Enable Button on valid TextBox

In WPF, I would like to have TextBox and Button. Button should be ena开发者_运维技巧bled only if the length of the text in TextBox is 10.

I am trying to do this using Binding, but it doesn't fire IsValid property reads as I type in the TextBox.

How can this be done?

If you have just this dependency and one value for which it is valid you can use a style:

<TextBox Name="tbTest"/>
<Button Content="Do Stuff">
    <Button.Style>
        <Style TargetType="{x:Type Button}">
            <Setter Property="IsEnabled" Value="False"/>
            <Style.Triggers>
                <DataTrigger Binding="{Binding ElementName=tbTest, Path=Text.Length}" Value="10">
                    <Setter Property="IsEnabled" Value="true"/>
                </DataTrigger>
            </Style.Triggers>
        </Style>
    </Button.Style>
</Button>

Otherwise you should define a ValidationRule which should be added to the Text-binding. Then you can use code-behind to check if it is valid or bind the IsEnabled property to Validation.HasError (using a ValueConverter to invert the boolean).

You have a number of ways to do it.

For example you can use Binding converter:

<TextBox>
    <Binding Path="Text" UpdateSourceTrigger="PropertyChanged">
        <Binding.ValidationRules>
            <WpfApplication1:MyValidationRule />
        </Binding.ValidationRules>
    </Binding>
</TextBox>

<Button>
     <Button.IsEnabled>
         <Binding ElementName="TB" Path="(Validation.HasError)">
             <Binding.Converter>
                 <WpfApplication1:TrueToFalseConverter/>
             </Binding.Converter>
         </Binding>
     </Button.IsEnabled>
 </Button>

public class TrueToFalseConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        return !(bool) value;
    }

    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
    {
        return !(bool)value;
    }
}

public class MyValidationRule : ValidationRule
{
    public override ValidationResult Validate(object value, CultureInfo cultureInfo)
    {
        return new ValidationResult((value as string).Length == 10, null);
    }
}

Or (I'd recommend it) you can use commands and CanExecute:

<Button Command="{Binding Path=MyCommand}" />
<TextBox Text="{Binding Path=Text, UpdateSourceTrigger=PropertyChanged}" />

public class MainWindowViewModel
{
    public RelayCommand MyCommand { get; private set; }

    public string Text { get; set; }

    public MainWindowViewModel()
    {
        Text = "";
        MyCommand = new RelayCommand(MyAction, CanExecute);
    }

    private bool CanExecute(object x)
    {
        return Text.Length == 10;
    }

    ....
}

if the length of the text in TextBox is 10 or more than 10

Try This

private void textBox1_TextChanged(object sender, TextChangedEventArgs e)
    {
        if (textBox1.Text.Length >= 10)
            button1.IsEnabled = true;
        else
            button1.IsEnabled = false;
    }

this not the best idea but it is useful : you can use TextChanged

   private void textBox1_TextChanged(object sender, TextChangedEventArgs e)
    {
        if (textBox1.Text.Length == 10)
            button1.IsEnabled = true;
        else
            button1.IsEnabled = false;
    }