iOS实现文件上传下载

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：

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);
        } 

异步下载文件：

- (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;
}

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。

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

#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：

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