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

  Iphone文件读写操作

 

好了，开始本文的征程吧

1，新建一个protocol文件ShowMsgProtocol.h

1 #import 
     
      2 3 @protocol ShowMsgProtocol 
      
       4 5 -(void)ShowMsg:(NSString *)msg;6 7 @end
      
     

2，添加一个HttpDownHelper的类

　　先看HttpDownHelper.h文件

1 #import 
     
       2 #import 
      
        3 #import "ShowMsgProtocol.h" 4 @interface HttpDownHelper : NSObject 5 { 6     //url 7     NSString *urlString; 8     //down data 9     NSMutableData  *dataNote;10     NSObject
       
           *showMsgDelegate;11 }12 13 @property (nonatomic, retain)  NSObject
        
          *showMsgDelegate;14 @property (nonatomic, retain) NSString *urlString;15 @property (nonatomic, retain) NSMutableData *dataNote;16 17 -(void) doDownFile:(NSString *)fileName;18 19 @end
        
       
      
     

　　在看HttpDownHelper.m文件

1 #import "HttpDownHelper.h" 2  3 @implementation HttpDownHelper 4  5 @synthesize urlString,dataNote; 6 @synthesize showMsgDelegate; 7  8 -(void) doDownFile:(NSString *)fileName{ 9     10     urlString = [[NSString alloc]init];11     dataNote = [[NSMutableData alloc]init];12  urlString = @"http://120.172.58.15:80/test.txt";13      NSLog(@"%@",urlString);14      NSURL *url = [NSURL URLWithString:urlString];15      NSURLRequest *request = [[NSURLRequest alloc]initWithURL:url];16      NSURLConnection *connect = [[NSURLConnection alloc]initWithRequest:request delegate:self];17      [connect release];18      [request release];19 20 }21 22 //接受数据23  -(void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data{24      [self.dataNote appendData:data];25  }26  27  //接受数据完成28  -(void)connectionDidFinishLoading:(NSURLConnection *)connection{29      //获取路径30      //参数NSDocumentDirectory要获取哪种路径31      NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);32      //除去需要的路径33      NSString *documentDirectory = [paths objectAtIndex:0];34      //更改到带操作的目录下35      NSString *path = [documentDirectory stringByAppendingPathComponent:@"test.txt"];36      NSLog(@"Path == %@",path);37      38      39      NSLog(@"dataNote:%@",[[NSString alloc]initWithData:dataNote encoding:NSUTF8StringEncoding]);40      41      [[NSFileManager defaultManager]createFileAtPath:path contents:dataNote attributes:nil];42      //将下载到的数据写入文件43      [dataNote writeToFile:path atomically:YES];44      45      NSData *reader = [NSData dataWithContentsOfFile:path];46      47      NSLog(@"length == %d",[reader length]);48      49      //读取刚才写入的文件内容50     NSString *gData2 = [[NSString alloc]initWithData:[reader subdataWithRange:NSMakeRange(0, [reader length])] encoding:NSUTF8StringEncoding];51               52      NSLog(@"gData2 == %@",gData2);53      [showMsgDelegate ShowMsg:gData2];//调用协议54     // lblText.text = gData2;55      56  }57  58  -(void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error{59      UIAlertView *errorAlert = [[UIAlertView alloc] initWithTitle:[error localizedDescription] message:[error localizedFailureReason] delegate:nil cancelButtonTitle:@"OK" otherButtonTitles:nil, nil];60      [errorAlert show];61      [error release];62  }63 @end

3，在界面上调用，SecondViewController.h

1 #import 
     
      2 #import "showMsgProtocol.h"3 #import "HttpDownHelper.h"4 5 @interface SecondViewController : UIViewController
      
       6 - (IBAction)btnDown:(id)sender;7 8 @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：