iOS - NSOperation内部的异步NSURLConnection [英] iOS - Async NSURLConnection inside NSOperation

问题描述

我知道这个问题在SO上被问了很多次，但我没有设法使它在我的项目中工作...

因此，我想子类 NSOperation ，并使用 NSURLConnection 下载文件。什么是正确的方式来做呢？
这里是我的代码不工作：
首先，我将所有的操作添加到一个循环：

  DownloadFileOperation * operation; 
 NSOperationQueue * queue = [[NSOperationQueue alloc] init]; 
 for（int i = 0; i <10; i ++）{
 operation = [[DownloadFileOperation alloc] init]; 
 operation.urlString = pdfUrlString; 
 [queue addOperation：operation]; 
 operation = nil; } 
  

这是我的子类：

  @interface DownloadHandbookOperation：NSOperation< NSURLConnectionDelegate> 
 {
 
} 
 
 @property（强，非原子）NSString * urlString; 
 
 @end 
 
 
 @implementation DownloadHandbookOperation 
 {
 NSString * filePath; 
 NSFileHandle * file; 
 NSURLConnection * connection; 
} 
 
  - （void）start 
 {
 if（！[NSThread isMainThread]）
 {
 [self performSelectorOnMainThread：@selector （start）withObject：nil waitUntilDone：NO]; 
 return; 
} 
 
 NSURL * url = [[NSURL alloc] initWithString：[self.urlString stringByAddingPercentEscapesUsingEncoding：NSUTF8StringEncoding]]; 
 
 NSMutableURLRequest * req = [NSMutableURLRequest requestWithURL：url]; 
 [req addValue：@Basic *** =forHTTPHeaderField：@Authorization]; 
 connection = [[NSURLConnection alloc] initWithRequest：req委托：self startImmediately：YES]; 
 
} 
 
  - （void）connection（NSURLConnection *）conn didReceiveResponse：（NSURLResponse *）response 
 {
 NSString * filename = [[ conn.originalRequest.URL absoluteString] lastPathComponent]; 
 filename = [filename stringByReplacingPercentEscapesUsingEncoding：NSUTF8StringEncoding]; 
 
 filePath = [[NSSearchPathForDirectoriesInDomains（NSDocumentDirectory，NSUserDomainMask，YES）objectAtIndex：0] stringByAppendingPathComponent：filename]; 
 [[NSFileManager defaultManager] createFileAtPath：filePath contents：nil attributes：nil]; 
 
 file = [NSFileHandle fileHandleForUpdatingAtPath：filePath]; 
 if（file）
 {
 [file seekToEndOfFile]; 
} 
 else 
 [self finish]; 
} 
 
  - （void）connection（NSURLConnection *）conn didReceiveData：（NSData *）data 
 {
 if（file）{
 [ file seekToEndOfFile]; 
} 
 [file writeData：data]; 
} 
 
  - （void）connectionDidFinishLoading：（NSURLConnection *）conn 
 {
 [file closeFile]; 
 [self finish]; 
} 
 
  - （void）connection：（NSURLConnection *）conn didFailWithError：（NSError *）error 
 {
 connection = nil; 
 
 [self finish]; 
} 
 
  - （void）cancel 
 {
 [super cancel]; 
 [connection cancel]; 
} 
 
 
  - （void）finish 
 {
 NSLog（@operationfinished。 
} 
 
 
 @end 
  

我错了？

解决方案

您需要正确配置操作以作为并发操作执行

并发编程指南：配置并发执行操作

您需要返回 isConcurrent = YES 并正确管理其他状态标志， isExecuting 和 isFinished KVO兼容的方式。

---

为了说明这里的一般想法是Pulse的工程师的一篇文章，容易跟踪演示代码，你可以下载和审查。

Pulse工程博客：使用NSOperationQueues并发下载 **

此代码还处理NSURLConnection在

（**链接现在到archive.org，我想脉搏已被获取并且已经采取了他们的旧网站）

I know this question was asked many times on SO, but I didn't manage to make it work in my project...

So, I want to subclass NSOperation and make it download a file using NSURLConnection. What is the right way to do it? here is my code which doesn't work: First, I'm adding all my operations in a loop:

DownloadFileOperation *operation;
NSOperationQueue *queue = [[NSOperationQueue alloc] init];
for (int i=0; i<10; i++) {
operation = [[DownloadFileOperation alloc] init];
operation.urlString = pdfUrlString;
[queue addOperation:operation];
operation = nil; }

And here is my subclass:

@interface DownloadHandbookOperation : NSOperation <NSURLConnectionDelegate>
{

}

@property (strong, nonatomic) NSString *urlString;

@end


@implementation DownloadHandbookOperation
{
    NSString *filePath;
    NSFileHandle *file;
    NSURLConnection * connection;
}

- (void)start
{
    if (![NSThread isMainThread])
    {
        [self performSelectorOnMainThread:@selector(start) withObject:nil waitUntilDone:NO];
        return;
    }

    NSURL *url = [[NSURL alloc] initWithString:[self.urlString stringByAddingPercentEscapesUsingEncoding: NSUTF8StringEncoding]];

    NSMutableURLRequest *req = [NSMutableURLRequest requestWithURL:url];
    [req addValue:@"Basic ***=" forHTTPHeaderField:@"Authorization"];
    connection = [[NSURLConnection alloc] initWithRequest:req delegate:self startImmediately:YES];

}

- (void)connection:(NSURLConnection *)conn didReceiveResponse:(NSURLResponse *)response
{
    NSString *filename = [[conn.originalRequest.URL absoluteString] lastPathComponent];
    filename = [filename stringByReplacingPercentEscapesUsingEncoding:NSUTF8StringEncoding];

    filePath = [[NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) objectAtIndex:0] stringByAppendingPathComponent:filename];
    [[NSFileManager defaultManager] createFileAtPath:filePath contents:nil attributes:nil];

    file = [NSFileHandle fileHandleForUpdatingAtPath:filePath] ;
    if (file)
    {
        [file seekToEndOfFile];
    }
    else
        [self finish];
}

- (void)connection:(NSURLConnection *)conn didReceiveData:(NSData *)data
{
    if (file) {
        [file seekToEndOfFile];
    }
    [file writeData:data];
}

- (void)connectionDidFinishLoading:(NSURLConnection *)conn
{
    [file closeFile];
    [self finish];
}

- (void)connection:(NSURLConnection *)conn didFailWithError:(NSError *)error
{
    connection = nil;

    [self finish];
}

- (void)cancel
{
    [super cancel];
    [connection cancel];
}


- (void)finish
{
    NSLog(@"operationfinished.");
}


@end

What am I doing wrong?

解决方案

You need to properly configure your operation to execute as a "concurrent operation"

Concurrency Programming Guide: Configuring Operations for Concurrent Execution

You need to return isConcurrent = YES and properly manage the other state flags, isExecuting and isFinished in a KVO compliant manner.

---

To illustrate the general idea here is a post from the engineers at Pulse that describes their solution with some easy to follow demo code you can download and review.

Pulse Engineering Blog: Concurrent Downloads using NSOperationQueues **

This code also handles the requirement that NSURLConnection is started on a thread with an active runloop by ensuring that it starts it on the main thread.

(** link is now to archive.org, I think pulse was acquired and have taken their old site down)

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