Question

Essentially what I’m trying to do is trigger a sort of ‘dirty’ state for my canvas, so that I know if there are unsaved changes.

Is there an event in the WPF InkCanvas that I can use to handle any time when the strokes change?

If there isn’t, what events should I listen to for the equivalent? My first guess would be these:

StrokeCollected
StrokeErased
StrokesReplaced

Though I could be wrong, and be missing an edge case.

Note: It’s not a big deal if I get false positives (marked dirty when it is in fact not), but I don’t want false negatives.

Answer 1

It seems like these events will do the job:

• InkCanvas.StrokesReplaced (occurs when the Strokes property is set)
• StrokeCollection.StrokesChanged (occurs when a stroke is added or removed)
• Stroke.StylusPointsChanged (occurs when the shape of a stroke is changed)
• Stroke.StylusPointsReplaced (occurs when the StylusPoints property is set)
• Stroke.DrawingAttributesChanged (occurs when the attributes of a stroke are changed)
• Stroke.DrawingAttributesReplaced (occurs when the DrawingAttributes property is set)

In my case, I never replace properties, or change drawing attributes, so I only use StrokeCollection.StrokesChanged and Stroke.StylusPointsChanged. Here is a snippet of my code.

public MainWindow()
{
    inkCanvas.Strokes.StrokesChanged += Strokes_StrokesChanged;
}

private void Strokes_StrokesChanged(object sender, StrokeCollectionChangedEventArgs e)
{
    // Mark dirty
    foreach (Stroke stroke in e.Added)
    {
        stroke.StylusPointsChanged += stroke_StylusPointsChanged;
    }
    foreach (Stroke stroke in e.Removed)
    {
        stroke.StylusPointsChanged -= stroke_StylusPointsChanged;
    }
}

private void stroke_StylusPointsChanged(object sender, System.EventArgs e)
{
    // Mark dirty
}