前两篇是自己写的下载图片方法，现在用第三方框架只要几行代码就可以实现图片的下载。SDWebImage底层实现的思路也是和前面说的一样。 SDWebImage是网络图片处理框架，封装很很多方法，例如：图片下载、图片缓存、下载进度监听、gif处理等等。大大提高了网络图片处理的效率。值得使用
。
github托管地址：https://github.com/rs/SDWebImage
实现cell图片下载之前，先了解一下SDWebImage的使用：
1、导入框架，引入头文件：
#import "UIImageView+WebCache.h"
UIImageView+WebCache.h
//得到当前图片的url - (NSURL *)sd_imageURL; /** * 异步下载图片并缓存 */ - (void)sd_setImageWithURL:(NSURL *)url; /** * 异步下载图片并缓存，没下载完之前先显示占位图片，下载完之后再替换 */ - (void)sd_setImageWithURL:(NSURL *)url placeholderImage:(UIImage *)placeholder; /** * 异步下载图片并缓存 * @param url 下载图片路径 * @param placeholder 占位图片，直到下载完成才替换 * @param options 下载图片选择方式 */ - (void)sd_setImageWithURL:(NSURL *)url placeholderImage:(UIImage *)placeholder options:(SDWebImageOptions)options; /** * 异步下载图片并缓存，完成后可以在block中做事情 * @param url 下载图片url * @param completedBlock SDWebImageCompletionBlock：UIImage *image, NSError *error, SDImageCacheType cacheType, NSURL *imageURL) block中可以得到下载图片，错误信息，缓存类型，下载图片地址 参数，给用户做相应操作 */ - (void)sd_setImageWithURL:(NSURL *)url completed:(SDWebImageCompletionBlock)completedBlock; /** * 异步下载图片并缓存，提供占位图片，并完成后可以在block中做事情 * * @param url T下载图片url * @param placeholder T占位图片，直到下载完成才替换 * @param completedBlock SDWebImageCompletionBlock：UIImage *image, NSError *error, SDImageCacheType cacheType, NSURL *imageURL) block中可以得到下载图片，错误信息，缓存类型，下载图片地址 参数，给用户做相应操作 */ - (void)sd_setImageWithURL:(NSURL *)url placeholderImage:(UIImage *)placeholder completed:(SDWebImageCompletionBlock)completedBlock; /** * 异步下载图片并缓存，完成后可以在block中做事情 * @param url 下载图片路径 * @param placeholder 占位图片，直到下载完成才替换 * @param options 下载图片选择方式 * @param completedBlock 同上 */ - (void)sd_setImageWithURL:(NSURL *)url placeholderImage:(UIImage *)placeholder options:(SDWebImageOptions)options completed:(SDWebImageCompletionBlock)completedBlock; /** * 异步下载图片并缓存，可以监听下载进度，完成后可以在block中做事情 * @param url 下载图片路径 * @param placeholder 占位图片，直到下载完成才替换 * @param options 下载图片选择方式 * @param progress * SDWebImageDownloaderProgressBlock:NSInteger receivedSize(当前下载大小), NSInteger expectedSize(总大小) * @param completedBlock 同上 */ - (void)sd_setImageWithURL:(NSURL *)url placeholderImage:(UIImage *)placeholder options:(SDWebImageOptions)options progress:(SDWebImageDownloaderProgressBlock)progressBlock completed:(SDWebImageCompletionBlock)completedBlock; /** * 异步下载图片并缓存，可以监听下载进度，完成后可以在block中做事情 * @param url 下载图片路径 * @param placeholder 占位图片，直到下载完成才替换 * @param options 下载图片选择方式 * @param progress * SDWebImageDownloaderProgressBlock:NSInteger receivedSize(当前下载大小), NSInteger expectedSize(总大小) * @param completedBlock 同上 */ - (void)sd_setImageWithPreviousCachedImageWithURL:(NSURL *)url placeholderImage:(UIImage *)placeholder options:(SDWebImageOptions)options progress:(SDWebImageDownloaderProgressBlock)progressBlock completed:(SDWebImageCompletionBlock)completedBlock;
3、options所有选项
//失败后重新下载
SDWebImageRetryFailed = 1 << 0,
//最低优先级，当正在进行UI交互时，自动暂停内部的一些下载操作
SDWebImageLowPriority = 1 << 1,
//只缓存内存
SDWebImageCacheMemoryOnly = 1 << 2,
//渐进式下载,显示的图像是逐步在下载
SDWebImageProgressiveDownload = 1 << 3,
//刷新缓存
SDWebImageRefreshCached = 1 << 4,
//后台下载
SDWebImageContinueInBackground = 1 << 5,
/**
* Handles cookies stored in NSHTTPCookieStore by setting
* NSMutableURLRequest.HTTPShouldHandleCookies = YES;
