How to capitalize value in text boxes when using wpf mvvm?

Question

Hello

I am using Mvvm Toolkit with wpf. I'm saving the data I get from the text boxes to the database with EF. However, I want to do something like this. Capitalize the first letter of the entered value when the focus leaves the text box. I want to do it this way for all string types. What is the easiest and most convenient method? How can I do this?

Thanks.

Answer 1

To capitalize the first letter of the entered value when the focus leaves the text box, you can use the LostFocus event of the TextBox control. In the event handler, you can get the entered text, capitalize the first letter, and set the modified text back to the TextBox. Here's how you can do it in MVVM:

1. Create a new class called TextBoxBehavior that inherits from Behavior<TextBox>.

public class TextBoxBehavior : Behavior<TextBox>

{
protected override void OnAttached()

{

    base.OnAttached();

    AssociatedObject.LostFocus += AssociatedObject_LostFocus;

}

protected override void OnDetaching()

{

    base.OnDetaching();

    AssociatedObject.LostFocus -= AssociatedObject_LostFocus;

}

private void AssociatedObject_LostFocus(object sender, RoutedEventArgs e)

{

    var textBox = sender as TextBox;

    if (textBox != null && textBox.Text.Length > 0 && char.IsLower(textBox.Text[0]))

    {

        textBox.Text = char.ToUpper(textBox.Text[0]) + textBox.Text.Substring(1);

    }

  }

}

1. In your XAML, add the xmlns:i and xmlns:local namespaces:

xmlns:i="http://schemas.microsoft.com/expression/2010/interactivity"

xmlns:local="clr-namespace:YourNamespace"

3. Add the TextBoxBehavior to your TextBox control:

<TextBox Text="{Binding YourProperty}" >
    <i:Interaction.Behaviors>
        <local:TextBoxBehavior />
    </i:Interaction.Behaviors>
</TextBox>

This will capitalize the first letter of the entered text when the focus leaves the TextBox. Note that this solution only works for single-line TextBox controls. If you want to support multi-line TextBox controls, you'll need to modify the behavior to handle line breaks.

Answer 2

Hi,@fatih uyanık. Welcome Microsoft Q&A.

You could refer to the example below to convert the first letter to uppercase using the converter.

 <Window.Resources>
        <local:CapitalizeFirstLetterConverter x:Key="CapitalizeConverter"/>
    </Window.Resources>

    <Window.DataContext>
        <local:ViewModel/>
    </Window.DataContext>
    <StackPanel>
        <TextBox Text="{Binding MyText, UpdateSourceTrigger=LostFocus, Converter={StaticResource CapitalizeConverter}}" Background="AliceBlue" Height="50"/>
        <TextBox Text="{Binding MyText1, UpdateSourceTrigger=LostFocus, Converter={StaticResource CapitalizeConverter}}" Background="AliceBlue" Height="50"/>
      

    </StackPanel>

codebedhind:

 public class ViewModel : INotifyPropertyChanged
    {

        public ViewModel()
        {
           
        }
        private string myText;
        public string MyText
        {
            get { return myText; }
            set
            {
                if (myText != value)
                {
                    myText = value;
                    OnPropertyChanged("MyText");
                }
            }
        }
        private string myText1;
        public string MyText1
        {
            get { return myText1; }
            set
            {
                if (myText1 != value)
                {
                    myText1 = value;
                    OnPropertyChanged("MyText1");
                }
            }
        }
        
        public event PropertyChangedEventHandler PropertyChanged;
        protected void OnPropertyChanged([CallerMemberName] string name = null)
        {
            PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(name));
        }
    }
    [ValueConversion(typeof(string), typeof(string))]
    public class CapitalizeFirstLetterConverter : IValueConverter
    {
        public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
        {
            return value;
        }
        public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
        {
            if (value is string)
            {
                var castValue = (string)value;
                return char.ToUpper(castValue[0]) + castValue.Substring(1);
            }
            else
            {
                return value;
            }
        }
    }

The result:

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