ComboBox Control how to define MaxLength of input Text

Question

ComboBox Control how to define MaxLength of input Text

Dmtr_Grms 331

Hi, a client asked me a change. I have an app with several STANDARD ComboBoxes Control. Until this morning they were all defined with IsEditable="False". Now I have to give the possibility to the user to input a value even if it is not in the ItemSource. I changed one table with IsEditable="True". It's ok user can insert a "free value" but testing I have met a problem. If user input a value with a number of characters greater than the Binded field of DataBase, pgm go in DUMP with msg sqlException.Number 2628. I would like to define what is the MaxLength for the input field of the CombBox but I don't find the parameter in the XAML properties. I tried different solutions proposed on Community Web sites without success. My request is quite simple how to block a ComboBox user input to 10 digits? I'm developing with .Net 6.0, WPF, XAML, C# 10, Entity FrameworkCore 6.20 ComboBox is Binded to a field in SQL Express Database. Thanks for your help.

Viorel 122.6K Reputation points

2023-09-08T17:04:19.3133333+00:00

Does the client agree to truncate the user's data silently, without any alert?
Dmtr_Grms 331 Reputation points

2023-09-08T17:18:28.6466667+00:00

I didn't discuss that with the Client and it is not a really clean solution but tell me how to do that. Thanks
Viorel 122.6K Reputation points

2023-09-11T13:42:18.3566667+00:00

For example, if the used technologies are under your control, you can handle the OK (Save, Accept, etc.) button, or an event like Validating, where you check the inputs and inform the user about the problems. In addition, you can show some indicators (icons, red borders, etc.) during the user's work.

3 answers

Your answer

Viorel 122.6K Reputation points

2023-09-08T17:04:19.3133333+00:00

Does the client agree to truncate the user's data silently, without any alert?
Dmtr_Grms 331 Reputation points

2023-09-08T17:18:28.6466667+00:00

I didn't discuss that with the Client and it is not a really clean solution but tell me how to do that. Thanks
Viorel 122.6K Reputation points

2023-09-11T13:42:18.3566667+00:00

For example, if the used technologies are under your control, you can handle the OK (Save, Accept, etc.) button, or an event like Validating, where you check the inputs and inform the user about the problems. In addition, you can show some indicators (icons, red borders, etc.) during the user's work.

Answer 1

Castorix31 90,686

I tried different solutions proposed on Community Web sites without success.

Did you try the solutions from this old thread ? : MaxLength for editable ComboBox

Dmtr_Grms 331 Reputation points

2023-09-08T17:17:00.9666667+00:00

Yes I tried some of them without success. I'm looking something simple without changing the standard control. Any change will potentially create other problems or misfunction... and I don't want to modify the way other ComboBoxes are operating in the app. I'm looking something simple and safe I also have seen some solution proposals on GitHub but reading comments often you can see that it doesn't work properly or only in specific condition... I'm asking something quite basic, I was told it works as default on WinForms I cannot understand why they don't give that possibility as for example for the TextBox in WPF because at the end in the control it seems to be a TextBox. Other ideas? thanks

Answer 2

Hi,@Dimitri Garmaise. Welcome Microsoft Q&A.

WPF considers ControlTemplates to be a boundry, and will not apply implicit styles (styles without an x:Key) inside of templates.

But there is one exception to this rule: anything that inherits from Control will apply implicit styles.

You could use the Combobox's default style and modify the TextBox(PART_EditableTextBox)'s style(ComboBoxEditableTextBox) to set the maximum length. <Setter Property="MaxLength" Value="10"/>

