How do I add a dependency property to an image in WPF?

Question

How do I add my property called weight to an image and use it like this:?

myImage.weight

(assuming i have already defined myImage in XAML)

here's my code:

public partial class MainWindow : Window
{
    public double Weight
    {
        get
        {
            return (double)GetValue(WeightProperty);
        }
        set
        {
            SetValue(WeightProperty, value);
        }
    }
    public static readonly DependencyProperty WeightProperty = DependencyProperty.Register("Weight", typeof(Double), typeof(Image));


    public MainWindow()
    {
        this.InitializeComponent();
                    myImage.Weight = 2;'

here the last line doesn't work because the property Weight does not attach to myImage.

This below also doesn't work in XAML:

<Image x:Name="myImage" Weight="2" />

Answer 1

You need to create an attached property:

public static double GetWeight(DependencyObject obj)
        {
            return (double)obj.GetValue(WeightProperty);
        }

        public static void SetWeight(DependencyObject obj, double value)
        {
            obj.SetValue(WeightProperty, value);
        }

        public static readonly DependencyProperty WeightProperty =
            Dependenc**strong text**yProperty.RegisterAttached("Weight", typeof(double), typeof(MainWindow));

You can then use this in the XAML as below:

<Image x:Name="myImage" MainWindow.Weight="2" />

I would generally put the attached property on something other than MainWindow though.

You can then access the value of the property in code through:

    double weight = (double)myImage.GetValue(MainWindow.Weight);
    myImage.SetValue(MainWindow.Weight, 123.0);

Answer 2

I would recommend just inheriting the Image class and adding your new dependency property.

Eg.

public class MyImage : System.Windows.Controls.Image
{
    public double Weight
    {
        get { return (double)GetValue(WeightProperty); }
        set { SetValue(WeightProperty, value); }
    }

    // Using a DependencyProperty as the backing store for Weight.  This enables animation, styling, binding, etc...
    public static readonly DependencyProperty WeightProperty =
        DependencyProperty.Register("Weight", typeof(double), typeof(MyImage), new UIPropertyMetadata(0.0));

}

Then in your XAML code, with this local namespace:

xmlns:local="clr-namespace:[LIBRARYNAME]"

you can use:

<local:MyImage Weight="10.0"/>

It's a tad cumbersome, but I think it gives you the most control.