wpf - MVVM 主窗口控件从子用户控件绑定(bind)

Question

我是 MVVM 的新手，现在正在完成我的第一个 POC。但是，为了解决一个问题 2 天，我一直在努力解决问题。向你们解释的想法可能会帮助并如此迅速地解决问题。现在让我简要介绍一下我的问题。我有一个 WPF MVVM 应用程序，其中一个主视图绑定(bind)到 MainViewModel。我在此处使用 Textblock 来绑定(bind) View 模型中的一些内容，同时加载运行良好的屏幕。我还将 ChildUserControl 绑定(bind)到 ChildViewModel。现在，我需要将不同的内容绑定(bind)到主窗口中的文本 block ，从用户控件到用户控件级别发生的某些操作。怎么可能？

这是我的示例代码主窗口.Xaml

<Window.Resources>
    <viewModel:MainViewModel x:Key="mainWindowViewModel"/></Window.Resources>

<TextBlock Name="txtStatus" Text="{Binding StatusMessage, Mode=OneWay }"/>

子用户控件.xaml

<UserControl.Resources>
    <viewModel:ChildModelView x:Key="ChildModelView"/> </UserControl.Resources>

public class ChildModelView : BaseViewModel
{
// Some child level logic..
// then need to update the txtStatus text block from parent
}

非常感谢您的帮助..!

Answer 1

实现此目的的一种简单方法是使用 IoC。创建 subview 模型时，将主视图模型的引用传递给 subview 模型，并将其作为私有(private)只读变量保存。您现在可以访问所有主要 VM 公开。

另一种解决方案可能是使用中介者模式。

搭建了一个简单的应用程序来演示 IoC 解决方案。

App.xaml.cs

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

        var window = new MainWindow() {DataContext = new MainWindowViewModel() };
        window.Show();
    }
}

MainWindowViewModel.cs

public class MainWindowViewModel : ViewModelBase
{
    private string _statusMessage;

    public string StatusMessage
    {
        get { return _statusMessage; }
        set { _statusMessage = value; this.OnPropertyChanged("StatusMessage"); }
    }

    public ICommand OpenChildCommand { get; private set; }

    public MainWindowViewModel()
    {
        this.StatusMessage = "No status";
        this.OpenChildCommand = new DelegateCommand((o) => this.OpenChild());
    }

    private void OpenChild()
    {
        var window = new ChildWindow {DataContext = new ChildWindowViewModel(this)};
        window.Show();
    }
}

ChildWindowViewModel.cs

public class ChildWindowViewModel : ViewModelBase
{
    private readonly MainWindowViewModel _mainvm;

    public ChildWindowViewModel(MainWindowViewModel mainvm)
    {
        _mainvm = mainvm;
        this.UpdateStatusCommand = new DelegateCommand((o) => this.UpdateStatus());
    }

    public ICommand UpdateStatusCommand { get; private set; }

    private void UpdateStatus()
    {
        this._mainvm.StatusMessage = "New Status";
    }
}

ViewModelBase.cs

public abstract class ViewModelBase : INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;

    protected void OnPropertyChanged(string propertyName)
    {
        this.OnPropertyChanged(new PropertyChangedEventArgs(propertyName));
    }

    protected virtual void OnPropertyChanged(PropertyChangedEventArgs e)
    {
        var handler = this.PropertyChanged;
        if (handler != null)
        {
            handler(this, e);
        }
    }
}

DelegateCommand.cs

public class DelegateCommand : ICommand
{
    /// <summary>
    /// Action to be performed when this command is executed
    /// </summary>
    private Action<object> executionAction;

    /// <summary>
    /// Predicate to determine if the command is valid for execution
    /// </summary>
    private Predicate<object> canExecutePredicate;

    /// <summary>
    /// Initializes a new instance of the DelegateCommand class.
    /// The command will always be valid for execution.
    /// </summary>
    /// <param name="execute">The delegate to call on execution</param>
    public DelegateCommand(Action<object> execute)
        : this(execute, null)
    {
    }

    /// <summary>
    /// Initializes a new instance of the DelegateCommand class.
    /// </summary>
    /// <param name="execute">The delegate to call on execution</param>
    /// <param name="canExecute">The predicate to determine if command is valid for execution</param>
    public DelegateCommand(Action<object> execute, Predicate<object> canExecute)
    {
        if (execute == null)
        {
            throw new ArgumentNullException("execute");
        }

        this.executionAction = execute;
        this.canExecutePredicate = canExecute;
    }

    /// <summary>
    /// Raised when CanExecute is changed
    /// </summary>
    public event EventHandler CanExecuteChanged
    {
        add { CommandManager.RequerySuggested += value; }
        remove { CommandManager.RequerySuggested -= value; }
    }

    /// <summary>
    /// Executes the delegate backing this DelegateCommand
    /// </summary>
    /// <param name="parameter">parameter to pass to predicate</param>
    /// <returns>True if command is valid for execution</returns>
    public bool CanExecute(object parameter)
    {
        return this.canExecutePredicate == null ? true : this.canExecutePredicate(parameter);
    }

    /// <summary>
    /// Executes the delegate backing this DelegateCommand
    /// </summary>
    /// <param name="parameter">parameter to pass to delegate</param>
    /// <exception cref="InvalidOperationException">Thrown if CanExecute returns false</exception>
    public void Execute(object parameter)
    {
        if (!this.CanExecute(parameter))
        {
            throw new InvalidOperationException("The command is not valid for execution, check the CanExecute method before attempting to execute.");
        }
        this.executionAction(parameter);
    }
}

主窗口.xaml

<Window x:Class="WpfApplication2.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="MainWindow" Height="350" Width="525">
<StackPanel>
    <TextBlock Text="{Binding StatusMessage, Mode=OneWay}" />
    <Button HorizontalAlignment="Center" VerticalAlignment="Center" Content="Open Child Window" 
            Command="{Binding Path=OpenChildCommand}"/>
</StackPanel>

子窗口.xaml

<Window x:Class="WpfApplication2.ChildWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="ChildWindow" Height="300" Width="300">
<Grid>
    <Button HorizontalAlignment="Center" VerticalAlignment="Center" Content="UpdateStatus"
            Command="{Binding Path=UpdateStatusCommand}" />
</Grid>

点击更新状态前的图片

点击updatestatus后的图片