Windows Phone 7 列表框加载数据的进度条

当列表框完成加载其数据时，是否有一个我可以监听的事件？我有一个文本框和一个列表框，当用户按 Enter 键时，列表框将填充来自 Web 服务的结果。我想在列表框加载时运行进度栏，并在完成后折叠它......

UPDATE

    <controls:PivotItem Header="food" Padding="0 110 0 0">

            <Grid x:Name="ContentFood" Grid.Row="2" >

                <StackPanel>
                    ...
                    ...

                    <toolkit:PerformanceProgressBar Name="ppbFoods" HorizontalAlignment="Left" 
                        VerticalAlignment="Center"
                        Width="466" IsIndeterminate="{Binding IsDataLoading}" 
                        Visibility="{Binding IsDataLoading, Converter={StaticResource BoolToVisibilityConverter}}"
                        />


                    <!--Food Results-->
                    <ListBox x:Name="lbFoods" ItemsSource="{Binding Foods}" Padding="5" 
                             SelectionChanged="lbFoods_SelectionChanged" Height="480" >
                        ....
                    </ListBox>

                </StackPanel>
            </Grid>


        </controls:PivotItem>

这是我的助手转换器类......

    public class BoolToValueConverter<T> : IValueConverter
{
    public T FalseValue { get; set; }
    public T TrueValue { get; set; }

    public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        if (value == null)
            return FalseValue;
        else
            return (bool)value ? TrueValue : FalseValue;
    }

    public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        return value != null ? value.Equals(TrueValue) : false;
    }
}

public class BoolToStringConverter : BoolToValueConverter<String> { }
public class BoolToBrushConverter : BoolToValueConverter<Brush> { }
public class BoolToVisibilityConverter : BoolToValueConverter<Visibility> { }
public class BoolToObjectConverter : BoolToValueConverter<Object> { }

在我的 App.xaml 中...

    xmlns:HelperClasses="clr-namespace:MyVirtualHealthCheck.HelperClasses"
    ...
    <HelperClasses:BoolToVisibilityConverter x:Key="BoolToVisibilityConverter" TrueValue="Visible" FalseValue="Collapsed" />

视图模型....

    ...
    public bool IsDataLoading
    {
        get;
        set;
    }
    ...
    public void GetFoods(string strSearch)
    {
        IsDataLoading = true;
        WCFService.dcFoodInfoCollection localFoods = IsolatedStorageCacheManager<WCFService.dcFoodInfoCollection>.Retrieve("CurrentFoods");

            if (localFoods != null)
            {
                Foods = localFoods;
            }
            else
            {
                GetFoodsFromWCF(strSearch);
            }
    }


    public void GetFoodsFromWCF(string strSearch)
    {
        IsDataLoading = true;
        wcfProxy.GetFoodInfosAsync(strSearch);
        wcfProxy.GetFoodInfosCompleted += new EventHandler<WCFService.GetFoodInfosCompletedEventArgs>(wcfProxy_GetFoodInfosCompleted);
    }

    void wcfProxy_GetFoodInfosCompleted(object sender, WCFService.GetFoodInfosCompletedEventArgs e)
    {
        WCFService.dcFoodInfoCollection foods = e.Result;
        if (foods != null)
        {
            //set current foods to the results from the web service
            this.Foods = foods;
            this.IsDataLoaded = true;

            //save foods to phone so we can use cached results instead of round tripping to the web service again
            SaveFoods(foods);
        }
        else
        {
            Debug.WriteLine("Web service says: " + e.Result);
        }
        IsDataLoading = false;
    }

没有为此的内置功能。完成加载数据后，您必须更新进度条。
或者更新视图模型中的布尔依赖属性并将进度条绑定到该属性。

Update
一些基于注释的粗略示例代码。这是写在这里并没有检查，但你应该明白：

The VM:

public class MyViewModel : INotifyPropertyChanged
{
    private bool isLoading;
    public bool IsLoading
    {
        get { return isLoading; }

        set
        {
            isLoading = value;
            NotifyPropertyChanged("IsLoading");
        }
    }

    public void SimulateLoading()
    {
        var bw = new BackgroundWorker();

        bw.RunWorkerCompleted += (s, e) => 
            Deployment.Current.Dispatcher.BeginInvoke(
                () => { IsLoading = false; });

        bw.DoWork += (s, e) =>
        {
            Deployment.Current.Dispatcher.BeginInvoke(() => { IsLoading = true; });
            Thread.Sleep(5000);
        };

        bw.RunWorkerAsync();
    }

    public event PropertyChangedEventHandler PropertyChanged;

    private void NotifyPropertyChanged(String propertyName)
    {
        PropertyChangedEventHandler handler = PropertyChanged;
        if (null != handler)
        {
            handler(this, new PropertyChangedEventArgs(propertyName));
        }
    }
}

XAML:

<toolkit:PerformanceProgressBar IsEnabled="{Binding IsLoading}" 
                                IsIndeterminate="{Binding IsLoading}"/>

将页面的DataContext设置为视图模型的实例，然后调用SimulateLoading()在视图模型实例上。

再次更新:
我的错IsIndeterminate是一个布尔值，因此不需要转换器。