How to execute some action on TextBox.Triggers (event trigger)?

Question

I have to disable a some button.

How I can use TextBox.Triggers for that?

Are there any samples?

Thank you for reply!

Answer 1

I am assuming this is related to your other question about triggering the Enabled property on a Button based on if a TextBox has a validation error or not.

If that's so, you would use a DataTrigger to test the TextBox.Validation.HasError property to see if it has any errors, and if so disable the Button

<Style x:Key="MyButtonStyle" TargetType="{x:Type Button}">
    <Setter Property="IsEnabled" Value="True" />
    <DataTrigger Binding="{Binding ElementName=MyTextBox, Path=Validation.HasError" Value="True">
        <Setter Property="IsEnabled" Value="False"/>
    </DataTrigger>
</Style>

Be sure you bind your TextBox with ValidatesOnDataErrors="True" for this to work

<TextBox x:Name="MyTextBox" Text="{Binding SomeText, ValidatesOnDataErrors=True }" />

As a side note, my comment on your other question still applies here. I would personally implement IDataErrorInfo in your ViewModel and make the SaveCommand.CanExecute() only return true if ViewModel.IsValid. Then it will automatically take care of disabling the button if the SaveCommand is not supposed to execute

Answer 2

Let's say you have a TextBox and a Button, and you want to disable your Button when TextBox is empty. This can be easily achieved with DataTriggers:

<TextBox x:Name="textBox" />
<Button>
    <Button.Style>
        <Style>
            <Style.Triggers>
                <DataTrigger Binding="{Binding Text, ElementName=textBox}" Value="">
                    <Setter Property="Button.IsEnabled" Value="False" />
                </DataTrigger>
            </Style.Triggers>
        </Style>
    </Button.Style>
</Button>

Answer 3

Although posting code sample would be helpful and would allow a much better solution, I can still recommend data binding. Something like

<Button Name="btnFoo"
        Enabled="{Binding ElementName=txtblkBar, Converter={StaticResource ButtonVisibilityConverter}"/>

where the resources section of your control contains

<local:ButtonVisibilityConverter Name="ButtonVisibilityConverter"/>

and you have defined a class ButtonVisibilityConverter in the namespace referenced by local. The Data Conversion section of the page I linked to above has an example converter class.

EDIT:

Code that sets the button to disabled whenever txtblkBar is empty:

[ValueConversion(typeof(TextBlock), typeof(bool?))]
public class ButtonVisibilityConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        TextBlock txtblk = value as TextBlock;
        if (null == txtblk)
            return false;
        return !string.IsNullOrEmpty(txtblk.Text);
    }

    public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        // Don't need to use the back conversion
        throw new NotImplementedException();
    }
}