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);
            }
        }
    }
}