Cocoa Drag and Drop, reading back the data

Question

Ok, I have a NSOutlineView set up, and I want it to capture PDF's if a pdf is dragged into the NSOutlineView.

My first question, I have the following code:

[outlineView registerForDraggedTypes:[NSArray arrayWithObjects:NSStringPboardType, NSFilenamesPboardType, nil]];

In all the apple Docs and examples I've seen I've also seen something like MySupportedType being an object registered for dragging. What does this mean? Do I change the code to be:

[outlineView registerForDraggedTypes:[NSArray arrayWithObjects:@"pdf", NSStringPboardType, NSFilenamesPboardType, nil]];

Currently I have it set up to recognize drag and drop, and I can even make it spit out the URL of the dragged file once the drag is accepted, however, this leads me to my second question. I want to keep a copy of those PDF's app side. I suppose, and correct me if I'm wrong, that the best way to do this is to grab the data off the clipboard, save it in some persistant store, and that's that. (as apposed to using some sort of copy command and literally copying the file to the app director.)

That being said, I'm not sure how to do that. I've the code:

- (BOOL)outlineView:(NSOutlineView *)ov acceptDrop:(id <NSDraggingInfo>)info item:(id)item childIndex:(NSInteger)childIndex 
{
    NSPasteboard *pboard = [info draggingPasteboard];
    NSURL *fileURL;
    if ( [[pboard types] containsObject:NSURLPboardType] ) {
        fileURL = [NSURL URLFromPasteboard:pboard];
        // Perform operation using the file’s URL
    }

    NSData *data = [pboard dataForType:@"NSPasteboardTypePDF"];

But this never actually gets any data. Like I said before, it does get the URL, just not the data. Does anyone have any advise on how to get this going? Thanks so much!

Answer 1

Dragged Types

Dragged types are just strings that define a system pasteboard type (like NSFilenamesPboardType) or your app's own internal type (like "MyWidgetIdentifierType" to identify a widget by some internal ID).

A drag type of "PDF" doesn't get you anything. You might as well call it "Bob8374Type" ... if you don't give your app the ability to recognize the type (or nothing ever puts anything into the pasteboard for that type), it's utterly useless. You're working with dragged files, so NSFilenamesPboardType is correct.

NSPasteboardTypePDF won't help you unless there is NSPasteboardTypePDF data on the pasteboard. When files are dragged, you get NSFilenamesPboardType. Doesn't matter if the file is .pdf or .xyz; you're only getting paths.

Copy the File or Store a Path

You need to decide whether you intend to copy the dropped PDF or just store a path (or better yet, file system reference) to it. If you're going to copy the PDF, you'll need to make sure you're aware of the proper storage locations (like the Application Support folder, etc).

Assuming you really do want to copy the dropped pdfs somewhere, you don't need the PDF data. You can use NSFileManager to copy (or move) the file at the given path to a new location. If you have some other storage mechanism (ie, you want to suck the PDF data of the file into some other data structure), you can just get the PDF data directly using NSData's +dataWithContentsOfURL:options:error: and do with its data what you please.