多线程的实现：NSThread
1.子线程的创建：两种方法
第一种： [NSThread detachNewThreadSelector:@selector(downloadImage:) toTarget:self withObject:kURL];
第二种：NSThread *thread = [[NSThread alloc]initWithTarget:self selector:@selector(downloadImage:) object:kURL];
[thread start];
差异：第一种直接方便，第二种在启动前可以对其的stack等参数配置，更具灵活性。
2.在子线程中召唤主线程做事：
[self performSelectorOnMainThread:@selector(函数名) withObject:nil waitUntilDone:YES];
//如果waitUntilDone参数为YES，那么当前线程会被阻拦，直到selector运行完。
3.代码简单示例一：登录
//此为多线程实现登录放UI卡死的代码
//成功进行登录验证后进入到下一ViewController
-(void)presentToNextview{
//到下一界面
} //登录验证
-(void)loginCheck{
//包含POST或GET请求来完成数据的验证,验证成功就跳转到下一界面
if(账号密码匹配){
//召唤主线程跳转到下一界面
[self performSelectorOnMainThread:@selector(presentToNextview) withObject:nil waitUntilDone:YES];
}
} -(void)showindicator{
//显示登录时转圈圈的菊花
} //登录按钮的点击事件
-(IBAction)loginBTN:(id)sender{
//执行的函数有:
[self showindicator]; //开辟新的线程，执行需要联网耗时的函数loginCheck
[NSThread detachNewThreadSelector:@selector(loginCheck) toTarget:self withObject:nil];
}
4.代码示例二：显示一张网上的图片，源代码：
DownloadViewController.h
#import <UIKit/UIKit.h>
#import "FileConnection.h"
@interface DownloadViewController : UIViewController @end
DownloadViewController.m
#import "DownloadViewController.h"
#define kURL @"http://b.hiphotos.baidu.com/image/pic/item/32fa828ba61ea8d37ccb6e0e950a304e241f58ca.jpg"
@interface DownloadViewController () @property UIImageView *imageView; @end UIActivityIndicatorView* activityIndicatorView; @implementation DownloadViewController -(void)downloadImage:(NSString *) url{
NSData *data = [[NSData alloc] initWithContentsOfURL:[NSURL URLWithString:url]];
UIImage *image = [[UIImage alloc]initWithData:data];
if(image == nil){
NSLog(@"没有图片");
}else{
NSLog(@"刷新图片");
[ activityIndicatorView stopAnimating ];//停止
//通知主线程做事
[self performSelectorOnMainThread:@selector(updateUI:) withObject:image waitUntilDone:NO];
//如果waitUntilDone参数为YES，那么当前线程会被阻拦，直到selector运行完。
}
} -(void)updateUI:(UIImage*) image{
self.imageView.image = image;
//sleep(5);
} -(void)showindicatior{
activityIndicatorView = [ [ UIActivityIndicatorView alloc ] initWithFrame:CGRectMake(,,30.0,30.0)];
activityIndicatorView.activityIndicatorViewStyle= UIActivityIndicatorViewStyleGray;
[self.view addSubview:activityIndicatorView];
[activityIndicatorView startAnimating];//启动 }
- (void)viewDidLoad
{
[super viewDidLoad]; self.imageView=[[UIImageView alloc] initWithFrame:CGRectMake(, , , )]; [self.view addSubview:self.imageView]; //显示菊花
[self showindicatior]; //开辟一个新的线程 2种方法
[NSThread detachNewThreadSelector:@selector(downloadImage:) toTarget:self withObject:kURL];
//NSThread *thread = [[NSThread alloc]initWithTarget:self selector:@selector(downloadImage:) object:kURL];
//[thread start];
} - (void)didReceiveMemoryWarning
{
[super didReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
} @end