方法1：使用 绑定和转换器 实现

创建类文件 HalfWidthConverter

    public class HalfWidthConverter : IValueConverter{public object Convert(object value, Type targetType, object parameter, CultureInfo culture){if (value is double width){return width / 4;}return value;}public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture){throw new NotImplementedException();}}

<Windowx:Class="WpfApp2.MainWindow"xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"xmlns:local="clr-namespace:WpfApp2"Title="MainWindow"Width="525"Height="350"><Window.Resources><local:HalfWidthConverter x:Key="halfWidthConverter" /></Window.Resources><Grid><Grid.ColumnDefinitions><ColumnDefinition Width="{Binding RelativeSource={RelativeSource AncestorType=Grid}, Path=ActualWidth, Converter={StaticResource halfWidthConverter}}" /><!--  这里使用Converter来设置宽度为父Grid宽度的一半  --><ColumnDefinition Width="*" /><!--  另一个列自动填充剩余空间  --></Grid.ColumnDefinitions><!--  其他UI元素  --><Button Background="Red" /></Grid>
</Window>

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