我有一个聊天应用程序。它发送消息和文本。目前我遇到一个问题，即从本地加载图像到表格单元格的速度问题。
首先，我将第一次下载的图像保存在文档目录中。然后我检查它是否已经存在。如果是，那么我在后台线程上从本地获取该图像，这使得我的滚动速度很快，但是当表的双端队列方法正在工作时然后 imageview 得到白色背景，片刻之后图像反射(reflect)在 imageview 中，这意味着从本地获取图像需要时间...... . . .
所以帮助我，我需要它和 whatsapp messanger 应用程序一样。
static NSString *simpleTableIdentifier = @"ZImageChatCell";
ZImageChatCell *cell = (ZImageChatCell *)[tableView dequeueReusableCellWithIdentifier:simpleTableIdentifier];
if (cell == nil)
{
NSArray *nib = [[NSBundle mainBundle] loadNibNamed:@"ZImageChatCell" owner:self options:nil];
cell = [nib objectAtIndex:0];
}
ChatMessageModel *messagemodel = [chatArray objectAtIndex:indexPath.row];
if([messagemodel.ismymessage boolValue])
{
NSData *imgdata = [Base64 decode:messagemodel.previewimage];
UIImage *effectImage = [UIImageEffects imageByApplyingLightEffectToImage:[UIImage imageWithData:imgdata]];
[cell.rightimageview setImage:effectImage];
BOOL imageexist = [self checkImageExistsInLocal:messagemodel.message];
if(imageexist)
{
dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0ul);
dispatch_async(queue, ^{
UIImage *tempimage = [self fetchImageFromLocal:messagemodel.message];
UIImage *newimage = [APPDELEGATE imageWithImage:tempimage scaledToFillSize:CGSizeMake(175, 175)];
dispatch_async(dispatch_get_main_queue(), ^{
cell.rightimageview.image = newimage;
});
});
}
else
{
if(messagemodel.message.length>0)
{
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), ^{
UIImage * imggot = [UIImage imageWithData:[NSData dataWithContentsOfURL:[NSURL URLWithString:messagemodel.message]]];
UIImage *newimage = [APPDELEGATE imageWithImage:imggot scaledToFillSize:CGSizeMake(175, 175)];
[self saveImageLocally:imggot withUrlString:messagemodel.message];
dispatch_async(dispatch_get_main_queue(), ^{
cell.rightimageview.image = newimage;
[cell.rightactivityloader stopAnimating];
});
});
}
}
}
else
{
NSData *imgdata = [Base64 decode:messagemodel.previewimage];
UIImage *effectImage = [UIImageEffects imageByApplyingLightEffectToImage:[UIImage imageWithData:imgdata]];
[cell.leftimageview setImage:effectImage];
BOOL imageexist = [self checkImageExistsInLocal:messagemodel.message];
if(imageexist)
{
dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0ul);
dispatch_async(queue, ^{
UIImage *tempimage = [self fetchImageFromLocal:messagemodel.message];
UIImage *newimage = [APPDELEGATE imageWithImage:tempimage scaledToFillSize:CGSizeMake(SCREEN_WIDTH, SCREEN_WIDTH)];
dispatch_async(dispatch_get_main_queue(), ^{
cell.leftimageview.image = newimage;
});
});
}
else
{
if(messagemodel.message.length>0)
{
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), ^{
UIImage * imggot = [UIImage imageWithData:[NSData dataWithContentsOfURL:[NSURL URLWithString:messagemodel.message]]];
UIImage *newimage = [APPDELEGATE imageWithImage:imggot scaledToFillSize:CGSizeMake(175, 175)];
[self saveImageLocally:imggot withUrlString:messagemodel.message];
dispatch_async(dispatch_get_main_queue(), ^{
cell.leftimageview.image = newimage;
[cell.leftactivityloader stopAnimating];
});
});
}
}
最佳答案
尝试制作 UIImageView 类别文件以从 url 下载图像，它会将文件保存在设备的缓存内存中，当你想再次加载该图像时，它将从缓存内存加载该图像。
UIImageView+Download.h
-(void)downloadFromURL:(NSString *)url withPlaceholder:(UIImage *)placehold;
UIImageView+Download.m
-(void)downloadFromURL:(NSString *)url withPlaceholder:(UIImage *)placehold
{
if (placehold) {
[self setImage:placehold];
}
if (url) {
//
if ([url rangeOfString:@"/Caches/"].location != NSNotFound) {
NSData *imageData=[NSData dataWithContentsOfFile:url];
UIImage* image = [[UIImage alloc] initWithData:imageData];
if (image) {
[self setImage:image];
[self setNeedsLayout];
}
return;
}
NSString *strImgName = [[[url stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding] componentsSeparatedByString:@"/"] lastObject];
NSString *imagePath = [NSString stringWithFormat:@"%@/%@",[self applicationCacheDirectoryString],strImgName];
NSFileManager *fileManager = [NSFileManager defaultManager];
NSString *aURL=[url stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding];
if ([fileManager fileExistsAtPath:imagePath]==NO)
{
dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0ul);
dispatch_async(queue, ^(void) {
NSData *imageData = [NSData dataWithContentsOfURL:[NSURL URLWithString:aURL]];
[imageData writeToFile:imagePath atomically:YES];
UIImage* image = [[UIImage alloc] initWithData:imageData];
if (image) {
dispatch_async(dispatch_get_main_queue(), ^{
[self setImage:image];
[self setNeedsLayout];
});
}
});
}
else{
NSData *imageData=[NSData dataWithContentsOfFile:imagePath];
UIImage* image = [[UIImage alloc] initWithData:imageData];
if (image) {
[self setImage:image];
[self setNeedsLayout];
}
}
}
}
- (NSString *)applicationCacheDirectoryString
{
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES);
NSString *cacheDirectory = ([paths count] > 0) ? [paths objectAtIndex:0] : nil;
return cacheDirectory;
}
在这里你只需要从你的类中调用这个方法
[cell.imageView downloadFromURL:YOUR_IMAGE_URL withPlaceholder:PLACEHOLDER_IMAGE];
这段代码对我有用
关于ios - 在聊天中加载图像，像 whatsapp 一样在本地保存得更快，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/36354256/