 <Window.Resources>
        
        <Style x:Key="FocusVisual">
            <Setter Property="Control.Template">
                <Setter.Value>
                    <ControlTemplate>
                        <Rectangle Margin="2" StrokeDashArray="1 2" Stroke="{DynamicResource {x:Static SystemColors.ControlTextBrushKey}}" SnapsToDevicePixels="true" StrokeThickness="1"/>
                    </ControlTemplate>
                </Setter.Value>
            </Setter>
        </Style>
        <SolidColorBrush x:Key="TextBox.Static.Background" Color="#FFFFFFFF"/>
     **   <Style x:Key="ComboBoxEditableTextBox" TargetType="{x:Type TextBox}">**
            <Setter Property="OverridesDefaultStyle" Value="true"/>
            <Setter Property="AllowDrop" Value="true"/>
            <Setter Property="MinWidth" Value="0"/>
            <Setter Property="MinHeight" Value="0"/>
            <Setter Property="FocusVisualStyle" Value="{x:Null}"/>
            <Setter Property="ScrollViewer.PanningMode" Value="VerticalFirst"/>
            <Setter Property="Stylus.IsFlicksEnabled" Value="False"/>
          **  <Setter Property="MaxLength" Value="10"/>**
            <Setter Property="Template">
                <Setter.Value>
                    <ControlTemplate TargetType="{x:Type TextBox}">
                        <ScrollViewer x:Name="PART_ContentHost" Background="Transparent" Focusable="false" HorizontalScrollBarVisibility="Hidden" VerticalScrollBarVisibility="Hidden"/>
                    </ControlTemplate>
                </Setter.Value>
            </Setter>
        </Style>
        <LinearGradientBrush x:Key="ComboBox.Static.Background" EndPoint="0,1" StartPoint="0,0">
            <GradientStop Color="#FFF0F0F0" Offset="0.0"/>
            <GradientStop Color="#FFE5E5E5" Offset="1.0"/>
        </LinearGradientBrush>
        <SolidColorBrush x:Key="ComboBox.Static.Border" Color="#FFACACAC"/>
        <SolidColorBrush x:Key="ComboBox.Static.Glyph" Color="#FF606060"/>
        <SolidColorBrush x:Key="ComboBox.Static.Editable.Background" Color="#FFFFFFFF"/>
        <SolidColorBrush x:Key="ComboBox.Static.Editable.Border" Color="#FFABADB3"/>
        <SolidColorBrush x:Key="ComboBox.Static.Editable.Button.Background" Color="Transparent"/>
        <SolidColorBrush x:Key="ComboBox.Static.Editable.Button.Border" Color="Transparent"/>
        <LinearGradientBrush x:Key="ComboBox.MouseOver.Background" EndPoint="0,1" StartPoint="0,0">
            <GradientStop Color="#FFECF4FC" Offset="0.0"/>
            <GradientStop Color="#FFDCECFC" Offset="1.0"/>
        </LinearGradientBrush>
        <SolidColorBrush x:Key="ComboBox.MouseOver.Border" Color="#FF7EB4EA"/>
        <SolidColorBrush x:Key="ComboBox.MouseOver.Glyph" Color="#FF000000"/>
        <SolidColorBrush x:Key="ComboBox.MouseOver.Editable.Background" Color="#FFFFFFFF"/>
        <SolidColorBrush x:Key="ComboBox.MouseOver.Editable.Border" Color="#FF7EB4EA"/>
        <LinearGradientBrush x:Key="ComboBox.MouseOver.Editable.Button.Background" EndPoint="0,1" StartPoint="0,0">
            <GradientStop Color="#FFEBF4FC" Offset="0.0"/>
            <GradientStop Color="#FFDCECFC" Offset="1.0"/>
        </LinearGradientBrush>
        <SolidColorBrush x:Key="ComboBox.MouseOver.Editable.Button.Border" Color="#FF7EB4EA"/>
        <LinearGradientBrush x:Key="ComboBox.Pressed.Background" EndPoint="0,1" StartPoint="0,0">
            <GradientStop Color="#FFDAECFC" Offset="0.0"/>
            <GradientStop Color="#FFC4E0FC" Offset="1.0"/>
        </LinearGradientBrush>
        <SolidColorBrush x:Key="ComboBox.Pressed.Border" Color="#FF569DE5"/>
        <SolidColorBrush x:Key="ComboBox.Pressed.Glyph" Color="#FF000000"/>
        <SolidColorBrush x:Key="ComboBox.Pressed.Editable.Background" Color="#FFFFFFFF"/>
        <SolidColorBrush x:Key="ComboBox.Pressed.Editable.Border" Color="#FF569DE5"/>
        <LinearGradientBrush x:Key="ComboBox.Pressed.Editable.Button.Background" EndPoint="0,1" StartPoint="0,0">
            <GradientStop Color="#FFDAEBFC" Offset="0.0"/>
            <GradientStop Color="#FFC4E0FC" Offset="1.0"/>
        </LinearGradientBrush>
