我正在寻找有关如何将从URL加载的图像缓存到uitableview单元格中的教程。
我在这里找到了一个示例:
http://www.ericd.net/2009/05/iphone-caching-images-in-memory.html#top
但是代码不完整。我是一个Objective-C新手,所以发现很难填补缺失的部分。
我正在寻找有关如何将从URL加载的图像缓存到uitableview单元格中的教程。
我在这里找到了一个示例:
http://www.ericd.net/2009/05/iphone-caching-images-in-memory.html#top
但是代码不完整。我是一个Objective-C新手,所以发现很难填补缺失的部分。
这里是使用NSCache实现的简单ImageCache,它是一个单例。
ImageCache.h
#import <Foundation/Foundation.h>
@interface ImageCache : NSObject
@property (nonatomic, retain) NSCache *imgCache;
#pragma mark - Methods
+ (ImageCache*)sharedImageCache;
//- (void) AddImage:(NSString *)imageURL: (UIImage *)image;
- (void) AddImage:(NSString *)imageURL withImage:(UIImage *)image;
- (UIImage*) GetImage:(NSString *)imageURL;
- (BOOL) DoesExist:(NSString *)imageURL;
@end
ImageCache.m
#import "ImageCache.h"
@implementation ImageCache
@synthesize imgCache;
#pragma mark - Methods
static ImageCache* sharedImageCache = nil;
+(ImageCache*)sharedImageCache
{
@synchronized([ImageCache class])
{
if (!sharedImageCache)
sharedImageCache= [[self alloc] init];
return sharedImageCache;
}
return nil;
}
+(id)alloc
{
@synchronized([ImageCache class])
{
NSAssert(sharedImageCache == nil, @"Attempted to allocate a second instance of a singleton.");
sharedImageCache = [super alloc];
return sharedImageCache;
}
return nil;
}
-(id)init
{
self = [super init];
if (self != nil)
{
imgCache = [[NSCache alloc] init];
}
return self;
}
// - (void) AddImage:(NSString *)imageURL: (UIImage *)image
- (void) AddImage:(NSString *)imageURL withImage:(UIImage *)image
{
[imgCache setObject:image forKey:imageURL];
}
- (NSString*) GetImage:(NSString *)imageURL
{
return [imgCache objectForKey:imageURL];
}
- (BOOL) DoesExist:(NSString *)imageURL
{
if ([imgCache objectForKey:imageURL] == nil)
{
return false;
}
return true;
}
@end
例子
UIImage *image;
// 1. Check the image cache to see if the image already exists. If so, then use it. If not, then download it.
if ([[ImageCache sharedImageCache] DoesExist:imgUrl] == true)
{
image = [[ImageCache sharedImageCache] GetImage:imgUrl];
}
else
{
NSData *imageData = [[NSData alloc] initWithContentsOfURL: [NSURL URLWithString: imgUrl]];
image = [[UIImage alloc] initWithData:imageData];
// Add the image to the cache
//[[ImageCache sharedImageCache] AddImage:imgUrl :image];
[[ImageCache sharedImageCache] AddImage:imgUrl withImage:image];
}
git clone http://ezekiel.vancouver.wsu.edu/~cs458/demos/YellowJackets/.git
链接 - wcochran我写了这个(其中的概念和一些代码来自于Lane Roathe的优秀UIImageView+Cache类别),用于我正在开发的一个应用程序。它也使用了ASIHTTPRequest类,这些类非常棒。这个程序肯定还有改进的空间...例如,如果不再需要,可以允许取消请求,或者利用通知userInfo来允许更精确的UI更新...但是对于我的目的来说,它已经很好地工作了。
@implementation ImageFetcher
#define MAX_CACHED_IMAGES 20
static NSMutableDictionary* cache = nil;
+ (void)asyncImageFetch:(UIImage**)anImagePtr withURL:(NSURL*)aUrl {
if(!cache) {
cache = [[NSMutableDictionary dictionaryWithCapacity:MAX_CACHED_IMAGES] retain];
}
UIImage* newImage = [cache objectForKey:aUrl.description];
if(!newImage) { // cache miss - doh!
ASIHTTPRequest *imageRequest = [ASIHTTPRequest requestWithURL:aUrl];
imageRequest.userInfo = [NSDictionary dictionaryWithObject:[NSValue valueWithPointer:anImagePtr] forKey:@"imagePtr"];
imageRequest.delegate = self;
[imageRequest setDidFinishSelector:@selector(didReceiveImage:)];
[imageRequest setDidFailSelector:@selector(didNotReceiveImage:)];
[imageRequest startAsynchronous];
}
else { // cache hit - good!
*anImagePtr = [newImage retain];
}
}
+ (void)didReceiveImage:(ASIHTTPRequest *)request {
NSLog(@"Image data received.");
UIImage **anImagePtr = [(NSValue*)[request.userInfo objectForKey:@"imagePtr"] pointerValue];
NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
UIImage *newImage = [[UIImage imageWithData:[request responseData]] retain];
if(!newImage) {
NSLog(@"UIImageView: LoadImage Failed");
}
else {
*anImagePtr = newImage;
// check to see if we should flush existing cached items before adding this new item
if( [cache count] >= MAX_CACHED_IMAGES)
[cache removeAllObjects];
[cache setValue:newImage forKey:[request url].description];
NSNotificationCenter *nc = [NSNotificationCenter defaultCenter];
[nc postNotificationName: @"ImageDidLoad" object: self userInfo:request.userInfo];
}
[pool drain];
}
你可以这样调用这段代码:
[ImageFetcher asyncImageFetch:&icon withURL:url];
我也在使用通知,好或不好都会让相应 UIImage 的所有者知道何时应该重新显示 - 在这种情况下,它是在 tableView 上下文中:
- (void)viewDidLoad {
[super viewDidLoad];
NSNotificationCenter *nc = [NSNotificationCenter defaultCenter];
[nc addObserver:self selector:@selector(imageDidLoad:) name:@"ImageDidLoad" object:nil];
}
- (void)imageDidLoad:(NSNotification*)notif {
NSLog(@"Received icon load notification.");
// reload table view so that new image appears.. would be better if I could
// only reload the particular UIImageView that holds this image, oh well...
[self.tableView reloadData];
}
- (void)dealloc {
NSNotificationCenter *nc = [NSNotificationCenter defaultCenter];
[nc removeObserver:self];
// ...
}