NSTimer 类别 +阻止实现以替换选择器

Question

我对块和 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，它将接收一个块作为参数，并且该块将在选择器调用中使用。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] * 由于以下原因终止应用程序未捕获的异常 'NSInvalidArgumentException'，原因：'+[NSTimer theBlock]：无法识别的选择器发送到类 0x7fff70bb0a18'

我怎样才能使这个类别工作？

Answer 1

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。

使用块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，因为没有释放块的好点。

---

使用关联引用的早期方法

您可以使用 关联引用将块附加到 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

Answer 2

利用 userInfo 来承载你的区块怎么样？ （这是用ARC完成的）

void (^callback)(void) = ^{
    NSLog(@"do stuff");
}

NSTimer *timer = [NSTimer timerWithTimeInterval:10.0 target:self selector:@selector(handleTimeout:) userInfo:[NSDictionary dictionaryWithObject:[callback copy] forKey:@"block"] repeats:NO];
[[NSRunLoop currentRunLoop] addTimer:timer forMode:NSDefaultRunLoopMode];

然后添加静态选择器：

+ (void)handleTimeout:(NSTimer *)timer
{
    void (^callback)(void) = [timer.userInfo objectForKey:@"block"];
    callback();

    [timer invalidate];
    timer = nil;
};

Answer 3

这应该可行：

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

问题是您将新 NSTimer 实例的目标设置为 self。但是，在 + ScheduleTimerWithTimeInterval:repeats:actions: 的上下文中（注意 +），self 是 NSTimer ，而不是（正如您可能认为的那样）新创建的 NSTimer 实例。

从错误消息中可以看出，您的应用程序崩溃是因为 NSTimer 没有响应类方法 + theBlock，这当然是正确的，因为您只定义了实例方法- theBlock。