Implementing ITextWatcher on EditText throws error

Question

Alright, so I'm setting up an all inclusive control for accepting scan input then doing some functions as text is changed. I've implemented ITextWatcher on my EditText and when I navigate to a fragment with that control on it I get an error. Here's the necessary elements in the control

public class ScannerEditText : EditText, View.IOnKeyListener, View.IOnFocusChangeListener, ITextWatcher
{
    private void Init()
    {
        this.Focusable = true;
        this.FocusableInTouchMode = true;
        //this.SetOnKeyListener(this);
        this.AddTextChangedListener(this);
        //this.OnFocusChangeListener = this;
    }

    private Timer _refreshTimer = null;
    private string _priorText = null;

    public ScannerEditText(Context context)
        : base(context)
    {
        this.Init();
    }

    public ScannerEditText(Context context, IAttributeSet attrs)
        :base(context, attrs)
    {
        this.Init();
    }

    public ScannerEditText(Context context, IAttributeSet attrs, int defStyleAttr)
        :base(context, attrs, defStyleAttr)
    {
        this.Init();
    }

    public ScannerEditText(Context context, IAttributeSet attrs, int defStyleAttr, int defStyleRes)
        :base(context, attrs, defStyleAttr, defStyleRes)
    {
        this.Init();
    }

    void ITextWatcher.AfterTextChanged(IEditable s)
    {
        if (this._refreshTimer != null) this._refreshTimer.Dispose();
        this._refreshTimer = new Timer(delegate (object state)
        {
            this._refreshTimer = null;
            OnUpdateData(this, new EventArgs());
        }, false, 500, 0);
    }

    void ITextWatcher.BeforeTextChanged(ICharSequence s, int start, int count, int after)
    {
        this._priorText = s.ToString();
    }

    void ITextWatcher.OnTextChanged(ICharSequence s, int start, int before, int count)
    {
        string newText = s.ToString();

        //if isEmpty do not advance
        if (string.IsNullOrWhiteSpace(newText))
            return;

        if (newText.Length < this._priorText.Length)
        {
            //if 1 character deleted do not advance
            if (newText == this._priorText.Substring(0, this._priorText.Length - 1))
                return;
        }
        else if (this._priorText.Length < newText.Length)
        {
            //if 1 character added do not advance
            if (newText.Substring(0, newText.Length - 1) == this._priorText)
                return;
        }

        UIUtil.HideKeyboard((Activity)this.Context, (View)this);

        ((View)this.Parent).FindViewById<EditText>(this.NextFocusRightId).RequestFocus();
    }
}

Then I navigate to the any fragment this control on and get the following error: System.NotSupportedException: Unable to activate instance of type AndroidMobileBarcodeForMieTrakAPI.Xamarin.Controls.ScannerEditText from native handle

Now if I remove the ITextWatcher interface and the implementation everything else works

Everything I'm seeing after searching is mostly java which works a little different overriding the members instead of implementing them.

Answer 1

You need to expose the constructor with IntPtr and JniHandleOwnership:

protected ScannerEditText(IntPtr javaReference, JniHandleOwnership transfer)
    : base(javaReference, transfer)
{
}