我有一个uitableview，它将一个图像存储在一个单元格中。它的图像从互联网上加载。问题是应用程序变慢，直到其图像从Internet加载。所以我想放置一个首先加载默认图像的机制，当它获得原始图像时，默认图像将被原始图像替换。
给我任何教程或任何示例代码。
提前致谢。
答案 0 :(得分：1)
通过其他线程获取您的图像....并使用通知或委托来跟踪图像下载中的任何更改...假设您正在使用通知....然后在您设置为观察者的类中通知重新加载tableView的数据....所以你的表图像将更新到有默认图像的地方....更多细节让我们举一个例子.....制作一个操作类来下载我们称之为的图像拇指....在这个例子中我制作了2个班级
1. PhotoGalleryVC显示拇指列表和每个拇指的一些细节
2. LoadGalleryThumbOp [操作=操作]下载拇指并在完成后发布通知
@protocol LoadGalleryThumbDelegate;
@interface LoadGalleryThumbOp : NSObject{
NSIndexPath* indexPathInTableView;
id <LoadGalleryThumbDelegate> delegate;
NSMutableData *activeDownload;
NSURLConnection *imageConnection;
NSString * documentPath;
BOOL imageDownload;
}
@property (nonatomic, assign) NSIndexPath* indexPathInTableView;
@property (nonatomic, retain) NSMutableData *activeDownload;
@property (nonatomic, retain) NSURLConnection *imageConnection;
@property (nonatomic, assign) id <LoadGalleryThumbDelegate> delegate;
@property (nonatomic, retain) NSString * documentPath;
@property (nonatomic) BOOL imageDownload;
- (void)startDownload;
- (void)cancelDownload;
- (void) persistData:(NSData*) data;
@end
@protocol LoadGalleryThumbDelegate
- (void)appImageDidLoad:(NSIndexPath *)indexPath;
@end
将其作为
@implementation LoadGalleryThumbOp
@synthesize year;
@synthesize indexPathInTableView;
@synthesize delegate;
@synthesize activeDownload;
@synthesize imageConnection,documentPath,imageDownload;
#pragma mark
- (void)startDownload
{
self.imageDownload = YES;
self.activeDownload = [NSMutableData data];
NSFileManager* fm = [NSFileManager defaultManager];
NSString* galleryDocumentPath = [self.documentPath stringByAppendingPathComponent:[NSString stringWithFormat:@"images/thumb.jpg"]];
if ([fm fileExistsAtPath:galleryDocumentPath])
{
UIImage *image = [[UIImage alloc] initWithContentsOfFile:galleryDocumentPath ];
self.gallery.thumpImage = image;
self.activeDownload = nil;
[image release];
self.imageConnection = nil;
[delegate appImageDidLoad:self.indexPathInTableView];
}
else {
NSURLConnection *conn = [[NSURLConnection alloc] initWithRequest:
[NSURLRequest requestWithURL:
[NSURL URLWithString:#error yourImageUrl]] delegate:self];
self.imageConnection = conn;
[conn release];
}
}
- (void)cancelDownload
{
[self.imageConnection cancel];
self.imageConnection = nil;
self.activeDownload = nil;
}
#pragma mark -
#pragma mark Download support (NSURLConnectionDelegate)
- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data
{
[self.activeDownload appendData:data];
}
- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error
{
self.activeDownload = nil;
self.imageConnection = nil;
self.imageDownload = NO;
[NSString stringWithFormat:@"images/thumb.jpg"]];
[delegate appImageDidLoad:self.indexPathInTableView];
}
- (void)connectionDidFinishLoading:(NSURLConnection *)connection
{
[self persistData:self.activeDownload];
self.activeDownload = nil;
self.imageConnection = nil;
[delegate appImageDidLoad:self.indexPathInTableView];
}
- (void) persistData:(NSData*) data
{
NSFileManager* fm = [NSFileManager defaultManager];
NSString* galleryDocumentPath = [self.documentPath stringByAppendingPathComponent:[NSString stringWithFormat:@"images/thumb.jpg"]];
if ([[NSFileManager defaultManager] fileExistsAtPath:galleryDocumentPath])
{
NSError* err = nil;
[fm removeItemAtPath:galleryDocumentPath error:&err];
if (err)
NSLog(@"%s:%@",__FUNCTION__,err);
}
[fm createFileAtPath:galleryDocumentPath contents:data attributes:nil];
}
此课程将下载您想要的图像，并在下载图像时调用其委托。
现在它在PhotoGalleryVC中的使用部分就像这样使用
@interface PhotoGalleryVC : UIViewController <LoadGalleryThumbDelegate>{
IBOutlet UITableView* albumListTableView;
NSMutableDictionary *imageDownloadsInProgress;
NSArray* allThumbs;
}
@property (nonatomic, retain) NSMutableDictionary *imageDownloadsInProgress;
- (void)appImageDidLoad:(NSIndexPath *)indexPath;
@end
在.m部分
- (void)viewDidLoad {
self.imageDownloadsInProgress = [NSMutableDictionary dictionary];
.....
