Validation of input wpf datagrid

Question

I am trying to validate the input that is entered in the Datagrid in WPF.

I've added a validation rule to the XAML.

The input is an object anymore but a string or int. Though the method i use expects an object.

How can i solve the problem and make it work with an int or string. The input can only be an int between 1 and 20.

XAML :

<DataGridTextColumn Header="Niveau">                                
    <DataGridTextColumn.Binding>                                                                 
        <Binding Path="Niveau" UpdateSourceTrigger="LostFocus">
            <Binding.ValidationRules>                                       
                <valRule:NiveautredeValidationRule  />                                             
            </Binding.ValidationRules>
        </Binding>                                          
    </DataGridTextColumn.Binding>                                               
</DataGridTextColumn>

C#

public class NiveautredeValidationRule : ValidationRule
{
    public override System.Windows.Controls.ValidationResult Validate(object value, System.Globalization.CultureInfo cultureInfo)
    {
        NiveaudoelenViewModel doel = (value as BindingGroup).Items[0] as NiveaudoelenViewModel;
        if (doel.Niveau <= 0 || doel.Niveau > 20)
        {
            return new System.Windows.Controls.ValidationResult(false, "Niveau moet tussen de 1 en 20 zijn!");
        }
        else
        {
            return System.Windows.Controls.ValidationResult.ValidResult;
        }
    }
}

Answer 1

You can try this :

public override System.Windows.Controls.ValidationResult Validate(object value, 
    System.Globalization.CultureInfo cultureInfo)
{
    int myInt = 0;

    try
    {
        if (((string)value).Length > 0)
            myInt = int.Parse((String)value);
    }
    catch (Exception e)
    {
        return new ValidationResult(false, "Illegal characters or " + e.Message);
    }

    if (myInt < 0 || myInt > 20)
    {
        return new ValidationResult(false,
          "Please enter a number in the range: 0 - 20");
    }
    else
    {
        return new ValidationResult(true, null);
    }
}

Source : https://docs.microsoft.com/en-us/dotnet/framework/wpf/data/how-to-implement-binding-validation

Answer 2

You should consider updating the acepted answer to this, this eliminates the try catch and use TryParse instead

public override System.Windows.Controls.ValidationResult Validate(object value, 
    System.Globalization.CultureInfo cultureInfo)
{
    int myInt;
    if (!int.TryParse(System.Convert.ToString(value), out myInt))
        return new ValidationResult(false, "Illegal characters");

    if (myInt < 0 || myInt > 20)
    {
        return new ValidationResult(false, "Please enter a number in the range: 0 - 20");
    }
    else
    {
        return new ValidationResult(true, null);
    }
}