//
//  UIImageView+YXImageView.h
//  PicDemo
//
//  Copyright (c) 2014年 Y.X. All rights reserved.
//

#import <UIKit/UIKit.h>@interface UIImageView (YXImageView)- (void)setImageWithURL:(NSString *)url placeholderImage:(UIImage *)placeholder;@end

//
//  UIImageView+YXImageView.m
//  PicDemo
//
//  Copyright (c) 2014年 Y.X. All rights reserved.
//

#import "UIImageView+YXImageView.h"@implementation UIImageView (YXImageView)- (void)setImageWithURL:(NSString *)url placeholderImage:(UIImage *)placeholder
{// 先设置placeholderself.image = placeholder;// 异步下载完了之后再加载新的图片if (url){// 子线程下载dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{NSURLRequest *request = [NSURLRequest requestWithURL:[NSURL URLWithString:url]];NSData *data          = [NSURLConnection sendSynchronousRequest:requestreturningResponse:nilerror:nil];// 主线程更新dispatch_async(dispatch_get_main_queue(), ^{if (data){self.image = [UIImage imageWithData:data];[self setNeedsDisplay];}});});}
}@end

//
//  RootViewController.m
//  PicDemo
//
//  Copyright (c) 2014年 Y.X. All rights reserved.
//

#import "RootViewController.h"
#import "UIImageView+YXImageView.h"@interface RootViewController ()@end@implementation RootViewController- (void)viewDidLoad
{[super viewDidLoad];UIImageView *imageView = [[UIImageView alloc] initWithFrame:self.view.bounds];[self.view addSubview:imageView];[imageView setImageWithURL:@"http://pic.cnitblog.com/avatar/572952/20140226185251.png"placeholderImage:[UIImage imageNamed:@"1.png"]];
}@end