绝对设置方式：使用设备无关单位准确的设置尺寸

自动设置方式：行列的长度刚好满足需要

按比例设置尺寸方式：按比例将空间分割到一组行或列中

<Window x:Class="WpfApplication1.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="350" Width="525">
    <Grid ShowGridLines="True">
        <Grid.RowDefinitions>
            <RowDefinition></RowDefinition>
            <RowDefinition></RowDefinition>
        </Grid.RowDefinitions>
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="100"></ColumnDefinition>
            <ColumnDefinition Width="Auto"></ColumnDefinition>
            <ColumnDefinition Width="*"></ColumnDefinition>
            <ColumnDefinition Width="2*"></ColumnDefinition>
        </Grid.ColumnDefinitions>
        
        <Button Grid.Column="1" Grid.Row="0">123</Button>
    </Grid>
</Window>