The Old New Thing

There's a default implementation for WM_SETREDRAW, but you might be able to do better

January 24, 2011 Jan 24, 2011 01/24/11

Raymond Chen

If your window doesn't have a handler for the message, then will give you a default implementation which suppresses messages for your window when redraw is disabled, and re-enables (and triggers a full repaint) when redraw is re-enabled. (This is internally accomplished by making the window pseudo-invisible, but that's an implementation ...

Modality, part 9: Setting the correct owner for modal UI, practical exam

January 21, 2011 Jan 21, 2011 01/21/11

Raymond Chen

Here's a question that came from a customer. You can answer it yourself based on what you know about modal UI. (If you're kind of rusty on the topic, you can catch up here.) I've left in some irrelevant details just to make things interesting. Our program launches a helper program to display an Aero Wizard to guide the user through ...

How to turn off the exception handler that COM "helpfully" wraps around your server

January 20, 2011 Jan 20, 2011 01/20/11

Raymond Chen

Historically, COM placed a giant around your server's methods. If your server encountered what would normally be an unhandled exception, the giant would catch it and turn it into the error . It then marked the exception as handled, so that the server remained running, thereby "improving robustness by keeping the server running even when it ...

What's the difference between an asynchronous PIPE_WAIT pipe and a PIPE_NOWAIT pipe?

January 14, 2011 Jan 14, 2011 01/14/11

Raymond Chen

When you operate on named pipes, you have a choice of opening them in mode or mode. When you read from a pipe, the read blocks until data becomes available in the pipe. When you read from a pipe, then the read completes immediately even if there is no data in the pipe. But how is this different from a pipe opened in asynchronous mode by ...

The MARGINS parameter to the DwmExtendFrameIntoClientArea function controls how far the frame extends into the client area

January 13, 2011 Jan 13, 2011 01/13/11

Raymond Chen

A customer wrote a program that calls to extend the frame over the entire client area, but then discovered that this made programming difficult: I have a window which I want to have a glassy border but an opaque body. I made my entire window transparent by calling , and I understand that this means that I am now responsible for managing the ...

Why does SHGetSpecialFolderPath take such a long time before returning a network error?

January 5, 2011 Jan 5, 2011 01/5/11

Raymond Chen

A customer reported that their program was failing to start up because the call to was taking a long time and then eventually returning with . The account that was experiencing this problem had a redirected network profile, "but even if he's redirecting, why would we get the bad net path error? Does calling actually touch the folder/network...

What makes RealGetWindowClass so much more real than GetClassName?

December 31, 2010 Dec 31, 2010 12/31/10

Raymond Chen

There's and then there's . What makes more real? Recall from last time that the functions were added to support Windows accessibility. The goal with is to help accessibility tools identify what kind of window it is working with, even if the application did a little disguising in the form of superclassing. If you ask for the class ...

WindowFromPoint, ChildWindowFromPoint, RealChildWindowFromPoint, when will it all end?

December 30, 2010 Dec 30, 2010 12/30/10

Raymond Chen

Oh wait, there's also . There are many ways of identifying the window that appears beneath a point. The documentation for each one describes how they work, but I figured I'd do a little compare/contrast to help you decide which one you want for your particular programming problem. The oldest functions are and . The primary difference ...

Psychic debugging: When I copy a file to the clipboard and then paste it, I get an old version of the file

December 29, 2010 Dec 29, 2010 12/29/10

Raymond Chen

A customer reported the following strange problem: I tried to copy some text files from my computer to another computer on the network. After the copy completes, I looked at the network directory and found that while it did contain files with the same names as the ones I copied, they have completely wrong timestamps. Curious, I opened up the...

What is the correct way of temporarily changing a thread's preferred UI language?

December 23, 2010 Dec 23, 2010 12/23/10

Raymond Chen

A customer ran into a crashing bug in their shell extension. The shell extension wants to change the thread's preferred UI language temporarily, so that it can load its resources from a specific language. You'd think this would be easy: Approximately ten seconds after this code runs, Explorer crashes with the exception whose description ...