Windows Phone 实现类似“微博”下拉刷新效果

< UserControl  x:Class ="sdkRSSReaderCS.LoadingBox"
    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"
    mc:Ignorable ="d"
    FontFamily =" {StaticResource PhoneFontFamilyNormal} "
    FontSize =" {StaticResource PhoneFontSizeNormal} "
    Foreground =" {StaticResource PhoneForegroundBrush} "
    d:DesignHeight ="480"  d:DesignWidth ="480" >

     < Grid  x:Name ="LayoutRoot" >
         < StackPanel  Orientation ="Horizontal" >
             < Grid  Margin ="8,0,0,0"  Width ="50"  Height ="50" >
                 < Image  x:Name ="PulldownArrow"  Width ="50"  Height ="50"  Source ="/sdkRSSReaderCS;component/images/pulldown_arrow.png" >
                     < Image.RenderTransform >
                         < RotateTransform  x:Name ="FlipTransform"  CenterX ="25"  CenterY ="25"  Angle ="180" />
                     </ Image.RenderTransform >
                     < Image.Resources >
                         < Storyboard  x:Name ="FlipDown" >
                             < DoubleAnimation  Storyboard.TargetName ="FlipTransform"
                               Storyboard.TargetProperty ="Angle"
                               From ="0"  To ="180"  Duration ="0:0:0.2" />
                         </ Storyboard >
                         < Storyboard  x:Name ="FlipUp" >
                             < DoubleAnimation  Storyboard.TargetName ="FlipTransform"
                               Storyboard.TargetProperty ="Angle"
                               From ="180"  To ="0"  Duration ="0:0:0.2" />
                         </ Storyboard >
                     </ Image.Resources >
                 </ Image >
                 < Image  x:Name ="SpinningBall"  Source ="/sdkRSSReaderCS;component/images/spinning_ball.png"  Width ="36"  Height ="36" >
                     < Image.RenderTransform >
                         < RotateTransform  x:Name ="SpinTransform"  CenterX ="18"  CenterY ="18" />
                     </ Image.RenderTransform >
                     < Image.Resources >
                         < Storyboard  x:Name ="Spin" >
                             < DoubleAnimation  Storyboard.TargetName ="SpinTransform"
                               Storyboard.TargetProperty ="Angle"
                               From ="0"  To ="360"  Duration ="0:0:1"
                               RepeatBehavior ="Forever" />
                         </ Storyboard >
                     </ Image.Resources >
                 </ Image >
             </ Grid >
             < TextBlock  x:Name ="TextBlock"  Margin ="10,0,0,0"
                 VerticalAlignment ="Center"  FontSize ="26"
                 Style =" {StaticResource PhoneTextExtraLargeStyle} "
                 Foreground =" {StaticResource PhoneAccentBrush} "   />
         </ StackPanel >
     </ Grid >
</ UserControl >

     public  partial  class LoadingBox : UserControl
    {
         private  string arrow;
         public  static  readonly DependencyProperty BusyProperty = DependencyProperty.Register( " Busy ",  typeof( bool),  typeof(LoadingBox),  new PropertyMetadata( false));

         public LoadingBox()
        {
            InitializeComponent();
        }
         //  Properties
         public  string Arrow
        {
             get
            {
                 return  this.arrow;
            }
             set
            {
                 if ( this.arrow ==  null)
                {
                     if (value ==  " Invisible ")
                         this.PulldownArrow.Visibility = Visibility.Collapsed;
                     else  if (value ==  " Up ")
                    {
                         this.FlipTransform.Angle =  0.0;
                         this.PulldownArrow.Visibility = Visibility.Visible;
                    }
                     else  if (value ==  " Down ")
                    {
                         this.FlipTransform.Angle =  180.0;
                         this.PulldownArrow.Visibility = Visibility.Visible;
                    }
                }
                 else  if (value ==  " Invisible ")
                     this.PulldownArrow.Visibility = Visibility.Collapsed;
                 else  if (value ==  " Up ")
                {
                     if ( this.arrow ==  " Invisible ")
                    {
                         this.FlipTransform.Angle =  0.0;
                         this.PulldownArrow.Visibility = Visibility.Visible;
                    }
                     else  if ( this.arrow ==  " Down ")  this.FlipUp.Begin();
                }
                 else  if (value ==  " Down ")
                {
                     if ( this.arrow ==  " Invisible ")
                    {
                         this.FlipTransform.Angle =  180.0;
                         this.PulldownArrow.Visibility = Visibility.Visible;
                    }
                     else  if ( this.arrow ==  " Up ")  this.FlipDown.Begin();
                }
                 this.arrow = value;
            }
        }

         public  bool Busy
        {
             get
            {
                 return ( bool) base.GetValue(BusyProperty);
            }
             set
            {
                 base.SetValue(BusyProperty, value);
                 if (value)
                {
                     this.Arrow =  " Invisible ";
                     this.SpinningBall.Visibility = Visibility.Visible;
                     this.Spin.Begin();
                }
                 else
                {
                     this.SpinningBall.Visibility = Visibility.Collapsed;
                     this.Spin.Stop();
                }
            }
        }

         public  string Text
        {
             get
            {
                 return  this.TextBlock.Text;
            }
             set
            {
                 this.TextBlock.Text = value;
            }
        }

    }

#region ScrollView

         private  void NewsScrollViewer_Loaded( object sender, RoutedEventArgs e)
        {
             this.newsScrollViewer = sender  as ScrollViewer;
        }


         private  void ScrollViewer_ManipulationCompleted( object sender, ManipulationCompletedEventArgs e)
        {
             this.actualOffset =  this.startOffset +  this.startPoint - e.ManipulationOrigin.Y;
             if ( this.actualOffset < - 100 && !headLoadingBox.Busy)
            {
                Update();
            }
             if ( this.actualOffset +  250 >  this.newsScrollViewer.ScrollableHeight && !tailLoadingBox.Busy)
            {
                NextPage();
            }

        }

         private  void ScrollViewer_ManipulationStarted( object sender, ManipulationStartedEventArgs e)
        {
             this.startOffset =  this.newsScrollViewer.VerticalOffset;
             this.startPoint = e.ManipulationOrigin.Y;
        }

         private  void ScrollViewer_MouseEnter( object sender, MouseEventArgs e)
        {
             // this.startRelativePoint = e.GetPosition(this.TopPlaceholder).Y;
        }

         private  void ScrollViewer_MouseMove( object sender, MouseEventArgs e)
        {
             this.actualOffset =  this.startOffset +  this.startRelativePoint - e.GetPosition( this.TopPlaceholder).Y;
             if (actualOffset < - 100)
            {
                 this.headLoadingBox.Arrow =  " Up ";
                 this.headLoadingBox.Text =  " 松开就可以更新！ ";
            }
             if ( this.actualOffset +  250 >  this.newsScrollViewer.ScrollableHeight && !tailLoadingBox.Busy)
            {
                 this.tailLoadingBox.Arrow =  " Down ";
                 this.tailLoadingBox.Text =  " 松开就可以更新！ ";
            }
        }