C# WPF应用双显示器扩展显示问题（ComboBox弹窗位置异常）

以下是几种可行的解决方法：

方法1：监听DropDownOpened事件动态调整位置 #

通过监听ComboBox的下拉展开事件，获取控件所在屏幕，手动调整下拉Popup的位置，确保其显示在当前屏幕内：

using System.Windows.Forms;
using System.Windows.Interop;

private void ComboBox_DropDownOpened(object sender, EventArgs e)
{
    var comboBox = sender as ComboBox;
    if (comboBox == null) return;

    // 获取ComboBox所属窗口的句柄，定位到当前屏幕
    var windowHandle = new WindowInteropHelper(Window.GetWindow(comboBox)).Handle;
    var currentScreen = Screen.FromHandle(windowHandle);
    var screenWorkingArea = currentScreen.WorkingArea;

    // 找到ComboBox模板内的Popup控件
    var popup = comboBox.Template.FindName("PART_Popup", comboBox) as Popup;
    if (popup == null) return;

    // 设置Popup相对于ComboBox的位置
    popup.Placement = PlacementMode.Relative;
    var comboBoxScreenPos = comboBox.PointToScreen(new Point(0, comboBox.ActualHeight));
    var comboBoxLocalPos = comboBox.PointToScreen(new Point(0, 0));
    
    popup.HorizontalOffset = comboBoxScreenPos.X - comboBoxLocalPos.X;
    popup.VerticalOffset = comboBoxScreenPos.Y - comboBoxLocalPos.Y;
}

注意：需要在项目中引用System.Windows.Forms程序集，并且在XAML的ComboBox上绑定该事件：<ComboBox DropDownOpened="ComboBox_DropDownOpened"/>

方法2：自定义ComboBox模板修正Popup定位 #

修改ComboBox的ControlTemplate，确保下拉Popup的定位目标为ComboBox自身，而非依赖系统默认的屏幕定位：

<Style TargetType="{x:Type ComboBox}">
    <Setter Property="Template">
        <Setter.Value>
            <ControlTemplate TargetType="{x:Type ComboBox}">
                <Grid x:Name="templateRoot" SnapsToDevicePixels="True">
                    <ToggleButton x:Name="toggleButton" 
                                  Background="{TemplateBinding Background}"
                                  BorderBrush="{TemplateBinding BorderBrush}"
                                  IsChecked="{Binding IsDropDownOpen, Mode=TwoWay, RelativeSource={RelativeSource TemplatedParent}}">
                        <!-- ToggleButton内容，可保留默认样式 -->
                    </ToggleButton>
                    <ContentPresenter x:Name="contentPresenter"
                                      Content="{TemplateBinding SelectionBoxItem}"
                                      ContentTemplate="{TemplateBinding SelectionBoxItemTemplate}"
                                      Margin="{TemplateBinding Padding}"/>
                    <Popup x:Name="PART_Popup" 
                           AllowsTransparency="True"
                           IsOpen="{Binding IsDropDownOpen, RelativeSource={RelativeSource TemplatedParent}}"
                           Placement="Bottom"
                           PlacementTarget="{Binding ElementName=toggleButton}"
                           PopupAnimation="{DynamicResource {x:Static SystemParameters.ComboBoxPopupAnimationKey}}">
                        <Border x:Name="dropDownBorder"
                                Background="{DynamicResource {x:Static SystemColors.WindowBrushKey}}"
                                BorderBrush="{DynamicResource {x:Static SystemColors.WindowFrameBrushKey}}"
                                BorderThickness="1">
                            <ScrollViewer x:Name="dropDownScrollViewer">
                                <ItemsPresenter x:Name="itemsPresenter"
                                                KeyboardNavigation.DirectionalNavigation="Contained"/>
                            </ScrollViewer>
                        </Border>
                    </Popup>
                </Grid>
            </ControlTemplate>
        </Setter.Value>
    </Setter>
</Style>

核心是将Popup的PlacementTarget绑定到ComboBox内的ToggleButton，Placement设为Bottom，确保下拉列表跟随控件位置。

方法3：窗口移动时更新控件布局 #

监听窗口的位置变化事件，当窗口跨屏幕移动时，强制所有ComboBox刷新布局，避免定位缓存：

private void Window_LocationChanged(object sender, EventArgs e)
{
    // 遍历窗口内所有ComboBox并更新布局
    foreach (var comboBox in FindVisualChildren<ComboBox>(this))
    {
        comboBox.UpdateLayout();
        if (comboBox.IsDropDownOpen)
        {
            var popup = comboBox.Template.FindName("PART_Popup", comboBox) as Popup;
            popup?.UpdateLayout();
        }
    }
}

// 辅助方法：递归查找所有子ComboBox控件
private IEnumerable<T> FindVisualChildren<T>(DependencyObject depObj) where T : DependencyObject
{
    if (depObj == null) yield break;
    
    for (int i = 0; i < VisualTreeHelper.GetChildrenCount(depObj); i++)
    {
        var child = VisualTreeHelper.GetChild(depObj, i);
        if (child is T target)
        {
            yield return target;
        }
        foreach (var subChild in FindVisualChildren<T>(child))
        {
            yield return subChild;
        }
    }
}

记得在窗口的XAML中绑定事件：<Window LocationChanged="Window_LocationChanged">

内容的提问来源于stack exchange，提问作者Pranav Kulkarni