(翻译)在MVVM模式中打开子窗体(Child Window)

　　这篇文章主要展示在Silverlight4的应用程序中，用MVVM模式【编者注：如果你对MVVM模式不太理解，请先去熟悉一下关于这方面的资料】怎么打开一个子窗体(Child Window),怎么向子窗体传值，以及怎么从子窗体返回值到主窗体等等

　　我使用的方法不是严格意义上的MVVM模式，因为我实际上在ViewModel中实例化了子窗体，这通常很不方便的。但是在Google上找了好长时间，仅仅找到了打开子窗体的工具包的向导，我认为最好的方法就是亲自去实现它。我期望最方便且有严格意义上的MVVM的解决方案在SilverLight5中能够实现。

　　本篇文章只仅仅是一个概念的验证，并且是基于一个最简单的例子。MainPage.xaml文件包含两个TextBox控件，即Name和Address,另外，子窗体和主窗体一样，也有两个的控件。当用户在主窗体输入他们的名字，然后点击按钮，那么子窗体就弹出来。并且显示刚才输入的名字(请看下面的图片)。用户可以在子窗体中输入地址然后点击按钮，返回到主窗体【编者注：子窗体同时关闭】，那么主窗体上的地址框中就会显示刚才在子窗体中输入的地址。【编者注：这样就可以达到主窗体和子窗体之间互相传值】

　　实现上面的功能是很简单的，仅仅在View Model工程中创建一个子窗体。然后就可以实现子窗体和主窗体之间传递数据。然后创建每一个TextBox建一个属性，为Button创建Command，这是为了打开和关闭子窗体并且传递属性值。需要注意的是子窗体没有ViewModel，所有的需要实现的业务都在主窗体的ViewModel中实现

　　第一步：在ViewModel工程中创建一个子窗体，把它命名为MyChildWindow.xmal.

　　第二步：为MainPage创建一个ViewModel层。命名为：MainPage_ViewModel.cs

　　第三步：通过MainPage_ViewModel.cs来实现 MainPage.xaml.cs和MyChildWindow.xaml.cs 相互传值。【编者注：下面为各个文件的代码】

　　MainPage.xaml.cs:

namespace View
{
    public partial class MainPage : UserControl
    {

        public MainPage()
        {
            InitializeComponent();
            this.DataContext = new MainPage_ViewModel();
         }
     }
}

 MyChildWindow.xaml.cs:

namespace ViewModel
{
    public partial class MyChildWindow : ChildWindow
    {
        public MyChildWindow(MainPage_ViewModel ma)
        {
            InitializeComponent();
            this.DataContext = ma;
        }

    }
}

　　第四步：在 MainPage_ViewModel.cs为主窗体每个TextBox建属性和ViewModel

using System.ComponentModel;
using System.Collections.ObjectModel;
using ViewModel; 

namespace ViewModel
{
    public class MainPage_ViewModel : INotifyPropertyChanged
    {
//Properties of Mainpage
private string myNameVM = "";
        public string MyNameVM
        {

            get { return myNameVM; }
            set {
                myNameVM = value;
                RaisePropertyChanged("myNameVM");
            }
        }

        private string myAddressVM = "";
        public string MyAddressVM
        {

            get { return myAddressVM; }
            set
            {
                myAddressVM = value;
                RaisePropertyChanged("MyAddressVM");
            }
        }

//Properties of ChildWindow
        private string myNameCW = "";
        public string MyNameCW
        {

            get { return myNameCW; }
            set
            {
                myNameCW = value;
                RaisePropertyChanged("MyNameCW");
            }
        }

        private string myAddressCW = "";
        public string MyAddressCW
        {

            get { return myAddressCW; }
            set
            {
                myAddressCW = value;
                RaisePropertyChanged("MyAddressCW");
            }
        }

          //EventHandler
        public event PropertyChangedEventHandler PropertyChanged;
        private void RaisePropertyChanged(string propertyname)
        {
            if (PropertyChanged != null)
            {
                PropertyChanged(this, new PropertyChangedEventArgs(propertyname));
            }
        }
    }

 }

　　第五步：如果以前没有创建这个，你就必须得在ViewModel中创建一个类DelegateCommand，主要是处理Button的命令。因此，你必须创建这个类。代码如下：

using System;
using System.Windows.Input;

namespace ViewModel
{
    public class DelegateCommand : ICommand //
    {
        private Predicate<object> _canExecute;
        private Action<object> _method;
        public event EventHandler CanExecuteChanged;

        public DelegateCommand(Action<object> method)
            : this(method, null)
        {
        }

        public DelegateCommand(Action<object> method, Predicate<object> canExecute)
        {
            _method = method;
            _canExecute = canExecute;
        }

        public bool CanExecute(object parameter)
        {
            if (_canExecute == null)
            {
                return true;
            }

            return _canExecute(parameter);
        }

        public void Execute(object parameter)
        {
            _method.Invoke(parameter);
        }

        protected virtual void OnCanExecuteChanged(EventArgs e)
        {
            var canExecuteChanged = CanExecuteChanged;

            if (canExecuteChanged != null)
                canExecuteChanged(this, e);
        }

        public void RaiseCanExecuteChanged()
        {
            OnCanExecuteChanged(EventArgs.Empty);
        }
    }
}

