When I develop an iOS app, I add a UITextField in the app UI programmatically. And I also add some constraints to the UITextField object in swift source code to make it auto layout. But when I run the app, it throws an exception with the error message ‘NSGenericException’, reason: ‘Unable to activate constraint with …
When i upgrade my Xcode to version 10.3 and build my iOS project, i meet an error message like this Failed to find or create execution context for description ‘<IBCocoaTouchPlatformToolDescription: 0x7fe0cfa54080> System content for IBCocoaTouchFramework-ElevenAndLater <IBScaleFactorDeviceTypeDescription: 0x7fe0cfa63cb0> scaleFactor=2x’. These intermediate objects were non-nil:. This error confused me a lot of time. But finally i find …
When i add swift constraints to button programmatically in source code, i meet an error message like this. [LayoutConstraints] Unable to simultaneously satisfy constraints. Probably at least one of the constraints in the following list is one you don’t want.
Swift optional variable is a variable that can have nil ( same to null ) value. And you do not need to initialize an optional variable before using it. If not initialized, the optional variable value is nil. It does not like none optional variable which you must assign an initial value before using it.
