闭包可以作为Handler来使用。
When creating a
UIAlertAction object, we can specify a block of code as a handler.
The block of code will be executed when a user selects the action.
The block of code will be executed when a user selects the action.
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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