How to display a message box on wpf textblock validation error

Question

I have implemented a validation for Datagrid cell template using IDataErrorInfo and can able to show a tooltip error message. How can i display a messagebox with error information instead of tooltip?

  <DataGridTemplateColumn Header="Code" MinWidth="150">
                <DataGridTemplateColumn.CellTemplate>
                    <DataTemplate>
                        <TextBlock Text="{Binding Code, ValidatesOnDataErrors=True, NotifyOnValidationError=True}" Style="{StaticResource TextBlockStyle}"/>
                    </DataTemplate>
                </DataGridTemplateColumn.CellTemplate>
                <DataGridTemplateColumn.CellEditingTemplate>
                    <DataTemplate>
                        <TextBox Text="{Binding Code, UpdateSourceTrigger=LostFocus}"/>
                    </DataTemplate>
                </DataGridTemplateColumn.CellEditingTemplate>
  </DataGridTemplateColumn>

  <Style x:Key="TextBlockStyle" TargetType="{x:Type TextBlock}">
           <Style.Triggers>
              <Trigger Property="Validation.HasError" Value="true">
                 <Setter Property="ToolTip" Value="{Binding RelativeSource={RelativeSource Self},Path=(Validation.Errors)[0].ErrorContent}"/>
              </Trigger>
           </Style.Triggers>
  </Style>

IDataErrorInfo implemented class

public class CurrencyExchangeRate : ObservableObject, IDataErrorInfo
{
    private string _code;
    public string Code
    {
        get { return _code; }
        set
        {
             if (_code != value)
            {
                _code = value;
                if (!string.IsNullOrEmpty(_code))
                {
                    RaisePropertyChangedEvent("Code");
                }
            }
        }
    }  

    public string this[string columnName]
    {
        get
        {
            string error = string.Empty;

            switch (columnName)
            {
                case "Code":

                    if (string.IsNullOrEmpty(_code))
                    {
                        error = "Code cannot be empty";
                        ShowMessage(error);
                    }
                    break;
            }
            return error;
        }
    }  
    public static void ShowMessage(string error)
    {
        System.Windows.Threading.Dispatcher.CurrentDispatcher.BeginInvoke(new Action(() =>
        {
            System.Windows.Forms.MessageBox.Show(error);
        }));
    }
}

You surely have to use code behind, XAML can't help in this case. — King King
– King King, Commented Aug 25, 2014 at 11:41
I have a ViewModel implemented. How to get the error information in the ViewModel whenever error is occurred? — chenk
– chenk, Commented Aug 25, 2014 at 11:53
In indexer where you set your error content display Messagebox. — Maximus
– Maximus, Commented Aug 25, 2014 at 11:53
@Maximus when set the display MessageBox in indexer MessageBox displays more than once. How to display only once like whenever user leave the textblock or something? — chenk
– chenk, Commented Aug 25, 2014 at 12:47
What kind of message box you want to display? any screen shot — yo chauhan
– yo chauhan, Commented Aug 25, 2014 at 13:56

Maximus · Accepted Answer · 2014-08-25 12:50:05Z

1

In your class implementing IDataErrorInfo add in indexer MessageBox. In order to show it only once after leaving TextBox set

 <TextBox Text="{Binding Code, UpdateSourceTrigger=LostFocus}"/>

it will provide checking validation after losing focus.

answered Aug 25, 2014 at 12:50

Maximus

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10 Comments

chenk Over a year ago

I updated the code with the UpdateSourceTrigger=LostFocus. However it displays twice.

Maximus Over a year ago

First time when apply second on validation, am I right?

Maximus Over a year ago

_code should be checked, if (string.IsNullOrEmpty(_code))

chenk Over a year ago

Corrected. It seems to be first time displayed on Lost Focus and second time appears after click 'Ok' button of the first message box.

Maximus Over a year ago

Why are you using Dispatcher? If your ViewModel is a DataContext of View it works on UI.

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