将数据传递给片段视图模型 mvvmcross

Question

所以我有一个 activity，它有一个包含 2 个片段的标签页。

  public class RecipeDetailActivity : BaseFragmentActivity<RecipeDetailViewModel>
    {
        protected override void OnCreate(Bundle savedInstanceState)
        {
            base.OnCreate(savedInstanceState);

            SetContentView(Resource.Layout.RecipeDetailView);

            AttachActionBar();
            SupportActionBar.SetDisplayHomeAsUpEnabled(true);
            SupportActionBar.Title = "Recipe details";

            var viewPager = FindViewById<ViewPager>(Resource.Id.main_view_pager);

            if (viewPager != null)
            {
                var fragments = new List<MvxViewPagerFragmentInfo>();
                fragments.Add(
                    new MvxViewPagerFragmentInfo("Ingrediente", typeof(RecipeFlavoursFragment), typeof(RecipeFlavoursViewModel)));
                fragments.Add(
                    new MvxViewPagerFragmentInfo("Flavours", typeof(RecipeIngridientsFragment), typeof(RecipeIngridientsViewModel)));

                viewPager.Adapter = new MvxFragmentPagerAdapter(this, SupportFragmentManager, fragments);


                viewPager.Adapter = new MvxFragmentPagerAdapter(this, SupportFragmentManager, fragments);
                var tabLayout = FindViewById<TabLayout>(Resource.Id.main_tablayout);
                tabLayout.SetupWithViewPager(viewPager);
            }
        }
    }

我使用以下代码显示此页面。

   private void SelectRecipe(RecipeModel recipe)
   {
            var recipeJson = JsonConvert.SerializeObject(recipe);

            ShowViewModel<RecipeDetailViewModel>(new { recipe = recipeJson });
   }

现在我想要将一些数据传递给子视图模型。 RecipeFlavoursViewModel RecipeIngridientsViewModel

到目前为止我已经尝试过：使用 parameterValueObject

        fragments.Add(
            new MvxViewPagerFragmentInfo("Ingrediente", typeof(RecipeFlavoursFragment), typeof(RecipeFlavoursViewModel), new { recipe = ViewModel.Recipe }));

使用 IMvxBundle

在RecipeDetailViewModel

 protected override void SaveStateToBundle(IMvxBundle bundle)
 {
            bundle.Data["Recipe"] = JsonConvert.SerializeObject(Recipe);

            base.SaveStateToBundle(bundle);
 }

在RecipeIngridientsViewModel

protected override void InitFromBundle(IMvxBundle parameters)
        {
            base.InitFromBundle(parameters);

            if (parameters.Data.Count != 0)
            {
                Recipe = JsonConvert.DeserializeObject<RecipeModel>(parameters.Data["recipe"]);
            }
        }

到目前为止，

None 个已经成功。任何想法我做错了什么？我是否必须使用 MvvmCross 5 的导航服务才能使用 InitFromBundle 和 SaveStateToBundle。

InitFromBundle 每次显示我的片段时都会调用它，但是 SaveStateToBundle 来自 RecipeDetailViewModel 永远不会得到打电话。

Answer 1

为此，您可以利用 MvxViewPagerFragmentPresentationAttribute 以便 Presenter 负责显示片段，而您只需显示传递给 Recipe 的 ViewModel参数和其他任何参数一样，但目前有一些小错误。

然而，解决此问题的一种方法是在 RecipeDetailViewModel 属性中包含您想在 ViewPager 中包含的片段视图模型，然后将它们加载到 Initialize 中您可以从 RecipeDetailActivity:

中引用它们

使用 Mvx 5，您可以使用新的 Navigation 来显示 ViewModel。如果从 RecipeListViewModel 打开详细信息，则：

public class RecipeDetailViewModelArgs
{
    public RecipeDetailViewModelArgs(RecipeModel recipe)
    {
        this.Recipe = recipe;
    }

    public RecipeModel Recipe { get; }
}

public class RecipeListViewModel : MvxViewModel
{
    private readonly IMvxNavigationService navigationService;

    public RecipeListViewModel(IMvxNavigationService navigationService)
    {
        this.navigationService = navigationService;
    }

    private async Task SelectRecipe(RecipeModel recipe)
    {
        await this.navigationService.Navigate<RecipeDetailViewModel, RecipeDetailViewModelArgs>(new RecipeDetailViewModelArgs(recipe));
    }
}

