Keep OldValue when cell is not valid in CellValidating event

[Patryk]

I want to lose focus and keep e.OldValue if cell is not valid in CellValidating event. Similar behavior to pressing ESC.
I wrote this code:

private object _cachedOldValue;
private bool _isValidValue;

private void radGridViewIssues_CellValidating(object sender, CellValidatingEventArgs e)
{
    _isValidValue = true;
    RadGridView radGridView = sender as RadGridView;

    if (radGridView == null || !radGridView.IsInEditMode)
    {
        return;
    }

    ValidationResult validationResult = _presenter.ValidateCurrentValue(e.Column.Name, e.Value);

    if (!validationResult)
    {
        _isValidValue = false;
        _cachedOldValue = e.OldValue;
    }
}

private void radGridViewIssues_CellValidated(object sender, CellValidatedEventArgs e)
{
    RadGridView radGridView = sender as RadGridView;

    if (radGridView == null)
    {
        return;
    }

    if (!_isValidValue)
    {
        radGridView.CurrentCell.Value = _cachedOldValue;
    }
}

My column has float? datatype. It works with digits, but throws an exception, when I write some letters.

How can I achieve the desired functionality?

[Dess | Tech Support Engineer, Principal]

Hello Patryk,

Thank you for contacting Telerik Support.

In order to achieve your goal, please have a look at the following code snippet:

public partial class Form1 : Form
{
    public Form1()
    {
        InitializeComponent();

        List<MyObject> list = new List<MyObject>();

        for (int i = 0; i < 10; i++)
        {
            list.Add(new MyObject(i,"Title" + i,1.5f * (i + 1)));
        }

        this.radGridView1.AutoGenerateColumns = false;

        GridViewTextBoxColumn idBoxColumn = new GridViewTextBoxColumn("ID");
        this.radGridView1.MasterTemplate.Columns.Add(idBoxColumn);
        GridViewTextBoxColumn titleBoxColumn = new GridViewTextBoxColumn("Title");
        this.radGridView1.MasterTemplate.Columns.Add(titleBoxColumn);
        GridViewTextBoxColumn priceBoxColumn = new GridViewTextBoxColumn("Price");
        this.radGridView1.MasterTemplate.Columns.Add(priceBoxColumn);

        this.radGridView1.DataSource = list;

        //register the custom row selection behavior
        BaseGridBehavior gridBehavior = this.radGridView1.GridBehavior as BaseGridBehavior;
        gridBehavior.UnregisterBehavior(typeof(GridViewDataRowInfo));
        gridBehavior.RegisterBehavior(typeof(GridViewDataRowInfo), new CustomGridBehavior());
    }

    public class CustomGridBehavior : GridDataRowBehavior
    {
        protected override bool ProcessEnterKey(KeyEventArgs keys)
        {
            if (this.GridControl.IsInEditMode &&
                !ValidateCurrentValue(this.GridControl.CurrentColumn.Name,
                    this.GridControl.ActiveEditor.Value))
            {
                this.GridViewElement.CancelEdit();
            }
            return base.ProcessEnterKey(keys);
        }

        public bool ValidateCurrentValue(string columnName, object currentValue)
        {
            bool isValid = true;

            // Perform validation logic here and set isValid to true or false.
            if (columnName == "Price")
            {
                float val;
                if (currentValue != string.Empty && !float.TryParse(currentValue.ToString(), out val))
                {
                    isValid = false;
                }
            }

            return isValid;
        }
    }

    public class MyObject
    {
        public int ID { get; set; }

        public string Title { get; set; }

        public float? Price { get; set; }

        public MyObject(int iD, string title, float? price)
        {
            this.ID = iD;
            this.Title = title;
            this.Price = price;
        }
    }
}

Note that the Price column allows an empty value or a valid float value when ending edit mode with pressing Enter key. All string values are ignored and the old value will be returned in the cell.

I hope this information helps. Should you have further questions, I would be glad to help.

Regards,
Desislava
Telerik