Implement document drag to application in macOS using swift - swift

Question

I am trying to associate a certain filename extension with my macOS application, which I have managed to do by following this guide and can drag my file in to my application.
When I drag my file in, I get this exception in the console:
2017-11-06 09:56:23.944202+0000 Test App[64192:2356795] [General] readFromData:ofType:error: is a subclass responsibility but has not been overridden.
2017-11-06 09:56:23.958166+0000 Test App[64192:2356795] [General] (
0 CoreFoundation 0x00007fff45f560fb exceptionPreprocess + 171
1 libobjc.A.dylib 0x00007fff6c844c76 objc_exception_throw + 48
2 CoreFoundation 0x00007fff45fe7bfd +[NSException raise:format:] + 205
3 AppKit 0x00007fff43a0b860 -[NSDocument readFromData:ofType:error:] + 253
4 AppKit 0x00007fff43a0b544 -[NSDocument readFromURL:ofType:error:] + 620
5 AppKit 0x00007fff436eb9b9 -[NSDocument _initWithContentsOfURL:ofType:error:] + 172
6 AppKit 0x00007fff436eb89e -[NSDocument initWithContentsOfURL:ofType:error:] + 231
7 AppKit 0x00007fff437c12dd -[NSDocumentController makeDocumentWithContentsOfURL:ofType:error:] + 628
8 AppKit 0x00007fff43a42578 __97-[NSDocumentController makeDocumentWithContentsOfURL:alternateContents:ofType:completionHandler:]_block_invoke + 91
9 AppKit 0x00007fff43a42512 -[NSDocumentController makeDocumentWithContentsOfURL:alternateContents:ofType:completionHandler:] + 176
10 AppKit 0x00007fff437c0493 __80-[NSDocumentController openDocumentWithContentsOfURL:display:completionHandler:]_block_invoke + 880
11 AppKit 0x00007fff43a411b9 __144-[NSDocumentController _coordinateReadingAndGetAlternateContentsForOpeningDocumentAtURL:resolvingSymlinks:thenContinueOnMainThreadWithAccessor:]_block_invoke_4 + 31
12 AppKit 0x00007fff43a41542 __144-[NSDocumentController _coordinateReadingAndGetAlternateContentsForOpeningDocumentAtURL:resolvingSymlinks:thenContinueOnMainThreadWithAccessor:]_block_invoke_2.970 + 149
13 AppKit 0x00007fff43a4147d __144-[NSDocumentController _coordinateReadingAndGetAlternateContentsForOpeningDocumentAtURL:resolvingSymlinks:thenContinueOnMainThreadWithAccessor:]_block_invoke.969 + 138
14 AppKit 0x00007fff43a4133f __144-[NSDocumentController _coordinateReadingAndGetAlternateContentsForOpeningDocumentAtURL:resolvingSymlinks:thenContinueOnMainThreadWithAccessor:]_block_invoke.964 + 254
15 CoreFoundation 0x00007fff45eee52c __CFRUNLOOP_IS_CALLING_OUT_TO_A_BLOCK + 12
16 CoreFoundation 0x00007fff45ed0f43 __CFRunLoopDoBlocks + 275
17 CoreFoundation 0x00007fff45ed0d08 __CFRunLoopRun + 3128
18 CoreFoundation 0x00007fff45ecfe43 CFRunLoopRunSpecific + 483
19 HIToolbox 0x00007fff451ef866 RunCurrentEventLoopInMode + 286
20 HIToolbox 0x00007fff451ef5d6 ReceiveNextEventCommon + 613
21 HIToolbox 0x00007fff451ef354 _BlockUntilNextEventMatchingListInModeWithFilter + 64
22 AppKit 0x00007fff434ec9f7 _DPSNextEvent + 2085
23 AppKit 0x00007fff43c81d98 -[NSApplication(NSEvent) _nextEventMatchingEventMask:untilDate:inMode:dequeue:] + 3044
24 AppKit 0x00007fff434e1805 -[NSApplication run] + 764
25 AppKit 0x00007fff434b09a6 NSApplicationMain + 804
26 Test App 0x000000010004cd1d main + 13
27 libdyld.dylib 0x00007fff6d433145 start + 1
28 ??? 0x0000000000000003 0x0 + 3
I've tried implementing the NSApplicationDelegate openFile functions but none of them are called when I drag the file on to the app:
#NSApplicationMain
class AppDelegate: NSObject, NSApplicationDelegate {
func application(_ application: NSApplication, open urls: [URL]) {
}
func application(_ sender: NSApplication, openFile filename: String) -> Bool {
return false
}
func application(_ sender: NSApplication, openFiles filenames: [String]) {
}
func application(_ sender: NSApplication, openTempFile filename: String) -> Bool {
return false
}
func applicationDidFinishLaunching(_ aNotification: Notification) {
