iOS UIImage DownLoad图片的下载缓存全部在此

         iOS图片的下载缓存全部在此
分类： iOS编程 -- : 2075人阅读 评论() 收藏 举报
注意: 我的文章只写给自己看
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(一)这部分(感觉out了), 但是还是保留,  算是学习的痕迹.
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()最简单的下载,显示图片的方法:
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   UIImageView *imageView = [[UIImageView alloc] initWithFrame:[self.view bounds]];
   imageView.image = [self loadImageFromUrl:@"http://storage.live.com/items/72A00BF5A838647C!1616?filename=meinv004.jpg"];
   [self.view addSubview:imageView];  

   -(UIImage*)loadImageFromUrl: (NSString*)url
{
    NSURL  *imageUrl = [NSURL URLWithString:url];
    NSData *imageData = [NSData dataWithContentsOfURL:imageUrl];
    UIImage *image = [UIImage imageWithData:imageData];
    return image;
}  

这种最简单的图片加载方式阻塞了main线程. 使得流程不能流畅进行.

()开辟线程来解决这个问题.

[plain] view plaincopy
   // set imageview
   UIImageView *imageView = [[UIImageView alloc] initWithFrame:[self.view bounds]];
   imageView.backgroundColor = [UIColor yellowColor];
   imageView.tag = imageView_tag;
   [self.view addSubview:imageView];  

   // load image in background
   NSString *url = IMAGE_URL;
   [self performSelectorInBackground:@selector(loadImageFromUrl:) withObject:url];  

-(void)loadImageFromUrl: (NSString*)url {
    NSURL  *imageUrl = [NSURL URLWithString:url];
    NSData *imageData = [NSData dataWithContentsOfURL:imageUrl];
    [self performSelectorOnMainThread:@selector(updateImageView:) withObject:imageData waitUntilDone:NO];
}
-(void) updateImageView:(NSData*) data {
    UIImageView *imageView = (UIImageView *)[self.view viewWithTag:imageView_tag];
    imageView.image = [UIImage imageWithData:data];
}  

并且只能在main线程中设置UI的内容, 所以代码量增加了较多. 代码量暂且不管, 这里还有一个比较严重的问题就是每次都要加载图片, 

使用SDWebImage:
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#import <SDWebImage/UIImageView+WebCache.h>
[imageView setImageWithURL:[NSURL URLWithString:[_objects objectAtIndex:indexPath.row]]
                  placeholderImage:[UIImage imageNamed:@"placeholder.png"]];
SDWebImage可以实现:
*下载和缓存图片.
*相同的url不会被重复下载.
*坏的url不会一直请求.

使用HJCache:
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// 目前HJCache不支持ARC, 所以这是个问题.  

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(二)多线程初步实现TableView的图片显示(之前用第三库老是不稳定) 这个算是比较满意的.
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@interface c:NSOperation  

@property NSString *url;
@property NSString *imageName;
@property UIImage *image;
@property UIImageView *delegate;  

-(void) main;
-(id) initWith:(NSString *)url imageName:(NSString *)imageName delegate:(UIImageView *)delegate;  

@end  

@implementation c:NSOperation
@synthesize url = _url,imageName=_imageName, image=_image, delegate=_delegate;  

-(id) initWith:(NSString *)url imageName:(NSString *)imageName delegate:(UIImageView *)delegate{
    if (self = [super init]) {
        self.url = url;
        self.imageName = imageName;
        self.delegate = delegate;
    }
    return self;
}  

-(void) main{
    //
    NSString *cachefile = [NSTemporaryDirectory() stringByAppendingPathComponent: self.imageName];
    NSData *data = [NSData dataWithContentsOfURL:[NSURL URLWithString:self.url]];
    [data writeToFile:cachefile atomically:YES];  

    //
    self.image = [UIImage imageWithData:data];
    [self performSelectorOnMainThread:@selector(u) withObject:nil waitUntilDone:NO];
}
-(void)u{
    [self.delegate setImage:self.image];
}  

[plain] view plaincopy
queue = [[NSOperationQueue alloc] init];//这是成员队列的实例化
设置TableView cell中的图片:
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NSString *filename = [NSString stringWithFormat:@"%d", indexPath.row];
NSString *cachefile = [NSTemporaryDirectory() stringByAppendingPathComponent: filename];
UIImage *image = [UIImage imageWithContentsOfFile:cachefile];
if (image) {
    cell.imageView.image = image;
} else {
    c *o = [[c alloc] initWith:[_objects objectAtIndex:indexPath.row] imageName:[NSString stringWithFormat:@"%d",indexPath.row] delegate:cell.imageView];
    [queue addOperation:o];
    cell.imageView.image= [UIImage imageNamed:@"placeholder.png"];
}  

注: 保存一下测试图片  urls

http://blog.csdn.net/deep_explore/article/details/8144613

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