UIScrollView: How to kick start keyboard dismiss interactively operation (Like WhatsApp) before the drag down operation touching the keyboard? - ios

Question

In UIScrollView, there is a feature named "Keyboard Dismiss interactively"
By using such option, this enables me to implement the following drag down to hide keyboard
However, the keyboard dismiss operation only kick start, when the UIScrollView drag action touches keyboard edge.
What I would like to achieve is, the keyboard dismiss operation kick start, when the UIScrollView drag operation touches the bottom toolbar edge.
What I wish to achieve (Same as WhatsApp)
As you can see from the video, the keyboard dismiss operation will kick start, when the drag operation touches the bottom bar edge, even before touching keyboard edge.
May I know, what technique WhatsApp is using, to achieve such behavior?
Side note
You may notice our bottom toolbar does move along with keyboard. This is because there is a bottom constraint for bottom toolbar's bottom with Safe Area's bottom.
We adjust the bottom constraint's constant value, by installing a gesture recognizer in global Window. This is the code snippet to achieve such technique.
#objc private func didPan(_ sender: UIPanGestureRecognizer){
if keyboardHeight > 0 {
let mainScrollView = editable.mainScrollView
let isScrolling = (mainScrollView.isDragging || mainScrollView.isDecelerating)
if isScrolling {
if let mainScrollViewGlobalOrigin = mainScrollView.globalOrigin {
let point = sender.location(in: sender.view!)
// Take safe area into consideration, like iPhone 12 Pro Max.
let key = UIWindow.key
let bottomSafeArea = key?.safeAreaInsets.bottom ?? 0
let dy = point.y - (
mainScrollViewGlobalOrigin.y +
mainScrollView.frame.height +
toolbarHeightLayoutConstraint.constant +
bottomSafeArea -
bottomLayoutConstraint.constant -
self.keyboardHeight
)
if dy > 0 {
bottomLayoutConstraint.constant = -(keyboardHeight - dy)
}
}
}
}
}

Answer 1

The reason that WhatsApp behaves like this is that their view is considered to be part of the keyboard, so when the swipe gesture reaches their custom view it will begin interactive dismissal.
To achieve this yourself all you need to do is provide the toolbar view as the inputAccessoryView for your view controller. You won't need the constraints for positioning as the keyboard window would then control your toolbar's position.
There is also inputAccessoryViewController for the times where your toolbar may not be a UIView, but instead an entire UIViewController.
The views in either of these properties will only be visible when the keyboard is visible, so to get around that you'll still want to put it into your view hierarchy, but remove/add it based on becoming/resigning first responder.
EDIT: Also, you should be using UIApplication.keyboardDidChangeFrameNotification to detect when the keyboard changes size/position/etc and allow you to adjust insets/positions of views appropriately. In modern iOS there are plenty of ways the keyboard can change size while open, and observing that notification is the correct way to handle the keyboard size.