WindowStyle

设置：WindowStyle="None"，窗口无法拖拽，但可纵向和横向拉伸

<Window x:Class="WPFDemo.MainWindow.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:WPFDemo.MainWindow"
        mc:Ignorable="d"
        WindowStyle="None" 
        Title="MainWindow" Height="450" Width="800">
    <Grid>

    </Grid>
</Window>

运行效果：

AllowsTransparency

设置：AllowsTransparency="True"，但是必须同时设置WindowStyle="None"，不然会报错，也不支持拖拽和拉伸

<Window x:Class="WPFDemo.MainWindow.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:WPFDemo.MainWindow"
        mc:Ignorable="d"
        WindowStyle="None"  AllowsTransparency="True"
        Title="MainWindow" Height="450" Width="800">
    <Grid>

    </Grid>
</Window>

运行效果：

WindowChrome（推荐使用）

设置：<WindowChrome GlassFrameThickness="0" >，不影响拖拽和拉伸

<Window x:Class="WPFDemo.MainWindow.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:WPFDemo.MainWindow"
        mc:Ignorable="d"
        Title="MainWindow" Height="450" Width="800">
    
    <WindowChrome.WindowChrome>
        <WindowChrome GlassFrameThickness="0" >
        </WindowChrome>
    </WindowChrome.WindowChrome>
</Window>

运行效果：