C# MVVM中ComboBox绑定异常：选中值无法传递至关机命令

Hey, let's figure out why your selected ComboBox values aren't making it to your shutdown command! I spotted a couple key issues in your code, starting with the most critical one:

1. Case Mismatch in Binding Property Names #

WPF binding is case-sensitive, and this is where your main problem lies. In your XAML, you're binding SelectedValue to lowercase-starting properties selectedHours and selectedMinutes, but your ViewModel defines uppercase-starting properties SelectedHours and SelectedMinutes. These don't match, so the selected values never sync to your ViewModel.

Fix the XAML Binding: #

<!-- Updated Hours ComboBox -->
<ComboBox x:Name="HoursCB" Margin="5" Width="40" 
          ItemsSource="{Binding myHours}" 
          SelectedValue="{Binding SelectedHours, UpdateSourceTrigger=PropertyChanged}" />

<!-- Updated Minutes ComboBox -->
<ComboBox x:Name="MinutesCB" Margin="5" Width="40" 
          ItemsSource="{Binding myMinutes}" 
          SelectedValue="{Binding SelectedMinutes, UpdateSourceTrigger=PropertyChanged}" />

2. Verify DataContext is Set #

Another common gotcha: if you haven't set the DataContext of your MainWindow to your ViewModel, none of your bindings will work at all. Add this to your MainWindow constructor:

public MainWindow()
{
    InitializeComponent();
    // Link the View to its ViewModel
    DataContext = new MainWindowViewModel();
}

3. Command Implementation Improvements #

Your command works, but we can make it cleaner and more maintainable:

• Rename AddNameCommand to something semantic like StartShutdownCommand (it has nothing to do with adding names!)
• Use CommandManager.RequerySuggested for CanExecuteChanged instead of manually subscribing to PropertyChanged—this is the standard WPF approach.

Updated Command Code: #

class StartShutdownCommand : ICommand
{
    private readonly MainWindowViewModel _parent;

    public StartShutdownCommand(MainWindowViewModel parent)
    {
        _parent = parent;
    }

    // Let WPF handle command revalidation automatically
    public event EventHandler CanExecuteChanged
    {
        add => CommandManager.RequerySuggested += value;
        remove => CommandManager.RequerySuggested -= value;
    }

    public bool CanExecute(object parameter) => true;

    public void Execute(object parameter)
    {
        int totalSeconds = _parent.SelectedHours * 3600 + _parent.SelectedMinutes * 60;
        MessageBox.Show($"Shutting down the computer in {totalSeconds} seconds!");
        // Uncomment when ready to test:
        // Process.Start("shutdown", $"/s /t {totalSeconds}");
    }
}

4. Debugging Binding Issues (For Future Troubleshooting) #

If you ever run into binding problems again, enable WPF binding tracing to see errors in the Visual Studio Output window. Add this to your App.xaml:

<Application.Resources>
    <Style TargetType="Binding">
        <Setter Property="PresentationTraceSources.TraceLevel" Value="High"/>
    </Style>
</Application.Resources>

This will log any binding failures, making it easy to spot typos or missing properties.

内容的提问来源于stack exchange，提问作者Igor Bieńkowski