        <SolidColorBrush x:Key="ComboBox.Pressed.Editable.Button.Border" Color="#FF569DE5"/>
        <SolidColorBrush x:Key="ComboBox.Disabled.Background" Color="#FFF0F0F0"/>
        <SolidColorBrush x:Key="ComboBox.Disabled.Border" Color="#FFD9D9D9"/>
        <SolidColorBrush x:Key="ComboBox.Disabled.Glyph" Color="#FFBFBFBF"/>
        <SolidColorBrush x:Key="ComboBox.Disabled.Editable.Background" Color="#FFFFFFFF"/>
        <SolidColorBrush x:Key="ComboBox.Disabled.Editable.Border" Color="#FFBFBFBF"/>
        <SolidColorBrush x:Key="ComboBox.Disabled.Editable.Button.Background" Color="Transparent"/>
        <SolidColorBrush x:Key="ComboBox.Disabled.Editable.Button.Border" Color="Transparent"/>
        <Style x:Key="ComboBoxToggleButton" TargetType="{x:Type ToggleButton}">
            <Setter Property="OverridesDefaultStyle" Value="true"/>
            <Setter Property="IsTabStop" Value="false"/>
            <Setter Property="Focusable" Value="false"/>
            <Setter Property="ClickMode" Value="Press"/>
            <Setter Property="Template">
                <Setter.Value>
                    <ControlTemplate TargetType="{x:Type ToggleButton}">
                        <Border x:Name="templateRoot" Background="{StaticResource ComboBox.Static.Background}" BorderBrush="{StaticResource ComboBox.Static.Border}" BorderThickness="{TemplateBinding BorderThickness}" SnapsToDevicePixels="true">
                            <Border x:Name="splitBorder" BorderBrush="Transparent" BorderThickness="1" HorizontalAlignment="Right" Margin="0" SnapsToDevicePixels="true" Width="{DynamicResource {x:Static SystemParameters.VerticalScrollBarWidthKey}}">
                                <Path x:Name="arrow" Data="F1 M 0,0 L 2.667,2.66665 L 5.3334,0 L 5.3334,-1.78168 L 2.6667,0.88501 L0,-1.78168 L0,0 Z" Fill="{StaticResource ComboBox.Static.Glyph}" HorizontalAlignment="Center" Margin="0" VerticalAlignment="Center"/>
                            </Border>
                        </Border>
                        <ControlTemplate.Triggers>
                            <MultiDataTrigger>
                                <MultiDataTrigger.Conditions>
                                    <Condition Binding="{Binding IsEditable, RelativeSource={RelativeSource AncestorType={x:Type ComboBox}}}" Value="true"/>
                                    <Condition Binding="{Binding IsMouseOver, RelativeSource={RelativeSource Mode=Self}}" Value="false"/>
                                    <Condition Binding="{Binding IsPressed, RelativeSource={RelativeSource Mode=Self}}" Value="false"/>
                                    <Condition Binding="{Binding IsEnabled, RelativeSource={RelativeSource Mode=Self}}" Value="true"/>
                                </MultiDataTrigger.Conditions>
                                <Setter Property="Background" TargetName="templateRoot" Value="{StaticResource ComboBox.Static.Editable.Background}"/>
                                <Setter Property="BorderBrush" TargetName="templateRoot" Value="{StaticResource ComboBox.Static.Editable.Border}"/>
                                <Setter Property="Background" TargetName="splitBorder" Value="{StaticResource ComboBox.Static.Editable.Button.Background}"/>
                                <Setter Property="BorderBrush" TargetName="splitBorder" Value="{StaticResource ComboBox.Static.Editable.Button.Border}"/>
                            </MultiDataTrigger>
                            <Trigger Property="IsMouseOver" Value="true">
                                <Setter Property="Fill" TargetName="arrow" Value="{StaticResource ComboBox.MouseOver.Glyph}"/>
                            </Trigger>
                            <MultiDataTrigger>
                                <MultiDataTrigger.Conditions>
                                    <Condition Binding="{Binding IsMouseOver, RelativeSource={RelativeSource Mode=Self}}" Value="true"/>
                                    <Condition Binding="{Binding IsEditable, RelativeSource={RelativeSource AncestorType={x:Type ComboBox}}}" Value="false"/>
                                </MultiDataTrigger.Conditions>
