Associate MVVM with InkCanvas

Question

I think I ran into a road block. We use MVVM with Prism and have a view that requires an ink canvas. I create a StrokeCollection that is bound from my ViewModel to the view. I can install the collection from my view model, but the changes will not appear in the ViewModel while the user is drawing. Is there any way to make this work?

My property in my ViewModel is as follows:

private StrokeCollection _strokes;
public StrokeCollection Signature
{
     get
     {
         return _strokes;
     }
     set
     {
         _strokes = value;
         OnPropertyChanged("Signature");
     }
}

Here is my XAML binding string:

<InkCanvas x:Name="MyCanvas" Strokes="{Binding Signature, Mode=TwoWay}" />

For some reason, apparently, InkCanvas never notifies the ViewModel of any changes.

Answer 1

, , InkCanvas StrokeCollection. - . (.. null), , InkCanvas . :

• StrokeCollection
• , ,

:

public class ViewModel : INotifyPropertyChanged
{
    private readonly StrokeCollection _strokes;

    public ViewModel()
    {
        _strokes = new StrokeCollection();
        (_strokes as INotifyCollectionChanged).CollectionChanged += delegate
        {
            //the strokes have changed
        };
    }

    public event PropertyChangedEventHandler PropertyChanged;

    public StrokeCollection Signature
    {
        get
        {
            return _strokes;
        }
    }

    private void OnPropertyChanged(string propertyName)
    {
        var handler = PropertyChanged;

        if (handler != null)
        {
            handler(this, new PropertyChangedEventArgs(propertyName));
        }
    }
}

XAML:

<InkCanvas Strokes="{Binding Signature}"/>

Answer 2

StrokeCollection , "StrokesChanged", , - . .

XAML:

<Grid>
    <InkCanvas Strokes="{Binding Signature}"/>
</Grid>

VM:

public class TestViewModel : INotifyPropertyChanged
{
    public StrokeCollection Signature { get; set; }

    public event PropertyChangedEventHandler PropertyChanged;

    public TestViewModel()
    {
        Signature = new StrokeCollection();
        Signature.StrokesChanged += Signature_StrokesChanged;
    }

    void Signature_StrokesChanged(object sender, StrokeCollectionChangedEventArgs e)
    {
        //PUT A BREAKPOINT HERE AND CHECK
        Signature = (System.Windows.Ink.StrokeCollection)sender;
    }

}

, !