NSURLConnection下载文件时，如何显示进度

转自：http://iliunian.diandian.com/post/2011-12-27/17217880

这里以下载图片举例。

1，首先创建一个connection

downloadImage是一个线程函数，在子线程中下载图片。

//url 图片的url地址

- (void) downloadImage:(NSString*)url{

self.uploadPool = [[NSAutoreleasePool alloc] init];

self.characterBuffer = [NSMutableData data];

done = NO;

[[NSURLCache sharedURLCache] removeAllCachedResponses];

NSMutableURLRequest *theRequest = [NSMutableURLRequest requestWithURL:[NSURL URLWithString:url]];

self.connection = [[NSURLConnection alloc] initWithRequest:theRequest delegate:self];

[self performSelectorOnMainThread:@selector(httpConnectStart) withObject:nil waitUntilDone:NO];

if (connection != nil) {

do {

[[NSRunLoop currentRunLoop] runMode:NSDefaultRunLoopMode beforeDate:[NSDate distantFuture]];

} while (!done);

}

self.photo = [UIImage imageWithData:characterBuffer];

[self performSelectorOnMainThread:@selector(fillPhoto) withObject:nil waitUntilDone:NO];

// Release resources used only in this thread.

self.connection = nil;

[uploadPool release];

self.uploadPool = nil;

}

2， 在NSURLConnection的delegate中接收数据

// Forward errors to the delegate.

- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error {

done = YES;

[self performSelectorOnMainThread:@selector(httpConnectEnd) withObject:nil waitUntilDone:NO];

//NSLog(@"%@",[error localizedDescription]);

[characterBuffer setLength:0];

}

// Called when a chunk of data has been downloaded.

- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data {

// Process the downloaded chunk of data.

//NSLog(@"%d", [data length]);

received_ += [data length];

[self performSelectorOnMainThread:@selector(updateProgress) withObject:nil waitUntilDone:NO];

[characterBuffer appendData:data];

}

- (void)connectionDidFinishLoading:(NSURLConnection *)connection {

//NSLog(@"%lld", received_);

[self performSelectorOnMainThread:@selector(httpConnectEnd) withObject:nil waitUntilDone:NO];

// Set the condition which ends the run loop.

done = YES;

}

上面三个方法，第一个是连接出错的情况，第二个是接收数据，reveived_纪录一共接收了多少子节的数据。第三个是连接结束。

还有一个方法，我们可以从http返回的response中拿到一些连接的信息。这里我拿到了要下载的数据的大小，保存在"Content-Length"的字段中，详细的理论见HTTP协议。

- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response{

NSHTTPURLResponse *httpResponse = (NSHTTPURLResponse *)response;

if(httpResponse && [httpResponse respondsToSelector:@selector(allHeaderFields)])

{

NSDictionary *httpResponseHeaderFields = [httpResponse allHeaderFields];

total_ = [[httpResponseHeaderFields objectForKey:@"Content-Length"] longLongValue];

//NSLog(@"%lld", total_);

}

}

有了要下载的数据的总大小，和已经下载的大小，进度自然就出来了。