Strange Behavior When Pasting Text in UITextField

Question

Here's what I did:

1. Open the App Store App
2. Type in "123" in search box
3. Cut the text "123" from search box
4. Type "xx" in search box
5. Move search box cursor to between both "x"
6. Paste "123" to search box

The result should be "x123x", but what I get is "x 123 x". This happened on all the UITextField of all apps.

Please refer to this gif: demo

Is this an iOS bug? Or am I missing something here?

Answer 1

This is intended behavior. There is a property to disable this on iOS 11:

if #available(iOS 11.0, *) {
    textField.smartInsertDeleteType = .no
}

See also: https://developer.apple.com/documentation/uikit/uitextinputtraits/2865828-smartinsertdeletetype?changes=_6