Swift中的catch异常的一种写法。
do {
let results = try managedContext.execute(fetchRequest)
} catch let error as NSError { }
然后在下面就可以catch到error了~
Delegate
Each delegate is responsible for a specific role or task to keep the system simple and clean.Whenever an object needs to perform a certain task, it depends on another object to handle it. This is usually known as “separation of concerns” in software design.
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