Official Apple documentation (developer.apple.com/library/mac … SView.html):
View instances that are created in Interface Builder don’t call initWithFrame: when their nib files are loaded, which often causes confusion. Remember that Interface Builder archives an object when it saves a nib file, so the view instance will already have been created and initWithFrame: will already have been called.
The awakeFromNib method provides an opportunity to provide initialization of a view when it is created as a result of a nib file being loaded. When a nib file that contains a view object is loaded, each view instance receives an awakeFromNib message when all the objects have been unarchived. This provides the object an opportunity to initialize any attributes that are not archived with the object in Interface Builder.