silverlighter下MVVM模式中利用Behavior和TargetedTriggerAction实现文本框的一些特效

　　在silverlight一般开发模式中，给文本框添加一些事件是轻而易举的，然而MVVM开发模式中，想要给文本框添加一些事件并非那么容易，因为MVVM模式中，只有ICommand接口，而且也只有Button中才有Command属性，通过ViewModel可以将方法绑定到Button上面，却无法绑定到文本框和其他一些控件。、

　　Behavior的出现解决了这一难题，下面就来说一下具体的实现方法：

　　实例一：在用户登录窗口，用户点击Reset按钮后，让用户名输入框自动获取焦点。

　　首先要先将ViewModel绑定到我们的控件上面，我们一步一步来做，第一步先写Model，下面是Model的代码：

　　

using System;
using System.Net;
using System.Runtime.Serialization;
using System.ComponentModel;

namespace BookModel
{
   [DataContract]
   public class UserModel : INotifyPropertyChanged
   {
      public event PropertyChangedEventHandler PropertyChanged;

      private string userName = String.Empty;
      private string passWord = String.Empty;

      [DataMember]
      public string UserName
      {
         get { return userName; }
         set { userName = value; OnPropertyChanged("UserName"); }
      }

      [DataMember]
      public string PassWord
      {
         get { return passWord; }
         set { passWord = value; OnPropertyChanged("PassWord"); }
      }

      /// <summary>
      /// Call the event PropertyChanged.
      /// </summary>
      /// <param name="PropertyName"></param>
      public void OnPropertyChanged(string PropertyName)
      {
         if (PropertyChanged != null)
         {
            PropertyChanged(this, new PropertyChangedEventArgs(PropertyName));
         }
      }
   }
}

　　写完了Model，下一步就是写ViewModel了，在ViewModel中引用Model的命名控件，下面是ViewModel的代码，例子比较简单，就不多解释了。

　　

using System;
using System.Net;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Documents;
using System.Windows.Ink;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Animation;
using System.Windows.Shapes;
using BookModel;
using System.Windows.Browser;

namespace BookViewModel
{
   public class VM_User
   {
      /// <summary>
      /// In the Constructors create the instance of User.
      /// </summary>
      public VM_User()
      {
         user = new UserModel();
         user.UserName = "Jack";
      }

      public UserModel user { get; set; }
      public LoginCommand Login
      {
         get { return new LoginCommand(); }
      }
      public ResteCommand Reset
      {
         get { return new ResteCommand(); }
      }
   }

   /// <summary>
   /// Login Button's method
   /// </summary>
   public class LoginCommand:ICommand
   {
      public bool CanExecute(object parameter)
      {
         return true;
      }

      public void Execute(object parameter)
      {
         VM_User VMUser = parameter as VM_User;
         if (VMUser.user.UserName.Equals("admin") && VMUser.user.PassWord.Equals("123"))
         {
            MessageBox.Show("Login success!", "System Info", MessageBoxButton.OK);
         }
         else
         {
            MessageBox.Show("Login failed!", "System Info", MessageBoxButton.OK);
         }
      }

      public event EventHandler CanExecuteChanged;
   }

   /// <summary>
   /// Reset buttom's method
   /// </summary>
   public class ResteCommand : ICommand
   {
      public bool CanExecute(object parameter)
      {
         return true;
      }

      public void Execute(object parameter)
      {
         VM_User VMUser = parameter as VM_User;
         VMUser.user.UserName = "";
         VMUser.user.PassWord = "";
      }
      public event EventHandler CanExecuteChanged;
   }
}

　　这里就不连接数据库了，那样代码量太大，也不方便大家查看。这里只做一个简单的验证，至此MVVM中的M和VM就都建好了，下面写前端的显示层，添加两个TextBlock和两个TextBox，两个按钮。用作登录用，分别为用户名，密码，登录和重置。

　　下面是绑定代码：

　　

<UserControl x:Class="BookLibrary.MainPage"
    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:BookViewModel;assembly=BookViewModel"
    mc:Ignorable="d"
    d:DesignHeight="600" d:DesignWidth="1000" 
    xmlns:i="http://schemas.microsoft.com/expression/2010/interactivity"
    xmlns:telerik="http://schemas.telerik.com/2008/xaml/presentation">

