Android MVVM - 如何在 ViewModel 中引用 Activity

Question

MVVM 架构，

这是我的 View ( Activity ):

private MyApp app;
private MainActivityVM viewModel;

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
app = (MyApp) this.getApplication();
ActivityMainBinding binding = DataBindingUtil.setContentView(this, R.layout.activity_main);

MainActivityVM.Factory factory = new MainActivityVM.Factory(app);

final MainActivityVM model = ViewModelProviders.of(this, factory)
.get(MainActivityVM.class);

viewModel = model;
binding.setVm(viewModel);
viewModel.onCreate();

和 View 模型:

public class MainActivityVM extends AndroidViewModel implements ViewModel {

    public MainActivityVM(@NonNull Application application) {
        super(application);
    }

    @Override public void onCreate() {
         model = new MyService();
         model.getData(); /* <-- how do i pass the activity here? */
    }

    @Override public void onPause() { }

    @Override public void onResume() { }

    @Override public void onDestroy() { }

    public static class Factory extends ViewModelProvider.NewInstanceFactory {

        @NonNull
        private final Application mApplication;

        public Factory(@NonNull Application application) {
            mApplication = application;
        }

        @Override
        public <T extends android.arch.lifecycle.ViewModel> T create(Class<T> modelClass) {
            return (T) new MainActivityVM(mApplication);
        }
    }
}

和模型:

public class myService{

    public getData(){
        if(permissionacquired(){
            getdata()
        }else{
            requestPermission();
        }
    }

    private void requestPermission() {
        PermissionKey permKey = new PermissionKey(HealthConstants.StepCount.HEALTH_DATA_TYPE, PermissionType.READ);
        HealthPermissionManager pmsManager = new HealthPermissionManager(mStore);
        try {
            // Show user permission UI for allowing user to change options

            /* BELOW CODE REQUIRE Activity reference to PASS */

            pmsManager.requestPermissions(Collections.singleton(permKey), MainActivity.this).setResultListener(result -> {

            /* ABOVE CODE REQUIRE Activity reference to PASS */

            Log.d(APP_TAG, "Permission callback is received.");
            Map<PermissionKey, Boolean> resultMap = result.getResultMap();

                if (resultMap.containsValue(Boolean.FALSE)) {
                    updateStepCountView("");
                    showPermissionAlarmDialog();
                } else {
                    // Get the current step count and display it
                    mReporter.start(mStepCountObserver);
                }
            });
        } catch (Exception e) { Log.e(APP_TAG, "Permission setting fails.", e); }
    }

}

编辑:如果您在我的模型中看到我的请求权限，API 需要通过 Activity - 我如何将 Activity 引用传递给请求权限？

我有一个来自模型的获取权限方法。这个从我的服务提供商那里获得许可的方法需要 Activity ，例如requestPermission( Activity )

所以在我的 ModelView 中，我有一个模型对象，它是来自另一个来源的数据服务。

那么，我如何在我的 ViewModel 中引用 Activity 以便我可以在我的 ViewModel 中调用:model.requestPermission(Activity);？

了解自here那:

Caution: A ViewModel must never reference a view, Lifecycle, or any class that may hold a reference to the activity context.

Answer 1

只要您在 onCreate() 方法中需要权限，您只需将具有权限请求的逻辑移动到 Activity 中，并将请求结果传递到 viewModel。