private int _count = -1;

public virtual int Count
{
    get
    {
        if (_count == -1)
        {
            LoadCount();
        }
        return _count;
    }
    protected set
    {
        _count = value;
    }
}

protected virtual void LoadCount()
{
    Count = FetchCount();
}

protected int FetchCount()
{
    return ItemsProvider.FetchCount();
}

public class DemoCustomerProvider : IItemsProvider
{
    private readonly int _count;
    private readonly int _fetchDelay;

    public DemoCustomerProvider(int count, int fetchDelay)
    {
        _count = count;
        _fetchDelay = fetchDelay;
    }

    public int FetchCount()
    {
        Thread.Sleep(_fetchDelay);
        return _count; 
    }

    public IList FetchRange(int startIndex, int count)
    {
        Thread.Sleep(_fetchDelay);

        List list = new List();
        for( int i=startIndex; i        {
            Customer customer = new Customer {Id = i+1, Name = "Customer " + (i+1)};
            list.Add(customer);
        }
        return list;
    }
}

    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="Data Virtualization Demo - By Paul McClean" Height="600" Width="600">
    
    
        
    
    
    
        
        
            
            
            
            
        

       
        
            
                                  TextAlignment="Right" VerticalAlignment="Center"/>
                                  Text="1000000" Width="60" VerticalAlignment="Center"/>
                                  TextAlignment="Right" VerticalAlignment="Center"/>
                                  Text="1000" Width="60" VerticalAlignment="Center"/>
            
        

        
            
                
                                          TextAlignment="Right" VerticalAlignment="Center"/>
                                          Margin="5" Content="List(T)" VerticalAlignment="Center"/>
                                          Margin="5" Content="VirtualizingList(T)" 
                      VerticalAlignment="Center"/>
                                          Margin="5" Content="AsyncVirtualizingList(T)" 
                      IsChecked="True" VerticalAlignment="Center"/>
                
                
                                          TextAlignment="Right" VerticalAlignment="Center"/>
                                          Text="100" Width="60" VerticalAlignment="Center"/>
                                          TextAlignment="Right" VerticalAlignment="Center"/>
                                          Text="30" Width="60" VerticalAlignment="Center"/>
                
             
        

        
                          VerticalAlignment="Center"/>
                          Width="80" VerticalAlignment="Center"/>

                          Margin="5" Width="100" VerticalAlignment="Center"/>

                                 Fill="Blue" Margin="5" VerticalAlignment="Center">
                
                    
                
                
                    
                        
                            
                                                                   Storyboard.TargetProperty=
                                     "(TextBlock.RenderTransform).(RotateTransform.Angle)" 
                                   From="0" To="360" Duration="0:0:5" 
                                   RepeatBehavior="Forever" />
                            
                        
                    
                
            
            
                          FontStyle="Italic" Text="Pause in animation indicates UI thread stalled."/>
            
        

        
        
    
                                        

沒(méi)有必要去探究XAML的細(xì)節(jié)。惟一要注意的是使用ListView的定制風(fēng)格改變其背景和響應(yīng)IsLoading屬性時(shí)的光標(biāo)。


public partial class DemoWindow
{
    /// 

    /// Initializes a new instance of the  class.
    /// 

    public DemoWindow()
    {
        InitializeComponent();
        
        // use a timer to periodically update the memory usage
        DispatcherTimer timer = new DispatcherTimer();
        timer.Interval = new TimeSpan(0, 0, 1);
        timer.Tick += timer_Tick;
        timer.Start();
    }

    private void timer_Tick(object sender, EventArgs e)
    {
        tbMemory.Text = string.Format("{0:0.00} MB", 
                             GC.GetTotalMemory(true)/1024.0/1024.0);
    }

    private void Button_Click(object sender, RoutedEventArgs e)
    {
        // create the demo items provider according to specified parameters
        int numItems = int.Parse(tbNumItems.Text);
        int fetchDelay = int.Parse(tbFetchDelay.Text);
        DemoCustomerProvider customerProvider = 
                       new DemoCustomerProvider(numItems, fetchDelay);

        // create the collection according to specified parameters
        int pageSize = int.Parse(tbPageSize.Text);
        int pageTimeout = int.Parse(tbPageTimeout.Text);

        if ( rbNormal.IsChecked.Value )
        {
            DataContext = new List(customerProvider.FetchRange(0, 
                                                   customerProvider.FetchCount()));
        }
        else if ( rbVirtualizing.IsChecked.Value )
        {
            DataContext = new VirtualizingCollection(customerProvider, pageSize);
        }
        else if ( rbAsync.IsChecked.Value )
        {
            DataContext = new AsyncVirtualizingCollection(customerProvider, 
                              pageSize, pageTimeout*1000);
        }
    }
}

 
窗體設(shè)計(jì)是相當(dāng)?shù)暮?jiǎn)單，只是為了演示這個(gè)解決方案。 
用戶可以在DomoCustomerProvider中配置項(xiàng)的數(shù)量和模擬抓取的延遲。