   <UserControl.Resources>
      <local:VM_User x:Key="User" />
   </UserControl.Resources>
    <Grid x:Name="LayoutRoot" Background="White" DataContext="{Binding Source={StaticResource User}}" Loaded="LayoutRoot_Loaded">
      <telerik:RadBusyIndicator Name="BusyIndicator">
         <Border>
            <Border.Background>
               <LinearGradientBrush EndPoint="0.5 1" StartPoint="0.5 0">
                  <GradientStop Color="#0369a9" Offset="0" />
                  <GradientStop Color="#046daf" Offset="0.5" />
                  <GradientStop Color="#2fa2e5" Offset="1" />
               </LinearGradientBrush>
            </Border.Background>
            <Border VerticalAlignment="Center" HorizontalAlignment="Center">
               <Border.Effect>
                  <DropShadowEffect BlurRadius="10" Opacity="0.4"/>
               </Border.Effect>
               <Border.Background>
                  <RadialGradientBrush>
                     <GradientStop Color="#0B7AC1" Offset="0" />
                     <GradientStop Color="#1182c7" Offset="1" />
                  </RadialGradientBrush>
               </Border.Background>
               <Grid>
                  <Grid.RowDefinitions>
                     <RowDefinition Height="60"/>
                     <RowDefinition Height="15"/>
                     <RowDefinition Height="45"/>
                     <RowDefinition Height="45"/>
                     <RowDefinition Height="60"/>
                  </Grid.RowDefinitions>
                  <Grid.ColumnDefinitions>
                     <ColumnDefinition Width="185"/>
                     <ColumnDefinition Width="90"/>
                     <ColumnDefinition Width="160"/>
                     <ColumnDefinition Width="100"/>
                  </Grid.ColumnDefinitions>
                  <TextBlock VerticalAlignment="Center" HorizontalAlignment="Left" 
                             Grid.Row="0" Grid.Column="0" Margin="20,0,0,0" FontWeight="Bold"   
                             Text="School System |" FontSize="16" Foreground="White"/>
                  <TextBlock Grid.Row="0" Grid.Column="1" HorizontalAlignment="Left" 
                             VerticalAlignment="Center" Text="User Login" FontSize="14"
                             Foreground="#b4e6ec"/>
                  <Image Source="Images/LoginPicture.png" Grid.Row="1" Grid.Column="0" Grid.RowSpan="3" />
                  <TextBlock FontSize="14" Grid.Row="2" Grid.Column="1" Text="UserName:" 
                             Foreground="White" VerticalAlignment="Center" HorizontalAlignment="Left" />
                  <TextBlock FontSize="14" Grid.Row="3" Grid.Column="1" Text="PassWord:" 
                             Foreground="White" VerticalAlignment="Center" HorizontalAlignment="Left" />
                  <TextBox Name="txtName"  Text="{Binding user.UserName,Mode=TwoWay}" HorizontalAlignment="Left" FontSize="14" Grid.Row="2" Grid.Column="2" Width="150" Height="26" />
                  <PasswordBox Password="{Binding user.PassWord,Mode=TwoWay}" HorizontalAlignment="Left" Grid.Row="3" Grid.Column="2" Width="150" Height="26" />
                  <Button Command="{Binding Login}" CommandParameter="{Binding}" HorizontalAlignment="Left" Width="80" Height="26" Grid.Row="2" Grid.Column="3" Content="Login" Click="Button_Click_1" />
                  <Button Command="{Binding Reset}" CommandParameter="{Binding}" HorizontalAlignment="Left" Width="80" Height="26" Grid.Row="3" Grid.Column="3" Content="Reset" Click="Button_Click" />
                  <CheckBox HorizontalAlignment="Left" VerticalAlignment="Top" Margin="0,10,0,0" Grid.Row="4" Grid.Column="2" Content="Save State" Foreground="White" />

               </Grid>
            </Border>
         </Border>
      </telerik:RadBusyIndicator>

   </Grid>
</UserControl>

　　这个时候，就实现登录和重置功能了，但是重置的时候用户名文本框并不会获得焦点，下面我们来讲实现方法：

　　第一种方法：TargetedTriggerAction绑定

　　先写一个类，叫做TextBoxGetFocusBahavior，代码如下：

　　

using System;
using System.Net;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Documents;
using System.Windows.Ink;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Animation;
using System.Windows.Shapes;
using System.Windows.Interactivity;

namespace BookLibrary
{
   public class TextBoxGetFocusBahavior:TargetedTriggerAction<TextBox>
   {
      public void GotFocusAction()
      {

      }
      protected override void Invoke(object parameter)
      {
         TextBox targetTextBox = Target;
         targetTextBox.SelectAll();
      }
   }
}

　　然后在前台绑定，绑定方法如下：

　　

xmlns:i="http://schemas.microsoft.com/expression/2010/interactivity"
<TextBox Height="23" Name="textBox" HorizontalAlignment="Left" Margin="36,28,0,0" VerticalAlignment="Top" Width="198">
         <i:Interaction.Triggers>
            <i:EventTrigger EventName="GotFocus">
               <local:TextBoxGetFocusBahavior TargetName="textBox" />
            </i:EventTrigger>
         </i:Interaction.Triggers>
         
 </TextBox>

　　注意我标红的地方，就是要引入命名空间。

　　第二种方法Behavior方法，和上面基本一样，不过我感觉这种方法比较灵活，推荐使用这种方法。新加一个类，AutoSetFocusBehavior，代码如下：

　　

using System;
using System.Net;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Documents;
using System.Windows.Ink;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Animation;
using System.Windows.Shapes;
using System.Windows.Interactivity;

namespace BookLibrary
{
   public class AutoSetFocusBehavior:Behavior<TextBox>
   {
      protected override void OnAttached()
      {
         base.OnAttached();
         AssociatedObject.TextChanged += OnTextChanged;
      }

      public void OnTextChanged(object sender, EventArgs e)
      {
         if(AssociatedObject.Text.Equals(""))
            AssociatedObject.Focus();
      }
   }
}

　　这里前端绑定方法为：

　　

 <TextBox Text="{Binding user.UserName}" x:Name="txtName" Height="27" HorizontalAlignment="Left" Margin="36,76,0,0" VerticalAlignment="Top" Width="332">
         <i:Interaction.Behaviors>
            <local:AutoSetFocusBehavior />
         </i:Interaction.Behaviors>
      </TextBox>

　　注意，同样要引入上面的命名空间。

　　其实，说了这么多，就是给TextBox加了个OnTextChanged事件，当内容被清空时，判断内容是否为空，为空则设置焦点。

　　希望这篇文章能给大家一点帮助。不足之处，还请赐教。