Weird in my UIImagePickerController with camera

Question

Hi everyone:

I met a problem on using camera by scratch on iphone. Other people's code just run fine on my 3GS. But my code doesn't.

When I implemented a UIViewController controller, and I add the following code in viewdidload:

UIImagePickerController *picker = [UIImagePickerController alloc] init];
picker.source = UIImagePickerControllerSourceTypeCamera;
picker.delegate = self; //Previously added all the delegate properly
[self presentModalViewController:picker animated:YES];

Nothing comes out. I checked in the debugger, it shows that the picker is allocated, but here is the major difference between my and success one. picker._imagepickerflag.visible = 0; //others show 1; picker.UINavigationController._containerView: 0x0 ; // others have value.

Can anyone help me on this, is there something wrong? Thank you.