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 error message ‘NSGenericException’, reason: ‘Unable to activate constraint with anchors, …
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 …
Swift optional variable is a variable which can has nil ( same to null ) value. And you do not need to initialize an optional variable before use it. If not initialized, the optional variable value is nil. It dose not like none optional variable which you must assign an initial value before using it.
