iOS Support External Keyboard Without Displaying One

问题

Given a UIViewController, I would like to receive text input only from the external keyboard. Think UIKeyCommand but for any character (not just 'modified' ones).

However, when I try to implement that using UIKeyInput, it seems that iOS desperately wants to display a keyboard if there is no external one connected.

Is there any way to circumvent that? Specifically, to have the options to receive keystrokes from the keyboard if, and only if, one is connected?

回答1:

After fiddling with a iPad for an hour, I finally have a good solution for this in swift. The other methods are weak or use 3rd party software. The reason why UIKeyboardWillShowNotification is getting fired even when an external keyboard is being used for an iPad is the shortcut bar existing. In order to disable the shortcut bar, do this:

    let item : UITextInputAssistantItem = textField.inputAssistantItem
    item.leadingBarButtonGroups = []
    item.trailingBarButtonGroups = []

This covers most cases of what you need, but UIKeyboardWillShowNotification can still be fired if someone plugs their keyboard in at certain points of use. If you have the screen adjust, you can't afford any case for the user to experience this. Plus, you might want the shortcut bar for some reason. Regardless of what your desires are, this covers all cases of an external keyboard being used:

Add to viewDidAppear

NSNotificationCenter.defaultCenter().addObserver(self, selector: #selector(LoginViewController.keyboardWillShow), name: UIKeyboardWillShowNotification, object: nil)
NSNotificationCenter.defaultCenter().addObserver(self, selector: #selector(LoginViewController.keyboardWillHide), name: UIKeyboardWillHideNotification, object: nil)

whenever you leave the view add this to anything that makes you leave

NSNotificationCenter.defaultCenter().removeObserver(self, name: UIKeyboardWillShowNotification, object: nil)
NSNotificationCenter.defaultCenter().removeObserver(self, name: UIKeyboardWillHideNotification, object: nil)

also add it to the deinit{} method to be thourough.

Now use these functions:

func keyboardWillShow(notification: NSNotification) {
    //   This code is an alternate way of checking for keyboard
    var userInfo: [NSObject: AnyObject] = notification.userInfo!
    let firstFrame = userInfo[UIKeyboardFrameBeginUserInfoKey] as! NSValue
    let secondFrame = userInfo[UIKeyboardFrameEndUserInfoKey] as! NSValue
    let firstRect = firstFrame.CGRectValue()
    let secondRect = secondFrame.CGRectValue()
    let diff = abs(firstRect.origin.y - secondRect.origin.y)
    let isFirstBigger = firstRect.origin.y > secondRect.origin.y
    if firstRect != secondRect && diff != 55 {
        if !isFirstBigger {
            //animateViewToDefaultPosition()
        } else {
            //animateViewToPositionWhenKeyboardActive()
        }
    }
}

func keyboardWillHide() {
    //animateViewToDefaultPosition()
}

The 55 is the height of the shortcut bar. You can remove it's functionality if you don't have one. The !isFirstBigger is used to check for when they unhook the keyboard and hook it back in during text field editing. It is also important that diff != 55 during that check because with a shortcut bar this would be the case when you did not want to animate the screen.

This is by far the best method I have seen after scouring Stack Overflow. If anyone finds a bug in the functionality, let me know, but I am confident it will take care of the pesky shortcut bar external keyboard issues. I hope this helps everyone else out there confused by all this!

来源：https://stackoverflow.com/questions/36846814/ios-support-external-keyboard-without-displaying-one

标签

ios

swift

keyboard

external