Что не так? (Для нестатического поля, метода требуется ссылка на объект)

<Window x:Class="Calc.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:Calc"
        mc:Ignorable="d"
        Title="Calc C# v.1.0.0" Height="379" Width="463">
    <Grid AutomationProperties.Name="from1">
        <TextBox HorizontalAlignment="Center" Margin="0,21,0,0" TextWrapping="Wrap"  Name="textBox1" Text="" VerticalAlignment="Top" Width="413" Height="32"/>
        <Button Content="1" HorizontalAlignment="Left" Margin="25,69,0,0" VerticalAlignment="Top" Width="33" Height="28" Click="Button_Click"/>
        <Button Content="2" HorizontalAlignment="Left" Margin="74,69,0,0" VerticalAlignment="Top" Width="32" Height="28" RenderTransformOrigin="-0.188,0.633" Click="Button_Click_1"/>
        <Button Content="+" HorizontalAlignment="Left" Margin="398,77,0,0" VerticalAlignment="Top" Width="40"/>
        <Button Content="=" HorizontalAlignment="Left" Margin="398,102,0,0" VerticalAlignment="Top" Width="40"/>
    </Grid>
</Window>

<Window x:Class="WpfApp5.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:WpfApp5"
        mc:Ignorable="d"
        Title="MainWindow" Height="450" Width="800">
    <Grid>
        <Grid.ColumnDefinitions>
            <ColumnDefinition/>
            <ColumnDefinition/>
        </Grid.ColumnDefinitions>
 
        <Grid.RowDefinitions>
            <RowDefinition/>
            <RowDefinition/>
        </Grid.RowDefinitions>
 
        <TextBox Grid.Row="0" Grid.Column="0"
                 x:Name="textBox"/>
 
        <Button Grid.Row="1" Grid.Column="1"
                Content="Click me" Click="Button_Click"/>
    </Grid>
</Window>