Почему TextBox не растягивается? - C# WPF - Ответ 13981714

<Window x:Class="WpfApp13.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:WpfApp13"
        mc:Ignorable="d"
        Title="Title" Height="450" Width="800">
    <Window.CommandBindings>
        <CommandBinding Command="New" Executed="NewCommand_Executed"></CommandBinding>
        <CommandBinding Command="Open" Executed="OpenCommand_Executed"></CommandBinding>
        <CommandBinding Command="Save" Executed="SaveCommand_Executed"></CommandBinding>
        <CommandBinding Command="Close" Executed="CloseCommand_Executed"></CommandBinding>
        <CommandBinding Command="Paste" Executed="PasteCommand_Executed"></CommandBinding>
        <CommandBinding Command="Copy" Executed="CopyCommand_Executed"></CommandBinding>
        <CommandBinding Command="Cut" Executed="CutCommand_Executed"></CommandBinding>
    </Window.CommandBindings>
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="auto" ></RowDefinition>
            <RowDefinition></RowDefinition>
        </Grid.RowDefinitions>
        <StackPanel>
        <Menu>
            <MenuItem Header="Файл">
                <MenuItem Command="New"></MenuItem>
                <MenuItem Command="Open"></MenuItem>
                <MenuItem Command="Save"></MenuItem>
                <MenuItem Command="Close"></MenuItem>
            </MenuItem>
        </Menu>
            
        <StackPanel Orientation="Horizontal" Grid.Row="0">
            <Button Command="New">New</Button>
            <Button Command="Open">Open</Button>
            <Button Command="Save">Save</Button>
            <Button Command="Cut">Cut</Button>
            <Button Command="Copy">Copy</Button>
            <Button Command="Paste">Paste</Button>
        </StackPanel>
            <TextBox Grid.Row="1" ></TextBox>
       
    </StackPanel>
    </Grid>
</Window>