                                <Setter Property="Background" TargetName="templateRoot" Value="{StaticResource ComboBox.MouseOver.Background}"/>
                                <Setter Property="BorderBrush" TargetName="templateRoot" Value="{StaticResource ComboBox.MouseOver.Border}"/>
                            </MultiDataTrigger>
                            <MultiDataTrigger>
                                <MultiDataTrigger.Conditions>
                                    <Condition Binding="{Binding IsMouseOver, RelativeSource={RelativeSource Mode=Self}}" Value="true"/>
                                    <Condition Binding="{Binding IsEditable, RelativeSource={RelativeSource AncestorType={x:Type ComboBox}}}" Value="true"/>
                                </MultiDataTrigger.Conditions>
                                <Setter Property="Background" TargetName="templateRoot" Value="{StaticResource ComboBox.MouseOver.Editable.Background}"/>
                                <Setter Property="BorderBrush" TargetName="templateRoot" Value="{StaticResource ComboBox.MouseOver.Editable.Border}"/>
                                <Setter Property="Background" TargetName="splitBorder" Value="{StaticResource ComboBox.MouseOver.Editable.Button.Background}"/>
                                <Setter Property="BorderBrush" TargetName="splitBorder" Value="{StaticResource ComboBox.MouseOver.Editable.Button.Border}"/>
                            </MultiDataTrigger>
                            <Trigger Property="IsPressed" Value="true">
                                <Setter Property="Fill" TargetName="arrow" Value="{StaticResource ComboBox.Pressed.Glyph}"/>
                            </Trigger>
                            <MultiDataTrigger>
                                <MultiDataTrigger.Conditions>
                                    <Condition Binding="{Binding IsPressed, RelativeSource={RelativeSource Mode=Self}}" Value="true"/>
                                    <Condition Binding="{Binding IsEditable, RelativeSource={RelativeSource AncestorType={x:Type ComboBox}}}" Value="false"/>
                                </MultiDataTrigger.Conditions>
                                <Setter Property="Background" TargetName="templateRoot" Value="{StaticResource ComboBox.Pressed.Background}"/>
                                <Setter Property="BorderBrush" TargetName="templateRoot" Value="{StaticResource ComboBox.Pressed.Border}"/>
                            </MultiDataTrigger>
                            <MultiDataTrigger>
                                <MultiDataTrigger.Conditions>
                                    <Condition Binding="{Binding IsPressed, RelativeSource={RelativeSource Mode=Self}}" Value="true"/>
                                    <Condition Binding="{Binding IsEditable, RelativeSource={RelativeSource AncestorType={x:Type ComboBox}}}" Value="true"/>
                                </MultiDataTrigger.Conditions>
                                <Setter Property="Background" TargetName="templateRoot" Value="{StaticResource ComboBox.Pressed.Editable.Background}"/>
                                <Setter Property="BorderBrush" TargetName="templateRoot" Value="{StaticResource ComboBox.Pressed.Editable.Border}"/>
                                <Setter Property="Background" TargetName="splitBorder" Value="{StaticResource ComboBox.Pressed.Editable.Button.Background}"/>
                                <Setter Property="BorderBrush" TargetName="splitBorder" Value="{StaticResource ComboBox.Pressed.Editable.Button.Border}"/>
                            </MultiDataTrigger>
                            <Trigger Property="IsEnabled" Value="false">
                                <Setter Property="Fill" TargetName="arrow" Value="{StaticResource ComboBox.Disabled.Glyph}"/>
                            </Trigger>
                            <MultiDataTrigger>
                                <MultiDataTrigger.Conditions>
                                    <Condition Binding="{Binding IsEnabled, RelativeSource={RelativeSource Mode=Self}}" Value="false"/>
                                    <Condition Binding="{Binding IsEditable, RelativeSource={RelativeSource AncestorType={x:Type ComboBox}}}" Value="false"/>
