在 iPad 编程中使用多线程时出现问题（用于加载大量图像）

Question

我应该将大量图像加载到滚动视图上，我想这会花费一些时间和内存。因此，我使用了一个单独的线程在后台加载这些图像。我使用了以下多线程方法

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

在单独的线程上加载图像。在实现此方法时，我在 GDB 中收到以下消息，

NSAutoreleaseNoPool(): Object 0x10647180 of class NSPathStore2 autoreleased with no pool in place - just leaking
NSAutoreleaseNoPool(): Object 0x10647300 of class NSPathStore2 autoreleased with no pool in place - just leaking
NSAutoreleaseNoPool(): Object 0x10646a00 of class NSCFString autoreleased with no pool in place - just leaking
NSAutoreleaseNoPool(): Object 0x10647480 of class NSPathStore2 autoreleased with no pool in place - just leaking
NSAutoreleaseNoPool(): Object 0x10646a20 of class UIImage autoreleased with no pool in place - just leaking

我不知道这意味着什么，因为我以前从未执行过此方法。所以，我的问题是

1 - 我是否应该使用一些 autoRelease 池以及此方法

2 - 有没有其他方法可以加载大量图像而不需要大量负载主线程

-(IBAction)prepareSliderView{
NSLog(@"Preparing slider view");

NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];

int totalPages=[kbDataSource numberOfPagesInBook];
sliderScrollView = [[UIScrollView alloc] initWithFrame:CGRectMake(0, self.view.frame.size.height-300, self.view.frame.size.width,200 )];
sliderScrollView.contentSize = CGSizeMake(totalPages*150+((totalPages-1)*10), 200); 
sliderScrollView.backgroundColor=[[UIColor blackColor] colorWithAlphaComponent:1.0];
thumbnailContentView = [[UIView alloc] initWithFrame:CGRectMake(10, 0, sliderScrollView.contentSize.width, sliderScrollView.contentSize.height)];

newPageSlider.continuous=YES;
newPageSlider.minimumValue=1;
newPageSlider.maximumValue=totalPages;

 thumbnailFrame = CGRectMake(0, 25, 120, 150);
 pageNumFieldFrame = CGRectMake(0, thumbnailFrame.size.height+10, thumbnailFrame.size.width, 50);
for(int i=1;i<totalPages;i++){
    thumbnailView = [[UIView alloc] initWithFrame:thumbnailFrame];
    thumbnailView.backgroundColor=[UIColor clearColor];
    UIButton *thumbnail = [[UIButton alloc] initWithFrame:thumbnailFrame];
    UILabel *pageNumField = [[UILabel alloc] initWithFrame:pageNumFieldFrame];
    pageNumField.backgroundColor=[UIColor clearColor];
    thumbnail.tag=i+1;
    thumbnailView.tag=i+1;

    id<PageDataSource> pd = [kbDataSource pageAtIndex:i];

    thumbnailFrame = CGRectMake(thumbnailFrame.origin.x+150+10, thumbnailFrame.origin.y, 120, 150);
    pageNumFieldFrame = CGRectMake(pageNumFieldFrame.origin.x+150+10, pageNumFieldFrame.origin.y, thumbnailFrame.size.width, 50);
    [thumbnail setBackgroundImage:[pd thumbnailImageForPageNumber:i] forState:UIControlStateNormal];
    pageNumField.text =[NSString stringWithFormat:@"Page %d",i];
    pageNumField.textColor=[UIColor whiteColor];
    [thumbnailContentView addSubview:thumbnailView];
    [sliderScrollView addSubview:pageNumField];
    [sliderScrollView addSubview:thumbnail];
    [sliderScrollView addSubview:thumbnailView];
    [sliderScrollView bringSubviewToFront:thumbnail];
    [sliderScrollView bringSubviewToFront:pageNumField];
    [self.view bringSubviewToFront:thumbnail];
    [thumbnailView release];
    [pageNumField release];
    [thumbnail release];
    [thumbnail addTarget:self action:@selector(navigateToPage:) forControlEvents:UIControlEventTouchUpInside];
    [pool release];
}

}

Answer 1

对于您在新线程中通过 NSThread 或通过 performsSelectorInBackground: 执行的每个 main 方法，您必须创建一个像这样的自动释放池：

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

   // Do some work.

   // At the very end, release the pool.
   [pool release];
}

另请参阅： ​​为什么没有自动释放池当我执行 PerformSelectorInBackground

但对于您的任务，我建议您还查看 NSOperationQueue.例如，请参阅文章 Cocoa 教程：NSOperation 和 NSOperationQueue 。

Answer 2

作为 文档说：

aSelector 负责的方法
用于设置自动释放池
新分离的线程并释放
该池在退出之前

因此，在您的 prepareSliderView 方法中，您需要创建并释放一个自动释放池

NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];

// some work

[pool release];