iOS中文件的上传下载功能

iOS开发中会经常用到文件上传下载的功能，这篇文件将介绍一下使用asp.net webservice实现文件上传下载。

首先，让我们看下文件下载。

这里我们下载cnblogs上的一个zip文件。使用NSURLRequest+NSURLConnection可以很方便的实现这个功能。

同步下载文件：
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    NSString *urlAsString = @"http://files.cnblogs.com/zhuqil/UIWebViewDemo.zip";    NSURL    *url = [NSURL URLWithString:urlAsString];    NSURLRequest *request = [NSURLRequest requestWithURL:url];    NSError *error = nil;    NSData   *data = [NSURLConnection sendSynchronousRequest:request                                           returningResponse:nil                                                       error:&error];    /* 下载的数据 */    if (data != nil){        NSLog(@"下载成功");        if ([data writeToFile:@"UIWebViewDemo.zip" atomically:YES]) {            NSLog(@"保存成功.");        }        else        {            NSLog(@"保存失败.");        }    } else {        NSLog(@"%@", error);    } 

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异步下载文件：
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• (void)viewDidLoad
  {
  [super viewDidLoad];
  //文件地址
  NSString *urlAsString = @”http://files.cnblogs.com/zhuqil/UIWebViewDemo.zip“;
  NSURL *url = [NSURL URLWithString:urlAsString];
  NSURLRequest *request = [NSURLRequest requestWithURL:url];
  NSMutableData *data = [[NSMutableData alloc] init];
  self.connectionData = data;
  [data release];
  NSURLConnection *newConnection = [[NSURLConnection alloc]
  initWithRequest:request
  delegate:self
  startImmediately:YES];
  self.connection = newConnection;
  [newConnection release];
  if (self.connection != nil){
  NSLog(@”Successfully created the connection”);
  } else {
  NSLog(@”Could not create the connection”);
  }
  }

• (void) connection:(NSURLConnection *)connection
  didFailWithError:(NSError *)error{
  NSLog(@”An error happened”);
  NSLog(@”%@”, error);
  }

• (void) connection:(NSURLConnection *)connection
  didReceiveData:(NSData *)data{
  NSLog(@”Received data”);
  [self.connectionData appendData:data];
  }

• (void) connectionDidFinishLoading
  :(NSURLConnection *)connection{
  /* 下载的数据 */

  NSLog(@"下载成功");if ([self.connectionData writeToFile:@"UIWebViewDemo.zip" atomically:YES]) {    NSLog(@"保存成功.");}else{    NSLog(@"保存失败.");}

  /* do something with the data here */
  }

• (void) connection:(NSURLConnection *)connection
  didReceiveResponse:(NSURLResponse *)response{
  [self.connectionData setLength:0];
  }

• (void) viewDidUnload{
  [super viewDidUnload];
  [self.connection cancel];
  self.connection = nil;
  self.connectionData = nil;
  }

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从上面两段代码中可以看到同步与异步下载的区别，大部分时候我们使用异步下载文件。在asp.net webservice中可以将文件的地址返回到iOS系统，iOS系统在去请求下载该文件。

上传文件

我们先使用VB.Net写一个webservice方法，用于接收上传上来的文件数据，代码如下。
?

<WebMethod(Description:="上传文件！")>

_

Public

Function
UploadFile() As

XmlDocument

    Dim

doc As

XmlDocument = New

XmlDocument()

    Try        Dim

postCollection As

HttpFileCollection = Context.Request.Files

        Dim

aFile As

HttpPostedFile = postCollection(“media”)

        aFile.SaveAs(Server.MapPath(".")

+ “/”

• Path.GetFileName(aFile.FileName))

      doc.LoadXml("<xml>ok</xml>")    Return

doc

    Catch

ex As

Exception

        doc.LoadXml("<xml>fail</xml>")        Return

doc

    End

Try

End

Function

文件上传接口

定义一个类PicOperation用于处理上传图片：
?

