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Some things weren't used. This needs a thorough review.
using Microsoft.Phone.Controls;
using System;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Controls.Primitives;
using System.Diagnostics;
using System.Collections.Generic;
using System.Linq;
namespace Ocell.Controls
{
/// <summary>
/// This class detects the pull gesture on a LongListSelector. How does it work?
///
/// This class listens to the change of manipulation state of the LLS, to the MouseMove event
/// (in WP, this event is triggered when the user moves the finger through the screen)
/// and to the ItemRealized/Unrealized events.
///
/// Listening to MouseMove, we can calculate the amount of finger movement. That is, we can
/// detect when the user has scrolled the list.
///
/// Then, when the ManipulationState changes from Manipulating to Animating (from user
/// triggered movement to inertia movement), we check the viewport changes. The viewport is
/// only constant when the user scrolls beyond the end of the list, either at the top or at the bottom.
/// If no items were added, check the direction of the scroll movement and fire the corresponding event.
/// </summary>
public class WP8PullDetector
{
LongListSelector listbox;
bool viewportChanged = false;
bool isMoving = false;
double manipulationStart = 0;
double manipulationEnd = 0;
public bool Bound { get; private set; }
public void Bind(LongListSelector listbox)
{
Bound = true;
this.listbox = listbox;
listbox.ManipulationStateChanged += listbox_ManipulationStateChanged;
listbox.MouseMove += listbox_MouseMove;
}
public void Unbind()
{
Bound = false;
if (listbox != null)
{
listbox.ManipulationStateChanged -= listbox_ManipulationStateChanged;
listbox.MouseMove -= listbox_MouseMove;
}
}
void listbox_MouseMove(object sender, System.Windows.Input.MouseEventArgs e)
{
var pos = e.GetPosition(null);
if (!isMoving)
manipulationStart = pos.Y;
else
manipulationEnd = pos.Y;
isMoving = true;
}
void listbox_ManipulationStateChanged(object sender, EventArgs e)
{
if (listbox.ManipulationState == ManipulationState.Idle)
{
isMoving = false;
viewportChanged = false;
}
else if (listbox.ManipulationState == ManipulationState.Manipulating)
{
viewportChanged = false;
}
else if (listbox.ManipulationState == ManipulationState.Animating)
{
if (!viewportChanged && Compression != null)
{
if (IsAtTop())
Compression(this, new CompressionEventArgs(CompressionType.Top));
else if (IsAtBottom())
Compression(this, new CompressionEventArgs(CompressionType.Bottom));
}
}
}
private bool IsAtTop()
{
if (listbox.ItemsSource.Count == 0)
return true;
ContentPresenter firstContainer;
ITweetable firstItem = listbox.ItemsSource[0] as ITweetable;
if (listbox.ViewportItems.TryGetValue(firstItem, out firstContainer))
{
var diff = listbox.GetRelativePosition(firstContainer);
if (diff.Y <2 )
return true;
}
return false;
}
private bool IsAtBottom()
{
if (listbox.ItemsSource.Count == 0)
return true;
ContentPresenter lastContainer;
ITweetable lastItem = listbox.ItemsSource[listbox.ItemsSource.Count - 1] as ITweetable;
if (listbox.ViewportItems.TryGetValue(lastItem, out lastContainer))
{
var diff = lastContainer.GetRelativePosition(listbox);
if (diff.Y <= listbox.ActualHeight - lastContainer.ActualHeight + 2)
return true;
}
return false;
}
public event OnCompression Compression;
}
}

LongListSelector do not have GetRelativePosition method in window phone 8.1 siverlight

Where can I find this GetRelativePosition?

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