About precompile prefix Header

In xcode Project Properties> build settings, the precompile prefix header is used to identify whether pre-compiled header files are used, and the prefix header is used to identify PCH files.

The content of the prefix. PCH file is as follows:

# Ifdef _ objc __

# Import <Foundation/Foundation. h>

# Import <uikit/uikit. h>

# Endif

Use the _ objc _ macro definition to ensure that files referenced in the macro are referenced only by files written in the objc language.

If the precompile prefix header is yes, PCH will be pre-compiled, and the pre-compiled PCH file will be cached to increase the compilation speed.

If the precompile prefix header is no, PCH will not be precompiled. Instead, it will be compiled once in every. M file of the framework class library that uses it for import.
For example, if the above PCH file references the uikit class library, you do not need to reference it in other SWIFT classes.

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About precompile prefix Header