Question

我有一个小型iPhone应用程序，第一个视图上有一个按钮。当我选择这个按钮时，我加载了我的新视图，上面有一个图像。我目前正在使用以下代码在单独的线程上从在线源加载图像，同时允许用户继续控制应用程序：

- (void) loadImageTest
{
    NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];

    NSURL *url = [[NSURL alloc] init];
    url = [NSURL URLWithString:logoPath];

    NSData *data = [[NSData alloc] init];
    data = [NSData dataWithContentsOfURL:url];

    loadingImage = [UIImage imageWithData:data];
    titleLogoImage.image = loadingImage;

    //[pool drain];
    [pool release];
}

这是从新视图的init：

中的这行代码调用的

[NSThread detachNewThreadSelector:@selector(loadImageTest) toTarget:self withObject:nil];

现在这个工作正常（ish），但如果我关闭新视图，然后快速连续再次加载一个新视图（或者在某些情况下只是后续），它将使用经典的EXC_BAD_ACCESS弹出。我确信这是由于线程池中的代码，但任何人都可以看到为什么会发生这种情况？

由于

Answer 1

此致：

//这没关系，您可以尝试使用NSURLConnections异步方法而不是制作 //你自己的线程 [NSThread detachNewThreadSelector：@selector（loadImageTest）toTarget：self withObject：nil];

- (void)loadImageTest
{
    // This is fine
    NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
    // you're making and then abandoning this url object so it will leak
    NSURL *url = [[NSURL alloc] init];
    // this is fine
    url = [NSURL URLWithString:logoPath];
    // again making and abandoning an object
    NSData *data = [[NSData alloc] init];
    data = [NSData dataWithContentsOfURL:url];
    // this works, but is not thread safe,
    // can't operate on UIKit objects off the
    // main thread
    loadingImage = [UIImage imageWithData:data];
    titleLogoImage.image = loadingImage;
    // this is fine
    //[pool drain];
    [pool release];
}

清理以使线程安全等等。应该有所帮助：

// I'm assuming you have a iVar for logoPath but we don't want to
// make threaded calls to an iVar (it's not mutable, so you could do it, but it's just bad form)
// If i'm wrong about logoPath being an iVar don't sweat copying it.
- (void)whateverMethodYouWant
{
    NSString *aLogoPath = [[logoPath copy] autorelease];
    [NSThread detachNewThreadSelector:@selector(loadImageForPath:) toTarget:self withObject:aLogoPath];
}
- (void)loadImageForPath:(NSString *)aLogoPath
{
    NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];

    NSData *data = [NSData dataWithContentsOfURL:[NSURL URLWithString:aLogoPath]];
    // the performSelector will retain the data until the method can be performed
    [self performSelectorOnMainThread:@selector(setImageForTitleLogo:) withObject:imgData waitUntilDone:NO];

    [pool release];
}
- (void)setImageForTitleLogo:(NSData *)imgData
{
    // This part is not strictly necessary
    // but it's a nice way to wrap a method that needs to happen on the main thread.
    if ([NSThread isMainThread])
    {
        // make the image (i'm assuming you meant loadingImage to be a local scope variable)
        UIImage *loadingImage = [UIImage imageWithData:imgData];
        // make sure the button still exists 
        // also make sure you're setting any references to this button to nil when you're releasing and making new views
        // so that you're not addressing a button that's been released
        // (assigning the image to the button will cause the button to retain it for you)
        if (titleLogoImage != nil)
            titleLogoImage.image = loadingImage;
    }
    else
    {
        [self performSelectorOnMainThread:@selector(setImageForTitleLogo:) withObject:imgData waitUntilDone:NO];
    }
}

Answer 2

你做的很奇怪。

NSURL *url = [[NSURL alloc] init];

表示您创建了一个NSURL对象，您拥有该对象。

url = [NSURL URLWithString:logoPath];

这意味着您创建另一个 NSURL对象，该对象已自动释放。您刚刚创建的NSURL，只是泄漏。这里的NSData也是如此。

loadingImage必须由titleLogoImage保留，否则将在NSAutoReleasePool的排水管上取消分配。什么是titleLogoImage并保留image？

编辑 ps：还有什么打扰了我，loadingImage并不局限于函数的范围。简而言之：

NSURL *url = [NSURL URLWithString:logoPath];
NSData *data = [NSData dataWithContentsOfURL:url];
titleLogoImage.image = [UIImage imageWithData:data];

至少可以省去一些麻烦。

Answer 3

发布的代码中没有任何内容会触发崩溃。根据titleLogoImage的定义方式，它可能会受到自动释放的影响。

但是，beyond the problems outlined by mvds，您对本地化自动释放池没有迫切需求。它在这里什么也不做，但会给你带来麻烦。

自动释放池很危险，不适合初学者。他们将杀死其中的任何自动释放的对象。通常，只有在快速创建大量内存密集型对象时才创建自己的池。这似乎不是这种情况。

尽管给予了关注，但很少使用自定义池。经过十多年的Apple API工作，我可以指望我使用自己的自定义池的次数。

iPhone上的NSAutoreleasePool问题

3 个答案: