iOS-NSComparisonResult和NSComparator介绍,比较,排序

什么是NSComparisonResult和NSComparator???

官方文档:https://developer.apple.com

typedef NS_ENUM(NSInteger, NSComparisonResult)
{
NSOrderedAscending = -1L, //值为－1
代表升序排列
NSOrderedSame, //值为0
NSOrderedDescending //值为1
待变降序排列
};

基础类库中声明了NSComparator块代码类型来进行两个条目的比较：
typedef NSComparisonResult (^NSComparator)(id obj1, id obj2);
NSComparator是一个块代码类型，并且使用两个对象作为参数，返回一个NSComparisonResult类型的值。它是NSSortDescriptor,NSArray,
和NSDictionary等类的方法的参数，用来进行排序.
比较

NSString *a = @"aaaA";//'A'的ASCII码值是65
NSString *b = @"aaaa";//'a'的ASCII码值是97
NSComparisonResult comparisonResult = [a compare:b];
if (comparisonResult == NSOrderedAscending) {
NSLog(@"b > a");
}
else if (comparisonResult == NSOrderedDescending)
{
NSLog(@"a > b");
}
else if (comparisonResult == NSOrderedSame)
{
NSLog(@"a = b");
}

NSLog(@"comparisonResult = %ld",comparisonResult);

//输出结果为－1，即：NSOrderedAscending。
//表示在两个字符串不相同，且第一个字符所在的字符串a比b的ASCII码值要小。

//比较
NSNumber *num1 = [[NSNumber alloc]initWithFloat:15.5];
NSNumber *num2 = [[NSNumber alloc]initWithFloat:15.5];

NSComparisonResult result = [num1 compare:num2];
if (result == NSOrderedSame) {
NSLog(@"a");
}
NSLog(@"result = %ld",result);

排序(升序)

NSArray *stringArray = [NSArray arrayWithObjects:@"abc 1", @"abc 21", @"abc 12",@"abc 13",@"abc 05",nil];
NSComparator sortBlock = ^(id string1, id string2)
{
return [string1 compare:string2];
};

//利用数组的sortedArrayUsingComparator调用 NSComparator ，obj1和obj2指的数组中的对象
NSArray *sortArray = [stringArray sortedArrayUsingComparator:sortBlock];
NSLog(@"sortArray = %@", sortArray);

//或者(升序)
NSArray *sortArray1 = [stringArray sortedArrayUsingComparator:^NSComparisonResult(id  _Nonnull obj1, id  _Nonnull obj2) {
return [obj1 compare:obj2];
}];
NSLog(@"sortArray1 = %@", sortArray1);

降序

NSArray *numArray = [NSArray arrayWithObjects:@1,@21,@12,@13,@05, nil];
NSArray *sortNumArray = [numArray sortedArrayUsingComparator: ^(id obj1, id obj2) {
if ([obj1 integerValue] > [obj2 integerValue]) {
return (NSComparisonResult)NSOrderedAscending;
}
if ([obj1 integerValue] < [obj2 integerValue]) {
return (NSComparisonResult)NSOrderedDescending;
}
return (NSComparisonResult)NSOrderedSame;
}];
NSLog(@"sortNumArray = %@",sortNumArray);