Objective-C create mapped file for PDF

Question

I am creating a file like so:

NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);

NSString *documentsDirectory = [paths objectAtIndex:0];

filePath = [NSString stringWithFormat:@"%@/%@", documentsDirectory,PDFFile];

if (![[NSFileManager defaultManager] fileExistsAtPath:filePath]) {
     [[NSFileManager defaultManager] createFileAtPath:filePath contents:dataBytes attributes:nil];
}

_previewItemURL = [NSURL fileURLWithPath:filePath];

and I am displaying it in an UIDocumentInteractionController like so:

if (_previewItemURL) {

    UIDocumentInteractionController *documentInteractionController =[UIDocumentInteractionController interactionControllerWithURL:_previewItemURL];
    documentInteractionController.delegate = self;

    [documentInteractionController presentPreviewAnimated:YES];
}

However, sometimes the PDF file I am saving off bytes are way too big, sometimes 5.5MB, which causes UIDocumentInteractionController to some time to load the PDF. I was doing some reading here https://stackoverflow.com/a/27863508/979331 and it is suggested to create a 'mapped' file. My question is I don't understand how to create one. I have been googling like crazy for the past two days and I just don't understand it.

I think the issue is with the PDF because I tried this:

NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *documentsDirectory = [paths objectAtIndex:0];
    NSString *pgnPath = [documentsDirectory stringByAppendingPathComponent:[NSString stringWithFormat:@"%@.pdf", @"example"]];

    //filePath = [NSString stringWithFormat:@"%@/%@", documentsDirectory,PDFFile];

    //if (![[NSFileManager defaultManager] fileExistsAtPath:filePath]) {

    NSString *newFile = [[NSBundle mainBundle] pathForResource:@"example" ofType:@"pdf"];

    [[NSFileManager defaultManager] copyItemAtPath:newFile toPath:pgnPath error:&error];

    //[[NSFileManager defaultManager] createFileAtPath:filePath contents:dataBytes attributes:nil];
//}

//_previewItemURL = [[NSBundle mainBundle] URLForResource:@"example" withExtension:@"pdf"];

_previewItemURL = [NSURL fileURLWithPath:pgnPath];

with a PDF that was 5.5MB and everything seemed fine, could the issue be with how I getting the PDF? I am getting the bytes from a web service, here is my call:

task = [dataSource.areaData GetPDFFileTestTwo:[NSString stringWithFormat:@"%@",encodedUrlStr] completion:^(NSData *data, NSURLResponse *response, NSError *error) {

    NSError *myError;
    NSArray *tableArray = [[NSArray alloc]initWithArray:[NSJSONSerialization JSONObjectWithData:data options:kNilOptions error:&myError]];

    NSData *dataBytes;

    for (NSDictionary *dict in tableArray) {
        NSString *base64 = dict[@"data"];
        dataBytes = [[NSData alloc] initWithBase64EncodedString:base64 options:0];
    }

    if (dataBytes) {

        NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
        NSString *documentsDirectory = [paths objectAtIndex:0];

        filePath = [NSString stringWithFormat:@"%@/%@", documentsDirectory,PDFFile];

        if (![[NSFileManager defaultManager] fileExistsAtPath:filePath]) {
            [[NSFileManager defaultManager] createFileAtPath:filePath contents:dataBytes attributes:nil];
        }

        _previewItemURL = [NSURL fileURLWithPath:filePath];

        if (_previewItemURL) {

            dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{

            UIDocumentInteractionController *documentInteractionController =[UIDocumentInteractionController interactionControllerWithURL:_previewItemURL];

            documentInteractionController.delegate = self;

            dispatch_async(dispatch_get_main_queue(), ^{

            [documentInteractionController presentPreviewAnimated:YES];

        });


    });
}


            }

        }];

And here is GetPDFFileTestTwo

-(NSURLSessionDataTask *)GetPDFFileTestTwo:(NSString *)PDFFile completion:(void (^)(NSData *data, NSURLResponse *response, NSError *error))completionHandler{

    NSString *FileBrowserRequestString = [NSString stringWithFormat:@"%@?PDFFile=%@",kIP,PDFFile];
    NSURL *JSONURL = [NSURL URLWithString:FileBrowserRequestString];
    NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:JSONURL];
    NSURLSession *session = [NSURLSession sharedSession];

    NSURLSessionDataTask *dataTask = [session dataTaskWithRequest:request completionHandler:^(NSData *data, NSURLResponse *response, NSError *error){

        if(completionHandler)
        {
            completionHandler(data, response, error);
        }

    }];

    [dataTask resume];

    return dataTask;

}

kIP is a string and that is the web service URL

Answer 1

Your questions;

1. create a 'mapped' file. My question is I don't understand how to create one.

So let me point out that UIDocumentInteractionController has no inputs that accept NSData, so you wouldn't be able to create a memory mapped file to use with it. I also examined the header for any other clues, and didn't find any. https://developer.apple.com/documentation/uikit/uidocumentinteractioncontroller

In looking for a solution, I saw that QLPreviewController mentions 'data' but I find it didn't accept NSData either. https://developer.apple.com/documentation/quicklook/qlpreviewcontroller

I finally settled on WKWebView in WebKit, which does support using NSData, that is Memory Mapped, and loads quite quickly with a 15 MB PDF full of pictures and text I made.

I created a project with the large PDF and tried it out, it works fine. Please feel free to examine it. https://github.com/eSpecialized/PDFDocViewerMapped

How 'mapped' works;

Anything that can take NSData can use a mapped file unless it needs the entire set of data at once. A PDF with a single image vs a multipage PDF are good examples of what can't be mapped and what can be mapped.

    NSError *errors;
    NSData *docFileData = [NSData dataWithContentsOfFile:docFileWithPath options:NSDataReadingMappedAlways error:&errors];

Options for NSData mapped;

https://developer.apple.com/documentation/foundation/nsdatareadingoptions?language=objc

NSDataReadingMappedIfSafe // Hint to map the file in if possible and safe
NSDataReadingMappedAlways // Hint to map the file in if possible. This takes precedence over NSDataReadingMappedIfSafe if both are given.

2. could the issue be with how I getting the PDF?

Fetching a PDF remotely means you must download the document. Think of what you are doing, fetching the Pdf, saving it locally, then opening it in the UIDocument Interaction controller which takes URL's and not NSData.

I hope this meets your criteria for a solution;

• UIDocumentInteractionController limitations with requiring URL's

• WKWebView - allows using NSData that can be memory mapped.

• 3rd party options for PDF viewing - anything that can accept NSData is a candidate for use. Look for CocoaPods and on GitHub for PDF, iOS PDF, etc.

Answer 2

You're not "creating" a mapped file. You're reading it into NSData as mapped to the bytes in the file. That means, that in-memory NSData bytes are underneath mapped to bytes in the file.

Here is a way to read a file as mapped:

https://github.com/atomicbird/atomictools/blob/master/NSData%2BreallyMapped.h

If you can't pass NSData to the controller for preview, mapping makes no sense. Even if you can, you have to be sure that controller won't copy your data before it is used.

Consider using PDFKit framework, where you can initialize PDFDocument with NSData and display it in PDFView.