@interface
PicOperation : NSOperation

{

UIImage

*theImage;

}

@property
(retain) UIImage *theImage;

@end
[objc] view plain copy

//  //  PicOperation.m  //  DownLoading  //  //  Created by skylin zhu on 11-7-30.  //  Copyright 2011年 mysoft. All rights reserved.  //  #import "PicOperation.h"  #define NOTIFY_AND_LEAVE(X) {[self cleanup:X]; return;}  #define DATA(X) [X dataUsingEncoding:NSUTF8StringEncoding]  // Posting constants  #define IMAGE_CONTENT @"Content-Disposition: form-data; name=\"%@\"; filename=\"image.jpg\"\r\nContent-Type: image/jpeg\r\n\r\n"  #define STRING_CONTENT @"Content-Disposition: form-data; name=\"%@\"\r\n\r\n"  #define MULTIPART @"multipart/form-data; boundary=------------0x0x0x0x0x0x0x0x"  @implementation PicOperation  @synthesize theImage;  //创建postdata  - (NSData*)generateFormDataFromPostDictionary:(NSDictionary*)dict  {      id boundary = @"------------0x0x0x0x0x0x0x0x";      NSArray* keys = [dict allKeys];      NSMutableData* result = [NSMutableData data];      for (int i = 0; i < [keys count]; i++)       {          id value = [dict valueForKey: [keys objectAtIndex:i]];          [result appendData:[[NSString stringWithFormat:@"--%@\r\n", boundary] dataUsingEncoding:NSUTF8StringEncoding]];          if ([value isKindOfClass:[NSData class]])           {              // handle image data              NSString *formstring = [NSString stringWithFormat:IMAGE_CONTENT, [keys objectAtIndex:i]];              [result appendData: DATA(formstring)];              [result appendData:value];          }          else           {              // all non-image fields assumed to be strings              NSString *formstring = [NSString stringWithFormat:STRING_CONTENT, [keys objectAtIndex:i]];              [result appendData: DATA(formstring)];              [result appendData:DATA(value)];          }          NSString *formstring = @"\r\n";          [result appendData:DATA(formstring)];      }      NSString *formstring =[NSString stringWithFormat:@"--%@--\r\n", boundary];      [result appendData:DATA(formstring)];      return result;  }  //上传图片  - (NSString *) UpLoading  {      if (!self.theImage)          NOTIFY_AND_LEAVE(@"Please set image before uploading.");      NSMutableDictionary* post_dict = [[NSMutableDictionary alloc] init];      [post_dict setObject:@"Posted from iPhone" forKey:@"message"];      [post_dict setObject:UIImageJPEGRepresentation(self.theImage, 0.75f) forKey:@"media"];      NSData *postData = [self generateFormDataFromPostDictionary:post_dict];      [post_dict release];      NSString *baseurl = @"http://10.5.23.121:7878/WorkflowService.asmx/UploadFile";       NSURL *url = [NSURL URLWithString:baseurl];      NSMutableURLRequest *urlRequest = [NSMutableURLRequest requestWithURL:url];      if (!urlRequest) NOTIFY_AND_LEAVE(@"Error creating the URL Request");      [urlRequest setHTTPMethod: @"POST"];      [urlRequest setValue:MULTIPART forHTTPHeaderField: @"Content-Type"];      [urlRequest setHTTPBody:postData];      // Submit & retrieve results      NSError *error;      NSURLResponse *response;      NSLog(@"Contacting TwitPic....");      NSData* result = [NSURLConnection sendSynchronousRequest:urlRequest returningResponse:&response error:&error];      if (!result)      {          [self cleanup:[NSString stringWithFormat:@"Submission error: %@", [error localizedDescription]]];          return;      }      // Return results      NSString *outstring = [[[NSString alloc] initWithData:result encoding:NSUTF8StringEncoding] autorelease];      return outstring;  }  @end  

这里我主要定义了两个方法，一个是generateFormDataFromPostDictionary用于创建post form data，一个是UpLoading供调用的类上传图片，这个类需要一个UIimage的对象。

类定义好了，上传图片就非常方便了，看下面代码：
[objc] view plain copy

PicOperation *pic = [[PicOperation alloc] init];  pic.theImage=[UIImage imageNamed:@"meinv4.jpg"];;  NSString *result = [pic UpLoading];  NSLog(result);