                                </MultiDataTrigger.Conditions>
                                <Setter Property="Background" TargetName="templateRoot" Value="{StaticResource ComboBox.Disabled.Background}"/>
                                <Setter Property="BorderBrush" TargetName="templateRoot" Value="{StaticResource ComboBox.Disabled.Border}"/>
                            </MultiDataTrigger>
                            <MultiDataTrigger>
                                <MultiDataTrigger.Conditions>
                                    <Condition Binding="{Binding IsEnabled, RelativeSource={RelativeSource Mode=Self}}" Value="false"/>
                                    <Condition Binding="{Binding IsEditable, RelativeSource={RelativeSource AncestorType={x:Type ComboBox}}}" Value="true"/>
                                </MultiDataTrigger.Conditions>
                                <Setter Property="Background" TargetName="templateRoot" Value="{StaticResource ComboBox.Disabled.Editable.Background}"/>
                                <Setter Property="BorderBrush" TargetName="templateRoot" Value="{StaticResource ComboBox.Disabled.Editable.Border}"/>
                                <Setter Property="Background" TargetName="splitBorder" Value="{StaticResource ComboBox.Disabled.Editable.Button.Background}"/>
                                <Setter Property="BorderBrush" TargetName="splitBorder" Value="{StaticResource ComboBox.Disabled.Editable.Button.Border}"/>
                            </MultiDataTrigger>
                        </ControlTemplate.Triggers>
                    </ControlTemplate>
                </Setter.Value>
            </Setter>
        </Style>
        <ControlTemplate x:Key="ComboBoxEditableTemplate" TargetType="{x:Type ComboBox}">
            <Grid x:Name="templateRoot" SnapsToDevicePixels="true">
                <Grid.ColumnDefinitions>
                    <ColumnDefinition Width="*"/>
                    <ColumnDefinition MinWidth="{DynamicResource {x:Static SystemParameters.VerticalScrollBarWidthKey}}" Width="0"/>
                </Grid.ColumnDefinitions>
                <Popup x:Name="PART_Popup" AllowsTransparency="true" Grid.ColumnSpan="2" IsOpen="{Binding IsDropDownOpen, RelativeSource={RelativeSource Mode=TemplatedParent}}" Placement="Bottom" PopupAnimation="{DynamicResource {x:Static SystemParameters.ComboBoxPopupAnimationKey}}">
                    <theme:SystemDropShadowChrome x:Name="shadow" Color="Transparent" MinWidth="{Binding ActualWidth, ElementName=templateRoot}" MaxHeight="{TemplateBinding MaxDropDownHeight}">
                        <Border x:Name="dropDownBorder" Background="{DynamicResource {x:Static SystemColors.WindowBrushKey}}" BorderBrush="{DynamicResource {x:Static SystemColors.WindowFrameBrushKey}}" BorderThickness="1">
                            <ScrollViewer x:Name="DropDownScrollViewer">
                                <Grid x:Name="grid" RenderOptions.ClearTypeHint="Enabled">
                                    <Canvas x:Name="canvas" HorizontalAlignment="Left" Height="0" VerticalAlignment="Top" Width="0">
                                        <Rectangle x:Name="opaqueRect" Fill="{Binding Background, ElementName=dropDownBorder}" Height="{Binding ActualHeight, ElementName=dropDownBorder}" Width="{Binding ActualWidth, ElementName=dropDownBorder}"/>
                                    </Canvas>
                                    <ItemsPresenter x:Name="ItemsPresenter" KeyboardNavigation.DirectionalNavigation="Contained" SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}"/>
                                </Grid>
                            </ScrollViewer>
                        </Border>
                    </theme:SystemDropShadowChrome>
                </Popup>
                <ToggleButton x:Name="toggleButton" Background="{TemplateBinding Background}" BorderBrush="{TemplateBinding BorderBrush}" BorderThickness="{TemplateBinding BorderThickness}" Grid.ColumnSpan="2" IsChecked="{Binding IsDropDownOpen, Mode=TwoWay, RelativeSource={RelativeSource Mode=TemplatedParent}}" Style="{StaticResource ComboBoxToggleButton}"/>
