关于WPF异步MVVM等待窗体的介绍

需求描述
•在ViewModel中处理Model中的数据需要一定时间的等待
•ViewModel或Model在获取数据或访问同步服务时有一定延迟需要等待
•ViewModel操作View加载数据需要一段时间
解决办法
•显示一个等待UI，当数据处理完毕或服务接口返回后等待UI消失
转动齿轮控件
•参考开源实现SprocketControl ：http://wpfspark.codeplex.com/
等待控件
复制代码 代码如下:

                                 Grid.Column="0"
                            Width="100"
                            Height="100"
                            Margin="0,0,0,0"
                            HorizontalAlignment="Center"
                            VerticalAlignment="Center"
                            Background="Transparent"
                            Interval="60"
                            IsIndeterminate="True"
                            StartAngle="-90"
                            TickColor="{DynamicResource MaskForegroundColor}"
                            TickCount="16"
                            TickWidth="5" />
  

等待效果

定义MVVM中的ViewModel的状态
复制代码 代码如下:
///

  /// 在MVVM模式中ViewModel的状态
  ///

  [Flags]
  public enum ViewModelStatus
  {
    ///

    /// ViewModel无状态
    ///

    None = 0x0,
    ///

    /// ViewModel正在初始化
    ///

    Initializing = 0x1,
    ///

    /// ViewModel初始化完毕
    ///

    Initialized = 0x2,
    ///

    /// ViewModel正在加载
    ///

    Loading = 0x4,
    ///

    /// ViewModel加载完毕
    ///

    Loaded = 0x8,
    ///

    /// ViewModel正在保存
    ///

    Saving = 0x16,
    ///

    /// ViewModel保存完毕
    ///

    Saved = 0x32
  }

ViewModel状态转变为控件状态
复制代码 代码如下:
public class StatusToAnimationVisibilityConverter : IValueConverter
   {
     #region IValueConverter Members

     public object Convert(
       object value, Type targetType, object parameter, CultureInfo culture)
     {
       try
       {
         string status = value.ToString();

         switch (status)
         {
           case "Initializing":
           case "Loading":
           case "Saving":
             return Visibility.Visible;
           case "Loaded":
           case "Saved":
           default:
             return Visibility.Collapsed;
         }
       }
       catch (Exception)
       {
         return Visibility.Collapsed;
       }
     }

     public object ConvertBack(
       object value, Type targetType, object parameter, CultureInfo culture)
     {
       return DependencyProperty.UnsetValue;
     }

     #endregion
   }

使UserControl支持异步显示
复制代码 代码如下:


  
    
      
        
          
            
                                Width="Auto"
                   Height="Auto"
                   HorizontalAlignment="Stretch"
                   VerticalAlignment="Stretch"
                   Panel.ZIndex="2000"
                   Visibility="{Binding Path=Status,
                                Converter={StaticResource StatusToAnimationVisibilityConverter}}">
                                    Height="Auto"
                     HorizontalAlignment="Stretch"
                     VerticalAlignment="Stretch"
                     Panel.ZIndex="0"
                     Background="{DynamicResource MaskGridBackgroundBrush}"
                     Opacity="0.2" />
              
            
          
        
      
    
  

应用Style至UserControl
复制代码 代码如下:
              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"
              d:DesignHeight="318"
              d:DesignWidth="632"
              Style="{DynamicResource AsyncWorkUserControlStyle}"
              mc:Ignorable="d">
 

定义基础ViewModel
复制代码 代码如下:
///

   /// 响应式的ViewModel模型
   ///

   public abstract class ViewModelResponsive : ViewModelbase, IViewModelResponsive
   {
     #region Fields

     private ViewModelStatus _status = ViewModelStatus.None;

     #endregion

     #region ViewModel Status

     ///

     /// 刷新UI数据
     ///

     public virtual void Refresh()
     {

     }

     ///

     /// ViewModel状态
     ///

     public ViewModelStatus Status
     {
       get
       {
         return _status;
       }
       protected set
       {
         if (_status != value)
         {
           _status = value;
           RaisePropertyChanged(@"Status");
         }
       }
     }

     #endregion
   }

ViewModel应用
复制代码 代码如下:
public class CameraManagementViewModel : ViewModelResponsive
   {
     protected override void BindCommands()
     {
       RefreshCommand = new RelayCommand(() =>
       {
         Refresh();
       });
     }

     public override void Refresh()
     {
       base.Refresh();

       Status = ViewModelStatus.Initializing;
       CameraCollection.Clear();
       Model.GetCameras(GetCamerasCallback);
     }

     private void GetCamerasCallback(object sender, AsyncWorkerCallbackEventArgs> args)
     {
       CameraCollection.Clear();
       Status = ViewModelStatus.Loaded;

       if (result)
       {
         foreach (var item in (args.Data as IList))
         {
           CameraCollection.Add(item);
         }
       }
     }
   }