Question

在我的应用中，我使用UIImageView和UIScrollView来显示大量图片（每次有大约20张图片，每张图片大约600px * 500px，大小约为600kb）。< / p>

我使用此代码来完成此功能：

// Here is pictures Data;
self.klpArry = self.pictureData;

CGSize size = self.klpScrollView1.frame.size;
for (int i=0; i < [klpArr count]; i++) {
    UIImageView *iv = [[UIImageView alloc] initWithFrame:CGRectMake((size.width * i)+300, 20, 546, 546)];
    NSString *filePath = [[NSBundle mainBundle] pathForResource:[klpArr objectAtIndex:i] ofType:@"jpg"];
    UIImage *imageData = [[UIImage alloc]initWithData:[NSData dataWithContentsOfFile:filePath]];
    [iv setImage:imageData];   
    iv.backgroundColor = [UIColor grayColor];
    [self.klpScrollView1 addSubview:iv];
    imageData = nil;
    iv = nil;
    iv.image = nil;
    filePath = nil;
    [imageData release];
    [filePath release];
    [iv release];
}
    // show the picture in scrollview;
[self.klpScrollView1 setContentSize:CGSizeMake(size.width * numImage, size.height)];
self.klpScrollView1.pagingEnabled = YES;
self.klpScrollView1.showsHorizontalScrollIndicator = NO;
self.klpScrollView1.backgroundColor = [UIColor grayColor];

但每次初始化此功能时，内存将增加约5MB。实际上我发布了UIImageView，UIimage和UIScrollView（vi.image=nil, [vi release]）但是它不起作用，分配的内存没有被释放。顺便说一句，我首先使用我朋友的代码vi.image = nil然后vi = nil;，但图片没有显示在滚动视图上。

Answer 1

正如我所看到的，主要问题是你将局部变量设置为nil，然后继续尝试在release等方法中使用这些局部变量，但因为它们已被设置为nil，这些方法现在什么都不做，而且retainCount（或现在为+2，因为你已将它们添加到视图中）的对象永远不会被释放。

因此，我建议如下：

//Here is pictures Data;
self.klpArry = self.pictureData;

CGSize size = self.klpScrollView1.frame.size;
for (int i=0; i < [klpArr count]; i++) {
    UIImageView *iv = [[UIImageView alloc] initWithFrame:CGRectMake((size.width * i)+300, 20, 546, 546)];
    NSString *filePath = [[NSBundle mainBundle] pathForResource:[klpArr objectAtIndex:i] ofType:@"jpg"];
    UIImage *imageData = [[UIImage alloc]initWithData:[NSData dataWithContentsOfFile:filePath]];
    [iv setImage:imageData];   
    iv.backgroundColor = [UIColor grayColor];
    [self.klpScrollView1 addSubview:iv];

    // Don't set these to nil, or else subsequent release statements do nothing!
    // These statements are actually not necessary because they refer to local
    // variables so you don't need to worry about dangling pointers. Make sure
    // you're not confusing the purpose of setting a pointer to nil in ARC to 
    // what you're doing in your non-ARC code.
    //
    // imageData = nil;
    // iv = nil;

    // You don't want to set this to nil because if iv is not nil, your image
    // will be removed from your imageview. So, not only is this not needed,
    // but it's undesired.
    //
    // iv.image = nil;

    // This statement is not necessary for the same reason you don't do it
    // to imageData or iv, either. This is probably even worse, though, because
    // filePath is not a variable that you initialized via alloc. You should 
    // only be releasing things you created with alloc (or new, copy, mutableCopy,
    // for which you issued a retain statement).
    //
    // filePath = nil;

    [imageData release];

    // filePath is a +0 retainCount already, so don't release. You only release
    // those items for which you increased retainCount (e.g. via new, copy, 
    // mutableCopy, or alloc or anything you manually retained).
    //
    // [filePath release];

    [iv release];
}

// show the picture in scrollview;
[self.klpScrollView1 setContentSize:CGSizeMake(size.width * numImage, size.height)];
self.klpScrollView1.pagingEnabled = YES;
self.klpScrollView1.showsHorizontalScrollIndicator = NO;
self.klpScrollView1.backgroundColor = [UIColor grayColor];

