WPF MVVM 自定义标题

Question

I decided to make a custom title for my program in WPF and encountered difficulties.

I started to study MVVM pattern and its essence to get rid of using standard events in View. I wanted to make buttons to close, minimize and maximize window, but ran into difficulties. I can't understand where the logic of these buttons should be. If you don't use standard events, but use commands, it won't work, because ViewModel doesn't know anything about the window. And I don't want to use events.

I found this solution for window close button

<i:Interaction.Triggers>
    <i:EventTrigger EventName="Click">
    <i:CallMethodAction MethodName="Close"
                        TargetObject="{Binding RelativeSource={RelativeSource
                                                Mode=FindAncestor,
                                                AncestorType=Window}}" />
    </i:EventTrigger>
</i:Interaction.Triggers>

But I don't know how to do the other two buttons the same way. I tried to find other MethodNames that can be used here, but I found only method Hide, but it does not suit me, because it hides the window completely, it is neither on the taskbar nor in the tray, but it is still running and visible in the task manager.

Can you tell me how I can do the same window minimizing and resizing through XAML code?

UPD:

I found a way to minimize the window, but I still do not know how to make a button that will change the WindowsState to Normal if the WindowState Maximized and vice versa.

<i:Interaction.Triggers>
    <i:EventTrigger EventName="Click">
        <i:ChangePropertyAction PropertyName="WindowState"
            TargetObject="{Binding RelativeSource={RelativeSource Mode=FindAncestor, AncestorType={x:Type Window}}}"
            Value="{Binding Source={x:Static sys:WindowState.Minimized}}"
        />
    </i:EventTrigger>
</i:Interaction.Triggers>

Answer 1

In MVVM any UI related logic must be in the View. This should be clear.

Commands are not View Model only. Your View can also define commands. Special ICommand implementation is the RoutedCommand . Don't think that because it is a command, then it must be handled in the View Model.

You should not use the Interaction.Triggers , especially not in your case. If you are not firm with MVVM, Interaction.Triggers will very likely introduce code smells.
Simply create an event handler for the Button.Click event in your Window class' code-behind eg, MainWindow.xaml.cs file.

Also, there is no reason to bind to a static variable or a constant or an enum. Just reference it directly:

<i:ChangePropertyAction Value="{x:Static sys:WindowState.Minimized}" ...  />

However, to solve your problem simply add an event handler in your code-behind:

MainWindow.xaml

<Button Click="OnMaximizeButtonClicked"
        Content="Toggle Maximize" />

MainWindow.xaml.cs

// Toggle the WindowState between Maximized and Normal
private void OnMaximizeButtonClicked(object sender, RoutedEventArgs e)
  => this.WindowState = this.WindowState == WindowState.Normal
    ? WindowState.Maximized
    : WindowState.Normal;

Alternatively, use routed commands ( How to: Create a RoutedCommand ):

MainWindow.xaml

<Button Command="{x:Static local:MainWindow.ToggleMaximizeStateCommand}"
        Content="Toggle Maximize" />

MainWindow.xaml.cs

partial class MainWindow : Window
{
  public static RoutedCommand ToggleMaximizeStateCommand { get; } = new RoutedCommand("ToggleMaximizeStateCommand", typeof(MainWindow));

  public MainWindow()
  {
    InitializeComponent();

    // Register the command handler
    var toggleMaximizeStateCommandBinding = new CommandBinding(
      ToggleMaximizeCommand, 
      ExecuteToggleMaximizeStateCommand, 
      CanExecuteToggleMaximizeStateCommand);
    this.CommandBindings.Add(toggleMaximizeCommandBinding);
  }
    
  // Toggle the WindowState between Maximized and Normal
  private void ExecuteToggleMaximizeStateCommand(object sender, ExecutedRoutedEventArgs e) 
    => this.WindowState = this.WindowState == WindowState.Normal
      ? WindowState.Maximized
      : WindowState.Normal;

  private void CanExecuteToggleMaximizeStateCommand(object sender, CanExecuteRoutedEventArgs e) 
    => e.CanExecute = true;
}