NSTimer的作用就是以一定的時間間隔向目標對象發送特殊的消息。最常見的是用來控制下載進度條的顯示。

創建一個 Timer

• + scheduledTimerWithTimeInterval: invocation: repeats:
• + (NSTimer *)scheduledTimerWithTimeInterval:(NSTimeInterval)ti invocation:(NSInvocation *)invocation repeats:(BOOL)yesOrNo;
• + scheduledTimerWithTimeInterval: target: selector: userInfo: repeats:
• + (NSTimer *)scheduledTimerWithTimeInterval:(NSTimeInterval)ti target:(id)aTarget selector:(SEL)aSelector userInfo:(id)userInfo repeats:(BOOL)yesOrNo;
  

  啟動 Timer

  • – fire

    停止 Timer

    • – invalidate

      Timer設置

      • – isValid
      • – fireDate
      • – setFireDate:
      • – timeInterval
      • – userInfo
      • 
        

        有碼有真相：

        //
        //  AppDelegate.m
        //  TimerDemo
        //
        //  Created by 李振傑 on 13-12-18.
        //  Copyright (c) 2013年 swplzj. All rights reserved.
        //
        
        #import "AppDelegate.h"
        
        //最大下載時間
        #define DOWNLOAD_TIMEOUT    60.0
        
        static int sec = 0;
        
        @interface AppDelegate ()
        {
            NSTimer *_timer;
        }
        
        
        @end
        
        @implementation AppDelegate
        
        - (void)dealloc
        {
            [_window release];
            [super dealloc];
        }
        
        - (void)initView
        {
            //創建一個進度條：用於顯示下載的進度
            UIProgressView *progress = [[UIProgressView alloc] initWithFrame:CGRectMake(20, 60, 220, 30)];
            [progress setBackgroundColor:[UIColor brownColor]];
            [progress setProgressViewStyle:UIProgressViewStyleBar];
            [progress setProgress:0];
            [progress setTag:0x123];
            [self.window addSubview:progress];
        }
        
        //更新進度條
        - (void)updateView
        {
            sec++;
            UIProgressView *pro = (UIProgressView *)[self.window viewWithTag:0x123];
            if (pro) {
                [pro setProgress:sec / DOWNLOAD_TIMEOUT animated:YES];
            }
            if (sec > DOWNLOAD_TIMEOUT) {
                //這是唯一的方法：從NSRunLoop中移除創建的定時器
                [_timer invalidate];
                _timer = nil;
            }
        }
        
        
        - (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
        {
            self.window = [[[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]] autorelease];
            // Override point for customization after application launch.
        
            [self initView];
            //在當前的runloop中添加一個定時器，每0.5s調用updateView函數一次
            _timer = [NSTimer scheduledTimerWithTimeInterval:0.5 target:self selector:@selector(updateView) userInfo:nil repeats:YES];
            
            self.window.backgroundColor = [UIColor whiteColor];
            [self.window makeKeyAndVisible];
            return YES;
        }
        
        @end
        

        
        下載例子鏈接