}
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
NSFileManager* fm = [NSFileManager defaultManager];
NSString* galleryDocumentPath = [[NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) objectAtIndex:0] stringByAppendingPathComponent:[NSString stringWithFormat:@"Gallery/%@/images/thumb.jpg",[someObj.title stringByReplacingOccurrencesOfString:@" " withString:@"_" ]]];
//this above line is just make a seperate folder for each object and store thumbs of that object in that folder ... so make it unique some how
if (![fm fileExistsAtPath:galleryDocumentPath])
{
LoadGalleryThumbOp *galleryThumbDownloader = [imageDownloadsInProgress objectForKey:indexPath];
if (galleryThumbDownloader != nil && galleryThumbDownloader.imageDownload == NO)
{
[cell.activityIndicator stopAnimating];
cell.albumCoverImageView.image = [UIImage imageNamed:@"no_thumb.png"];
}
else {
[cell.activityIndicator startAnimating];
}
[self startIconDownload:temp forIndexPath:indexPath andYear:[NSString stringWithFormat:@"%d",selectedYear]];
}
else
{
[cell.activityIndicator stopAnimating];
cell.albumCoverImageView.image = [UIImage imageWithContentsOfFile:galleryDocumentPath];
}
return cell ;
}
//The following method see if there is already so downloader that is downloading same image then it simply do nothing else it create a downloader and start it
- (void)startIconDownload:(Gallery *)gallery forIndexPath:(NSIndexPath *)indexPath andYear:(NSString*)yr
{
LoadGalleryThumbOp *galleryThumbDownloader = [imageDownloadsInProgress objectForKey:indexPath];
if (galleryThumbDownloader == nil)
{
NSString* documentsPath = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) objectAtIndex:0];
NSString* nameWithoutSpace = [gallery.title stringByReplacingOccurrencesOfString:@" " withString:@"_" ];
NSString* galleryDocumentPath = [documentsPath stringByAppendingPathComponent:[NSString stringWithFormat:@"Gallery//%@",nameWithoutSpace]];
galleryThumbDownloader = [[LoadGalleryThumbOp alloc] init];
galleryThumbDownloader.documentPath = galleryDocumentPath;
galleryThumbDownloader.indexPathInTableView = indexPath;
galleryThumbDownloader.delegate = self;
[imageDownloadsInProgress setObject:galleryThumbDownloader forKey:indexPath];
[galleryThumbDownloader startDownload];
[galleryThumbDownloader release];
}
else if(galleryThumbDownloader.imageDownload == NO)
{
if (albumListTableView.dragging || albumListTableView.decelerating) {
[galleryThumbDownloader startDownload];
}
}
}
最后下载特定图像时调用的方法
- (void)appImageDidLoad:(NSIndexPath *)indexPath
{
CustomCellPhotoGalary* cell = (CustomCellPhotoGalary*)[albumListTableView cellForRowAtIndexPath:indexPath];
LoadGalleryThumbOp *galleryThumbDownloader = [imageDownloadsInProgress objectForKey:indexPath];
if (galleryThumbDownloader != nil)
{
if (galleryThumbDownloader.imageDownload)
{
[cell.activityIndicator stopAnimating];
NSString* documentsPath = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) objectAtIndex:0];
NSString* nameWithoutSpace = [temp.title stringByReplacingOccurrencesOfString:@" " withString:@"_" ];
NSString* galleryDocumentPath = [documentsPath stringByAppendingPathComponent:[NSString stringWithFormat:@"Gallery/%@",nameWithoutSpace]];
cell.albumCoverImageView.image = [UIImage imageWithContentsOfFile:galleryDocumentPath];
//galleryThumbDownloader = nil;
}
else {
[cell.activityIndicator stopAnimating];
cell.albumCoverImageView.image = [UIImage imageNamed:@"no_thumb.png"];
[self startIconDownload:temp forIndexPath:indexPath andYear:[NSString stringWithFormat:@"%d",selectedYear]];
}
[albumListTableView reloadData];
}
}
woooh .....！这就是一个例子的很多代码 注意：我删除了这么多行，所以这段代码可能不适用于你直接{可能有很多错误..}，但我希望你得到幕后的主要想法...... :)
答案 1 :(得分：0)
This示例代码很棒，它教会了我很多。 这使用ASIHttpRequest框架，如果您打算使用这种技术，我建议您使用here中的最新版本，因为示例代码中的版本现在已经很老了。
此示例代码可以帮助您自定义单元格委派等。
答案 2 :(得分：0)
根据上述情况，使用LazyTableImages总是更好。
给出here
的最佳示例