实现的功能：1）演示多线程NSOperation&NSOperationQueue开发；2）子线程中执行下载图片工作，图片下载完成前显示等待框和下载进度条；
关键词：多线程 NSOperation NSOperationQueue 等待框
效果图如下：
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1、新建视图控制器ViewController（不带xib），作为根视图控制器，通过ViewController的-(void)loadView方法构建UI。
2、新建继承自NSOperation且实现协议NSURLConnectionDelegate的类DownLoadImageTask，DownLoadImageTask.h如下：
#import <Foundation/Foundation.h>@protocol DownLoadImageDelegate;@interface DownLoadImageTask : NSOperation<NSURLConnectionDelegate>{ int operationId; long long totalLength; BOOL done;}@property int operationId;@property(nonatomic,assign) id<DownLoadImageDelegate>downloadImageDelegate;@property(nonatomic,retain) NSMutableData *buffer;@property(nonatomic,retain) NSURLRequest *request;@property(nonatomic,retain) NSURLConnection *connection;- (id)initWithURLString:(NSString *)url;@end@protocol DownLoadImageDelegate//图片下载完成的委托-(void)imageDownLoadFinished:(UIImage *)img;//更新图片下载进度条的值-(void)updateDownProgress:(double) value;@endDownLoadImageTask.m如下：
@implementation DownLoadImageTask@synthesize operationId;@synthesize downloadImageDelegate;@synthesize buffer;@synthesize request;@synthesize connection;- (id)initWithURLString:(NSString *)url{ NSLog(@"url=%@",url); self = [super init]; if(self){ request = [NSURLRequest requestWithURL:[NSURL URLWithString:url]]; buffer = [NSMutableData data]; } return self;}//主要处理方法-(void)start{ //或者main NSLog(@"DownLoadImageTask-start"); if(![self isCancelled]){ //暂停一下 [NSThread sleepForTimeInterval:1]; //设置connection及其代理 connection = [[NSURLConnection alloc]initWithRequest:request delegate:self]; if(connection!=nil){ while(!done){ [[NSRunLoop currentRunLoop]runMode:NSDefaultRunLoopMode beforeDate:[NSDate distantFuture]]; } } }}-(void)httpConnectEndWithError{ //[self hiddenWaiting]; NSLog(@"httpConnectEndWithError");}-(void)dealloc{ buffer = nil; connection = nil; request = nil; downloadImageDelegate = nil;}#pragma NSURLConnection delegate methods//不执行缓存-(NSCachedURLResponse *)connection:(NSURLConnection *)connection willCacheResponse:(NSCachedURLResponse *)cachedResponse{ return nil;}//连接发生错误-(void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error{ [self performSelectorOnMainThread:@selector(httpConnectEndWithError) withObject:self waitUntilDone:NO]; [buffer setLength:0];}//收到响应- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response{ NSHTTPURLResponse *httpResponse = (NSHTTPURLResponse *)response; if(httpResponse && [httpResponse respondsToSelector:@selector(allHeaderFields)]){ NSDictionary *httpResponseHeaderFields = [httpResponse allHeaderFields]; totalLength = [[httpResponseHeaderFields objectForKey:@"Content-Length"] longLongValue]; NSLog(@"totalLength is %lld",totalLength); }}//接收数据-(void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data{ //NSLog(@"didReceiveData..."); [buffer appendData:data]; double progressValue = totalLength==0?0:((double)([buffer length])/(double)totalLength); //更新进度条值 [downloadImageDelegate updateDownProgress:progressValue];}//下载完毕-(void)connectionDidFinishLoading:(NSURLConnection *)connection{ done = YES; UIImage *img = [[UIImage alloc] initWithData:buffer]; [downloadImageDelegate imageDownLoadFinished:img];}-(BOOL)isConcurrent { //返回yes表示支持异步调用，否则为支持同步调用 return YES; }- (BOOL)isExecuting{ return connection == nil; }- (BOOL)isFinished{ return connection == nil; }@endDownLoadImageTask中定义了协议DownLoadImageDelegate，ViewController需要实现协议DownLoadImageDelegate；DownLoadImageTask下载工作完成后，会回调ViewController实现的DownLoadImageDelegate协议中的方法。
2、ViewController.h如下：
