Tag Archives: wpf

Issue with Xaml Designer – An error occurred loading this property page

So after installing Visual Studio 2015 Update 2, my Xaml Designer decided to stop working. Every time I open the designer by clicking on a xaml file, it would show an error dialog that says “Visual Studio has encountered an unexpected error.” – not very helpful. Going to the menu, Options > Xaml Designer > General property page would yield an error “An error occurred loading this property page”.

I then tried re-installing Visual Studio 2015. Same issue. I then tried opening Expression Blend, it doesn’t work, but I got a some more interesting clues – it tells me to check ActivityLog.xml – In it, there was a telling error:

SetSite failed for package [XamlDesignerPackage][This access control list is not in canonical form and therefore cannot be modified.

Basically my permissions were corrupted somewhere in some file. I had a hunch. A test by logging on to a fresh Windows user account and opening VS xaml editor confirmed that the issue was limited to my profile account. I tried remove all traces of Visual Studio from profile but removing the obvious AppData folder didn’t fix the issue. There were just too many places it hides files. As a last resort, I reset all permissions on my profile folder such that I was the owner and had write access and surprise! it works!! Now I know what to try next time.

Getting the intersection points of two [path] geometries in WPF

While working on an app that utilises geometries in WPF, I needed a way to get the intersection points of the lines of two arbitrary geometries. A google search didn’t yield any useful hints except a post suggesting to use mathematics. That would be ideal for very simple geometries like lines, but with complex geometries, it becomes tiresome real quick. The framework doesn’t seem to have any built in functions that calculate that, so it’s time for some hack and slash.

After a few days of thinking, I came up with a simple, yet effective (but not the most efficient solution). For those who just want the intersection between two geometries, there is the CombinedGeometry geometry class which takes input in the form of two geometries. Setting the GeometryCombineMode to Intersect gives a geometry which is the intersection of the two. At the otherside of the WPF realm, we have Geometry.GetWidenedPathGeometry(). This method basically converts/strokes path lines to an approximate geometry. Combining these two concepts, we can produce an intersection from two widened path geometries (the two paths which we want the intersection of).

public static Point[] GetIntersectionPoints(Geometry g1, Geometry g2)
{
Geometry og1 = g1.GetWidenedPathGeometry(new Pen(Brushes.Black, 1.0));
Geometry og2 = g2.GetWidenedPathGeometry(new Pen(Brushes.Black, 1.0));

CombinedGeometry cg = new CombinedGeometry(GeometryCombineMode.Intersect, og1, og2);

PathGeometry pg = cg.GetFlattenedPathGeometry();
Point[] result = new Point[pg.Figures.Count];
for (int i = 0; i < pg.Figures.Count; i++)
{
Rect fig = new PathGeometry(new PathFigure[] { pg.Figures[i] }).Bounds;
result[i] = new Point(fig.Left + fig.Width / 2.0, fig.Top + fig.Height / 2.0);
}
return result;
}

The function will return an array of zero or more points of intersection. To test it

sg1 = StreamGeometry.Parse("M0,0 L100,100");
sg2 = StreamGeometry.Parse("M0,100 L100,0");
Point[] pts = GetIntersectionPoints(sg1, sg2);
// pts[0] is {50,50}

Hope this helps someone.