如何將參數列表應用於Objective C中的塊？

Question

目標C是否有像Smalltalk的Block valueWithArguments這樣的功能？

我正在尋找一個函數像一個簽名：

apply(^(), NSArray* args) 

另外，有一個方法來調用過的參數列表中選擇？

Answer 1

有了塊，你可能需要做一些va_args魔法。調用可變參數的選擇器可以完成，但您可能需要一些幫助器使其不那麼痛苦。

NSObject的+ performSelectorWithArgsArray.h

@interface NSObject (performSelectorWithArgsArray) 
- (id)performSelector:(SEL)sel withArgsArray:(NSArray *)args; 
@end 

NSObject的+ performSelectorWithArgsArray.m

@implementation NSObject (performSelectorWithArgsArray) 
- (id)performSelector:(SEL)sel withArgsArray:(NSArray *)args { 
    NSInvocation *inv = [NSInvocation invocationWithMethodSignature: 
         [self methodSignatureForSelector:sel]]; 
    [inv setSelector:sel]; 
    [inv setTarget:self]; 
    for (int i = 0; i < args.count; i++) { 
    id a = [args objectAtIndex:i]; 
    [inv setArgument:&a atIndex:2 + i]; // 0 is target, 1 is cmd-selector 
    } 
    [inv invoke]; 

    NSNumber *r; 
    [inv getReturnValue:&r]; 
    return r; 
} 
@end 

，然後用它是這樣的：

#import "NSObject+performSelectorWithArgs.h" 

@interface SomeClass : NSObject 
@end 

@implementation SomeClass 
- (NSNumber *)withA:(NSNumber *)a withB:(NSNumber *)b { 
    return [NSNumber numberWithInt:a.intValue + b.intValue]; 
} 
@end 

- (void)someMethod { 
    SomeClass *a = [[SomeClass alloc] init]; 
    SEL sel = @selector(withA:withB:); 
    NSArray *args = [NSArray arrayWithObjects: 
        [NSNumber numberWithInt:2], 
        [NSNumber numberWithInt:3], 
        nil]; 
    NSNumber *r = [a performSelector:sel withArgsArray:args]; 
    NSLog(@"%d", r.intValue); 
} 

如果你選擇做這樣的事情我建議你真正閱讀NSInvocation如何工作，因爲它可以咬很難。不確定是否可以做到這一點，而不要求所有參數和返回值都是對象。

Answer 2

NSArray有方法enumerateObjectsUsingBlock:和enumerateObjectsWithOptions:usingBlock:是你在找什麼？

[[NSArray arrayWithObjects:@"a", @"b", @"c", nil] 
enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL *stop) { 
    NSLog(@"%d: %@", idx, obj); 
}];