build - Visual Studio 2010 doesn't rebuild changed code unless I manually select "Rebuild"

Question

In the past week or so, I've noticed that Visual Studio 2010 is not recompiling code unless I force it to. This is a C# 4.0 project with WPF. I hit F5, which seems like it used rebuild, if the code had changed, and then launch the app. Instead, it now says in the bottom left status bar "Build Successful" and launches the application. It doesn't actually rebuild the app, though. I can tell because:

1. even if I make a large number of changes, it "compiles" very quickly and
2. if I try to set a breakpoint, it gives the warning that the code has changed and doesn't set the breakpoint.

This happens regardless of whether there are errors in the code or not, so I don't believe it's the thing where it launches an older version if the build fails.

If I instead select from the menu to rebuild the project, it then works. This kind of impedes my usual workflow, however. I semi-frequently forget to do this, and then spend 10 minutes trying to figure out what the hell is wrong with my changes. Even worse, sometimes there are build errors that I don't notice right away.

Pressing F6 to "rebuild" the solution does not do anything either. What settings might I have mucked with that would cause this behavior?

Answer 1

Gah, I figured this out. It was naturally something stupid I did when messing around with build settings after a too-late night. Here are the things to check:

1. Tools >> Options >> Project and Solution >> Build and Run >> Check that "On run, when projects are out of date" is set to "Always build" or "Prompt to build"
2. Build >> Configuration Manager >> Check that "Build" is checked for all of the projects you want to build for each of the configurations you need to use.