Android Java创建ViewModel新api

背景

项目使用Java，创建ViewModel发现之前旧api不管用了。不要问为什么项目还要用Java，别问。老项目不让升级。

ViewModel创建新方式

新方式是因为依赖新版本库，其实用旧版本库就回到旧方式了。
依赖：

    def lifecycle_version = "2.5.0"
    // ViewModel
    implementation "androidx.lifecycle:lifecycle-viewmodel:$lifecycle_version"
    // LiveData
    implementation "androidx.lifecycle:lifecycle-livedata:$lifecycle_version"
    // Lifecycles only (without ViewModel or LiveData)
    implementation "androidx.lifecycle:lifecycle-runtime:$lifecycle_version"

从2.4开始换新方式，当然传递参数更容易了。

public class LauncherViewModel extends ViewModel {
    private static final String TAG = "LauncherViewModel";

    public static final ViewModelInitializer<LauncherViewModel> initializer = new ViewModelInitializer<>(
            LauncherViewModel.class,
            creationExtras -> {
                return new LauncherViewModel();
            }
    );
}    

传递参数的案例：
也可以参考传递参数，变得简单了

public class MyViewModel extends ViewModel {

    public MyViewModel(
        MyRepository myRepository,
        SavedStateHandle savedStateHandle
    ) { /* Init ViewModel here */ }

    static final ViewModelInitializer<MyViewModel> initializer = new ViewModelInitializer<>(
        MyViewModel.class,
        creationExtras -> {
            MyApplication app = (MyApplication) creationExtras.get(APPLICATION_KEY);
            assert app != null;
            SavedStateHandle savedStateHandle = createSavedStateHandle(creationExtras);

            return new MyViewModel(app.getMyRepository(), savedStateHandle);
        }
    );
}

初始化：

MyViewModel myViewModel = new ViewModelProvider(
    this,
    ViewModelProvider.Factory.from(MyViewModel.initializer)
).get(MyViewModel.class);

没错，就是这样，比之前多了2个参数。