类似对象之间通信的静态变量
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04-10-2019 - |
题
我有一种异步下载图像的方法。如果图像与对象数组有关(我构建的应用程序中的常见用例),我想缓存它们。这个想法是,我传递了一个索引编号(基于我通过桌子的indexpath。浏览的桌子),然后将图像藏在静态的nsmutablearray中,并在我要处理的桌子的行上钥匙和。
因此:
@implementation ImageDownloader
...
@synthesize cacheIndex;
static NSMutableArray *imageCache;
-(void)startDownloadWithImageView:(UIImageView *)imageView andImageURL:(NSURL *)url withCacheIndex:(NSInteger)index
{
self.theImageView = imageView;
self.cacheIndex = index;
NSLog(@"Called to download %@ for imageview %@", url, self.theImageView);
if ([imageCache objectAtIndex:index]) {
NSLog(@"We have this image cached--using that instead");
self.theImageView.image = [imageCache objectAtIndex:index];
return;
}
self.activeDownload = [NSMutableData data];
NSURLConnection *conn = [[NSURLConnection alloc]
initWithRequest:[NSURLRequest requestWithURL:url] delegate:self];
self.imageConnection = conn;
[conn release];
}
//build up the incoming data in self.activeDownload with calls to didReceiveData...
- (void)connectionDidFinishLoading:(NSURLConnection *)connection
{
NSLog(@"Finished downloading.");
UIImage *image = [[UIImage alloc] initWithData:self.activeDownload];
self.theImageView.image = image;
NSLog(@"Caching %@ for %d", self.theImageView.image, self.cacheIndex);
[imageCache insertObject:image atIndex:self.cacheIndex];
NSLog(@"Cache now has %d items", [imageCache count]);
[image release];
}
我的索引可以通过,我可以通过我的NSLOG输出来看到这一点。但是即使在我的插入后:atindex:呼叫, [imageCache count]
永远不要离开零。
这是我第一次涉足静态变量,所以我想我做错了什么。
(上述代码大量修剪只能显示发生的事情的主要内容,因此在您看它时牢记这一点。)
解决方案
您似乎永远不会初始化 imageCache
可能很幸运有价值 0
. 。初始化最好在班级的初始化中进行,例如:
@implementation ImageDownloader
// ...
+(void)initialize {
imageCache = [[NSMutableArray alloc] init];
}
// ...
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