oap_labs/WpfApp2/MainWindow.xaml.cs

using System.Globalization;
using System.Text;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;

namespace WpfApp2
{
 
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
        }
    }
    private void button1_Click (object sender, RoutedEventArgs e)
    {
        button1.Content = "Текст";
    }
}