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Launch macos app from URL

7/21/2018

If you want to launch your app from a URL, Cocoa provided a nice way of doing it.

First, you have to register for the event. You can do it anytime, but I put this code on my AppDelegate class:

open func applicationWillFinishLaunching(_ notification: Notification) {
    initializeURIOptions()
}

fileprivate func initializeURIOptions() {
    // register to listen to the url event
    let appleEventManager = NSAppleEventManager.shared()
    appleEventManager.setEventHandler(self, andSelector: #selector(handleGetURLEvent(event:withReplyEvent:)), forEventClass: AEEventClass(kInternetEventClass), andEventID: AEEventID(kAEGetURL))
}

Then, we have to actually handle the URL parameters. In this example, we assume that the URL is of the form myapp://param1=val1&param2=val2

So we must parse the URL and extract the "param=value" pairs

@objc fileprivate func handleGetURLEvent(event: NSAppleEventDescriptor?, withReplyEvent replyEvent: NSAppleEventDescriptor?) {
    guard let event = event else {
        return
    }
    // our URL event is in this format:
    // myapp://param1=val1&param2=val2&paramN=valN
    
    // grab the query pairs, that is the pairs separated by '&'
    guard let paramDesc = event.paramDescriptor(forKeyword: AEKeyword(keyDirectObject))?.stringValue,
        let url = NSURL(string: paramDesc),
        let queryPairs = url.query?.components(separatedBy: "&") else {
            return
    }
    
    // parse the key/value pair
    // querypairs is assumed to be in the form of "key=value"
    var settingPairs = [String: String]()
    for query in queryPairs {
        let kvp = query.components(separatedBy: "=")
        if kvp.count != 2 {
            continue
        }
        
        let key = kvp[0].lowercased()
        let value = kvp[1].lowercased()
        settingPairs[key] = value
    }
    
    // do stuff with settingPairs
}

Finally, we have to let the OS know to associate the "myapp" URL scheme with our app.

We can do this by editing the app's info.plist and adding a URL Schemes item under the URL types item. The value for this key is the scheme that the OS will associate with your app.

Now, you should be able to launch your app by going to Safari (or any web browser and Terminal), and typing myapp://

If you want to pass parameters to the app you can simply add them to the URL myapp://?param1=val1&param2=val2

When you do this from Safari, you will get a notification such as this:

To debug an app that is launched this way, you can modify XCode's setting to wait until your app is launched before attaching the debugger to the app.

XCode will now automatically attach the debugger to your app when you launch your app via the URL myapp://

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NSSecureTextField Shenanigans

7/14/2018

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Interesting finding:

From the get go, you're not able to input accented characters with keyboard shortcut (alt+e e, alt+u o, etc) on a NSSecureTextField.
But I find this interesting "feature" (maybe a bug or loophole in Apple's implementation of secure text field?) which allows you to do just that.

Here's what to do:

Make sure key repeat is on at System Preference > Keyboard > Keyboard

I created a simple app with a basic NSSecureTextField and a label to display the content of the secure text field.

Go to the NSSecureTextField
Hold e (or any letter that has accented character), until the key repeats

After this point, key combinations (alt+e e, alt+y, alt+u o, etc) will work as expected

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NSPopUpButton shenanigans

7/8/2018

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action/value bound to NSPopupButton is only triggered when user changes the value from the UI. It doesnt get triggered when you change the value programmatically.

For example, if we bind the NSPopupButton's selected index property:

internal var selectedIndex: AnyObject! {
    didSet {
        let oldIndex = oldValue as? Int
        let newIndex = selectedIndex as? Int
        print("selectedIndex didSet, old: \(oldIndex), new: \(newIndex)")
    }
}

changing the selected value via the UI will trigger selectedIndex.didSet as expected

However, when we change the index programmatically such as this:

popUpButton.selectItem(at: 2)

Doing so will change the value in the UI, but it won't trigger selectedIndex.didSet as expected.

A bigger issue happens when we have this scenario:

User selects index 1 from the UI
We programmatically call popupButton.selectItem(at: 2), the UI changed to show that index 2 is selected
User reselects index 1 from the UI
selectedIndex.didset is not called for the user action!!

This happens because when we change the selected item programmatically to 2, selectedIndex's value doesn't actually change, it stayed at 1. So when the user change the index back to 1 via the UI, Cocoa realized that the value of selectedIndex is still the same (1), so it decided not to call the didset function.

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Launch macos app from URL

NSSecureTextField Shenanigans

NSPopUpButton shenanigans

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