strange multiple files download - NSURLConnection

问题:

I encounter a problem by following your comment. I would like to download different file at same time with different delegate:

.h:

NSMutableData *fileData;

.m:

NSString *imgfile = [NSString stringWithFormat:@"http://xxxx/01.jpg"];
NSURL *fileURL1 = [NSURL URLWithString:imgfile];

NSString *audiofile = [NSString stringWithFormat:@"http://xxxx/01.mp3"];
NSURL *fileURL2 = [NSURL URLWithString:audiofile];

NSURLRequest *request1 = [NSURLRequest requestWithURL:fileURL1 cachePolicy:NSURLRequestUseProtocolCachePolicy timeoutInterval:10.0 ];
NSURLRequest *request2 = [NSURLRequest requestWithURL:fileURL2 cachePolicy:NSURLRequestUseProtocolCachePolicy timeoutInterval:10.0 ];

NSArray *connections = [[NSArray alloc] initWithObjects:
[[NSURLConnection alloc] initWithRequest:request1 delegate:self ],
[[NSURLConnection alloc] initWithRequest:request2 delegate:self ],
nil];

- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response {
    fileData = [[NSMutableData alloc] init];
}

- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data {
    [fileData appendData:data];        
}

- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error {
    NSLog(@"Unable to fetch data");
}

ok, the download process works, but, the file size of jpg and mp3 are incorrect, the only correct thing is the total file size (jpg+mp3), please could you have a look on the code, what is missing?

Another question is, I put the file in a NSMutableArray, my question is, how to check which index of array is the correct file type (jpg and mp3)? because I need to save them to the device folder.

回答1:

It looks like both your connections write to the same fileData object and all your problems follow from that.
How to deal with multiple connections you can see relevant question asked here on SO, there's also nice blog post containing NSURLConnection subclass that addresses this issue.

回答2:

Here is what I am doing, I set a counter to identify the file type to save:

  - (void)connectionDidFinishLoading:(NSURLConnection *)connection {
    NSMutableData *dataForConnection = [self dataForConnection:(CustomURLConnection*)connection];
    [connection release];

   // Do something with the dataForConnection.

   downloadCount ++;

//  Copy Image Data to ur location using FileManager
//UIImage *img = [UIImage imageWithData:fileData];
NSString *saveDir;
if (downloadCount ==1)
    saveDir = [NSString stringWithFormat:@"001.jpg"];
if (downloadCount == 2)
    saveDir = [NSString stringWithFormat:@"001.mp3"];

//NSLog(@"saveDir=%@",saveDir);
NSArray  * sysPaths = NSSearchPathForDirectoriesInDomains( NSDocumentDirectory, NSUserDomainMask, YES );
NSString * filePath = [[NSString alloc] initWithFormat: @"%@/%@", [sysPaths objectAtIndex: 0], saveDir];
NSLog(@"filePath=%@",filePath);

if([dataForConnection writeToFile:filePath atomically:YES])
    NSLog(@"DONE COPYING");
else
    NSLog(@"Write to device error");
//[fileData setLength:0];

if (downloadCount == 2)
{
    downloadCount = 0;
    play the MP3 and display the image file;
}

}

even I run the app on simulator, the file was download without error reported, but sometimes the file can not be opened, even I tried to open it from the folder, I was told the file was corrupted, I do not understand what was wrong, hope you do understand what I am saying.