本文主要是介绍IT English Collection(17) of Selector，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！
1 前言
本文是一篇关于选择器（Selector）的文章，Selector可以理解为一个方法名，具体见下文。
转载请注明出处：http://blog.csdn.net/developer_zhang
2 详述
2.1 原文
A selector is the name used to select a method to execute for an object, or the unique identifier that replaces the name when the source code is compiled. A selector by itself doesn’t do anything. It simply identifies a method. The only thing that makes the selector method name different from a plain string is that the compiler makes sure that selectors are unique. What makes a selector useful is that (in conjunction with the runtime) it acts like a dynamic function pointer that, for a given name, automatically points to the implementation of a method appropriate for whichever class it’s used with. Suppose you had a selector for the method run, and classes Dog, Athlete, and ComputerSimulation (each of which implemented a method run). The selector could be used with an instance of each of the classes to invoke its run method—even though the implementation might be different for each.
Getting a Selector
Compiled selectors are of type SEL. There are two common ways to get a selector:
-
At compile time, you use the compiler directive
@selector.SEL aSelector = @selector(methodName); -
At runtime, you use the
NSSelectorFromStringfunction, where the string is the name of the method:SEL aSelector = NSSelectorFromString(@"methodName");You use a selector created from a string when you want your code to send a message whose name you may not know until runtime.
Using a Selector
You can invoke a method using a selector with performSelector: and other similar methods.
SEL aSelector = @selector(run); |
[aDog performSelector:aSelector]; |
[anAthlete performSelector:aSelector]; |
[aComputerSimulation performSelector:aSelector]; |
(You use this technique in special situations, such as when you implement an object that uses the target-action design pattern. Normally, you simply invoke the method directly.)
2.2 生词
plain [pleɪn] adj. 平的；简单的
conjunction [kən'dʒʌŋ(k)ʃ(ə)n] n. 结合；[语] 连接词
dynamic [daɪ'næmɪk] adj. 动态的；动力的
appropriate [ə'prəʊprɪət] adj. 适当的 vt. 占用；拨出
Athlete ['æθliːt] n. 运动员，体育家
directive [dɪ'rektɪv; daɪ-] n. 指示；指令
technique [tek'niːk] n. 技巧，技术
situations [ˌsitjuˈeiʃənz] n. 状况；情境
3 结语
以上是所有内容，希望对大家有所帮助。
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