WPF window rendering woes

Today, I started adding some functionality to a new WPF app, and noticed that as I resized my window to be larger, there were black strips appearing on the bottom and right sides of the client area, that were eventually filled with the controls on the page.

This looked horrible, and it appears I’m not the first one to run across this, however, there still seems to be no resolution.

As I’m an old school MFC/C++ guy, I figured there had to be a way to do this.

My first strategy was to hook in a new WndProc handler, and process WM_ERASEBKGND messages.  I thought, claiming I’d erased it would do the job, but that made no difference.

So, I actually implemented code to fill the clip region with the WINDOW_COLOR brush, and that did fix the problem.  No more black edges, but that was all a little bit unsatisfactory.  What I really wanted to do was register my own class for the WPF window, and set the background brush correctly to match the window.

That doesn’t appear to be possible, but it is possible to PInvoke and call SetClassLong on the background brush.

So my preferred solution is set the class background brush, and watch WPF draw it correctly. It appears that WPF creates a new class for each application so this should be safe, though if it’s not the previously described solution would definitely work.

Why isn’t my TaskDialog PInvoke call working?

I’m trying to track down a problem today where one of our programs apparently locks up.

Here’s the screengrab:

Notice the partially drawn window around the center, with leftover high scores from the previous window.  I’m pretty sure this outer box is the window frame for the task dialog, as that’s where it’s positioned when it is shown correctly.  The high scores dialog box that was on the screen was larger, and the buttons and bottom of the screen have redrawn.

Here’s how I declare the signature:

[DllImport("comctl32.dll", PreserveSig = false, CharSet = CharSet.Unicode)]
        private static extern TaskDialogResult TaskDialog(IntPtr hwndParent, IntPtr hInstance,
            string title, string mainInstruction, string content,
            TaskDialogButtons buttons, TaskDialogIcon icon);

And here’s how I call it:

int split = text.IndexOf('\n');

TaskDialogResult tdr = TaskDialog(hWnd, IntPtr.Zero, caption,
    text.Substring(0, split),
    text.Substring(split + 1), taskBtn, taskIcon);

Now, what I think is probably happening is that for some reason, the two strings passed into the TaskDialog are being garbage collected, but that’s just a wild guess at the moment.