#import和 @class Differences in iOS

1. #import会包含这个类的所有信息, including entity variables and methods, and @class just tells the compiler that the name that is declared after it is the name of the class, at compile time, tell the compiler, this is a class name, no error.

2. In the header file, it is generally only necessary to know the name of the referenced class. There is no need to know the entity variables and methods inside, so it is common to use @class in the header file to declare that the name is the name of the class. In the implementation class, you need to use #import to include the header file of the referenced class, because it will use the internal entity variables and methods of the referenced class.

3. In terms of compilation efficiency, if you have 100 header files that #import the same head file, or if the files are referenced in turn, such as A–>b, B–>c, C–>d, and so on. When the first header file changes, all the subsequent classes that reference it need to be recompiled, which can take a lot of time if you have a lot of classes. Instead of using @class, you don't.

4. If there are cyclic dependencies, such as A–>b, b–>a such interdependencies, if the use of #import to each other, then there will be a compilation error, resulting in a dead loop problem. If you use @class to declare each other in a header file of two classes, there will be no compilation errors.

In summary [email protected] generally appear in the header file. #import一般出现在实现, in. M.

#import和 @class Differences in iOS