One example of button and textbox stretching together to fill view:

<Window x:Class="IoCtest.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:local="clr-namespace:IoCtest"
        Title="MainWindow" Height="350" Width="525">
    <Grid OverridesDefaultStyle="True">
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="*" />
        </Grid.ColumnDefinitions>
        <Grid.RowDefinitions>
            <RowDefinition Height="*"></RowDefinition>
            <RowDefinition Height="30"></RowDefinition>
        </Grid.RowDefinitions>
        <TextBox Grid.Row="0" Grid.Column="0" TextWrapping="Wrap" Text="TextBox" AcceptsReturn="True"  HorizontalScrollBarVisibility="Visible" VerticalScrollBarVisibility="Visible"/>
        <Button Grid.Row="1" Content="Write to memo" Height="30" VerticalAlignment="Bottom"></Button>
    </Grid>
</Window>

Important lines to notice are:

<Grid.ColumnDefinitions>
	<ColumnDefinition Width="*" />
</Grid.ColumnDefinitions>
<Grid.RowDefinitions>
	<RowDefinition Height="*"></RowDefinition>
	<RowDefinition Height="30"></RowDefinition>
</Grid.RowDefinitions>

and attributes:

Grid.Row="0" Grid.Column="0"

and

Grid.Row="1" VerticalAlignment="Bottom"