NSComparisonResult和NSComparator-它们是什么?

^ 表示 块类型

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

这意味着 NSComparator 块 它接受两个类型的对象 id 打电话 obj1 和 obj2 ,并返回 NSComparisonResult .

明确地 N压缩机 定义在 Foundation Data Types reference

要了解更多关于C块的信息,请参阅这篇ADC文章 Blocks Programming Topics

例子:

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

NSComparisonResult compResult = compareStuff(someObject, someOtherObject);

雅各布的回答是好的,但是回答“这与函数指针有何不同?”:

1) 一个街区是 函数指针。方块是苹果公司在C/C++/Objtovi-C中实现功能第一类公民的方法。它对iOS 4是新的。

2) 为什么要引入这个奇怪的概念?事实证明,一级函数在很多场景中都很有用,例如管理可以并行执行的工作块,比如在Grand Central Dispatch中。除了GCD之外,这个理论非常重要,以至于整个软件系统都基于它。Lisp是第一个。

3) 您将在许多其他语言中看到这个概念,但名称不同。例如,Microsoft.Net有lambdas和delegates(与Objective-C委托没有关系),而最通用的名称可能是匿名函数或 first class functions .

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