Silverlight中使用MVVM(6):AutoComplteBox的异步过滤

            Silverlight中使用MVVM(1)--基础

            Silverlight中使用MVVM(2)—提高

            Silverlight中使用MVVM(3)—进阶

            Silverlight中使用MVVM(4)—演练

           Silverlight中使用MVVM(5)-Command II

       

       Toolkit中AutoCompleteBox控件的功能非常强大，其用法可以参考AutoCompleteBox的基本使用这篇文章。

        在实际的开发中，数据一般通过WCF异步传递的,要实现AutoCompleteBox的过滤数据，主要用到的是Populating事件和PopulateComplete方法

      private void autoCompleteBox1_Populating(object sender, PopulatingEventArgs e)
      {
          ServiceAPI.FilterServiceClient filterServiceClient = new FilterServiceClient();
          filterServiceClient.DoWorkCompleted += (obj, arg) =>
                                                     {
                                                         this.autoCompleteBox1.ItemsSource = arg.Result;
                                                         this.autoCompleteBox1.PopulateComplete();
                                                     };
          filterServiceClient.DoWorkAsync();
      }

        上面的代码是比较常见的操作方式，这里我们关注一下如何使用MVVM的方式将其分离到ViewModel中

        首先定义名为FilterAsyncParameters的类，其有2个属性，FilterCriteria表示过滤参数，即文本框中的值，FilterComplete 则封装了下PopulateComplete方法

      public class FilterAsyncBehavior : Behavior<AutoCompleteBox>
    {
    public ICommand FilterAsyncCommand
    {
        get
        {
            return (ICommand)GetValue(FilterAsyncCommandProperty);
        }
        set
        {
            SetValue(FilterAsyncCommandProperty, value);
        }
    }
    public static readonly DependencyProperty FilterAsyncCommandProperty = DependencyProperty.Register("FilterAsyncCommand",
        typeof(ICommand),
        typeof(FilterAsyncBehavior),
        new PropertyMetadata(null));
      ...
   }

       这里定义的FilterAsyncCommand用于执行ViewModel里面的ICommand，FilterAsyncBehavior重写了OnAttached，OnDetaching方法

     protected override void OnAttached()
       {
           base.OnAttached();
           AssociatedObject.Populating += AssociatedObject_Populating;
       }

       protected override void OnDetaching()
       {
           AssociatedObject.Populating -= AssociatedObject_Populating;
           base.OnDetaching();
       }

       private void AssociatedObject_Populating(object sender, PopulatingEventArgs e)
       {
           ICommand filterCommand = FilterAsyncCommand;

           if (filterCommand != null)
           {
               //创建过滤参数
               var parameters = new FilterAsyncParameters(AssociatedObject.PopulateComplete, e.Parameter);
               filterCommand.Execute(parameters);
               e.Cancel = true;
           }
       }

        ViewModel中定义了ICommand属性

     public AcbAsyncViewModel()
     {
         FilterCommand = new RelayCommand<FilterAsyncParameters>(ExecuteFilter);
     }
     private void ExecuteFilter(FilterAsyncParameters filterAsyncParameters)
     {
         ServiceAPI.FilterServiceClient filterServiceClient=new FilterServiceClient();
         filterServiceClient.DoWorkCompleted += (obj, arg) =>
                                                    {
                                                         …..
                                                        var filter = arg.UserState as FilterAsyncParameters;
                                                        filter.FilterComplete();
                                                    };
         filterServiceClient.DoWorkAsync(filterAsyncParameters);
     }

       View中Xaml代码

    <sdk:AutoCompleteBox  ItemsSource="{Binding Data}">
    <interactivity:Interaction.Behaviors>
        <utilities:FilterAsyncBehavior FilterAsyncCommand="{Binding FilterCommand}" />
    </interactivity:Interaction.Behaviors>
    </sdk:AutoCompleteBox>

     这样就实现了以MVVM实现了AutoCompleteBox的异步过滤数据，实现过程中需要对Behavior等概念有一定理解,希望这篇文章给各位提供一点思路。

 

 

 

     代码下载：   AutoComplateBoxSamples.rar