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中，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];

以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这个方法。所以，我的问题是

1-我应该使用一些autoRelease池和这个方法吗

2-有没有其他方法可以加载大量图像而不在主线程中加载大量图像

-(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performsSelectorInBackground:执行的每个main方法，您必须创建一个自动释放池，如下所示：

- (void)myBackgroundOperation
{
   NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
   // Do some work.
   // At the very end, release the pool.
   [pool release];
}

另请参阅：当我执行SelectInBackground 时，为什么没有自动释放池

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

Answer 2

正如文档所说：

方法aSelector负责用于为设置自动释放池新分离的线程和释放在退出之前

因此，在prepareSliderView方法中，您需要创建并发布一个自动释放池：

NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
// some work
[pool release];