The easiest way to write NSData to a file

Question

NSData *data;
data = [self fillInSomeStrangeBytes];

My question is now how I can write this data on the easiest way to an file.

(I've already an NSURL file://localhost/Users/Coding/Library/Application%20Support/App/file.strangebytes)

Answer 1

NSData has a method called writeToURL:atomically: that does exactly what you want to do. Look in the documentation for NSData to see how to use it.

Answer 2

Notice that writing NSData into a file is an IO operation that may block the main thread. Especially if the data object is large.

Therefore it is advised to perform this on a background thread, the easiest way would be to use GCD as follows:

// Use GCD's background queue
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0), ^{
    // Generate the file path
    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES);
    NSString *documentsDirectory = [paths objectAtIndex:0];
    NSString *dataPath = [documentsDirectory stringByAppendingPathComponent:@"yourfilename.dat"];

     // Save it into file system
    [data writeToFile:dataPath atomically:YES];
});

Answer 3

writeToURL:atomically: or writeToFile:atomically: if you have a filename instead of a URL.

Answer 4

You also have writeToFile:options:error: or writeToURL:options:error: which can report error codes in case the saving of the NSData failed for any reason. For example:

NSError *error;

NSURL *folder = [[NSFileManager defaultManager] URLForDirectory:NSApplicationSupportDirectory inDomain:NSUserDomainMask appropriateForURL:nil create:true error:&error];
if (!folder) {
    NSLog(@"%s: %@", __FUNCTION__, error);        // handle error however you would like
    return;
}

NSURL *fileURL = [folder URLByAppendingPathComponent:filename];
BOOL success = [data writeToURL:fileURL options:NSDataWritingAtomic error:&error];
if (!success) {
    NSLog(@"%s: %@", __FUNCTION__, error);        // handle error however you would like
    return;
}

Answer 5

The easiest way, if you want to do this a few times manually instead of coding, is to only use your mouse:

1. Put a breakpoint one line after your NSdata are fulfilled.

2. Hold your mouse over your NSData variable, click on the Eye button, and then export.

3. After that chose the storage details (name/extension/location of the file).

4. Click on "Save" and you are done!