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：
复制代码

    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);
    } 

复制代码

异步下载文件：
复制代码

• (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);