　　第六步：在MainPage_ViewModel.cs创建一个Commands,它可以绑定到主窗体和子窗体中的按钮上。

using System.ComponentModel;
using System.Collections.ObjectModel;
using ViewModel; 

namespace ViewModel
{
    public class MainPage_ViewModel : INotifyPropertyChanged
    {
//Properties of Mainpage
private string myNameVM = "";
        public string MyNameVM
        {
            get { return myNameVM; }
            set {myNameVM = value;
                RaisePropertyChanged("myNameVM");
                 }
            }

        private string myAddressVM = "";
        public string MyAddressVM
        {

            get { return myAddressVM; }
            set
            { myAddressVM = value;
                RaisePropertyChanged("MyAddressVM");
            }
        }

//Properties of ChildWindow
        private string myNameCW = "";
        public string MyNameCW
        {

            get { return myNameCW; }
            set
            {  myNameCW = value;
                RaisePropertyChanged("MyNameCW");
            }
        }

        private string myAddressCW = "";
        public string MyAddressCW
        {

            get { return myAddressCW; }
            set
            {  myAddressCW = value;
                RaisePropertyChanged("MyAddressCW");
            }
        }

         //When the button is pressed in MainPage, executes method ExecuteOpenChildWindow
        private DelegateCommand _openChildWindow;
        public DelegateCommand OpenChildWindow
        {
            get
            {
                if (_openChildWindow == null)
                    _openChildWindow = new DelegateCommand(executeOpenChildWindow);

                return _openChildWindow;
            }
        }

        // New instance of ChildWindow. Sets the NameProperty of the ChildWindow equal to the Name entered in the MainPage.
        MyChildWindow cw;
        private void executeOpenChildWindow(object parameter)
        {
            cw = new MyChildWindow(this);
            MyNameCW = MyNameVM;
            cw.Show();
        }

      //When OK-button is pressed in ChildWindow
        private DelegateCommand _okChildWindow;
        public DelegateCommand OkChildWindow
        {
            get {
                if (_okChildWindow == null)
                    _okChildWindow = new DelegateCommand(OkSaveChildWindow);

                return _okChildWindow;
            }
        }
        //MainPage Address property is set to the value entered in the address textbox in Child Window. Child Window is closed.
        private void OkSaveChildWindow(object parameter)
        {
            MyAddressVM = MyAddressCW;
            cw.Close();
        }

          //EventHandler
        public event PropertyChangedEventHandler PropertyChanged;
        private void RaisePropertyChanged(string propertyname)
        {
            if (PropertyChanged != null)
            {
                PropertyChanged(this, new PropertyChangedEventArgs(propertyname));
            }
        }
  }
}

　　第七步:在MainPage.xaml 和 MyChildWindow.xaml中分别新增两个TextBox，然后把他们分别绑定到MainPage_ViewModel中的属性上。然后再分别建一个按钮，绑定到Command上。

MainPage.xaml

<StackPanel>

        <Grid Margin="0 10 0 5" Width="350">

    <Grid.RowDefinitions>
        <RowDefinition Height="*"/>
        <RowDefinition Height="*"/>
        <RowDefinition Height="*"/>

    </Grid.RowDefinitions>
    <Grid.ColumnDefinitions>
        <ColumnDefinition Width="150"/>
        <ColumnDefinition Width="*"/>

    </Grid.ColumnDefinitions>

    <!--TextBlocks-->
    <TextBlock Text="Name:" TextWrapping="Wrap" Margin="5,5,0,5" Grid.Row="0"  />
    <TextBlock Text="Address:" Grid.Row="1" Grid.Column="0"  />

   <!--TextBox, where the users enters data. Binds to the properties of MainPage_ViewModel-->
  <TextBox Text="{Binding MyNameVM, Mode=TwoWay}" Grid.Row="0" Grid.Column="1"/>
  <TextBox Text="{Binding MyAddressVM, Mode=TwoWay}"  Grid.Row="1" Grid.Column="1"/>

    <Button Content="Open Child Window"
            VerticalAlignment="Center"
            HorizontalAlignment="left"
            Width="auto"
            Margin="5"
            Grid.Row="2"
            Command="{Binding OpenChildWindow}" <!--Binds to CommandDelegate from the ViewModel -->
        />
        </Grid>
    </StackPanel>

MyChildWindow.xaml

<Grid Margin="0 30 0 5" Width="350">

    <Grid.RowDefinitions>
        <RowDefinition Height="auto"/>
        <RowDefinition Height="auto"/>
        <RowDefinition Height="205*"/>

    </Grid.RowDefinitions>
    <Grid.ColumnDefinitions>
        <ColumnDefinition Width="150"/>
        <ColumnDefinition Width="*"/>

    </Grid.ColumnDefinitions>

    <TextBlock Text="Name: " Grid.Row="0" />
    <TextBlock Text="Address:" Grid.Row="1" Grid.Column="0"  />

    <!-- TextBoxes are bind to the properties from the ViewModel.  -->
    <TextBox x:Name="InputName" Text="{Binding MyNameCW, Mode=TwoWay}" Grid.Row="0" Grid.Column="1" Height="20"/>
    <TextBox x:Name="OutputAddress" Text="{Binding MyAddressCW, Mode=TwoWay}" Grid.Row="1" Grid.Column="1" Height="20"/>

   <!-- Button comand bind to CommandDelegate from ViewModel -->
  <Button x:Name="OKButton" Command="{Binding OkChildWindow}" Content="OK" Width="75" Height="23" Margin="0,12,79,0" Grid.Row="2" Grid.Column="1"/>
</Grid>

　　翻译的不足之处，请多多指教。原文地址http://mariaevert.dk/thesis/?p=710