                <Border x:Name="border" Background="{StaticResource TextBox.Static.Background}" Margin="{TemplateBinding BorderThickness}">
                    **<TextBox x:Name="PART_EditableTextBox" HorizontalContentAlignment="{TemplateBinding HorizontalContentAlignment}" 
                             IsReadOnly="{Binding IsReadOnly, RelativeSource={RelativeSource Mode=TemplatedParent}}" Margin="{TemplateBinding Padding}"
                             Style="{StaticResource ComboBoxEditableTextBox}" VerticalContentAlignment="{TemplateBinding VerticalContentAlignment}"/>**
                </Border>
            </Grid>
            <ControlTemplate.Triggers>
                <Trigger Property="IsEnabled" Value="false">
                    <Setter Property="Opacity" TargetName="border" Value="0.56"/>
                </Trigger>
                <Trigger Property="IsKeyboardFocusWithin" Value="true">
                    <Setter Property="Foreground" Value="Black"/>
                </Trigger>
                <Trigger Property="HasDropShadow" SourceName="PART_Popup" Value="true">
                    <Setter Property="Margin" TargetName="shadow" Value="0,0,5,5"/>
                    <Setter Property="Color" TargetName="shadow" Value="#71000000"/>
                </Trigger>
                <Trigger Property="HasItems" Value="false">
                    <Setter Property="Height" TargetName="dropDownBorder" Value="95"/>
                </Trigger>
                <MultiTrigger>
                    <MultiTrigger.Conditions>
                        <Condition Property="IsGrouping" Value="true"/>
                        <Condition Property="VirtualizingPanel.IsVirtualizingWhenGrouping" Value="false"/>
                    </MultiTrigger.Conditions>
                    <Setter Property="ScrollViewer.CanContentScroll" Value="false"/>
                </MultiTrigger>
                <Trigger Property="ScrollViewer.CanContentScroll" SourceName="DropDownScrollViewer" Value="false">
                    <Setter Property="Canvas.Top" TargetName="opaqueRect" Value="{Binding VerticalOffset, ElementName=DropDownScrollViewer}"/>
                    <Setter Property="Canvas.Left" TargetName="opaqueRect" Value="{Binding HorizontalOffset, ElementName=DropDownScrollViewer}"/>
                </Trigger>
            </ControlTemplate.Triggers>
        </ControlTemplate>
        <ControlTemplate x:Key="ComboBoxTemplate" TargetType="{x:Type ComboBox}">
            <Grid x:Name="templateRoot" SnapsToDevicePixels="true">
                <Grid.ColumnDefinitions>
                    <ColumnDefinition Width="*"/>
                    <ColumnDefinition MinWidth="{DynamicResource {x:Static SystemParameters.VerticalScrollBarWidthKey}}" Width="0"/>
                </Grid.ColumnDefinitions>
                <Popup x:Name="PART_Popup" AllowsTransparency="true" Grid.ColumnSpan="2" IsOpen="{Binding IsDropDownOpen, Mode=TwoWay, RelativeSource={RelativeSource Mode=TemplatedParent}}" Margin="1" Placement="Bottom" PopupAnimation="{DynamicResource {x:Static SystemParameters.ComboBoxPopupAnimationKey}}">
                    <theme:SystemDropShadowChrome x:Name="shadow" Color="Transparent" MinWidth="{Binding ActualWidth, ElementName=templateRoot}" MaxHeight="{TemplateBinding MaxDropDownHeight}">
                        <Border x:Name="dropDownBorder" Background="{DynamicResource {x:Static SystemColors.WindowBrushKey}}" BorderBrush="{DynamicResource {x:Static SystemColors.WindowFrameBrushKey}}" BorderThickness="1">
                            <ScrollViewer x:Name="DropDownScrollViewer">
                                <Grid x:Name="grid" RenderOptions.ClearTypeHint="Enabled">
                                    <Canvas x:Name="canvas" HorizontalAlignment="Left" Height="0" VerticalAlignment="Top" Width="0">
                                        <Rectangle x:Name="opaqueRect" Fill="{Binding Background, ElementName=dropDownBorder}" Height="{Binding ActualHeight, ElementName=dropDownBorder}" Width="{Binding ActualWidth, ElementName=dropDownBorder}"/>
                                    </Canvas>
