出现找不到xib指定的图片，需要指定图片的完整路径，不能只是图片名
详见：http://vocaro.com/trevor/blog/2012/10/21/xcode-groups-vs-folder-references/
An image stored as a folder reference will not work with Interface Builder! When editing, IB is able to find the image file and allows you to select it, but when it generates the XIB, it strips the folder location, which prevents it from being found. The result is a blank image and a runtime error:"Could not load the "MyImage.png" image referenced from a nib in the bundle with identifier "com.mytest.MyProject"
When loading a resource, you must specify the full path. Instead of:
[UIImage imageNamed:@"GoPago"];
you must do:
[UIImage imageNamed:@"Images/Icons/GoPago"];