我对 block 和 Objective-C 很陌生，我正在尝试使用两者来编写我的第一个类别。我的想法是在 NSTimer 上创建一个类别，它将接收一个 block 作为参数，这个 block 将用于选择器调用。现在我有这个。

// NSTimer+Additions.h

#import <Foundation/Foundation.h>

typedef void (^VoidBlock)();

@interface NSTimer (NSTimer_Additions)


+ (NSTimer *)scheduleTimerWithTimeInterval:(NSTimeInterval)theSeconds repeats:(BOOL)repeats actions:(VoidBlock)actions;
@end

#import "NSTimer+Additions.h"

static VoidBlock _voidBlock;

@interface NSTimer (AdditionsPrivate) // Private stuff
- (void)theBlock;
@end


@implementation NSTimer (NSTimer_Additions)


+ (NSTimer *)scheduleTimerWithTimeInterval:(NSTimeInterval)theSeconds repeats:(BOOL)repeats actions:(VoidBlock)actions {

    [_voidBlock release];
    _voidBlock = [actions copy];

    NSTimer* timer = [[NSTimer alloc] initWithFireDate:[NSDate date] 
                                          interval:theSeconds
                                            target:self 
                                          selector:@selector(theBlock) 
                                          userInfo:nil 
                                           repeats:repeats];
    [timer fire];

    return [timer autorelease];
}


- (void)theBlock {
    _voidBlock();
}

@end

代码要点:https://gist.github.com/1065235

一切都编译正常，但我有以下错误:

2011-07-05 14:35:47.068 TesteTimer[37716:903] * 由于未捕获的异常“NSInvalidArgumentException”而终止应用程序，原因:“+[NSTimer theBlock]:无法识别的选择器发送到类 0x7fff70bb0a18'

我怎样才能让这个类别发挥作用？

最佳答案

除了错误的目标之外，您的主要缺陷是您使用了静态变量。您将无法支持超过一个计时器。

使用 block 作为调用方法的参数。

@interface NSTimer (AdditionsPrivate) // Private stuff
- (void)theBlock:(VoidBlock)voidBlock;
@end


@implementation NSTimer (NSTimer_Additions)

+ (NSTimer *)scheduledTimerWithTimeInterval:(NSTimeInterval)theSeconds repeats:(BOOL)repeats actions:(VoidBlock)actions {
    NSInvocation * invocation = [NSInvocation invocationWithMethodSignature:[self instanceMethodSignatureForSelector:@selector(theBlock:)]];
    NSTimer * timer = [NSTimer scheduledTimerWithTimeInterval:theSeconds
                                                   invocation:invocation
                                                      repeats:repeats];
    [invocation setTarget:timer];
    [invocation setSelector:@selector(theBlock:)];
    
    Block_copy(actions);
    [invocation setArgument:&actions atIndex:2];
    Block_release(actions);

    return timer;
}


- (void)theBlock:(VoidBlock)voidBlock {
    voidBlock();
}

@end

使用关联引用的问题是泄漏，因为没有释放 block 的好点。

使用关联引用的早期方法

您可以使用 associative references将 block 附加到 NSTimer 的特定实例。

@implementation NSTimer (NSTimer_Additions)

+ (NSTimer *)scheduledTimerWithTimeInterval:(NSTimeInterval)theSeconds repeats:(BOOL)repeats actions:(VoidBlock)actions {
    NSInvocation * invocation = [NSInvocation invocationWithMethodSignature:[self instanceMethodSignatureForSelector:@selector(theBlock)]];
    NSTimer * timer = [NSTimer scheduledTimerWithTimeInterval:theSeconds
                                                   invocation:invocation
                                                      repeats:repeats];
    [invocation setTarget:timer];
    [invocation setSelector:@selector(theBlock)];

    objc_setAssociatedObject(timer, @"Block", actions, OBJC_ASSOCIATION_COPY);
    
    return timer;
}


- (void)theBlock {
    VoidBlock _voidBlock = (VoidBlock)objc_getAssociatedObject(self, @"Block");
    _voidBlock();
}

@end

关于ios - NSTimer Category + Blocks 替换选择器的实现，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/6586662/