*/
SDWebImageHandleCookies = 1 << 6,
//允许使用无效的SSL证书
SDWebImageAllowInvalidSSLCertificates = 1 << 7,
//高优先级下载
SDWebImageHighPriority = 1 << 8,
//延迟占位符
SDWebImageDelayPlaceholder = 1 << 9,
//改变动画形象
SDWebImageTransformAnimatedImage = 1 << 10,
/**
* By default, image is added to the imageView after download. But in some cases, we want to
* have the hand before setting the image (apply a filter or add it with cross-fade animation for instance)
* Use this flag if you want to manually set the image in the completion when success
*/
SDWebImageAvoidAutoSetImage = 1 << 11 SDWebImageManager *manager = [SDWebImageManager sharedManager];
// 取消正在下载的操作
[manager cancelAll];
// 清除内存缓存
[manager.imageCache clearMemory];
//释放磁盘的缓存
[manager.imageCache cleanDisk];
cell下载图片(SDWebImage) demo：
//
// AppsViewController.m
// cell图片下载-SDWebImage
//
#import "AppsViewController.h"
#import "App.h"
#import "UIImageView+WebCache.h"
@interface AppsViewController ()
@property(nonatomic,strong) NSArray *apps;
@end
@implementation AppsViewController
- (void)viewDidLoad {
[super viewDidLoad];
}
- (void)didReceiveMemoryWarning {
[super didReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
}
-(NSArray *)apps{
if (!_apps) {
NSMutableArray *appArr = [NSMutableArray array];
NSString *file = [[NSBundle mainBundle]pathForResource:@"apps" ofType:@"plist"];
NSArray *dictArr = [NSArray arrayWithContentsOfFile:file];
for (NSDictionary *dict in dictArr) {
App *app = [App appWithDict:dict];
[appArr addObject:app];
}
_apps = appArr;
}
return _apps;
}
#pragma mark - Table view data source
- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView {
return 1;
}
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section {
return self.apps.count;
}
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
static NSString *ID = @"app";
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:ID];
if (!cell) {
cell = [[UITableViewCell alloc]initWithStyle:UITableViewCellStyleSubtitle reuseIdentifier:ID];
}
App *app = self.apps[indexPath.row];
cell.textLabel.text = app.name;
cell.detailTextLabel.text = app.download;
//下载图片
NSURL *url = [NSURL URLWithString:app.icon];
//[cell.imageView sd_setImageWithURL:url];
//[cell.imageView sd_setImageWithURL:url placeholderImage:[UIImage imageNamed:@"placeholder"]];
//[cell.imageView sd_setImageWithURL:url completed:^(UIImage *image, NSError *error, SDImageCacheType cacheType, NSURL *imageURL) {
// NSLog(@"%@",imageURL);
//}];
//SDWebImage下载图片
SDWebImageOptions options = SDWebImageRetryFailed | SDWebImageLowPriority;
[cell.imageView sd_setImageWithPreviousCachedImageWithURL:url placeholderImage:[UIImage imageNamed:@"placeholder"] options:options progress:^(NSInteger receivedSize, NSInteger expectedSize) {
NSLog(@"下载进度:%f",(double)receivedSize/expectedSize);
} completed:^(UIImage *image, NSError *error, SDImageCacheType cacheType, NSURL *imageURL) {
NSLog(@"下载图片完成%@",image);
}];
return cell;
}
@end
-(void)applicationDidReceiveMemoryWarning:(UIApplication *)application{
SDWebImageManager *manager = [SDWebImageManager sharedManager];
// 1.取消正在下载的操作
[manager cancelAll];
// 2.清除内存缓存
[manager.imageCache clearMemory];
}
原文：http://blog.csdn.net/zhixinhuacom/article/details/50568825