Windows Phone 7 MVVM模式通讯方式之实现Command

MVVM模式的View与ViewModel的三大通讯方式：Binding Data（实现数据的传递）、Command（实现操作的调用）和Attached Behavior（实现控件加载过程中的操作）。
(1)Windows Phone 7 MVVM模式通讯方式之实现Binding Data。
(2)Windows Phone 7 MVVM模式通讯方式之实现Command。
(3)Windows Phone 7 MVVM模式通讯方式之实现Attached Behavior。
下面通过一个实例实现MVVM模式的Command通讯



（1）MainPage.xaml文件的代码,实现View层

<phone:PhoneApplicationPage
x:Class="CommandDemo.MainPage"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:phone="clr-namespace:Microsoft.Phone.Controls;assembly=Microsoft.Phone"
xmlns:shell="clr-namespace:Microsoft.Phone.Shell;assembly=Microsoft.Phone"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:my="clr-namespace:CommandDemo.ViewModel"
xmlns:my_Interactivity="clr-namespace:CommandDemo.Command"
xmlns:Custom="clr-namespace:System.Windows.Interactivity;assembly=System.Windows.Interactivity" xmlns:ic="clr-namespace:Microsoft.Expression.Interactivity.Core;assembly=Microsoft.Expression.Interactions"
mc:Ignorable="d" d:DesignWidth="480" d:DesignHeight="768"
FontFamily="{StaticResource PhoneFontFamilyNormal}"
FontSize="{StaticResource PhoneFontSizeNormal}"
Foreground="{StaticResource PhoneForegroundBrush}"
SupportedOrientations="Portrait" Orientation="Portrait"
shell:SystemTray.IsVisible="True">
<!--设置整个页面的上下文数据DataContext为RadiusViewModel-->
<phone:PhoneApplicationPage.DataContext>
<my:RadiusViewModel/>
</phone:PhoneApplicationPage.DataContext>

<Grid x:Name="LayoutRoot" Background="Transparent">
<Grid.RowDefinitions>
<RowDefinition Height="Auto"/>
<RowDefinition Height="*"/>
</Grid.RowDefinitions>

<StackPanel x:Name="TitlePanel" Grid.Row="0" Margin="12,17,0,28">
<TextBlock x:Name="ApplicationTitle" Text="MY APPLICATION" Style="{StaticResource PhoneTextNormalStyle}"/>
<TextBlock x:Name="PageTitle" Text="Command" Margin="9,-7,0,0" Style="{StaticResource PhoneTextTitle1Style}"/>
</StackPanel>

<Grid x:Name="ContentPanel" Grid.Row="1" Margin="12,0,12,0">
<Ellipse Fill="Red"
Height="{Binding Radius}" Width="{Binding Radius}"
HorizontalAlignment="Left" Margin="119,84,0,0" Name="ellipse1" Stroke="Black" StrokeThickness="1" VerticalAlignment="Top" />
<Button Content="小" Height="72" HorizontalAlignment="Left" Margin="0,385,0,0" Name="button1" VerticalAlignment="Top" Width="160">
<Custom:Interaction.Triggers>
<Custom:EventTrigger EventName="Click">
<my_Interactivity:ExecuteCommandAction CommandName="MinRadius"/>
</Custom:EventTrigger>
</Custom:Interaction.Triggers>
</Button>
<Button Content="中" Height="72" HorizontalAlignment="Left" Margin="149,384,0,0" Name="button2" VerticalAlignment="Top" Width="160" >
<Custom:Interaction.Triggers>
<Custom:EventTrigger EventName="Click">
<my_Interactivity:ExecuteCommandAction CommandName="MedRadius"/>
</Custom:EventTrigger>
</Custom:Interaction.Triggers>
</Button>
<Button Content="大" Height="72" HorizontalAlignment="Left" Margin="299,382,0,0" Name="button3" VerticalAlignment="Top" Width="160" >
<Custom:Interaction.Triggers>
<Custom:EventTrigger EventName="Click">
<my_Interactivity:ExecuteCommandAction  CommandName="MaxRadius"/>
</Custom:EventTrigger>
</Custom:Interaction.Triggers>
</Button>
</Grid>
</Grid>

</phone:PhoneApplicationPage>

（2）RadiusViewModel.cs文件的代码,实现ViewModel层

using System;
using System.Windows.Input;
using System.ComponentModel;
using Microsoft.Expression.Interactivity.Core;

namespace CommandDemo.ViewModel
{
public class RadiusViewModel : INotifyPropertyChanged
{
private Double radius;

public RadiusViewModel()
{
Radius = 0;
MinRadius = new ActionCommand(p => Radius = 100);
MedRadius = new ActionCommand(p => Radius = 200);
MaxRadius = new ActionCommand(p => Radius = 300);
}

public event PropertyChangedEventHandler PropertyChanged;

public ICommand MinRadius
{
get; private set;
}

public ICommand MedRadius
{
get;
private set;
}

public ICommand MaxRadius
{
get;
private set;
}

public Double Radius
{
get
{
return radius;
}
set
{
radius = value;
OnPropertyChanged("Radius");
}
}

protected virtual void OnPropertyChanged(string propertyName)
{
var propertyChanged = PropertyChanged;

if(propertyChanged != null)
propertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
}
}

（3）ExecuteCommandAction.cs类，实现Command操作

using System;
using System.Windows;
using System.Windows.Input;
using System.Windows.Interactivity;
using System.Reflection;

namespace CommandDemo.Command
{
public class ExecuteCommandAction : TriggerAction<FrameworkElement>
{
public static readonly DependencyProperty CommandNameProperty =
DependencyProperty.Register("CommandName", typeof(string), typeof(ExecuteCommandAction), null);

public static readonly DependencyProperty CommandParameterProperty =
DependencyProperty.Register("CommandParameter", typeof(object), typeof(ExecuteCommandAction), null);

protected override void Invoke(object parameter)
{
if (AssociatedObject == null)
return;

ICommand command = null;

var dataContext = AssociatedObject.DataContext;

foreach (var info in dataContext.GetType().GetProperties(BindingFlags.Public | BindingFlags.Instance))
{
if (IsCommandProperty(info) && String.Equals(info.Name, CommandName, StringComparison.Ordinal))
{
command = (ICommand)info.GetValue(dataContext, null);
break;
}
}

if ((command != null) && command.CanExecute(CommandParameter))
{
command.Execute(CommandParameter);
}
}

private static bool IsCommandProperty(PropertyInfo property)
{
return typeof(ICommand).IsAssignableFrom(property.PropertyType);
}

public string CommandName
{
get
{
return (string)GetValue(CommandNameProperty);
}
set
{
SetValue(CommandNameProperty, value);
}
}

public object CommandParameter
{
get
{
return GetValue(CommandParameterProperty);
}
set
{
SetValue(CommandParameterProperty, value);
}
}
}
}