转：iphone网络编程总结一

一、确认网络环境3G/WiFi

1). 要在应用程序中使用Reachability，首先要完成以下两步骤：
1.1 添加源文件：将Reachability.h和Reachability.m拷贝到你工程中。
1.2 添加必要框架：将SystemConfiguration.framework添加到工程项目中。 

2). 检查网络状态

Reachability *r = [Reachability reachabilityWithHostName:@"www.apple.com"];
switch([r  currentReachabilityStatus]) {
    case NotReachable:
           //没有网络连接
           break;
     case ReachableViaWWAN:
           //使用3G网络
           break;
      case ReachableViaWiFi:
           //使用WiFi网络
           break;
}

3). 检查当前网络环境

程序启动时，如果想检测可用的网络环境，可以这样：

// 是否WiFi
+ (BOOL) IsEnableWIFI {
    return ([[Reachability reachabilityForLocalWiFi] currentReachabilityStatus] != NotReachable);
}

// 是否3G
+ (BOOL) IsEnable3G {
    return ([[Reachability reachabilityForInternetConnection] currentReachabilityStatus] != NotReachable);
} 

- (void)viewWillAppear:(BOOL)animated {
   if(([Reachability reachabilityForInternetConnection].currentReachabilityStatus == NotReachable) && ([Reachability reachabilityForLocalWiFi].currentReachabilityStatus == NotReachable)) {
        self.navigationItem.hidesBackButton = YES;
        [self.navigationItem setLeftBarButtonItem:nil  animated:NO];
   }
}

4). 链接状态的实时通知

网络连接状态的实时检查，通知在网络应用中也是十分必要的。接续状态发生变化时，需要及时地通知用户。
Reachability 1.5版本

// My.AppDelegate.h
#import "Reachability.h"

@interface MyAppDelegate : NSObject <UIApplicationDelegate> {
    NetworkStatus  remoteHostStatus;
}
@property NetworkStatus  remoteHostStatus;

@end

// My.AppDelegate.m
@import "MyAppDelegate.h"

@implementation  MyAppDelegate
@synthesize  remoteHostStatus;

// 更新网络状态
- (void)updateStatus {
   self.remoteHostStatus = [[Reachability sharedReachability] remoteHostStatus];
}

// 通知网络状态
- (void)reachabilityChanged : (NSNotification *)note {
   [self updateStatus];
   if (self.remoteHostStatus == NotReachable) {
        UIAlertView  *alert = [[UIAlertView alloc] initWithTitle:NSLocalizedString(@"AppName",nil)
                       message:NSLocalizedStrng(@"NotReachable",nil)
                       delegate:nil
                       cancelButtonTitle:@"OK" otherButtonTitles:nil];
         [alert  show];
         [alert  release];
   }
}

// 程序启动器，启动网络监视
- (void)applicationDidFinishLaunching:(UIApplication *)application {
    // 设置网络检测的站点
    [[Reachability  sharedReachability] setHostName:@"www.apple.com"];
    [[Reachability  sharedReachability] setNetworkStatusNotificationsEnabled:YES];

     // 设置网络状态变化时的通知函数
     [[NSNotificationCenter  defaultCenter] addObserver:self  selector:@selector(reachabilityChanged:)  name:@"kNetworkReachabilityChangedNotification"  object:nil];
     [self  updateStatus];
}

- (void)dealloc {
   //删除通知对象
   [[NSNotificationCenter  defaultCenter]  removeObserver:self];
   [window  release];
   [super  dealloc];
}

Reachability 2.0版本

// MyAppDelegate.h
@class  Reachability;
@interface  MyAppDelegate:NSObject<UIApplicationDelegate> {
    Reachability  *hostReach;
}
@end

// MyAppDelegate.m
- (void)reachabilityChanged: (NSNotification *)note {
    Reachability  *curReach = [note object];
    NSParameterAssert([curReach  isKindOfClass:[Reachability class]]);
    NetworkStatus  status = [curReach  currentReachabilityStatus];

    if (status == NotReachable) {
        UIAlertView  *alert = [[UIAlertView  alloc] initWithTitle:@"AppName"
                             message:@"NotReachable"
                             delegate:nil
                             cancelButtonTitle:@"YES"  otherButtonTitles:nil];
         [alert  show];
         [alert  release];
    }
}

- (void)applicationDidFinishLaunching:(UIApplication *)application {

    // 监测网络情况
    [[NSNotificationCenter  defaultCenter] addObserver:self
                    selector:@selector(reachabilityChanged:)
                    name:kReachabilityChangedNotification
                    object:nil];
     hostReach = [[Reachability  reachabilityWithHostName:@"www.google.com"] retain];
     [hostReach  startNotifer];
     //.....
}

详细：http://www.cocoachina.com/bbs/read.php?tid=31300