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什么是NSComparisonResultNSComparator

我见过一种类型定义,类似这样的:

typedef NSComparisonResult (^NSComparator)(id obj1, id obj2);

它与函数指针有什么不同吗?

另外,我什至无法猜测^符号的含义。

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3 回答 3

22

^表示块类型,在概念上类似于函数指针。

typedef NSComparisonResult (^NSComparator)(id obj1, id obj2);
//          ^                      ^                ^
//   return type of block      type name       arguments

这意味着该类型NSComparator是一个,它接收两个类型idobj1and的对象obj2,并返回一个NSComparisonResult

具体NSComparator定义在Foundation Data Types 参考中

要了解有关 C 模块的更多信息,请查看这篇 ADC 文章Blocks Programming Topics

例子:

NSComparator compareStuff = ^(id obj1, id obj2) {
   return NSOrderedSame;
};

NSComparisonResult compResult = compareStuff(someObject, someOtherObject);
于 2010-11-07T15:10:08.567 回答
7

雅各布的回答很好,但是要回答关于“这与函数指针有何不同?”的部分:

1) 块不是函数指针。Blocks 是 Apple 关于如何在 C/C++/Objective-C 中使函数成为一等公民的方法。它是 iOS 4.0 的新功能。

2) 为什么要引入这个奇怪的概念?事实证明,一流的功能在很多场景中都很有用,例如管理可以并行执行的工作块,如在 Grand Central Dispatch 中。除了 GCD,该理论非常重要,以至于整个软件系统都基于它。Lisp 是最早的之一。

3) 你会在许多其他语言中看到这个概念,但名称不同。例如,Microsoft .Net 有 lambda 和委托(与 Objective-C 委托无关),而最通用的名称可能是匿名函数或第一类函数

于 2011-04-15T14:53:20.260 回答
0
NSComparisonResult comparisionresult;
NSString * alphabet1;
NSString * alphabet2;


// Case 1

alphabet1 = @"a";
alphabet2 = @"A";
comparisionresult = [alphabet1 caseInsensitiveCompare:alphabet2];

if (comparisionresult == NSOrderedSame)
    NSLog(@"a and a are same. And the NSComparisionResult Value is %ld \n\n", comparisionresult);
//Result: a and a are same. And the NSComparisionResult Value is 0

// Case 2
alphabet1 = @"a";
alphabet2 = @"B";
comparisionresult = [alphabet1 caseInsensitiveCompare:alphabet2];

if (comparisionresult == NSOrderedAscending)
    NSLog(@"a is greater than b. And the NSComparisionResult Value is %ld \n\n", comparisionresult);
//Result: a is greater than b. And the NSComparisionResult Value is -1

// Case 3
alphabet1 = @"B";
alphabet2 = @"a";
comparisionresult = [alphabet1 caseInsensitiveCompare:alphabet2];

if (comparisionresult == NSOrderedDescending)
    NSLog(@"b is less than a. And the NSComparisionResult Value is %ld", comparisionresult);

//Result: b is less than a. And the NSComparisionResult Value is 1
于 2016-01-15T10:57:45.233 回答