然后在您的详细信息 ViewModel 中，您只需缓存菜谱，加载 children ViewModel（成分和口味）并为它们设置菜谱：

public class RecipeDetailViewModel : MvxViewModel<RecipeDetailViewModelArgs>
{
    private readonly IMvxViewModelLoader mvxViewModelLoader;
    private readonly IMvxJsonConverter jsonConverter;
    private RecipeModel recipe;

    public RecipeDetailViewModel(IMvxViewModelLoader mvxViewModelLoader, IMvxJsonConverter jsonConverter)
    {
        this.mvxViewModelLoader = mvxViewModelLoader;
        this.jsonConverter = jsonConverter;
    }

    public override void Prepare(RecipeDetailViewModelArgs parameter)
    {
        this.recipe = parameter.Recipe;
    }

    protected override void SaveStateToBundle(IMvxBundle bundle)
    {
        base.SaveStateToBundle(bundle);

        bundle.Data["RecipeKey"] = this.jsonConverter.SerializeObject(this.recipe);
    }

    protected override void ReloadFromBundle(IMvxBundle state)
    {
        base.ReloadFromBundle(state);

        this.recipe = this.jsonConverter.DeserializeObject<RecipeModel>(state.Data["RecipeKey"]);
    }

    public override async Task Initialize()
    {
        await base.Initialize();

        this.InitializeChildrenViewModels();
    }

    public RecipeFlavoursViewModel FlavoursViewModel { get; private set; }

    public RecipeIngridientsViewModel IngredientsViewModel { get; private set; }

    protected virtual void InitializeChildrenViewModels()
    {
        // Load each childre ViewModel and set the recipe
        this.FlavoursViewModel = this.mvxViewModelLoader.LoadViewModel(new MvxViewModelRequest<RecipeFlavoursViewModel>(null, null), null);
        this.FlavoursViewModel.Recipe = this.recipe;

        this.IngredientsViewModel = this.mvxViewModelLoader.LoadViewModel(new MvxViewModelRequest<RecipeIngridientsViewModel>(null, null), null);
        this.FlavoursViewModel.Recipe = this.recipe;
    }
}

然后当您加载 ViewPager 时，您可以利用 MvxViewPagerFragmentInfo => public MvxViewPagerFragmentInfo (string title, string tag, Type fragmentType, IMvxViewModel viewModel, object parameterValuesObject = null) 的其他构造函数，这样您就可以传递之前加载的 ViewModel：

this.viewPager = view.FindViewById<ViewPager>(Resource.Id.viewPagerDetails);
if (viewPager != null)
{
    var fragments = new List<MvxViewPagerFragmentInfo>();
    fragments.Add(new MvxViewPagerFragmentInfo("Ingredients", "RecipeIngridientsViewModelTag", typeof(RecipeIngridientsView), this.ViewModel.IngridientsViewModel));
    fragments.Add(new MvxViewPagerFragmentInfo("Flavours", "RecipeFlavoursViewModelTag", typeof(RecipeFlavoursView), this.ViewModel.FlavoursViewModel));

    this.viewPager.Adapter = new MvxFragmentPagerAdapter(this.Activity, this.ChildFragmentManager, fragments);
}

就是这样。

顺便说一句，如果您不想使用导航或不使用 Mvx 5.x，那么您只需在 void Start() 方法中初始化 children ViewModel。

总结一下，如果您想从 children 更改 Recipe 的值，一种简单的方法是使用 Recipe 初始化单例，然后您只需注入构造函数中的单例，因此您始终可以引用相同的 Recipe，而不必将 Recipe object 来回传递给那些 ViewModel 并合并每个 ViewModel 所做的更改。 MvvmCross: Accessing models by reference from everywhere

中的更多信息

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将数据传递给片段视图模型 mvvmcross

Passing data to fragment viewmodel mvvmcross

c#

android-fragments

mvvmcross