iPhone開發【十五】多線程開發之NSThread——非同步下載圖片

轉載請註明出處，原文網址：http://blog.csdn.net/m_changgong/article/details/8220819  作者：張燕廣

實現的功能：1）示範多線程NSThread開發；2）子線程中執行下載圖片工作，圖片下載完成前顯示等待框；

關鍵詞：多線程 NSThread 等待框

1、建立視圖控制器ViewController（不帶xib），作為根視圖控制器，通過ViewController的-(void)loadView方法構建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{    //初始化視圖    [self initViews];        NSString *url = @"http://avatar.csdn.net/4/D/5/1_m_changgong.jpg";    //在子線程執行圖片下載操作    [NSThread detachNewThreadSelector:@selector(downloadAppImage:) toTarget:self withObject:url];}//初始化視圖組件-(void)initViews{    CGRect frame = [UIScreen mainScreen].applicationFrame;    imageView = [[UIImageView alloc]initWithFrame:frame];    self.view = imageView;    [self.view setBackgroundColor:[UIColor whiteColor]];}//下載圖片-(void)downloadAppImage:(NSString *) url{    //展示等待框    [self showWaiting];        done = NO;    //初始化緩衝區    buffer = [NSMutableData data];    [[NSURLCache sharedURLCache] removeAllCachedResponses];    //佈建要求及串連    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]];        }    }    //產生UIImage執行個體    UIImage *img = [UIImage imageWithData:buffer];    //通知主線程    [self performSelectorOnMainThread:@selector(showImage:) withObject:img waitUntilDone:NO];         request = nil;    connnection = nil;}//填充圖片-(void)showImage:(UIImage *)img{      [self.imageView setImage:img];        //關閉等待框    [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 = @"正在下載應用程式圖片...";    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];//設定tag    [self.view addSubview:waitingView];}//隱藏等待框-(void)hiddenWaiting{    //根據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//不執行緩衝-(NSCachedURLResponse *)connection:(NSURLConnection *)connection willCacheResponse:(NSCachedURLResponse *)cachedResponse{    return nil;}//串連發生錯誤-(void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error{    [self performSelectorOnMainThread:@selector(httpConnectEndWithError) withObject:self waitUntilDone:NO];    [buffer setLength:0];}//接收資料-(void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data{    [buffer appendData:data];}//下載完畢-(void)connectionDidFinishLoading:(NSURLConnection *)connection{    //NSLog(@"connectionDidFinishLoading");    [self performSelectorOnMainThread:@selector(httpConnectEnd) withObject:nil waitUntilDone:NO];     //self.done = YES;}@end

2、運行效果如下：