Pinch Zoom images bound in Listbox - windows-phone-7.1

Question

I am trying to implement pinch zoom in my application. I found this article (Correct Pinch-Zoom in Silverlight) and it works perfectly fine for one image. But the problem is, my images are within listbox as shown in below XAML:
<ListBox x:Name="lstImage" Margin="-20,-23,-12,32" Height="709" Width="480">
<ListBox.ItemTemplate>
<DataTemplate>
<Image Source="{Binding Path=ImageSource}" VerticalAlignment="Top" Margin="10,12,10,10" Width="640" Height="800">
</Image>
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>
I am not able to understand how to implement that solution. Thanks in advance.

Answer 1

Create a class with name PinchZomBehavior.cs and add the following code.
public class PinchZomBehavior : Behavior<Image>
{
private double _totalImageScale = 1d;
private Point _imagePosition = new Point(0, 0);
private const double MaxImageZoom = 5;
private Point _oldFinger1;
private Point _oldFinger2;
private double _oldScaleFactor;
private Image _imgZoom;
protected override void OnAttached()
{
_imgZoom = AssociatedObject;
_imgZoom.RenderTransform = new CompositeTransform { ScaleX = 1, ScaleY = 1, TranslateX = 0, TranslateY = 0 };
var listener = GestureService.GetGestureListener(AssociatedObject);
listener.PinchStarted += OnPinchStarted;
listener.PinchDelta += OnPinchDelta;
listener.DragDelta += OnDragDelta;
listener.DoubleTap += OnDoubleTap;
base.OnAttached();
}
#region Pinch and Zoom Logic
#region Event handlers
/// <summary>
/// Initializes the zooming operation
/// </summary>
private void OnPinchStarted(object sender, PinchStartedGestureEventArgs e)
{
_oldFinger1 = e.GetPosition(_imgZoom, 0);
_oldFinger2 = e.GetPosition(_imgZoom, 1);
_oldScaleFactor = 1;
}
/// <summary>
/// Computes the scaling and translation to correctly zoom around your fingers.
/// </summary>
private void OnPinchDelta(object sender, PinchGestureEventArgs e)
{
var scaleFactor = e.DistanceRatio / _oldScaleFactor;
if (!IsScaleValid(scaleFactor))
return;
var currentFinger1 = e.GetPosition(_imgZoom, 0);
var currentFinger2 = e.GetPosition(_imgZoom, 1);
var translationDelta = GetTranslationDelta(
currentFinger1,
currentFinger2,
_oldFinger1,
_oldFinger2,
_imagePosition,
scaleFactor);
_oldFinger1 = currentFinger1;
_oldFinger2 = currentFinger2;
_oldScaleFactor = e.DistanceRatio;
UpdateImageScale(scaleFactor);
UpdateImagePosition(translationDelta);
}
/// <summary>
/// Moves the image around following your finger.
/// </summary>
private void OnDragDelta(object sender, DragDeltaGestureEventArgs e)
{
var translationDelta = new Point(e.HorizontalChange, e.VerticalChange);
if (IsDragValid(1, translationDelta))
UpdateImagePosition(translationDelta);
}
/// <summary>
/// Resets the image scaling and position
/// </summary>
private void OnDoubleTap(object sender, GestureEventArgs e)
{
ResetImagePosition();
}
#endregion
#region Utils
/// <summary>
/// Computes the translation needed to keep the image centered between your fingers.
/// </summary>
private Point GetTranslationDelta(
Point currentFinger1, Point currentFinger2,
Point oldFinger1, Point oldFinger2,
Point currentPosition, double scaleFactor)
{
var newPos1 = new Point(
currentFinger1.X + (currentPosition.X - oldFinger1.X) * scaleFactor,
currentFinger1.Y + (currentPosition.Y - oldFinger1.Y) * scaleFactor);
var newPos2 = new Point(
currentFinger2.X + (currentPosition.X - oldFinger2.X) * scaleFactor,
currentFinger2.Y + (currentPosition.Y - oldFinger2.Y) * scaleFactor);
var newPos = new Point(
(newPos1.X + newPos2.X) / 2,
(newPos1.Y + newPos2.Y) / 2);
return new Point(
newPos.X - currentPosition.X,
newPos.Y - currentPosition.Y);
}
/// <summary>
/// Updates the scaling factor by multiplying the delta.
/// </summary>
private void UpdateImageScale(double scaleFactor)
{
_totalImageScale *= scaleFactor;
ApplyScale();
}
/// <summary>
/// Applies the computed scale to the image control.
/// </summary>
private void ApplyScale()
{
((CompositeTransform)_imgZoom.RenderTransform).ScaleX = _totalImageScale;
((CompositeTransform)_imgZoom.RenderTransform).ScaleY = _totalImageScale;
}
/// <summary>
/// Updates the image position by applying the delta.
/// Checks that the image does not leave empty space around its edges.
/// </summary>
private void UpdateImagePosition(Point delta)
{
var newPosition = new Point(_imagePosition.X + delta.X, _imagePosition.Y + delta.Y);
if (newPosition.X > 0) newPosition.X = 0;
if (newPosition.Y > 0) newPosition.Y = 0;
if ((_imgZoom.ActualWidth * _totalImageScale) + newPosition.X < _imgZoom.ActualWidth)
newPosition.X = _imgZoom.ActualWidth - (_imgZoom.ActualWidth * _totalImageScale);
if ((_imgZoom.ActualHeight * _totalImageScale) + newPosition.Y < _imgZoom.ActualHeight)
newPosition.Y = _imgZoom.ActualHeight - (_imgZoom.ActualHeight * _totalImageScale);
_imagePosition = newPosition;
ApplyPosition();
}
/// <summary>
/// Applies the computed position to the image control.
/// </summary>
private void ApplyPosition()
{
((CompositeTransform)_imgZoom.RenderTransform).TranslateX = _imagePosition.X;
((CompositeTransform)_imgZoom.RenderTransform).TranslateY = _imagePosition.Y;
}
/// <summary>
/// Resets the zoom to its original scale and position
/// </summary>
private void ResetImagePosition()
{
_totalImageScale = 1;
_imagePosition = new Point(0, 0);
ApplyScale();
ApplyPosition();
}
/// <summary>
/// Checks that dragging by the given amount won't result in empty space around the image
/// </summary>
private bool IsDragValid(double scaleDelta, Point translateDelta)
{
if (_imagePosition.X + translateDelta.X > 0 || _imagePosition.Y + translateDelta.Y > 0)
return false;
if ((_imgZoom.ActualWidth * _totalImageScale * scaleDelta) + (_imagePosition.X + translateDelta.X) < _imgZoom.ActualWidth)
return false;
if ((_imgZoom.ActualHeight * _totalImageScale * scaleDelta) + (_imagePosition.Y + translateDelta.Y) < _imgZoom.ActualHeight)
return false;
return true;
}
/// <summary>
/// Tells if the scaling is inside the desired range
/// </summary>
private bool IsScaleValid(double scaleDelta)
{
return (_totalImageScale * scaleDelta >= 1) && (_totalImageScale * scaleDelta <= MaxImageZoom);
}
#endregion
#endregion
}
And attach the behavior to image control like this
xmlns:i="clr-namespace:System.Windows.Interactivity;assembly=System.Windows.Interactivity"
<Image Stretch="Uniform" Source="{Binding Image}" CacheMode="BitmapCache">
<i:Interaction.Behaviors>
<Behaviors:PinchZomBehavior/>
</i:Interaction.Behaviors>
</Image>