它只节省了几行,但我在 NSArray 上使用了一个类别。您需要确保您的块永远不会返回零,但除此之外,对于以下情况,它可以节省时间-[NSArray valueForKey:]
行不通的。
@interface NSArray (Map)
- (NSArray *)mapObjectsUsingBlock:(id (^)(id obj, NSUInteger idx))block;
@end
@implementation NSArray (Map)
- (NSArray *)mapObjectsUsingBlock:(id (^)(id obj, NSUInteger idx))block {
NSMutableArray *result = [NSMutableArray arrayWithCapacity:[self count]];
[self enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL *stop) {
[result addObject:block(obj, idx)];
}];
return result;
}
@end
用法很像-[NSArray enumerateObjectsWithBlock:]
:
NSArray *people = @[
@{ @"name": @"Bob", @"city": @"Boston" },
@{ @"name": @"Rob", @"city": @"Cambridge" },
@{ @"name": @"Robert", @"city": @"Somerville" }
];
// per the original question
NSArray *names = [people mapObjectsUsingBlock:^(id obj, NSUInteger idx) {
return obj[@"name"];
}];
// (Bob, Rob, Robert)
// you can do just about anything in a block
NSArray *fancyNames = [people mapObjectsUsingBlock:^(id obj, NSUInteger idx) {
return [NSString stringWithFormat:@"%@ of %@", obj[@"name"], obj[@"city"]];
}];
// (Bob of Boston, Rob of Cambridge, Robert of Somerville)