WPF如何在windows（MVVM）之间传输数据？

Question

我知道有很多类似的问题，我花了两个小时尝试实施它们，但无法继续。所以问题看起来很简单。当我没有视图模型时，我可以将数据上下文设置为一个类，并且使用该类传输数据非常容易。但是当有 viewmodel 时，我必须将 datacontext 设置为那个，然后找不到返回任何值的方法。我试图为这个问题实施无数的解决方案，但似乎它们超出了我的技能水平。非常感谢您的帮助！

我的代码的重要部分（它是一个我要保存的简单游戏，其中保存由用户输入命名）第一个窗口，我想从第二个窗口获取数据

             case Key.Escape: {
                    Thread t = new Thread(() => {
                        SaveGameWindow pw = new SaveGameWindow();  //the second window
                        if ((pw.ShowDialog() == true) && (pw.Name != string.Empty)) //pw.Name always empty
                        {
                            ILogicSaveGame l = new LogicSaveGame();
                            l.Write(pw.Name, "saved_games.txt");
                            MessageBox.Show("game saved");
                        }
                    });
                    t.SetApartmentState(ApartmentState.STA);
                    t.Start();

XAML（从现在开始一切都属于 SaveGameWindow）：

 <Window.Resources>
    <local:SaveGameViewModel x:Key="my_viewmodel"/>
</Window.Resources>
<Grid DataContext="{StaticResource my_viewmodel}">
 <TextBox Text="{Binding Name}"/> //i want to acces this in the first window
  <Button Command="{Binding CloseCommand}"
                Content="Save"/>

后面的代码：

    private readonly SaveGameViewModel vm;
    public SaveGameWindow()
    {
        this.InitializeComponent();
        this.vm = this.FindResource("my_viewmodel") as SaveGameViewModel;
        if (this.vm.CloseAction == null)
        {
            this.vm.CloseAction = new Action(() => this.Close());
        }
    }

视图模型

 public class SaveGameViewModel : ViewModelBase
 {
    public SaveGameViewModel()
    {
        this.CloseCommand = new RelayCommand(() => this.Close());
    }

    public string Name { get; set; }

    public ICommand CloseCommand { get; private set; }

    public Action CloseAction { get; set; }

    private void Close()
    {
        this.CloseAction();
    }
}

我使用 galasoft mvvmlightlibs

Answer 1

这个问题有很多解决方案。最简单的解决方案是对窗口和数据绑定使用共享视图模型。由于两个窗口将共享相同的DataContext，因此两者都可以通过简单地引用它们的DataContext 属性来访问相同的数据或模型实例。

但如果您更喜欢单独的视图模型，您会选择不同的解决方案。

解决方案 1

如果您想为每个窗口使用专用的视图模型，您可以随时使用合成并制作例如SaveGameViewModel 的一个实例MainWindowViewModel 的成员。任何可以访问MainWindowViewModel 的类也可以直接或通过委托属性访问SaveGameViewModel 及其API。
此示例通过将SaveGameViewModel 公开为MainWindowViewModel 的公共属性来使用直接访问：

SaveGameViewModel.cs

public class SaveGameViewModel : INotifyPropertyChanged
{
  private string name;   
  public string Name
  {
    get => this.name;
    set 
    { 
      this.name = value; 
      OnPropertyChanged();
    }
  }

  public event PropertyChangedEventHandler PropertyChanged;
  protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null)
  {
    this.PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
  }
}

MainWindowViewModel.cs

public class MainWindowViewModel : INotifyPropertyChanged
{      
  public SaveGameViewModel SaveGameViewModel { get; set; }

  // Allow to create an instance using XAML
  public MainWindowViewModel() {}

  // Allow to create an instance using C#
  public MainWindowViewModel(SaveGameViewModel saveGameViewModel) 
    => this.SaveGameViewModel = saveGameViewModel; 
}

App.xaml

<Application>
  <Application.Resources>
    <MainWindowViewModel x:Key="MainWindowViewModel">
      <MainWindowViewModel.SaveGameViewModel>
        <SaveGameViewModel />
      </MainWindowViewModel.SaveGameViewModel>
    </MainWindowViewModel>
  </Application.Resources>
</Application>

SaveGameWindow.xaml

<Window DataContext="{Binding Source={StaticResource MainWindowViewModel}, Path=SaveGameViewModel}">
  <TextBox Text="{Binding Name}" />
<Window>

MainWindow.xaml

<Window DataContext="{StaticResource MainWindowViewModel}">

<Window>

MainWindow.xaml.cs

partial class MainWindow : Window
{
  private void OnKeyPressed(object sender, KeyEventArgs e)
  {
    if (e.Key == Key.Escape)
    {
      var mainWindowViewModel = this.DataContext as MainWindowViewModel;
      string saveGameName = mainWindowViewModel.SaveGameViewModel.Name;
    }
  }
}

---

解决方案 2

由于您只是显示一个对话框，因此您可以在对话框关闭后存储SaveGameViewModel 的当前实例或其感兴趣的值：

MainWindow.xaml.cs

partial class MainWindow : Window
{
  private SaveGameViewModel CurrentSaveGameViewModel { get; set; }
  private bool IsSaveGameValid { get; set; }

  private void ShowDialog_OnSaveButtonClick(object sender, RoutedEventArgs e)
  {        
    var saveGameDialog = new SaveGameWindow();
    this.IsSaveGameValid = saveGameDialog.ShowDialog ?? false;

    this.CurrentSaveGameViewModel = saveGameDialog.DataContext as SaveGameViewModel;
  }

  private void OnKeyPressed(object sender, KeyEventArgs e)
  {
    if (e.Key == Key.Escape && this.IsSaveGameValid)
    {
      string saveGameName = this.CurrentSaveGameViewModel.Name;
    }
  }
}

MainWindow.xaml

<Window>
  <Window.DataContext>
    <MainWindowViewModel />
  </Window.DataContext>
<Window>

SaveGameWindow.xaml

<Window>
  <Window.DataContext>
    <SaveGameViewModel />
  </Window.DataContext>

  <TextBox Text="{Binding Name}" />
<Window>