Cocoa-Touch:performSelectorOnMainThread:奇怪的行为+崩溃

Question

我有一种情况,我懒得从www加载图像.
这是一个项目列表,当点击一个项目时,详细视图被推送到导航控制器.

在该详细视图中,该项目具有图像,该图像首先是默认图像,我想从URL开始加载它的图像.

所以我要做的是创建一个对象,一旦初始化就会分离一个新线程,然后加载内容,然后通知我的视图数据已加载:

// in MyLoader:
- (MyLoader *)initWithUrl:(NSURL *)url requester:(id)requester {
    self.url = url;
    self.requester = requester; // both are nonatomic, retain properties
    [self performSelectorInBackground:@selector(loadIt) withObject:nil];
}

- (void)loadIt {
    NSAutoreleasePool *arp = [[NSAutoreleasePool alloc] init];
    NSData *data = [NSData dataWithContentsOfURL:url];
    [requester performSelectorOnMainThread:@selector(dataReady) withObject:data waitUntilDone:YES;
    [arp release];
}

// in MyRequester:
- (void)somewhere {
    MyLoader *loader = [[[MyLoader] alloc] initWithUrl:someUrl requester:self] autorelease];
    // then I retain loader somewhere, it's more complicated but I have verified that it's properly retained.
}

几点说明:

1. 首先,我认为某些变量可能存在问题.我之前设置了一个断点performSelectorOnMainThread并确认了这一点data并且requester都没问题.

2. 然后我认为这是通过将NSData传递给线程引起的,所以我改变了withObject:nil.它仍然崩溃.

3. 当我进一步调查时,崩溃非常奇怪.我指定的waitUntilDone:YES,我已经放在一个断点在requester的dataReady.但是performSelectorOnMainThread调用返回(它到达断点之后),而没有到达内部的断点dataReady.BTW,- (void)dataReady:(NSData*)现在的身体只包含int x = 1;(放置一个断点).此外,我尝试过设置waitUntilDone:NO,它仍然崩溃.

4. 未执行选择器(未到达断点),但在调用后短时间内发生崩溃.

有谁知道什么是错的？

这是显而易见的,但要明确的是,如果我只是注释掉[requester performSelectorOnMainThread...部分,它就不会崩溃.

此外,这是一个堆栈跟踪,但它根本没有用.

#0  0x00a71004 in ___TERMINATING_DUE_TO_UNCAUGHT_EXCEPTION___ ()
#1  0x93436e3b in objc_exception_throw ()
#2  0x0028aca6 in __NSThreadPerformPerform ()
#3  0x00a098e1 in CFRunLoopRunSpecific ()
#4  0x00a08c48 in CFRunLoopRunInMode ()
#5  0x0005a78d in GSEventRunModal ()
#6  0x0005a852 in GSEventRun ()
#7  0x0168a003 in UIApplicationMain ()
#8  0x000028d4 in main (argc=1, argv=0xbffff100) at /Users/myName/Document/appName/main.m:14

Answer 1

你有:

[requester performSelectorOnMainThread:@selector(dataReady) withObject:data waitUntilDone:YES;

应该:

[requester performSelectorOnMainThread:@selector(dataReady:) withObject:data waitUntilDone:YES;

注意:@selector(dataReady :)(带冒号) 因为你正在向方法传递一个参数,所以假设数据准备就像这样:

- (void) dataReady:(NSData *)theData ...