fix: #1784

src/Net_40/HandyControl_Net_40/Themes/Styles/DataGrid.xaml

@@ -71,6 +71,7 @@
                                             <hc:SimplePanel.Visibility>
                                                 <MultiBinding Converter="{StaticResource DataGridSelectAllButtonVisibilityConverter}">
                                                     <Binding Path="HeadersVisibility" RelativeSource="{RelativeSource AncestorType=DataGrid}"/>
+                                                    <Binding Path="SelectionMode" RelativeSource="{RelativeSource AncestorType=DataGrid}"/>
                                                     <Binding Path="(hc:DataGridAttach.ShowSelectAllButton)" RelativeSource="{RelativeSource AncestorType=DataGrid}"/>
                                                 </MultiBinding>
                                             </hc:SimplePanel.Visibility>

src/Net_40/HandyControl_Net_40/Themes/Theme.xaml

@@ -12522,6 +12522,7 @@
 											<hc:SimplePanel.Visibility>
 												<MultiBinding Converter="{StaticResource DataGridSelectAllButtonVisibilityConverter}">
 													<Binding Path="HeadersVisibility" RelativeSource="{RelativeSource AncestorType=DataGrid}" />
+													<Binding Path="SelectionMode" RelativeSource="{RelativeSource AncestorType=DataGrid}" />
 													<Binding Path="(hc:DataGridAttach.ShowSelectAllButton)" RelativeSource="{RelativeSource AncestorType=DataGrid}" />
 												</MultiBinding>
 											</hc:SimplePanel.Visibility>

src/Net_GE45/HandyControl_Net_GE45/HandyControl_Net_GE45.csproj

@@ -167,7 +167,7 @@
       <Link>Resources\Images\GlowWindow\topright.png</Link>
     </Resource>
   </ItemGroup>
-  <Target Name="PreBuild" BeforeTargets="Build" Condition="'$(IsCrossTargetingBuild)' == 'true'">
+  <Target Name="PreBuild" BeforeTargets="PreBuildEvent">
     <Exec Command="..\..\Shared\HandyControl_Shared\Themes\XamlCombine.exe ..\..\Shared\HandyControl_Shared\Themes\Theme_GE45.txt Theme.xaml" />
   </Target>
 </Project>

src/Shared/HandyControl_Shared/Themes/Styles/DataGrid.xaml

@@ -71,6 +71,7 @@
                                             <hc:SimplePanel.Visibility>
                                                 <MultiBinding Converter="{StaticResource DataGridSelectAllButtonVisibilityConverter}">
                                                     <Binding Path="HeadersVisibility" RelativeSource="{RelativeSource AncestorType=DataGrid}"/>
+                                                    <Binding Path="SelectionMode" RelativeSource="{RelativeSource AncestorType=DataGrid}"/>
                                                     <Binding Path="(hc:DataGridAttach.ShowSelectAllButton)" RelativeSource="{RelativeSource AncestorType=DataGrid}"/>
                                                 </MultiBinding>
                                             </hc:SimplePanel.Visibility>

src/Shared/HandyControl_Shared/Themes/Theme.xaml

@@ -12658,6 +12658,7 @@
 											<hc:SimplePanel.Visibility>
 												<MultiBinding Converter="{StaticResource DataGridSelectAllButtonVisibilityConverter}">
 													<Binding Path="HeadersVisibility" RelativeSource="{RelativeSource AncestorType=DataGrid}" />
+													<Binding Path="SelectionMode" RelativeSource="{RelativeSource AncestorType=DataGrid}" />
 													<Binding Path="(hc:DataGridAttach.ShowSelectAllButton)" RelativeSource="{RelativeSource AncestorType=DataGrid}" />
 												</MultiBinding>
 											</hc:SimplePanel.Visibility>

src/Shared/HandyControl_Shared/Tools/Converter/DataGridSelectAllButtonVisibilityConverter.cs

@@ -8,16 +8,23 @@ namespace HandyControl.Tools.Converter;
 
 public class DataGridSelectAllButtonVisibilityConverter : IMultiValueConverter
 {
+    private const int DesiredParamsCount = 3;
+
     public object Convert(object[] values, Type targetType, object parameter, CultureInfo culture)
     {
-        if (values?.Length is 2 &&
-            values[0] is DataGridHeadersVisibility.All &&
-            values[1] is bool showButton)
+        if (values?.Length is not DesiredParamsCount)
         {
-            return showButton ? Visibility.Visible : Visibility.Hidden;
+            return Visibility.Collapsed;
         }
 
-        return Visibility.Collapsed;
+        if (values[0] is not DataGridHeadersVisibility.All)
+        {
+            return Visibility.Hidden;
+        }
+
+        return values[1] is not SelectionMode.Single && values[2] is true
+            ? Visibility.Visible
+            : Visibility.Hidden;
     }
 
     public object[] ConvertBack(object value, Type[] targetTypes, object parameter, CultureInfo culture)