c# - 将 ContentControl 绑定(bind)到将确定要查看哪个用户控件的 ApplicationViewModel？

Question

我是 WPF 的新手，也是 C# 编程(一般编程)的新手，我正在尝试开发 WPF 应用程序。

我已经尝试过几篇与此类似的帖子，但我似乎无法找到为什么这不起作用的答案。

所以，我很难理解 MVVM 架构，它如何以及需要什么来在绑定(bind)到单个 <ContentControl /> 的多个用户控件之间切换.据我目前的理解和阅读，我必须像这样绑定(bind) View 模型:

<ContentControl Content="{Binding ApplicationViewModel}"/>

所以这就是我想要实现的目标:

安ApplicationWindow.xaml左侧边栏菜单将在应用程序运行时始终显示，以及 <ContentControl/>在剩余空间上。侧边栏菜单上显示的按钮将是:

• Main(将显示 MainView.xaml 用户控件，应为默认用户控件)
• 设置(将显示 SettingsView.xaml 用户控制)
• 退出(将关闭应用程序)

我知道我需要将按钮绑定(bind)到 ICommand命令，我理解 RelayCommand.cs 的概念类(class)。因此，让我们跳入我的想法的简化代码，找出我需要理解的内容以及我在这个过程中可能误解的内容。

什么 MainView.xaml和 SettingsView.xaml包含现在并不重要，因为我只是想弄清楚如何在我的应用程序中显示它们。

这是 ApplicationWindow.xaml :

<Window x:Class="WpfApp1.ApplicationWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:WpfApp1"
        xmlns:v="clr-namespace:WpfApp1.View"
        xmlns:vm="clr-namespace:WpfApp1.ViewModel"
        mc:Ignorable="d"
        Title="ApplicationWindow" Height="1080" Width="1920"
        WindowStyle="None" WindowState="Maximized">

    <Window.Resources>
        <DataTemplate DataType="{x:Type vm:MainViewModel}">
            <v:MainView/>
        </DataTemplate>
        <DataTemplate DataType="{x:Type vm:SettingsViewModel}">
            <v:SettingsView/>
        </DataTemplate>
    </Window.Resources>

    <DockPanel>
        <!--Menu bar on the left-->
        <Border DockPanel.Dock="Left">
            <StackPanel Orientation="Vertical" Background="Gray" Width="120">
                <Button Content="Main" Command="{Binding ShowMainCommand}"/>
                <Button Content="Settings" Command="{Binding ShowSettingsCommand}"/>
                <Button Content="Exit" Command="{Binding ExitApplicationCommand}"/>
            </StackPanel>
        </Border>
        <!--The content control that view the current view-->
        <ContentControl Content="{Binding ApplicationViewModel}"/>
    </DockPanel>
</Window>

注意: DataContext 设置为 ApplicationViewModel.cs在 App.xaml.cs 中重写 OnStartup() 方法。

public partial class App : Application
{
    protected override void OnStartup(StartupEventArgs e)
    {
        base.OnStartup(e);

        ApplicationWindow app = new ApplicationWindow
        {
            DataContext = new ApplicationViewModel()
        };
        app.Show();
    }
}

这是 ApplicationViewModel.cs :

public class ApplicationViewModel : ViewModelBase
{
    #region Fields

    private List<ViewModelBase> _viewModels;
    private ViewModelBase _currentViewModel;

    private ICommand _showMainCommand;
    private ICommand _showSettingsCommand;
    private ICommand _exitApplicationCommmand;

    #endregion

    #region Constructor

    public ApplicationViewModel()
    {
        ViewModels = new List<ViewModelBase>
        {
            new MainViewModel(),
            new SettingsViewModel()
        };

        CurrentViewModel = ViewModels[0];
    }

    #endregion

    #region Public Properties

    public List<ViewModelBase> ViewModels
    {
        get
        {
            return _viewModels;
        }
        set
        {
            if (_viewModels != value)
            {
                _viewModels = value;
                OnPropertyChanged(nameof(ViewModels));
            }
        }
    }

    public ViewModelBase CurrentViewModel
    {
        get
        {
            return _currentViewModel;
        }
        set
        {
            if(_currentViewModel != value)
            {
                _currentViewModel = value;
                OnPropertyChanged(nameof(CurrentViewModel));
            }
        }
    }

    #endregion

    #region Commands

    public ICommand ShowMainCommand
    {
        get
        {
            if(_showMainCommand == null)
            {
                _showMainCommand = new RelayCommand(action => ShowMain());
            }
            return _showMainCommand;
        }
    }

    public ICommand ShowSettingsCommand
    {
        get
        {
            if (_showSettingsCommand == null)
            {
                _showSettingsCommand = new RelayCommand(action => ShowSettings());
            }
            return _showSettingsCommand;
        }
    }

    public ICommand ExitApplicationCommand
    {
        get
        {
            if (_exitApplicationCommmand == null)
            {
                _exitApplicationCommmand = new RelayCommand(action => ExitApplication());
            }
            return _exitApplicationCommmand;
        }
    }

    #endregion

    #region Private Methods

    private void ShowMain()
    {
        CurrentViewModel = ViewModels[0];
    }

    private void ShowSettings()
    {
        CurrentViewModel = ViewModels[1];
    }

    private void ExitApplication()
    {
        MessageBoxResult result = MessageBox.Show("Are you sure you want to exit?", "Exit", MessageBoxButton.YesNo);
        if (result == MessageBoxResult.Yes)
        {
            System.Windows.Application.Current.Shutdown();
        }
    }

    #endregion
}

因此，据我了解，ApplicationWindow.xaml应该能够确定从 CurrentViewModel 中显示哪个 View 设置为。

为了提供信息(或遗漏信息)，这里有 ViewModelBase.cs :

public class ViewModelBase : INotifyPropertyChanged
{
    #region INotifyPropertyChanged

    public event PropertyChangedEventHandler PropertyChanged;

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

    #endregion
}

和RelayCommand.cs :

public class RelayCommand : ICommand
{
    #region Fields

    private readonly Action<object> _execute;
    private readonly Predicate<object> _canExecute;

    #endregion

    #region Constructors

    public RelayCommand(Action<object> execute, Predicate<object> canExecute)
    {
        if (execute == null)
            throw new ArgumentNullException("execute");

        _execute = execute;
        _canExecute = canExecute;
    }

    public RelayCommand(Action<object> execute) : this(execute, null)
    {
    }

    #endregion

    #region ICommand

    public bool CanExecute(object parameters)
    {
        return _canExecute == null ? true : _canExecute(parameters);
    }

    public event EventHandler CanExecuteChanged
    {
        add { CommandManager.RequerySuggested += value; }
        remove { CommandManager.RequerySuggested -= value; }
    }

    public void Execute(object parameters)
    {
        _execute(parameters);
    }

    #endregion
}

我希望您清楚我在这方面的思考过程，并且你们中的一位聪明的程序员可以帮助解决这个问题，并帮助我理解为什么这不是我想要的结果。

如果我尝试做的事情比 Elon Musk 的让生命成为多行星的项目更难，请随时解释原因并建议我更好的方法

Answer 1

您的内容控件绑定(bind)应指向您在切换 ViewModel 时更改的实际属性

<ContentControl Content="{Binding CurrentViewModel}"/>