[转+修改]iOS开发中会经常用到文件上传下载类

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如何结合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。在asp.net webservice中可以将文件的地址返回到iOS系统，iOS系统再通过这个url去请求下载该文件。这里为了简单起见，直接将url写道代码里面了。我们可以使用两种方式去下载文件。

1、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);
}

2、异步下载文件：DownLoadingViewController.h

// DownLoadingViewController.h
// DownLoading
//
// Created by skylin zhu on 11-7-30.
// Copyright 2011年 mysoft. All rights reserved.
//

#import <UIKit/UIKit.h>

@interface DownLoadingViewController : UIViewController {
NSURLConnection *connection;
NSMutableData *connectionData;
}
@property (nonatomic,retain) NSURLConnection *connection;
@property (nonatomic,retain) NSMutableData *connectionData;
@end

DownLoadingViewController.m

// DownLoadingViewController.m
// DownLoading
//
// Created by skylin zhu on 11-7-30.
// Copyright 2011年 mysoft. All rights reserved.
//

#import "DownLoadingViewController.h"

@implementation DownLoadingViewController
@synthesize connection,connectionData;
- (void)dealloc
{
[super dealloc];
}

- (void)didReceiveMemoryWarning
{
// Releases the view if it doesn't have a superview.
[super didReceiveMemoryWarning];

// Release any cached data, images, etc that aren't in use.
}

#pragma mark - View lifecycle

// Implement viewDidLoad to do additional setup after loading the view, typically from a nib.
- (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;
}

@end

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。

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，我们可以从Request.Files中获取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

定义一个类PicOperation用于处理上传图片：PicOperation.h

<textarea readonly name="code" class="plain">//
// PicOperation.h
// DownLoading
//
// Created by skylin zhu on 11-7-30.
// Copyright 2011年 mysoft. All rights reserved.
//

#import <Foundation/Foundation.h>

@interface PicOperation : NSOperation
{
UIImage *theImage;
}
@property (retain) UIImage *theImage;
@end

PicOperation.m：

// 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]; //原文此处“&”被翻译为"&apm;" 会导致编译错误 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);

总结：这篇文章讲述了如何在iOS中结合asp.net webservice实现文件的上传和下载功能。