I changed a Xib(which had an UIToolBar as one of its components) to auto layout and started adding constraints. It hanged the Xcode. The Interface builder cocoa touch tool was taking nearly 100% of the CPU. I recreated the xib without the toolbar and added constraints. It worked fine. I then added the UIToolBar and tried executing it hanged the Xcode. I didn't add any constraints for the UIToolBar.
So how to change an Xib which doesn't use auto layout to use auto layout and add constraints?
