iOS Black screen after upgrade universal app

[mikezang]

I tried the sample in book "Beginning iPhone Development", the screen becomes black after I upgrade it to universal app for both iPad/iPhone.

What happened? do I have to modify something in source?

 

[KoolStar]

Are you running it under the ipad simulator?

 

[mikezang]

Are you running it under the ipad simulator?

Yeah, I run it in simulator3.2 and 3.1.3, both just black screen.

But before upgraded it, the "Hello World" is displayed.

I guess that might be about Interface Builder, because the app is ok even if I upgraded it if there are no files in Interface Builder, but all app got black screen if there are files in Interface Builder.