Question

I am creating a wpf application. I have to make all textbox first letter to capital, if a user entered in small then it should be formatted in capital on mouse out.I need the best way to do it, please someone help me.

Answer 1

The best way of doing it greatly depends on how you are doing your app, but @H.B.’s answer is probably the way to go.
For the sake of completeness, another way if doing it would be to use a converter like so:

<!-- Your_Window.xaml -->
<Window x:Class="..."
        ...
        xmlns:cnv="clr-namespace:YourApp.Converters">
  <Window.Resources>
    <cnv.CapitalizeFirstLetterConverter x:Key="capFirst" />
  </Window.Resources>
  ...
  <TextBox Text="{Binding Path=SomeProperty, Converter={StaticResource capFirst}}" />

This assumes that your window’s data context is set to an instance of a class that has a read/write property named SomeProperty of type string.
The converter itself would be something like this:

// CapitalizeFirstLetterConverter.cs
using System;
using System.Data;
using System.Globalization;
namespace YourApp.Converters {
  [ValueConversion(typeof(string), typeof(string))]
  public class CapitalizeFirstLetterConverter : IValueConverter {
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture) {
      // this will be called after getting the value from your backing property
      // and before displaying it in the textbox, so we just pass it as-is
      return value;
    }
    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture) {
      // this will be called after the textbox loses focus (in this case) and
      // before its value is passed to the property setter, so we make our
      // change here
      if (value is string) {
        var castValue = (string)value;
        return char.ToUpper(castValue[0]) + castValue.Substring(1);
      }
      else {
        return value;
      }
    }
  }
}

You can learn more about converters here.