实现的功能：1）演示多线程开发。2）子线程中模拟耗时操作，然后通知主线程更新进度条。
关键词：多线程 NSThread 定时器
效果图：
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1、新建视图控制器ViewController.m（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{ CGFloat progressValue; //进度条的值}@property(strong,nonatomic)UIProgressView *progress; @property(strong,nonatomic)UILabel *showValue;@property(strong,nonatomic)UIButton *startThread;@endViewController.m如下：
#import "ViewController.h"@implementation ViewController@synthesize progress;@synthesize showValue;@synthesize startThread;-(void)loadView{ CGRect appFrame = [UIScreen mainScreen].applicationFrame; UIView *view = [[UIView alloc]initWithFrame:appFrame]; self.view = view; //设置背景颜色 UIColor *bgcolor = [UIColor grayColor]; [self.view setBackgroundColor:bgcolor]; [self initViews];}//初始化视图组件-(void)initViews{ //初始化progress CGRect frame = CGRectMake(50, 50, 200, 30); progress = [[UIProgressView alloc]initWithFrame:frame]; [self.view addSubview:progress]; //初始化showValue showValue = [[UILabel alloc]init]; frame = showValue.frame; frame.origin.x = CGRectGetMaxX(progress.frame)+10; frame.origin.y = CGRectGetMinY(progress.frame); frame.size.width = 35; frame.size.height = 15; showValue.frame = frame; showValue.backgroundColor = [UIColor redColor]; showValue.text = @"0.0"; [self.view addSubview:showValue]; //初始化startThread startThread = [[UIButton alloc]init]; frame = startThread.frame; frame.origin.x = 110; frame.origin.y = 80; frame.size.width = 100; frame.size.height = 50; startThread.frame = frame; UIImage *img = [UIImage imageNamed:@"btn.png"]; [startThread setBackgroundImage:img forState:UIControlStateNormal]; [startThread setTitleColor:[UIColor colorWithRed:1.0 green:0 blue:0 alpha:1.0] forState:UIControlStateNormal]; [startThread setTitle:@"开启子线程" forState:UIControlStateNormal]; //设置事件 [startThread addTarget:self action:@selector(startThreadButtonPressed) forControlEvents:UIControlEventTouchUpInside]; [self.view addSubview:startThread];}//开启子线程-(void)startThreadButtonPressed{ progress.progress = 0.0; showValue.text = @"0.0"; startThread.hidden = YES; //该语句会让主线程堵塞2秒，这就是为什么要将耗时操作放在子线程的原因之一 //[NSThread sleepForTimeInterval:2]; //开启一个新线程 [NSThread detachNewThreadSelector:@selector(doJobInBackground) toTarget:self withObject:nil];}//子线程，后台执行工作-(void)doJobInBackground{ //睡眠,模拟子线程中耗时操作 [NSThread sleepForTimeInterval:2]; //通知主线程执行更新操作 [self performSelectorOnMainThread:@selector(invalidateProgress) withObject:nil waitUntilDone:NO];}//更新进度-(void)invalidateProgress{ progressValue = [progress progress]; showValue.text = [NSString stringWithFormat:@"%.2f",progressValue]; if(progressValue < 1.0){ progress.progress = progressValue+0.02; //启动定时器 [NSTimer scheduledTimerWithTimeInterval:0.2 target:self selector:@selector(invalidateProgress) userInfo:nil repeats:NO]; }else{ progress.progress = 1.0; showValue.text = @"1.0"; startThread.hidden = NO; }}- (void)viewDidUnload{ [super viewDidUnload]; // Release any retained subviews of the main view. progress = nil; showValue = nil; startThread = nil;}- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation{ return (interfaceOrientation != UIInterfaceOrientationPortraitUpsideDown);}@end