Xcode Swift MacOS App, drag and drop file into NSTextField

Question

I'm implementing my first app for MacOS and the user should input a file path to be processed. I have a NSTextField on my NSViewController app and I'd like to let the user just drag and drop one file there so I could get the file path, open it and put on the NSTextField some text wi the info about the file.

Can you please help me? I saw that if I make the NSTextField editable I can drop the file but I don't want the NSTextField to be editable (just selectable to copy paste info)

Thanks!

Answer 1

First of all, you need to read this guide.

Second, I post here some code that I use to do something similar to what you are asking.

However, my strategy is not to subclass NSTextField but rather place this field inside an NSBox, which I subclass. This has the advantage of providing to the user some visual feedback using a focus ring.

Pay attention to performDragOperation where the string value is set via the window's controller, which then forwards it to the text field to set its string value to the path to the dropped file.

You can filter what you can accept by prepareForDragOperation. Check that too.

class DropBox: NSBox
{
     let dragType = NSPasteboard.PasteboardType(kUTTypeFileURL as String)
     var doHighlight = false

// ---------------------------------------------------------------------------------
// awakeFromNib
// ---------------------------------------------------------------------------------
override func awakeFromNib()
{
    registerForDraggedTypes([dragType])
}

// ---------------------------------------------------------------------------------
// acceptsFirstMouse
// ---------------------------------------------------------------------------------
// Accept activation click as click in window, so source doesn't have to be the
// active window
override func acceptsFirstMouse(for event: NSEvent?) -> Bool
{
    return true
}

// ---------------------------------------------------------------------------------
// draggingEntered
// ---------------------------------------------------------------------------------
override func draggingEntered(_ sender: NSDraggingInfo) -> NSDragOperation
{
    let pasteboard = sender.draggingPasteboard
    let mask = sender.draggingSourceOperationMask
    
    if let types = pasteboard.types, types.contains(dragType)
    {
        if mask.contains(.link)
        {
            doHighlight = true
            needsDisplay = true
            return .link
        }
    }
    
    return []
}

// ---------------------------------------------------------------------------------
// draggingExited
// ---------------------------------------------------------------------------------
override func draggingExited(_ sender: NSDraggingInfo?)
{
    doHighlight = false
    needsDisplay = true
}

// ---------------------------------------------------------------------------------
// drawRect
// ---------------------------------------------------------------------------------
override func draw(_ dirtyRect: NSRect)
{
    super.draw(dirtyRect)
    
    if doHighlight {
        let rect = NSRect(x: dirtyRect.origin.x,
                          y: dirtyRect.origin.y,
                          width: NSWidth(dirtyRect),
                          height: NSHeight(dirtyRect) - NSHeight(titleRect) + 1.0)
        
        NSFocusRingPlacement.only.set()
        let contentRect = rect.insetBy(dx: 4, dy: 4)
        NSBezierPath(rect: contentRect).fill()
    }
}

// ---------------------------------------------------------------------------------
// performDragOperation
// ---------------------------------------------------------------------------------
// Method to handle drop data
override func performDragOperation(_ sender: NSDraggingInfo) -> Bool
{
    if let source = sender.draggingSource as? NSBox {
        if source === self {
            return false
        }
    }
    
    let pasteboard = sender.draggingPasteboard
    let options = [NSPasteboard.ReadingOptionKey.urlReadingFileURLsOnly:true]
    if let urls = pasteboard.readObjects(forClasses: [NSURL.self], options: options) as? [URL],
        let controller = self.window?.delegate as? WindowController
    {
        for url in urls {
            if SchISCoreFileUtilities.isValid(url.path) {
                controller.setApplicationPath(url.path)
                return true
            }
        }
    }
    
    return false
}

// ---------------------------------------------------------------------------------
// prepareForDragOperation
// ---------------------------------------------------------------------------------
// Method to determine if we can accept the drop (filter for urls to apps)
override func prepareForDragOperation(_ sender: NSDraggingInfo) -> Bool
{
    doHighlight = false
    needsDisplay = true
    let pasteboard = sender.draggingPasteboard
    
    if let types = pasteboard.types, types.contains(dragType)
    {
        let options = [NSPasteboard.ReadingOptionKey.urlReadingFileURLsOnly:true]
        if let urls = pasteboard.readObjects(forClasses: [NSURL.self], options: options) as? [URL]
        {
            for url in urls {
                if url.pathExtension == "app" {
                    return true
                }
            }
        }
    }
    
    return false
}

}