How do I read an Image's Height and Width from my View Model?

Question

I want to do some line-drawing operations from my ViewModel (i.e. I will add to a collection of Lines which are bound to an ItemsControl on my view).

For this I need to know the height and width of an Image in my view. How do I get them ?

There are some workarounds mentioned in some other SO posts but they are for WPF and none of them work on Metro.

Answer 1

public static class SizeObserver
{
    public static readonly DependencyProperty ObserveProperty = DependencyProperty.RegisterAttached(
        "Observe",
        typeof(bool),
        typeof(SizeObserver), new PropertyMetadata(null, OnObserveChanged));
    //new FrameworkPropertyMetadata(OnObserveChanged));

    public static readonly DependencyProperty ObservedWidthProperty = DependencyProperty.RegisterAttached(
        "ObservedWidth",
        typeof(double),
        typeof(SizeObserver), null);

    public static readonly DependencyProperty ObservedHeightProperty = DependencyProperty.RegisterAttached(
        "ObservedHeight",
        typeof(double),
        typeof(SizeObserver), null);




    public static bool GetObserve(FrameworkElement frameworkElement)
    {
        //frameworkElement.AssertNotNull("frameworkElement");
        return (bool)frameworkElement.GetValue(ObserveProperty);
    }

    public static void SetObserve(FrameworkElement frameworkElement, bool observe)
    {
        //frameworkElement.AssertNotNull("frameworkElement");
        frameworkElement.SetValue(ObserveProperty, observe);
    }

    public static double GetObservedWidth(FrameworkElement frameworkElement)
    {
        //frameworkElement.AssertNotNull("frameworkElement");
        return (double)frameworkElement.GetValue(ObservedWidthProperty);
    }

    public static void SetObservedWidth(FrameworkElement frameworkElement, double observedWidth)
    {
        //frameworkElement.AssertNotNull("frameworkElement");
        frameworkElement.SetValue(ObservedWidthProperty, observedWidth);
    }

    public static double GetObservedHeight(FrameworkElement frameworkElement)
    {
        //frameworkElement.AssertNotNull("frameworkElement");
        return (double)frameworkElement.GetValue(ObservedHeightProperty);
    }

    public static void SetObservedHeight(FrameworkElement frameworkElement, double observedHeight)
    {
        //frameworkElement.AssertNotNull("frameworkElement");
        frameworkElement.SetValue(ObservedHeightProperty, observedHeight);
    }

    private static void OnObserveChanged(DependencyObject dependencyObject, DependencyPropertyChangedEventArgs e)
    {
        var frameworkElement = (FrameworkElement)dependencyObject;

        if ((bool)e.NewValue)
        {
            frameworkElement.SizeChanged += OnFrameworkElementSizeChanged;
            UpdateObservedSizesForFrameworkElement(frameworkElement);
        }
        else
        {
            frameworkElement.SizeChanged -= OnFrameworkElementSizeChanged;
        }
    }

    private static void OnFrameworkElementSizeChanged(object sender, SizeChangedEventArgs e)
    {
        UpdateObservedSizesForFrameworkElement((FrameworkElement)sender);
    }

    private static void UpdateObservedSizesForFrameworkElement(FrameworkElement frameworkElement)
    {
        // WPF 4.0 onwards
        frameworkElement.SetValue(ObservedWidthProperty, frameworkElement.ActualWidth);
        frameworkElement.SetValue(ObservedHeightProperty, frameworkElement.ActualHeight);

        // WPF 3.5 and prior
        ////SetObservedWidth(frameworkElement, frameworkElement.ActualWidth);
        ////SetObservedHeight(frameworkElement, frameworkElement.ActualHeight);
    }
}