viewmodel/livedata，并且这些视图模型应该存在于视图模型范围内。我怎样才能做到这一点？

Answer 1

您可以使用自定义 ViewModelFactory

@Singleton
class ViewModelFactory @Inject constructor() :
            ViewModelProvider.NewInstanceFactory() {

            override fun <T : ViewModel> create(modelClass: Class<T>) =
                Toothpick.openScope(ApplicationScope::class.java).getInstance(modelClass) as T
        }

并在您的 fragments/activities

中使用它

@Inject
lateinit var viewModelFactory: ViewModelFactory

val mainViewModel = ViewModelProviders.of(this, viewModelFactory).get(MainViewModel::class.java)

当存在多个片段实例时将视图模型注入片段

Injecting viewmodels into fragment when multiple instances of fragment exist

android

android-architecture-components

toothpick-di