iPhone 使用Http下载文件及Protocol的使用

文章下面有一个Demo，由于本人刚接触iPhone，所学的东西还很少，有错误和不足的地方还请各位大虾，大牛们多多指正。谢谢
本文的有些代码是在网上爬的,参考文章
http://blog.sina.com.cn/s/blog_5ccfd2d50100u04g.html  Iphone文件读写操作
http://blog.csdn.net/rhljiayou/article/details/7616365 iphone http下载文件

好了，开始本文的征程吧
1，新建一个protocol文件ShowMsgProtocol.h

#import <Foundation/Foundation.h>

@protocol ShowMsgProtocol <NSObject>

-(void)ShowMsg:(NSString *)msg;

@end

2，添加一个HttpDownHelper的类
　　先看HttpDownHelper.h文件

#import <UIKit/UIKit.h>
#import <Foundation/Foundation.h>
#import "ShowMsgProtocol.h"
@interface HttpDownHelper : NSObject
{
    //url
    NSString *urlString;
    //down data
    NSMutableData  *dataNote;
    NSObject<ShowMsgProtocol>   *showMsgDelegate;
}

@property (nonatomic, retain)  NSObject<ShowMsgProtocol> *showMsgDelegate;
@property (nonatomic, retain) NSString *urlString;
@property (nonatomic, retain) NSMutableData *dataNote;

-(void) doDownFile:(NSString *)fileName;

@end

　　在看HttpDownHelper.m文件

#import "HttpDownHelper.h"

@implementation HttpDownHelper

@synthesize urlString,dataNote;
@synthesize showMsgDelegate;

-(void) doDownFile:(NSString *)fileName{
    
    urlString = [[NSString alloc]init];
    dataNote = [[NSMutableData alloc]init];
 urlString = @"http://120.172.58.15:80/test.txt";
     NSLog(@"%@",urlString);
     NSURL *url = [NSURL URLWithString:urlString];
     NSURLRequest *request = [[NSURLRequest alloc]initWithURL:url];
     NSURLConnection *connect = [[NSURLConnection alloc]initWithRequest:request delegate:self];
     [connect release];
     [request release];

}

//接受数据
 -(void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data{
     [self.dataNote appendData:data];
 }
 
 //接受数据完成
 -(void)connectionDidFinishLoading:(NSURLConnection *)connection{
     //获取路径
     //参数NSDocumentDirectory要获取哪种路径
     NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
     //除去需要的路径
     NSString *documentDirectory = [paths objectAtIndex:0];
     //更改到带操作的目录下
     NSString *path = [documentDirectory stringByAppendingPathComponent:@"test.txt"];
     NSLog(@"Path == %@",path);
     
     
     NSLog(@"dataNote:%@",[[NSString alloc]initWithData:dataNote encoding:NSUTF8StringEncoding]);
     
     [[NSFileManager defaultManager]createFileAtPath:path contents:dataNote attributes:nil];
     //将下载到的数据写入文件
     [dataNote writeToFile:path atomically:YES];
     
     NSData *reader = [NSData dataWithContentsOfFile:path];
     
     NSLog(@"length == %d",[reader length]);
     
     //读取刚才写入的文件内容
    NSString *gData2 = [[NSString alloc]initWithData:[reader subdataWithRange:NSMakeRange(0, [reader length])] encoding:NSUTF8StringEncoding];
              
     NSLog(@"gData2 == %@",gData2);
     [showMsgDelegate ShowMsg:gData2];//调用协议
    // lblText.text = gData2;
     
 }
 
 -(void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error{
     UIAlertView *errorAlert = [[UIAlertView alloc] initWithTitle:[error localizedDescription] message:[error localizedFailureReason] delegate:nil cancelButtonTitle:@"OK" otherButtonTitles:nil, nil];
     [errorAlert show];
     [error release];
 }
@end

3，在界面上调用，SecondViewController.h

#import <UIKit/UIKit.h>
#import "showMsgProtocol.h"
#import "HttpDownHelper.h"

@interface SecondViewController : UIViewController<ShowMsgProtocol>
- (IBAction)btnDown:(id)sender;

@end

　　SecondViewController.m

#import "SecondViewController.h"
@interface SecondViewController ()

@end
@implementation SecondViewController

-(void)ShowMsg:(NSString *)msg{
    NSLog(@"ShowMsg=%@",msg);
}
-(IBAction)btnDown:(id)sender{
     HttpDownHelper *httpHepler = [[HttpDownHelper alloc]init];
     [httpHelper doDownFile:@"test.txt"];
     httpHelper.showMsgDelegate = self;
}
@end

 Ok, Demo下载处： HttpDownDemo