An app consists of code you write and frameworks Apple provides. A framework contains a library of methods your app can call. More than one app can access a framework library at the same time.
Any app that you develop will link to multiple frameworks. You can take advantage of a framework through its application programming interface (API). The API, published in header files, specifies the available classes, data structures, and protocols. Apple writes frameworks that anticipate the basic features you might want to implement. You should use frameworks both to save time and effort and to make sure your code is efficient and secure. The system frameworks are the only way to access the underlying hardware.
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