Machine Learning Blog Post: Snip 1

DownloadingAModel.m

// Once you get the NSData from the download task from where you hosted the file...

#pragma mark - Local Storage

// A 4 Step Process
// 1) Save off the NSData of the Core ML model to a temporary spot
// 2) Compile the model from that URL, whic gives us another temporary URL of where it's compiled at
// 3) Create a permanent URL by appending the temporary URL that was generated. This is what initlizes stuff
// 4) Save the permanent URL for later use
- (void)saveModelData:(NSData *)data {
    // First, save the raw NSData since MLModel uses a URL for compilation.
    NSURL *modelDataURL = [NSURL URLWithString:[NSString stringWithFormat:@"%@modelData.tmp", NSTemporaryDirectory()]];
    NSError *writeError;
    [data writeToFile:modelDataURL.path options:NSDataWritingAtomic error:&writeError];

    if (writeError != nil) {
        NSLog(@"Couldn't save data. Error: %@", writeError.localizedDescription);
        return;
    }
    
    // Now compile the model itself, which results in a temporary URL where the model is at
    NSError *compilationOrSaveError;
    NSURL *compiledModelURL = [MLModel compileModelAtURL:modelDataURL error:&compilationOrSaveError];
    
    if (compilationOrSaveError != nil) {
        NSLog(@"Couldn't compile model data. Error: %@", compilationOrSaveError.localizedDescription);
        return;
    }
    
    // Now save off the permanent URL so we can later access it in the app support directory
    NSFileManager *fileManager = [NSFileManager defaultManager];
    NSURL *appSupportDirectory = [fileManager URLForDirectory:NSApplicationSupportDirectory inDomain:NSUserDomainMask appropriateForURL:compiledModelURL create:YES error:&compilationOrSaveError];
    
    if (compilationOrSaveError != nil) {
        NSLog(@"Couldn't save compile model data permanent URL. Error: %@", compilationOrSaveError.localizedDescription);
        return;
    }
    
    NSURL *permanentURL = [appSupportDirectory URLByAppendingPathComponent:compiledModelURL.lastPathComponent];
    [self savePermanentFileURL:permanentURL];
    
    // Replace it or save it
    if ([fileManager fileExistsAtPath:permanentURL.absoluteString]) {
        [fileManager replaceItemAtURL:permanentURL withItemAtURL:compiledModelURL backupItemName:nil options:NSFileManagerItemReplacementWithoutDeletingBackupItem resultingItemURL:nil error:nil];
    } else {
        [fileManager copyItemAtURL:compiledModelURL toURL:permanentURL error:nil];
    }
    
    NSLog(@"Compilation successful and the URL was saved.");
}