#import "DownLoadImageTask.h"@interface ViewController:UIViewController<DownLoadImageDelegate>{}@property(strong,nonatomic)NSOperationQueue *queue;@property(strong,nonatomic)UIImageView *appImgView;@endViewController.m如下：
#import "ViewController.h"#import "DownLoadImageTask.h"@implementation ViewController@synthesize queue;@synthesize appImgView;-(void)loadView{ //初始化视图 [self initViews]; //显示等待框 [self showWaiting]; NSString *url = @"http://hiphotos.baidu.com/newwen666666/pic/item/01ec7750863e49600cf3e3cc.jpg"; int index = 1; DownLoadImageTask *task = [[DownLoadImageTask alloc]initWithURLString:url]; task.downloadImageDelegate = self; task.operationId = index++; queue = [[NSOperationQueue alloc]init]; [queue addOperation:task];}//初始化视图组件-(void)initViews{ CGRect frame = [UIScreen mainScreen].applicationFrame; UIView *appView = [[UIView alloc]initWithFrame:frame]; self.view = appView; [self.view setBackgroundColor:[UIColor colorWithWhite:1.0 alpha:1.0]]; frame = CGRectMake(0, 0, frame.size.width, frame.size.height); appImgView = [[UIImageView alloc]initWithFrame:frame]; [self.view addSubview:appImgView];}//展示等待框-(void)showWaiting{ CGRect frame = CGRectMake(0, -20, 320, 480); int x = frame.size.width; int progressWidth = 150; int progressHeight = 32; frame = CGRectMake((x-progressWidth)/2, 100, progressWidth, progressHeight); UIProgressView *progress = [[UIProgressView alloc]initWithProgressViewStyle:UIProgressViewStyleBar]; progress.frame = frame; progress.progress = 0.0; progress.backgroundColor = [UIColor whiteColor]; UILabel *showValue = [[UILabel alloc]init]; frame = showValue.frame; frame.origin.x = CGRectGetMaxX(progress.frame)+10; frame.origin.y = CGRectGetMinY(progress.frame); frame.size.width = 45; frame.size.height = 15; showValue.frame = frame; showValue.backgroundColor = [UIColor redColor]; showValue.text = @"0.0"; int progressIndWidth = 32; int progressIndHeight = 32; frame = CGRectMake((x-progressIndWidth)/2, 100+32, progressIndWidth, progressIndHeight); UIActivityIndicatorView *progressInd = [[UIActivityIndicatorView alloc]initWithFrame:frame]; [progressInd startAnimating]; progressInd.activityIndicatorViewStyle = UIActivityIndicatorViewStyleWhiteLarge; frame = CGRectMake((x-70)/2, 100+32+32, 80, 20); UILabel *waitinglabel = [[UILabel alloc]initWithFrame:frame]; waitinglabel.text = @"正在下载应用程序图片..."; waitinglabel.textColor = [UIColor redColor]; waitinglabel.font = [UIFont systemFontOfSize:15]; waitinglabel.backgroundColor = [UIColor clearColor]; frame = CGRectMake(0, -20, 320, 480); UIView *theView = [[UIView alloc]initWithFrame:frame]; theView.backgroundColor = [UIColor blackColor]; theView.alpha = 0.7; [progress setTag:100]; [theView addSubview:progress]; [showValue setTag:101]; [theView addSubview:showValue]; [theView addSubview:progressInd]; [theView addSubview:waitinglabel]; [theView setTag:110]; [self.view addSubview:theView];}//隐藏等待框-(void)hiddenWaiting{ [[self.view viewWithTag:110]removeFromSuperview];}- (void)viewDidUnload{ [super viewDidUnload]; // Release any retained subviews of the main view.}- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation{ return (interfaceOrientation != UIInterfaceOrientationPortraitUpsideDown);}#pragma mark DownLoadImageDelegate methods//展示下载完毕的图片-(void)imageDownLoadFinished:(UIImage *)img{ //退出等待框 [self hiddenWaiting]; [appImgView setImage:img];}//更新进度条的值-(void)updateDownProgress:(double) value{ UIProgressView *progresss = (UIProgressView *)[self.view viewWithTag:100]; UILabel *showValue = (UILabel*)[self.view viewWithTag:101]; progresss.progress = value; showValue.text = [NSString stringWithFormat:@"%.1f%",(double)(value*100)];}@end