// Insert code here to initialize your application
}
func applicationWillTerminate(_ aNotification: Notification) {
// Insert code here to tear down your application
}
}
How do I get access to the filename and contents of the "dragged in" file? I am using XCode 9.0.1 and Swift 4.
Edit:
Here is my Info.plist
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
<key>CFBundleDevelopmentRegion</key>
<string>en</string>
<key>CFBundleDocumentTypes</key>
<array>
<dict>
<key>CFBundleTypeExtensions</key>
<array>
<string>tal</string>
</array>
<key>CFBundleTypeIconFile</key>
<string></string>
<key>CFBundleTypeMIMETypes</key>
<array>
<string></string>
</array>
<key>CFBundleTypeName</key>
<string>Layout File</string>
<key>CFBundleTypeRole</key>
<string>Editor</string>
<key>LSHandlerRank</key>
<string>Owner</string>
<key>LSItemContentTypes</key>
<array>
<string>com.testapp.layout</string>
</array>
<key>LSTypeIsPackage</key>
<integer>0</integer>
<key>NSDocumentClass</key>
<string>NSDocument</string>
</dict>
</array>
<key>CFBundleExecutable</key>
<string>$(EXECUTABLE_NAME)</string>
<key>CFBundleIconFile</key>
<string></string>
<key>CFBundleIdentifier</key>
<string>$(PRODUCT_BUNDLE_IDENTIFIER)</string>
<key>CFBundleInfoDictionaryVersion</key>
<string>6.0</string>
<key>CFBundleName</key>
<string>$(PRODUCT_NAME)</string>
<key>CFBundlePackageType</key>
<string>APPL</string>
<key>CFBundleShortVersionString</key>
<string>v1.0.0</string>
<key>CFBundleSignature</key>
<string>????</string>
<key>CFBundleVersion</key>
<string></string>
<key>LSApplicationCategoryType</key>
<string>public.app-category.video</string>
<key>LSMinimumSystemVersion</key>
<string>$(MACOSX_DEPLOYMENT_TARGET)</string>
<key>NSAppTransportSecurity</key>
<dict>
<key>NSAllowsArbitraryLoads</key>
<true/>
</dict>
<key>NSHumanReadableCopyright</key>
<string>Copyright © 2017. All rights reserved.</string>
<key>NSMainStoryboardFile</key>
<string>Main</string>
<key>NSPrincipalClass</key>
<string>NSApplication</string>
<key>UTExportedTypeDeclarations</key>
<array>
<dict>
<key>UTTypeConformsTo</key>
<array>
<string>public.data</string>
</array>
<key>UTTypeDescription</key>
<string>Layout File</string>
<key>UTTypeIconFile</key>
<string></string>
<key>UTTypeIdentifier</key>
<string>com.testapp.layout</string>
<key>UTTypeTagSpecification</key>
<dict>
<key>public.filename-extension</key>
<array>
<string>tal</string>
</array>
</dict>
</dict>
<dict/>
</array>
</dict>
</plist>
So I would have expected application(_ sender: NSApplication, openFile filename: String) to be called when I drag the file on to the app when it's in the Dock...

Answer 1

There are a number of points here to address:
if you're working in macOS 10.12 or below, you should implement either openFile or openFiles. openURLs is 10.13+ - but you definitely don't need both
openFile will be called for each of multiple files; if openFiles is present, openFile will not be called, even if you open only a single file
I have no idea what openTempFile (or openUntitledFile) are about; I haven't been able to get anyone to call either
openFile(s) get called when you have successfully registered a UTI with the system; double-clicking an appropriate file(s) in the Finder, choosing 'open' or dragging the file onto the dock icon of your app all send an open message that gets handled by the AppDelegate.
I am not clear what you mean by 'When I drag my file in': if you drag your file onto the app icon in the Finder, openFile(s) should be called; your wording makes me think that your drag destination is part of your application's interface, in which case you need to handle dragging yourself.
Also check - because the linked (iOS) guide does not address this - that you have set your NSDocument class: your example says 'NSDocument', but there is an extreme likelihood that your application uses a custom subclass; so you need to set the 'Class' to that name.