多线程开发NSOperation&NSOperationQueue——异步下载图片

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：