因此，您的代码将被简化（并更正），可能只是：

//Here is pictures Data;
self.klpArry = self.pictureData;

CGSize size = self.klpScrollView1.frame.size;
for (int i=0; i < [klpArr count]; i++) {
    UIImageView *iv = [[UIImageView alloc] initWithFrame:CGRectMake((size.width * i)+300, 20, 546, 546)];
    NSString *filePath = [[NSBundle mainBundle] pathForResource:[klpArr objectAtIndex:i] ofType:@"jpg"];
    UIImage *imageData = [[UIImage alloc] initWithData:[NSData dataWithContentsOfFile:filePath]];
    [iv setImage:imageData];   
    iv.backgroundColor = [UIColor grayColor];
    [self.klpScrollView1 addSubview:iv];
    [imageData release];
    [iv release];
}

// show the picture in scrollview;
[self.klpScrollView1 setContentSize:CGSizeMake(size.width * numImage, size.height)];
self.klpScrollView1.pagingEnabled = YES;
self.klpScrollView1.showsHorizontalScrollIndicator = NO;
self.klpScrollView1.backgroundColor = [UIColor grayColor];

或者您可以通过autorelease：

进一步简化代码

//Here is pictures Data;
self.klpArry = self.pictureData;

CGSize size = self.klpScrollView1.frame.size;
for (int i=0; i < [klpArr count]; i++) {
    UIImageView *iv = [[[UIImageView alloc] initWithFrame:CGRectMake((size.width * i)+300, 20, 546, 546)] autorelease];
    NSString *filePath = [[NSBundle mainBundle] pathForResource:[klpArr objectAtIndex:i] ofType:@"jpg"];
    UIImage *imageData = [[[UIImage alloc] initWithData:[NSData dataWithContentsOfFile:filePath]] autorelease];
    [iv setImage:imageData];   
    iv.backgroundColor = [UIColor grayColor];
    [self.klpScrollView1 addSubview:iv];
}

// show the picture in scrollview;
[self.klpScrollView1 setContentSize:CGSizeMake(size.width * numImage, size.height)];
self.klpScrollView1.pagingEnabled = YES;
self.klpScrollView1.showsHorizontalScrollIndicator = NO;
self.klpScrollView1.backgroundColor = [UIColor grayColor];

顺便说一下，声明（autorelease）：

UIImage *imageData = [[[UIImage alloc] initWithData:[NSData dataWithContentsOfFile:filePath]] autorelease];

可能会简化为：

UIImage *imageData = [UIImage imageWithContentsOfFile:filePath];

这会从您的文件中为您提供UIImage，其中包含+0 retainCount（即您不必release）。

所以，最后几点意见：

你真的应该回顾和研究Advanced Memory Management Programming Guide。如果您不熟悉内存管理，那就是密集阅读，但掌握这些概念（特别是在非ARC代码中）至关重要。
如果还没有，我建议您通过静态分析器运行代码（“产品” - “分析”或 shift + 命令 + 乙）。如果分析仪无法识别出许多（如果不是大多数）这些问题，我会感到惊讶。通过分析仪运行代码时，应该没有警告。
如果您希望将其提升到新的水平，您可能希望对内存管理更加保守。管理原则是一个系统设计，它只在任何给定时间加载UI所需的图像，这不仅涉及calvinBhai对延迟加载图像的出色建议（即在你的UI 真的需要它们），但是一旦它们滚出屏幕，它们也会主动释放图像。也许你不需要在你的应用程序中担心它，因为你一次只处理20张图像，但如果你的任何投资组合/画廊扩展到100或1000张图像，那么保留所有这些图像的想法在任何给定时间记忆只是一个坏主意。这是一个更高级的概念，因此您可能首先应关注现有代码的基本内存管理问题，但从长远来看，您可能需要考虑延迟加载和主动释放图像。

Answer 2

如果你担心记忆，

尝试延迟加载图片=加载可见图片，下一张和上一张图片。您不必将所有图像添加到klpscrollview。

一旦你弄清楚将图像延迟加载到滚动视图上，那么你可以考虑修复未在滚动视图上显示的图像。

更容易搜索“lazy load uiimage uiscrollview”

UIImageView和UIScrollView加载了很多图片

2 个答案: