[转]网络编程总结
一：确认网络环境3G/WIFI
????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 {
??????????
????????[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];
