How can you implement the NSDocument method -canCloseDocumentWithDelegate:shouldCloseSelector:contextInfo: in Swift?

Question

In my application, a NSDocument subclass mission-critical hardware – users really don’t want to close a document by accident! So, I’ve implemented canClos

Answer 1

Here is a Swift solution to this issue that I received from Apple Developer Technical Support:

override func canCloseDocumentWithDelegate(delegate: AnyObject, shouldCloseSelector: Selector, contextInfo: UnsafeMutablePointer<Void>) {
    super.canCloseDocumentWithDelegate(self, shouldCloseSelector: "document:shouldClose:contextInfo:", contextInfo: contextInfo)
}

func document(doc:NSDocument, shouldClose:Bool, contextInfo:UnsafeMutablePointer<Void>) {
    if shouldClose {
        // <Your clean-up code>
        doc.close()
    }
}

Answer 2

You can solve this with some low level runtime functions:

override func canCloseDocumentWithDelegate(delegate: AnyObject, shouldCloseSelector: Selector, contextInfo: UnsafeMutablePointer<Void>) {

    let allowed = true // ...or false. Add your logic here.

    let Class: AnyClass = object_getClass(delegate)
    let method = class_getMethodImplementation(Class, shouldCloseSelector)

    typealias signature = @convention(c) (AnyObject, Selector, AnyObject, Bool, UnsafeMutablePointer<Void>) -> Void
    let function = unsafeBitCast(method, signature.self)

    function(delegate, shouldCloseSelector, self, allowed, contextInfo)
}

If you need to move this behaviour to another method (eg. after a sheet gets confirmation from the user), simply store the delegate and shouldCloseSelector in properties so you can access them later.

Answer 3

So, my current solution to this, is to keep using Objective-C to perform the NSInvocation. The NSDocument subclass is written in Swift, and calls an Objective-C category to do this bit of work.

Since NSInvocation does not exist in Swift, I really don’t see any other way.

- (void)respondToCanClose:(BOOL)shouldClose delegate:(id)delegate selector:(SEL)shouldCloseSelector contextInfo:(void *)contextInfo
{
    NSDocument *doc = self;

    NSInvocation *invocation = [NSInvocation invocationWithMethodSignature:[delegate methodSignatureForSelector:shouldCloseSelector]];
    invocation.target = delegate;
    invocation.selector = shouldCloseSelector;
    [invocation setArgument:&doc atIndex:2]; // Note index starts from 2 - 0 & 1 are self & selector
    [invocation setArgument:&shouldClose atIndex:3];
    [invocation setArgument:&contextInfo atIndex:4];

    [invocation invoke];
}

You can see my sample project: https://github.com/DouglasHeriot/canCloseDocumentWithDelegate

Another option is to use Objective-C to wrap around objc_msgSend, which is also unavailable in Swift. http://www.cocoabuilder.com/archive/cocoa/87293-how-does-canclosedocumentwithdelegate-work.html#87295

Answer 4

At least as of Swift 4.1, you can do something like:

// Application Logic
myDocument.canClose(
    withDelegate: self,
    shouldClose: #selector(MyClass.document(_:_:_:)),
    contextInfo: nil)

...

// Handler
@objc
private func document(_ doc: NSDocument, _ shouldClose: Bool, _ contextInfo: UnsafeMutableRawPointer) {
    ...
}