ios开发之网络编程（请求--响应）

这边我就以最简单的例子来引入几个常用的API中的类。
[cpp]
//
// NLViewController.m
// NetWorkTest
//
// Created by Nono on 12-5-16.
// Copyright (c) 2012年 NonoWithLilith. All rights reserved.
//
#import "NLViewController.h"

@interface NLViewController ()

@end

@implementation NLViewController
@synthesize label = _label;
@synthesize data = _data;
@synthesize connection = _connection;
- (void)dealloc{
[self.label release];
[self.data release];
[super dealloc];
}
- (void)viewDidLoad
{
[super viewDidLoad];
UILabel *label = [[UILabel alloc] initWithFrame:CGRectMake(10.0, 10.0, 300.0, 400)];
self.label = label;
label.textAlignment = UITextAlignmentCenter;
[label setNumberOfLines:0];
label.lineBreakMode = UILineBreakModeWordWrap;
self.label.text = @"正在在请求数据";
[self.view addSubview:label];
[label release];
//step 1:请求地址
NSString *urlString = @"www.2cto.com";
NSURL *url = [NSURL URLWithString:urlString];
//step 2:实例化一个request
NSURLRequest *requrst = [NSURLRequest requestWithURL:url cachePolicy:NSURLRequestUseProtocolCachePolicy timeoutInterval:30.0];
//step 3：创建链接
self.connection = [[NSURLConnection alloc] initWithRequest:requrst delegate:self];
if ( self.connection) {
NSLog(@"链接成功");
}else {
NSLog(@"链接失败");
}

[url release];
[urlString release];
[requrst release];
// Do any additional setup after loading the view, typically from a nib.
}

- (void)viewDidUnload
{
self.label = nil;
self.data = nil;
[super viewDidUnload];
// Release any retained subviews of the main view.
}

- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation
{
return (interfaceOrientation != UIInterfaceOrientationPortraitUpsideDown);
}

#pragma mark-
#pragma NSUrlConnectionDelegate methods
- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response
{
//接受一个服务端回话，再次一般初始化接受数据的对象

NSLog(@"返回数据类型：%@",[response textEncodingName]);
NSMutableData *d = [[NSMutableData alloc] init];
self.data = d;
[d release];
}

- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data
{
//接受返回数据，这个方法可能会被调用多次，因此将多次返回数据加起来

NSUInteger datalength = [data length];
NSLog(@"返回数据量：%d",datalength);
[self.data appendData:data];
}

- (void)connectionDidFinishLoading:(NSURLConnection *)connection
{
//连接结束

NSLog(@"%d:",[self.data length]);
NSStringEncoding enc = CFStringConvertEncodingToNSStringEncoding(kCFStringEncodingGB_18030_2000);
NSString *mystr = [[NSString alloc] initWithData:_data encoding:enc];
// string i
NSLog(@"最后的结果：%@",mystr);
self.label.text = mystr;
[mystr release];
[self.connection release];
}

- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error
{
//链接错误
}

@end
简单说下：
1.最简单的网络链接，一个url，一个request，一个connection以及一个response返回。默认的是get请求。
2.data转码问题，这个一开始有点纠结。即，在最后我们要把NSData转化成NSString时候需要一个转码格式，一开始我习惯性的用了UTF-8，
然后发现转化后String 是Null，于是去打印了下请求返回的一些参数，显示的是GB2312~。
然后NSStringEncoding enc = CFStringConvertEncodingToNSStringEncoding(kCFStringEncodingGB_18030_2000);
NSString *mystr = [[NSString alloc] initWithData:_data encoding:enc];
就ok了。
4.代理方法的实现，基本以上几个都需要实现吧。还有更多可选方法可以根据自身需要去选择性实现。