I Thought He Came With You is Robert Ellison’s blog about software, marketing, politics, photography and time lapse.

Debugging Treasure Trove

Updated on Thursday, November 12, 2015

Mark Jackson, my co-founder at Cucku, is blogging re-mastered debugging tips from StackHash at infopurge.tumblr.com. StackHash is now an open source project on CodePlex and all of the great content from the original site has been taken offline. This new project is a great resource for debugging on the Windows platform, especially post-mortem crash dump analysis. If that’s your thing do yourself a favor and subscribe to Mark’s blog.

WPF commands with nested focus scope

Updated on Sunday, September 30, 2018

Here's a frustrating WPF scenario — you use the ApplicationCommands class to add Cut, Copy and Paste commands to toolbar and then put a TextBox on another toolbar. Click in the TextBox and the commands remain disabled. WTF, WPF?

The problem is with focus scopes. Your window is a focus scope and so are any menus or toolbars. This has the desirable property of allowing commands to target the control you were in immediately before invoking the command. You want paste to target the text box you're editing, not the menu item or button you clicked to request the paste.

So far so good. The problem is that the commanding system isn't smart enough to target the control with keyboard focus if it's in a nested focus scope. Remember that the window itself is a focus scope so our TextBox in a ToolBar (also a focus scope) is nested and immune to commands from our menu or toolbar.

Here's a simple window that demonstrates the problem:

Ignore the PreviewCanExecute handler for now. If you run this window and click in the main TextBox the paste button and menu item are enabled. Click in the toolbar TextBox and pasting isn't an option. Well, Ctrl-V still works and there's a context menu but you know what I mean.

The problem can be fixed by adding a command binding for ApplicationCommands.Paste and handling the PreviewCanExecute event:

When the window loads we're making note of the focus scopes for the toolbar and menu. Then when PreviewCanExecute fires we check to see if the element with the keyboard focus is in a different focus scope (and also that the window doesn't have keyboard focus). We then set the CommandTarget for the menu item and button to the element that has keyboard focus.

A handler isn't required for CanExecute as the command will take care of this with respect to the new CommandTarget.

Run the window again and you'll see that the paste button is enabled for both of the TextBox controls. When you click the button (or menu item) our PreviewCanExecute handler ignores the new keyboard focus and the command is sent to the desired control. 

One drawback of this approach is that keyboard focus isn't returned to the TextBox after the command executes. The CommandTarget remains in place so you can keep pasting and the command remains enabled but you lose the visual cue that lets you know where the target is. I haven't figured out a clean approach to this yet. When I do, I'll update this post. Better yet, if you've figured it out leave a comment.

Do useful things with the volume shadow copy service (VSS)

Updated on Thursday, November 12, 2015

The Volume Shadow Copy Service (VSS) takes a snapshot of an NTFS drive at a point in time. The clever thing about VSS is that it doesn't copy anything — it starts with the assumption that nothing has changed and then keeps track of every change to the snapshot so only changes need to be stored.

From Windows Vista on it's possible to mount a shadow copy as a drive letter or share. ShadowTask is a command line tool that creates a VSS copy, mounts it as a drive and then runs a program or batch file. For example:

ShadowTask C V dostuff.bat

Creates a copy of C:, mounts it as V: and then runs dostuff.bat.

Let's say you want to copy a locked file — maybe some outlook personal folders. Dostuff.bat could contain:

copy V:\Users\You\AppData\Local\Microsoft\Outlook.pst C:\Users\You\Desktop\OutlookBackup.pst

Bingo, you have a copy of your PST without shutting down Outlook.

Download: ShadowTask.zip (50.86 kb)

The ZIP contains both 32 and 64 bit versions of the tool. You must use the version that matches your platform. ShadowTask supports Windows Vista and 7. XP doesn't support mounting a shadow copy so ShadowCopy will fail if you try to use it on XP. ShadowCopy must run as admin (elevated).