How can I interact with a xamarin forms image in Android? - xamarin

Question

I have an image in Xamarin Forms. I want to use the native android features to interact with this image. For example, when the image is tapped, I want to know the x,y coordinates of where the image was tapped. I can use Android ImageView but I'm not sure how to cast the Xamarin Forms image to Android ImageView
[assembly: ExportRenderer(typeof(Image), typeof(FloorplanImageRenderer))]
namespace EmployeeApp.Droid.Platform
{
public class FloorplanImageRenderer : ImageRenderer
{
protected override void OnElementChanged(ElementChangedEventArgs<Image> e)
{
if (Control == null)
{
var imageView = (ImageView)e.NewElement; // This is not right
}
base.OnElementChanged(e);
}
}
}

Answer 1

But the Control is null....
No, it shouldn't be null. Back to your question, I think first of all, you will need to attach a touch event to the image control in PCL and create a property to hold the coordinate when image get touched. And I think here in your code:
[assembly: ExportRenderer(typeof(Image), typeof(FloorplanImageRenderer))]
I think the Image here should be your custom image control which inherits from Image in PCL.
Create a interface for touch event:
public interface IFloorplanImageController
{
void SendTouched();
}
Create a custom control for image:
public class FloorplanImage : Image, IFloorplanImageController
{
public event EventHandler Touched;
public void SendTouched()
{
Touched?.Invoke(this, EventArgs.Empty);
}
public Tuple<float, float> TouchedCoordinate
{
get { return (Tuple<float, float>)GetValue(TouchedCoordinateProperty); }
set { SetValue(TouchedCoordinateProperty, value); }
}
public static readonly BindableProperty TouchedCoordinateProperty =
BindableProperty.Create(
propertyName: "TouchedCoordinate",
returnType: typeof(Tuple<float, float>),
declaringType: typeof(FloorplanImage),
defaultValue: new Tuple<float, float>(0, 0),
propertyChanged: OnPropertyChanged);
public static void OnPropertyChanged(BindableObject bindable, object oldValue, object newValue)
{
}
}
Implement the custom renderer:
[assembly: ExportRenderer(typeof(FloorplanImage), typeof(FloorplanImageRenderer))]
namespace EmployeeApp.Droid.Platform
{
public class FloorplanImageRenderer : ImageRenderer
{
protected override void OnElementChanged(ElementChangedEventArgs<Image> e)
{
base.OnElementChanged(e);
if (e.NewElement != null)
{
if (Control != null)
{
Control.Clickable = true;
Control.SetOnTouchListener(ImageTouchListener.Instance.Value);
Control.SetTag(Control.Id, new JavaObjectWrapper<FloorplanImage> { Obj = Element as FloorplanImage });
}
}
}
protected override void Dispose(bool disposing)
{
if (disposing)
{
if (Control != null)
{
Control.SetOnTouchListener(null);
}
}
base.Dispose(disposing);
}
private class ImageTouchListener : Java.Lang.Object, Android.Views.View.IOnTouchListener
{
public static readonly Lazy<ImageTouchListener> Instance = new Lazy<ImageTouchListener>(
() => new ImageTouchListener());
public bool OnTouch(Android.Views.View v, MotionEvent e)
{
var obj = v.GetTag(v.Id) as JavaObjectWrapper<FloorplanImage>;
var element = obj.Obj;
var controller = element as IFloorplanImageController;
if (e.Action == Android.Views.MotionEventActions.Down)
{
var x = e.GetX();
var y = e.GetY();
element.TouchedCoordinate = new Tuple<float, float>(x, y);
controller?.SendTouched();
}
else if (e.Action == Android.Views.MotionEventActions.Up)
{
}
return false;
}
}
}
public class JavaObjectWrapper<T> : Java.Lang.Object
{
public T Obj { get; set; }
}
}
Use this control like this:
<local:FloorplanImage HeightRequest="300" x:Name="image" WidthRequest="300"
Aspect="AspectFit" Touched="image_Touched" />
code behind:
private void image_Touched(object sender, EventArgs e)
{
var cor = image.TouchedCoordinate;
}