UWP - Button click event

MainPage.xaml

<Page
    x:Class="UniversalAppTutorials.MainPage"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="using:UniversalAppTutorials"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    mc:Ignorable="d">

    <RelativePanel BorderBrush="Black" BorderThickness="50" Background="AliceBlue">
        <TextBlock
            x:Name="text_block_1"
            Text="Click the button."
            FontSize="30"
            RelativePanel.Above="button_1"
            RelativePanel.AlignHorizontalCenterWith="button_1"
            Margin="25" 
            Foreground="BlueViolet"
            />
        <Button 
            x:Name="button_1" 
            Content="Click Me"
            Height="75" 
            Width="200"
            Click="button_click"
            RelativePanel.AlignHorizontalCenterWithPanel="True"
            RelativePanel.AlignVerticalCenterWithPanel="True"
            />
    </RelativePanel>
</Page>
MainPage.xaml.cs

using Windows.UI.Xaml;
using Windows.UI.Xaml.Controls;


namespace UniversalAppTutorials
{
    public sealed partial class MainPage : Page
    {
        public MainPage()
        {
            this.InitializeComponent();
        }

        private void button_click(object sender, RoutedEventArgs e) {
            // Change the text block text
            text_block_1.Text = "You clicked the button.";
        }
    }
}