                                    <ItemsPresenter x:Name="ItemsPresenter" KeyboardNavigation.DirectionalNavigation="Contained" SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}"/>
                                </Grid>
                            </ScrollViewer>
                        </Border>
                    </theme:SystemDropShadowChrome>
                </Popup>
                <ToggleButton x:Name="toggleButton" Background="{TemplateBinding Background}" BorderBrush="{TemplateBinding BorderBrush}" BorderThickness="{TemplateBinding BorderThickness}" Grid.ColumnSpan="2" IsChecked="{Binding IsDropDownOpen, Mode=TwoWay, RelativeSource={RelativeSource Mode=TemplatedParent}}" Style="{StaticResource ComboBoxToggleButton}"/>
                <ContentPresenter x:Name="contentPresenter" ContentStringFormat="{TemplateBinding SelectionBoxItemStringFormat}" ContentTemplate="{TemplateBinding SelectionBoxItemTemplate}" Content="{TemplateBinding SelectionBoxItem}" ContentTemplateSelector="{TemplateBinding ItemTemplateSelector}" HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}" IsHitTestVisible="false" Margin="{TemplateBinding Padding}" SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}" VerticalAlignment="{TemplateBinding VerticalContentAlignment}"/>
            </Grid>
            <ControlTemplate.Triggers>
                <Trigger Property="HasDropShadow" SourceName="PART_Popup" Value="true">
                    <Setter Property="Margin" TargetName="shadow" Value="0,0,5,5"/>
                    <Setter Property="Color" TargetName="shadow" Value="#71000000"/>
                </Trigger>
                <Trigger Property="HasItems" Value="false">
                    <Setter Property="Height" TargetName="dropDownBorder" Value="95"/>
                </Trigger>
                <MultiTrigger>
                    <MultiTrigger.Conditions>
                        <Condition Property="IsGrouping" Value="true"/>
                        <Condition Property="VirtualizingPanel.IsVirtualizingWhenGrouping" Value="false"/>
                    </MultiTrigger.Conditions>
                    <Setter Property="ScrollViewer.CanContentScroll" Value="false"/>
                </MultiTrigger>
                <Trigger Property="ScrollViewer.CanContentScroll" SourceName="DropDownScrollViewer" Value="false">
                    <Setter Property="Canvas.Top" TargetName="opaqueRect" Value="{Binding VerticalOffset, ElementName=DropDownScrollViewer}"/>
                    <Setter Property="Canvas.Left" TargetName="opaqueRect" Value="{Binding HorizontalOffset, ElementName=DropDownScrollViewer}"/>
                </Trigger>
            </ControlTemplate.Triggers>
        </ControlTemplate>
        <Style x:Key="ComboBoxStyle1" TargetType="{x:Type ComboBox}">
            <Setter Property="FocusVisualStyle" Value="{StaticResource FocusVisual}"/>
            <Setter Property="Background" Value="{StaticResource ComboBox.Static.Background}"/>
            <Setter Property="BorderBrush" Value="{StaticResource ComboBox.Static.Border}"/>
            <Setter Property="Foreground" Value="{DynamicResource {x:Static SystemColors.WindowTextBrushKey}}"/>
            <Setter Property="BorderThickness" Value="1"/>
            <Setter Property="ScrollViewer.HorizontalScrollBarVisibility" Value="Auto"/>
            <Setter Property="ScrollViewer.VerticalScrollBarVisibility" Value="Auto"/>
            <Setter Property="Padding" Value="6,3,5,3"/>
            <Setter Property="ScrollViewer.CanContentScroll" Value="true"/>
            <Setter Property="ScrollViewer.PanningMode" Value="Both"/>
            <Setter Property="Stylus.IsFlicksEnabled" Value="False"/>
            <Setter Property="Template" Value="{StaticResource ComboBoxTemplate}"/>
            <Style.Triggers>
                <Trigger Property="IsEditable" Value="true">
                    <Setter Property="IsTabStop" Value="false"/>
                    <Setter Property="Padding" Value="2"/>
                    <Setter Property="Template" Value="{StaticResource ComboBoxEditableTemplate}"/>
                </Trigger>
            </Style.Triggers>
        </Style>
    
