iPhone开发多线程开发之NSThread——异步下载图片 .

实现的功能：1）演示多线程NSThread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；

关键词：多线程 NSThread 等待框


运行效果图：
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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，ViewController.h如下：

#import <UIKit/UIKit.h>

@interface ViewController : UIViewController<NSURLConnectionDelegate>

@property(strong,nonatomic)UIImageView *imageView;
@property(strong,nonatomic)NSMutableData *buffer;
@property Boolean done;
@end

ViewController.m如下：

#import "ViewController.h"
@implementation ViewController
@synthesize imageView;
@synthesize buffer;
@synthesize done;

-(void)loadView{
    //初始化视图
    [self initViews];
    
    NSString *url = @"http://avatar.csdn.net/4/D/5/1_m_changgong.jpg";
    //在子线程执行图片下载操作
    [NSThread detachNewThreadSelector:@selector(downloadAppImage:) toTarget:self withObject:url];
}

//初始化视图组件
-(void)initViews{
    CGRect frame = [UIScreen mainScreen].applicationFrame;
    imageView = [[UIImageView alloc]initWithFrame:frame];
    self.view = imageView;
    [self.view setBackgroundColor:[UIColor whiteColor]];
}

//下载图片
-(void)downloadAppImage:(NSString *) url{
    //展示等待框
    [self showWaiting];
    
    done = NO;
    //初始化缓冲区
    buffer = [NSMutableData data];
    [[NSURLCache sharedURLCache] removeAllCachedResponses];
    //设置请求及连接
    NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:[NSURL URLWithString:url]];
    NSURLConnection *connnection = [[NSURLConnection alloc]initWithRequest:request delegate:self];
    if(connnection!=nil){
        while(!done){
             //NSLog(@"doing..");
            [[NSRunLoop currentRunLoop] runMode:NSDefaultRunLoopMode beforeDate:[NSDate distantFuture]];
        }
    }
    //生成UIImage实例
    UIImage *img = [UIImage imageWithData:buffer];
    //通知主线程
    [self performSelectorOnMainThread:@selector(showImage:) withObject:img waitUntilDone:NO]; 
    
    request = nil;
    connnection = nil;
}

//填充图片
-(void)showImage:(UIImage *)img{  
    [self.imageView setImage:img];
    
    //关闭等待框
    [self hiddenWaiting];
}

-(void)httpConnectEnd{
    NSLog(@"httpConnectEnd");
}

-(void)httpConnectEndWithError{
    [self hiddenWaiting];
    
    NSLog(@"httpConnectEndWithError");
}

//展示等待框
-(void)showWaiting{
    int width = 32;
    int height = 32;
    CGRect frame = CGRectMake(0, -20, 320, 480);
    int x = frame.size.width;
    int y = frame.size.height;
    NSLog(@"x=%d,y=%d",x,y);
    
    frame = CGRectMake((x-width)/2, (y-height)/2, width, height);
    UIActivityIndicatorView *progressInd = [[UIActivityIndicatorView alloc]initWithFrame:frame];
    [progressInd startAnimating];
    progressInd.activityIndicatorViewStyle = UIActivityIndicatorViewStyleWhiteLarge;
    
    frame = CGRectMake((x-70)/2, (y-height)/2+height, 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 *waitingView = [[UIView alloc]initWithFrame:frame];
    waitingView.backgroundColor = [UIColor blackColor];
    waitingView.alpha = 0.7;
    
    [waitingView addSubview:progressInd];
    [waitingView addSubview:waitinglabel];
    
    [waitingView setTag:110];//设置tag
    [self.view addSubview:waitingView];
}

//隐藏等待框
-(void)hiddenWaiting{
    //根据tag找到waitingView
    [[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 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];
}

//接收数据
-(void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data{
    [buffer appendData:data];
}

//下载完毕
-(void)connectionDidFinishLoading:(NSURLConnection *)connection{
    //NSLog(@"connectionDidFinishLoading");
    [self performSelectorOnMainThread:@selector(httpConnectEnd) withObject:nil waitUntilDone:NO]; 
    //self.done = YES;
}

@end