NSTimer错误访问 [英] NSTimer bad access

问题描述

我尝试创建一个NSTimer，然后失效并释放它，然后将其设置为一个新的计时器。

I'm trying to create an NSTimer, then invalidate and release it, then set it to a new timer. However, I am getting an EXC_BAD_ACCESS when trying to set the timer member var again.

代码如下：

1）我设置定时器成员var（设置为保留）

1) I set the timer member var (it's set to retain)

self.mPageTimer = [NSTimer scheduledTimerWithTimeInterval:kPageTimerInterval target:self selector:@selector(pageTimerCallback) userInfo:nil repeats:NO];

2）我放开

    [mPageTimer invalidate];
    [mPageTimer release];

当我尝试再次调用步骤1中的代码段时，会导致崩溃，肯定为什么。我保留它通过设置它，然后我释放它，所以不应该对象被照顾和我的成员var确定设置为一个新的分配的计时器？

This results in the crash when I try to call the snippet in step 1 again, but I am not sure why. I retained it by setting it, and then I release it, so shouldn't the object be taken care of and my member var ok to set to a new allocated timer?

如果我这样做，它不会崩溃，工作正常：

If I do this, it doesn't crash and works fine:

    [mPageTimer invalidate];
    [mPageTimer release];
    mPageTimer = nil;

我看不到我在发布对象时做错了什么，因为，如果是这样，我应该不能总是将我的成员var设置为任何新创建的nstimer，泄漏或不是？

I can't see how I'm doing something wrong with releasing the object, because, regardless of if that were the case, shouldn't I be able to always set my member var to whatever newly created nstimer, leak or not?

推荐答案

可以放心，假设...

Is it safe to assume, that...

1. 代码段2）不是 c c 合成mPageTimer 和


2. 定时器的声明为 @property（nonatomic，retain）NSTimer * mPageTimer ？
   
   （无论是非原子的还是无关紧要的）

1. snippet 2) is not from the setter of the @property, but from another method while you
2. simply @synthesize mPageTimer and
3. the declaration for the timer is @property (nonatomic, retain) NSTimer* mPageTimer?
   (whether nonatomic or atomic doesn't matter)

如果是这种情况，您的崩溃是预期的：

If that's the case, your crash is expected:

create timer (timer retains you, timer is autoreleased!)
schedule timer (runloop retains the timer)
assignment through setter (you retain the timer)
... (time passes)
has it fired?
Yes:
    since your timer is non-recurring, the runloop has marked it
    as invalid and released it after invocation of "pageTimerCallback:"
calling "invalidate":
    has it fired?
    No:
        runloop unschedules and releases
    Yes:
        noop or release (read: "I don't know and admittedly don't care")
calling "release" (you are no longer the owner)
... (time passes)
assignment through synthesized setter:
    [newTimer retain];
    [oldTimer release]; // Crash due to overrelease!

简而言之：

如果定时器的属性提供您自己的setter并使每个访问都使用。

（允许两个例外：1.在dealloc中实现setter 2.在< c $ c> release 定时器*）

So in short:
If you have a property for a timer, provide your own setter and make every access use it.
(Two exceptions allowed: 1. implementation of the setter 2. in dealloc where you release the timer*)

（*不要使定时器失效， a href =http://stackoverflow.com/questions/4945028/repeating-nstimer-weak-reference-owning-reference-or-ivar/4946038#4946038>这是绝对的无意义 a>！）

(* Don't invalidate a timer that you're the target of in dealloc: It is absolutely pointless!)

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