    </Window.Resources>

    <StackPanel>
        <ComboBox Style="{DynamicResource ComboBoxStyle1}" Name="comboBox1" Width="200" IsEditable="True">
        </ComboBox>
        <ComboBox Name="comboBox" Width="200" IsEditable="True">
        </ComboBox>
        <TextBox MaxLength="10"  Width="200"/>
    </StackPanel>

The result:

Update:

 <ComboBox local:ComboBoxMaxLengthBehavior.MaxLength="10" IsEditable="True" />
        <ComboBox local:ComboBoxMaxLengthBehavior.MaxLength="15" IsEditable="True" />

Code:


 public static class ComboBoxMaxLengthBehavior
    {
        public static readonly DependencyProperty MaxLengthProperty =
            DependencyProperty.RegisterAttached("MaxLength", typeof(int), typeof(ComboBoxMaxLengthBehavior), new PropertyMetadata(OnMaxLengthChanged));

        public static int GetMaxLength(DependencyObject obj)
        {
            return (int)obj.GetValue(MaxLengthProperty);
        }

        public static void SetMaxLength(DependencyObject obj, int value)
        {
            obj.SetValue(MaxLengthProperty, value);
        }

        private static void OnMaxLengthChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
        {
            if (d is ComboBox comboBox)
            {
                comboBox.Loaded += (sender, args) =>
                {
                    var editableTextBox = FindVisualChild<TextBox>(comboBox);
                    if (editableTextBox != null)
                    {
                        editableTextBox.MaxLength = (int)e.NewValue;
                    }
                };
            }
        }

        private static T FindVisualChild<T>(DependencyObject parent) where T : DependencyObject
        {
            for (int i = 0; i < VisualTreeHelper.GetChildrenCount(parent); i++)
            {
                var child = VisualTreeHelper.GetChild(parent, i);
                if (child is T result)
                {
                    return result;
                }

                var childOfChild = FindVisualChild<T>(child);
                if (childOfChild != null)
                {
                    return childOfChild;
                }
            }

            return null;
        }
    }

The result:

enter image description here

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Dmtr_Grms 331 Reputation points

2023-09-11T12:37:09.3033333+00:00

Hi, thanks for your answer. You mean that I have to implement the complete ComboBox control at the top of my XAML? And what if as I have in my XAML I have five ComboBoxes with different MaxLength? I have a bad experience with that kind of solution, I have made a complete copy of the Control, change only the colors when control is not enabled and after hours of tests I saw that the control doesn't consider anymore the flag IsEditable True or Not, I have lost hours with that problem.
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Hui Liu-MSFT 48,681 Reputation points Microsoft External Staff

2023-09-25T07:17:57.5833333+00:00

Hi,@Dimitri Garmaise . Is there any update to the question? Did my answer solve your problem? If so, you could accept it as the answer. It's helpful for community members with related questions.
Dmtr_Grms 331 Reputation points

2023-09-25T11:58:02.8066667+00:00

Hi @Hui Liu-MSFT sorry not answering before. I decided to manage it in another way because it was too complicate to modifiy whole application with most of transactions allready tested. I have simply develop an error msg interception and management with error msg indicating type of error and field name. Probably not the best solution but I was in hurry. Thanks the same for your help.
Hui Liu-MSFT 48,681 Reputation points Microsoft External Staff

2023-09-26T01:22:04.3733333+00:00

Hi,@Dimitri Garmaise .Glad your problem is solved. You could share your solution if you have time.

My second method has very little code (updated part in answer), you can also accept it as answer if you think it will be helpful to you. It's helpful for community members with related questions.

Answer 3

Had to find a quick and surely dirty solution, but was impossible to change all application transactions. Below what I have done. Thanks to all for their answers.

                catch (DbUpdateException ex)
                {
                    if (ex.InnerException is SqlException sqlException)
                    {
                        switch (sqlException.Number)
                        {
                            case 2628: // Input data is too long - Database MaxLength reached
                                MessageBox.Show("Inserted data is too long. Please modify . \n\n" + "(" + sqlException.Message + ")", "ERRORE", MessageBoxButton.OK, MessageBoxImage.Error);
                                break;
                            
                        }
                    }
                }

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ComboBox Control how to define MaxLength of input Text

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