xamarin forms image zoom and scroll - image

Question

I am using this pinchGestureRecognizer in order to zoom on an image, but the problem is that after zooming I am not able to scroll the image vertically, even though I've wrapped my image in a scrollView with Orientation="Both"
Here is the PinchToZoomContainer class:
public class PinchToZoomContainer : ContentView
{
double currentScale = 1;
double startScale = 1;
double xOffset = 0;
double yOffset = 0;
public PinchToZoomContainer()
{
var pinchGesture = new PinchGestureRecognizer();
pinchGesture.PinchUpdated += OnPinchUpdated;
GestureRecognizers.Add(pinchGesture);
}
void OnPinchUpdated(object sender, PinchGestureUpdatedEventArgs e)
{
if (e.Status == GestureStatus.Started)
{
// Store the current scale factor applied to the wrapped user interface element,
// and zero the components for the center point of the translate transform.
startScale = Content.Scale;
Content.AnchorX = 0;
Content.AnchorY = 0;
}
if (e.Status == GestureStatus.Running)
{
// Calculate the scale factor to be applied.
currentScale += (e.Scale - 1) * startScale;
currentScale = Math.Max(1, currentScale);
// The ScaleOrigin is in relative coordinates to the wrapped user interface element,
// so get the X pixel coordinate.
double renderedX = Content.X + xOffset;
double deltaX = renderedX / Width;
double deltaWidth = Width / (Content.Width * startScale);
double originX = (e.ScaleOrigin.X - deltaX) * deltaWidth;
// The ScaleOrigin is in relative coordinates to the wrapped user interface element,
// so get the Y pixel coordinate.
double renderedY = Content.Y + yOffset;
double deltaY = renderedY / Height;
double deltaHeight = Height / (Content.Height * startScale);
double originY = (e.ScaleOrigin.Y - deltaY) * deltaHeight;
// Calculate the transformed element pixel coordinates.
double targetX = xOffset - (originX * Content.Width) * (currentScale - startScale);
double targetY = yOffset - (originY * Content.Height) * (currentScale - startScale);
// Apply translation based on the change in origin.
Content.TranslationX = targetX.Clamp(-Content.Width * (currentScale - 1), 0);
Content.TranslationY = targetY.Clamp(-Content.Height * (currentScale - 1), 0);
// Apply scale factor
Content.Scale = currentScale;
}
if (e.Status == GestureStatus.Completed)
{
// Store the translation delta's of the wrapped user interface element.
xOffset = Content.TranslationX;
yOffset = Content.TranslationY;
}
}
}
This the Clamp method:
public static class DoubleExtensions
{
public static double Clamp(this double self, double min, double max)
{
return Math.Min(max, Math.Max(self, min));
}
}
And this is the image in my XAML file:
<StackLayout Grid.Row="0" Grid.Column="0" Grid.ColumnSpan="2" Grid.RowSpan="3">
<ScrollView x:Name="imageScroll" Orientation="Both" VerticalOptions="FillAndExpand">
<entry:PinchToZoomContainer>
<entry:PinchToZoomContainer.Content>
<Image x:Name="zoomImage" Source="{images:EmbeddedImage Vebko.Images.CB_Edite_Vb1_2.jpg}" Margin="0,0,0,10" HorizontalOptions="Center" VerticalOptions="Center"/>
</entry:PinchToZoomContainer.Content>
</entry:PinchToZoomContainer>
</ScrollView>
</StackLayout>
Can anybody please help?

Answer 1

What i guess is that while you scale the Content, the PinchToZoomContainer : ContentView size remains the same that is why scrollview doesn't react = change control's size with height/width requests in code when its content gets scaled.