Xamarin.Forms iOS CursorPosition不兑现

Question

In my Xamarin.Forms app, I have a behavior that sets the cursor's position (the behavior acts as a mask for our input field).

The CursorPosition is set by calling: targetEntry.CursorPosition = newCursorPosition . This works perfectly fine on Android, but on iOS the cursor always goes to the end of the text, is it an iOS version specific bug, or is it just across the board?

Everything else about the behavior (ensuring that the text is properly masked, that it properly removes the underline character which acts as the guide for where a user should input their data) works as it should. I can post more of my code if needed

Edit: newCursorPosition is a static int variable

Edit 2: Including my code

public class DurationViewMaskBehavior : Behavior { public static DurationViewMaskBehavior Instance = new DurationViewMaskBehavior(); private static int cursorPosition = 0;

    protected override void OnAttachedTo(BorderlessEntry entry) {
        entry.TextChanged += OnInput;
        base.OnAttachedTo(entry);
    }

    protected override void OnDetachingFrom(BorderlessEntry entry) {
        entry.TextChanged -= OnInput;
        base.OnDetachingFrom(entry);
    }

    /// <summary>
    /// This method exists to ensure that if the user tried to shape the field to be something it shouldn't
    /// that it will return the mask to the correct format; this is to ensure that we only have valid data and also that 
    /// </summary>
    /// <param name="text"></param>
    /// <returns></returns>
    private bool PatternMatchCheck(string text) {

        var regex = @"^(([0-9]\d{1}|__|[0-9]_|[0-9]|[0-9]*__|[0-9]\d{1}_| *) Min, ([0-9]\d{1}|__|[0-9]_|[0-9]|[0-9]__|[0-9]\d{1}_|) Sec|((Min, Sec)|[0-9]+ Min, Sec|Min, [0-9]+ Sec))$";

        var match = Regex.Match(text, regex, RegexOptions.IgnoreCase);

        return match.Success;
    }

    private void OnInput(object sender, TextChangedEventArgs args) {

        //Only fire this behavior when the user actually inputs some type of value
        if(!string.IsNullOrWhiteSpace(args.NewTextValue)) {

            var text = args.NewTextValue;

            //How this works so far:
            //At first you get the input, so text.length == 1 is fine. Then
            //it updates itself, so really for every input this event fires twice. 
            //After that we will have to look at the actual text itself so we can use 
            //the index instead

            var targetObject = ((BorderlessEntry)sender);

            if(!PatternMatchCheck(args.NewTextValue) && args.OldTextValue.Length > 2) {
                targetObject.Text = args.OldTextValue;
                return;
            }

            if (text.Length == 1) {
                targetObject.Text = $"{text}_ Min, __ Sec";
                cursorPosition = 1;
            } 

            if(text.Contains("_")) {
                if (text.Length > 1 && (text[2] != '_' || text[1] != '_')) {
                    if (text[2] == '_' && text[0] != '_') {
                        targetObject.Text = $"{text.Substring(0, 2)} Min, __ Sec";
                        cursorPosition = 8;
                    }
                }

                if (text.Length > 1 && text[8] != '_' && text[9] == '_' && text[8] != ' ') {
                    targetObject.Text = $"{text.Substring(0, 2)} Min, {text[8]}_ Sec";
                    cursorPosition = 9;
                }

                if (text.Length > 1 && text[8] != '_' && text[9] != '_') {
                    targetObject.Text = $"{text.Substring(0, 2)} Min, {text.Substring(8, 2)} Sec";
                    cursorPosition = text.Length-1;
                }
            }


            targetObject.CursorPosition = cursorPosition;
        }
    }
}

Answer 1

Figured out why, looks like iOS requires me to bind another .TextChanged event that handles the setting of the cursor. It is strange and backward, but it works.

private void SetCursor(object sender, TextChangedEventArgs args) {
            ((BorderlessEntry)sender).CursorPosition = cursorPosition;
        }

if(isRegistered) {
                    targetObject.TextChanged -= SetCursor;
                    isRegistered = false;
                }
                else {
                    targetObject.TextChanged += SetCursor;
                    isRegistered = true;
                }