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

[code]      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();

}

[/code]
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

[code]      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));

...

}

[/code]

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;
}
}

[/code]
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);
}

[/code]
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