iPhone开发【十七】多线程开发之NSOperation&NSOperationQueue——异步下载图片

转载请注明出处，原文网址：http://blog.csdn.net/m_changgong/article/details/8238093 作者：张燕广

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

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;
 @end

DownLoadImageTask.m如下：

 <span style="font-family:Microsoft YaHei;font-size:18px;">#import "DownLoadImageTask.h"

 @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;
 }

 @end</span>

DownLoadImageTask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：

 <span style="font-family:Microsoft YaHei;font-size:18px;">#import <UIKit/UIKit.h>
 #import "DownLoadImageTask.h"

 @interface ViewController:UIViewController<DownLoadImageDelegate>{
 }

 @property(strong,nonatomic)NSOperationQueue *queue;
 @property(strong,nonatomic)UIImageView *appImgView;

 @end</span>

ViewController.m如下：

 <span style="font-family:Microsoft YaHei;font-size:18px;">#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</span>

3、效果如下：