Wpf Multiple nested Usercontrols with MvvmCross

问题

I'm pretty new in MvvmCross but I'm working with mvvm for awhile. I know how to compose usercontrols with nested usercontrols. Now with mvvmcross I got stucked to show two or more usercontrols in another usercontrol. I don't use any other framework than MvvmCross. My Rootview looks like this:

`<views:MvxWpfView
    x:Class="MvvmCrossTest.Wpf.Views.RootView"
    xmlns:views="clr-namespace:MvvmCross.Platforms.Wpf.Views;assembly=MvvmCross.Platforms.Wpf"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
    mc:Ignorable="d" 
    d:DesignHeight="450" d:DesignWidth="800">

    <DockPanel>  
        <TextBlock Text="Root" DockPanel.Dock="Top"/>
        <ContentControl x:Name="MainMenuVM" Content="{Binding MainMenuVM}" DockPanel.Dock="Top" />
    </DockPanel>
</views:MvxWpfView>`

The corresponding ViewModel looks like this:

using MvvmCross.Commands;
using MvvmCross.Logging;
using MvvmCross.Navigation;
using MvvmCross.ViewModels;

namespace MvvmCrossTest.Core.ViewModels
{
    public class RootViewModel: MvxNavigationViewModel
    {
        private readonly IMvxViewModelLoader _mvxViewModelLoader;
        public RootViewModel(IMvxLogProvider logProvider, IMvxNavigationService navigationService, IMvxViewModelLoader mvxViewModelLoader) : base(logProvider, navigationService)
        {
            _mvxViewModelLoader = mvxViewModelLoader;
            ShowMainMenu();
        }

        private MainMenuViewModel _mainMenuVM;

        public MainMenuViewModel MainMenuVM
        {
            get { return _mainMenuVM; }
            set 
            {
                SetProperty(ref _mainMenuVM, value);
                RaisePropertyChanged(() => MainMenuVM);
            }
        }

         public MvxCommand ShowMainMenuCommand { get; set; }

        public void ShowMainMenu()
        {
            MainMenuVM = (MainMenuViewModel)_mvxViewModelLoader.LoadViewModel(MvxViewModelRequest.GetDefaultRequest(typeof(MainMenuViewModel)), null, null);
        }
    }
}

The simplified View I want to show in the contentcontrol looks like this:

<views:MvxWpfView
    x:Class="MvvmCrossTest.Wpf.Views.MainMenuView"
    xmlns:views="clr-namespace:MvvmCross.Platforms.Wpf.Views;assembly=MvvmCross.Platforms.Wpf"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
    mc:Ignorable="d"
    Background="Aqua"
    d:DesignHeight="450" d:DesignWidth="800">
    <Grid>
            
    </Grid>
</views:MvxWpfView>

And also the corresponding ViewModel.

using MvvmCross.Logging;
using MvvmCross.Navigation;
using MvvmCross.ViewModels;

namespace MvvmCrossTest.Core.ViewModels
{
    public class MainMenuViewModel : MvxNavigationViewModel
    {
        public MainMenuViewModel(IMvxLogProvider logProvider, IMvxNavigationService navigationService) : base(logProvider, navigationService)
        {

        }
    }
}

Instead of the View/ViewModel I see a text that says "MvvmCrossTest.Core.ViewModels.MainMenuViewModel".

I don't want to use Xamarin!

回答1:

I created a project where I show you some basics.

simple

You can find the samples here.

the RootView;

<views:MvxWpfView xmlns:local="clr-namespace:SomeProject.Views" ...>
     <Grid>
           <Label Content="Hello from RootView" />
           <local:NestedView />    
     </Grid>
</views:MvxWpfView>

the NestedView;

<views:MvxWpfView ...>
     <Grid>
           <Label Content="Hello from NestedView" />  
     </Grid>
</views:MvxWpfView>

extended (custom presenter)

With this custom wpf presenter you can easily navigate to views while specified themn in a container. With that, you can close and open views from the view model while using the mvvmcross navigation service.

I copied this from another project. You can find the whole implementation in my sample project here.

the RootView;

<views:MvxWpfView ...>
      <Grid>
           <Label Content="Hello" />
           <ItemsControl region:MvxContainer.Id="RootViewRegion"/>    
      </Grid>
</views:MvxWpfView>

the RootView code behind;

[MvxContentPagePresentation(WrapInNavigationPage = true, NoHistory = false)]
public partial class RootView: MvxWpfView<RootViewModel>
{
     public RootView()
     {
          InitializeComponent();
     }
}

the RootViewModel;

public class RootViewModel: MvxNavigationViewModel
{
      private readonly IMvxNavigationService _navigationService;

      public IMvxAsyncCommand ShowNestedViewModelCommand { get; protected set; }

      public RootViewModel(IMvxLogProvider logProvider, IMvxNavigationService navigationService) : base(logProvider, navigationService)
      {
            this._navigationService = navigationService;
    
            // navigate to nested view
            this.ShowNestedViewModelCommand = new MvxAsyncCommand(() => this._navigationService.Navigate<NestedViewModel>());

            ShowNestedViewModelCommand.Execute();
      }
}

the NestedView code behind;

[MvxWpfPresenter("RootViewRegion", mvxViewPosition.NewOrExsist)]
public partial class NestedView : MvxWpfView<NestedViewModel>
{
    public NestedView()
    {
        InitializeComponent();
    }
}

good to know

when you have problems with navigation and view model connection use this code behind. It loads the viewmodel for the specific view;

[MvxContentPagePresentation(WrapInNavigationPage = true, NoHistory = false)]
public partial class SomeView : MvxWpfView<ViewModels.SomeViewModel>
{
    public SomeView()
    {
         InitializeComponent();
    
         if (!(ViewModel is ViewModels.SomeViewModel))
         {
              if (Mvx.IoCProvider.TryResolve<ViewModels.SomeViewModel>(out var someViewModel))
              {
                   ViewModel = someViewModel;
                   return;
              }
    
              var _viewModelLoader = Mvx.IoCProvider.Resolve<IMvxViewModelLoader>();
              var request = new MvxViewModelInstanceRequest(typeof(ViewModels.SomeViewModel));
              request.ViewModelInstance = _viewModelLoader.LoadViewModel(request, null);
              ViewModel = request.ViewModelInstance as ViewModels.SomeViewModel;
    
              Mvx.IoCProvider.RegisterSingleton<ViewModels.SomeViewModel>(ViewModel);
         }
    }
}

回答2:

it seems that MvvmCross is wiring up Views and ViewModels automatically

I know nothing about MvvmCross, but for "automatically" to work there should be an agreement and rules, e.g. attributes or matching names (xViewModel <-> xView). Currently there is nothing I can see what connects MainMenuViewModel with views:MvxWpfView.

Anyway what you see

I see a text that says "MvvmCrossTest.Core.ViewModels.MainMenuViewModel"

is the view trying to visualize non-control as text due to missing data template.

It's easy to fix by just adding data template

<DataTemplate DataType="{x:Type local:MainMenuViewModel}">
    <views:MvxWpfView />
</DataTemplate>

somewhere (e.g. into views:MvxWpfView.Resources) and the view will be displayed.

来源：https://stackoverflow.com/questions/65319108/wpf-multiple-nested-usercontrols-with-mvvmcross