iOS网络编程总结

1. 添加源文件和framework

开发Web等网络应用程序的时候，需要确认网络环境，连接情况等信息。如果没有处理它们，是不会通过Apple的审(我们的)查的。
Apple 的 例程 Reachability 中介绍了取得/检测网络状态的方法。要在应用程序程序中使用Reachability，首先要完成如下两部：

1.1. 添加源文件：
在你的程序中使用 Reachability 只须将该例程中的 Reachability.h 和 Reachability.m 拷贝到你的工程中。如下图：

1.2.添加framework：
将SystemConfiguration.framework 添加进工程。如下图：

2. 网络状态

Reachability.h中定义了三种网络状态：
typedef enum {
NotReachable = 0, //无连接
ReachableViaWiFi, //使用3G/GPRS网络
ReachableViaWWAN //使用WiFi网络
} NetworkStatus;

因此可以这样检查网络状态：

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，可以像这样
// 是否wifi
+ (BOOL) IsEnableWIFI {
return ([[Reachability reachabilityForLocalWiFi] currentReachabilityStatus] != NotReachable);
}

// 是否3G
+ (BOOL) IsEnable3G {
return ([[Reachability reachabilityForInternetConnection] currentReachabilityStatus] != NotReachable);
}
例子：
- (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:NSLocalizedString (@"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];
// ...
}

二：使用NSConnection下载数据

1.创建NSConnection对象，设置委托对象

NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:[NSURL URLWithString:[self urlString]]];
[NSURLConnection connectionWithRequest:request delegate:self];

2. NSURLConnection delegate委托方法
- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response;
- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error;
- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data;
- (void)connectionDidFinishLoading:(NSURLConnection *)connection;

3. 实现委托方法
- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response {
// store data
[self.receivedData setLength:0]; //通常在这里先清空接受数据的缓存
}

- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data {
/* appends the new data to the received data */
[self.receivedData appendData:data]; //可能多次收到数据，把新的数据添加在现有数据最后
}

- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error {
// 错误处理
}

- (void)connectionDidFinishLoading:(NSURLConnection *)connection {
// disconnect
[UIApplication sharedApplication].networkActivityIndicatorVisible = NO;
NSString *returnString = [[NSString alloc] initWithData:self.receivedData encoding:NSUTF8StringEncoding];
NSLog(returnString);
[self urlLoaded:[self urlString] data:self.receivedData];
firstTimeDownloaded = YES;
}

三：使用NSXMLParser解析xml文件

1. 设置委托对象，开始解析
NSXMLParser *parser = [[NSXMLParser alloc] initWithData:data]; //或者也可以使用initWithContentsOfURL直接下载文件，但是有一个原因不这么做：
// It's also possible to have NSXMLParser download the data, by passing it a URL, but this is not desirable
// because it gives less control over the network, particularly in responding to connection errors.
[parser setDelegate:self];
[parser parse];

2. 常用的委托方法
- (void)parser:(NSXMLParser *)parser didStartElement:(NSString *)elementName
namespaceURI:(NSString *)namespaceURI
qualifiedName:(NSString *)qName
attributes:(NSDictionary *)attributeDict;
- (void)parser:(NSXMLParser *)parser didEndElement:(NSString *)elementName
namespaceURI:(NSString *)namespaceURI
qualifiedName:(NSString *)qName;
- (void)parser:(NSXMLParser *)parser foundCharacters:(NSString *)string;
- (void)parser:(NSXMLParser *)parser parseErrorOccurred:(NSError *)parseError;

static NSString *feedURLString = @"http://www.yifeiyang.net/test/test.xml";

3. 应用举例
- (void)parseXMLFileAtURL:(NSURL *)URL parseError:(NSError **)error
{
NSXMLParser *parser = [[NSXMLParser alloc] initWithContentsOfURL:URL];
[parser setDelegate:self];
[parser setShouldProcessNamespaces:NO];
[parser setShouldReportNamespacePrefixes:NO];
[parser setShouldResolveExternalEntities:NO];
[parser parse];
NSError *parseError = [parser parserError];
if (parseError && error) {
*error = parseError;
}
[parser release];
}

- (void)parser:(NSXMLParser *)parser didStartElement:(NSString *)elementName namespaceURI:(NSString *)namespaceURI
qualifiedName:(NSString*)qName attributes:(NSDictionary *)attributeDict{
// 元素开始句柄
if (qName) {
elementName = qName;
}
if ([elementName isEqualToString:@"user"]) {
// 输出属性值
NSLog(@"Name is %@ , Age is %@", [attributeDict objectForKey:@"name"], [attributeDict objectForKey:@"age"]);
}
}

- (void)parser:(NSXMLParser *)parser didEndElement:(NSString *)elementName namespaceURI:(NSString *)namespaceURI
qualifiedName:(NSString *)qName
{
// 元素终了句柄
if (qName) {
elementName = qName;
}
}

- (void)parser:(NSXMLParser *)parser foundCharacters:(NSString *)string
{
// 取得元素的text
}

NSError *parseError = nil;
[self parseXMLFileAtURL:[NSURL URLWithString:feedURLString] parseError:&parseError];