Does -dataWithContentsOfURL: of NSData work in a background thread?

问题

回答1:

No, it doesn't.

In order to get data from URL asynchronously you should use the NSURLRequest and NSURLConnection approach.

You will have to implement the NSURLConnectionDelegate methods:

-(void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response;
-(void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data;
-(void)connectionDidFinishLoading:(NSURLConnection *)connection;
-(void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error;

回答2:

I'm using dataWithContentsOfURL in a background thread fine.

-(void)loaddata {
    NSData* data = [NSData dataWithContentsOfURL:@"some url"];
    if (data == nil) {
        DLog(@"Could not load data from url: %@", url);
        return;
    }
}

Call something like this from main thread.

[self performSelectorInBackground:@selector(loaddata) withObject:nil];

If you want to perform updates to ui at end of loaddata, be sure to call a function on main thread.

回答3:

No. You can use NSURLSession instead, though.

NSURLSessionConfiguration *sessionConfig = [NSURLSessionConfiguration defaultSessionConfiguration];

NSString *imageURL = @"Direct link to your download";

NSURLSession *session = [NSURLSession sessionWithConfiguration:sessionConfig delegate:self delegateQueue:nil];

NSURLSessionDownloadTask *getImageTask = [session downloadTaskWithRequest:[NSURLRequest requestWithURL:[NSURL URLWithString:imageURL]] completionHandler:^(NSURL * _Nullable location, NSURLResponse * _Nullable response, NSError * _Nullable error) {
    dispatch_async(dispatch_get_main_queue(), ^{

        UIImage *downloadedImage = [UIImage imageWithData:[NSData dataWithContentsOfURL:location]];
    });
}]; 
[getImageTask resume];

回答4:

No, it blocks the current thread.

You need to use NSURLConnection in order to have asynchronous requests.

回答5:

Also you may use -dataWithContentsOfURL + NSOperation + NSOperationQueue

回答6:

I'm guessing this has changed a bit over the years. But, these days,

NSURLRequest* request = [[NSURLRequest alloc] initWithURL:[NSURL URLWithString:urlString]];
[NSURLConnection sendAsynchronousRequest:request queue:[NSOperationQueue mainQueue] completionHandler:^(NSURLResponse* response, NSData* data, NSError* error) {
}];

will give you an async network call.

回答7:

No, this will block the thread and you will load the contents of file into the RAM. You can download content directly into file without temporary NSData to avoid huge RAM usage. Something like this solution https://stackoverflow.com/a/6215458/2937913

来源：https://stackoverflow.com/questions/3078765/does-datawithcontentsofurl-of-nsdata-work-in-a-background-thread

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