How to change the CornerRadius of the Combobox WPF - wpf

Question

I want to use a ComboBox with different CornerRadius, how can I change that simply? I've tried with Style and ControlTemplate, but without any success.

Answer 1

I don't know if this is simple, but creating a ControlTemplate based on the default ComboBox should do the trick. Here is an example:
<Style x:Key="ComboBoxTextBoxStyle" TargetType="{x:Type TextBox}">
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type TextBox}">
<Grid>
<Border CornerRadius="5,0,0,5"
BorderThickness="1"
Background="{TemplateBinding Background}"
BorderBrush="Black">
<ScrollViewer x:Name="PART_ContentHost"/>
</Border>
</Grid>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
<Style TargetType="{x:Type ComboBox}">
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type ComboBox}">
<Grid>
<Grid.ColumnDefinitions>
<ColumnDefinition/>
<ColumnDefinition MaxWidth="18"/>
</Grid.ColumnDefinitions>
<TextBox Name="PART_EditableTextBox"
Style="{StaticResource ComboBoxTextBoxStyle}"
Padding="5,0,0,0"
Height="{TemplateBinding Height}"/>
<ToggleButton Grid.Column="1" Margin="0"
Height="{TemplateBinding Height}"
Style="{StaticResource ComboBoxButtonStyle}"
Focusable="False"
IsChecked="{Binding Path=IsDropDownOpen, Mode=TwoWay, RelativeSource={RelativeSource TemplatedParent}}"
ClickMode="Press">
<Path Grid.Column="1"
HorizontalAlignment="Center"
VerticalAlignment="Center"
Data="M 0 0 L 4 4 L 8 0 Z"
Fill="DodgerBlue" />
</ToggleButton>
<ContentPresenter Name="ContentSite"
Content="{TemplateBinding SelectionBoxItem}"
ContentTemplate="{TemplateBinding SelectionBoxItemTemplate}"
ContentTemplateSelector="{TemplateBinding ItemTemplateSelector}"
VerticalAlignment="Center"
HorizontalAlignment="Left"
Margin="5,0,0,0"/>
<Popup Name="Popup"
Placement="Bottom"
IsOpen="{TemplateBinding IsDropDownOpen}"
AllowsTransparency="True"
Focusable="False"
PopupAnimation="Slide">
<Grid Name="DropDown"
SnapsToDevicePixels="True"
MinWidth="{TemplateBinding ActualWidth}"
MaxHeight="{TemplateBinding MaxDropDownHeight}">
<Border
x:Name="DropDownBorder"
BorderThickness="1"
CornerRadius="5"
Background="Azure"
BorderBrush="Black"/>
<ScrollViewer Margin="4,6,4,6" SnapsToDevicePixels="True">
<StackPanel IsItemsHost="True" KeyboardNavigation.DirectionalNavigation="Contained" />
</ScrollViewer>
</Grid>
</Popup>
</Grid>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
You will need to define the VisualStates/Triggers in the Style if required

Answer 2

Thanks Richard E!
Here a clean version of Richard E's answer:
<Style x:Key="ComboBoxTextBoxStyle" TargetType="{x:Type TextBox}">
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type TextBox}">
<Grid>
<Border CornerRadius="5,0,0,5"
BorderThickness="1,1,0,1"
Background="{TemplateBinding Background}"
BorderBrush="Black">
<ScrollViewer x:Name="PART_ContentHost"/>
</Border>
</Grid>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
<Style x:Key="ComboBoxButtonStyle" TargetType="{x:Type ToggleButton}">
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type ToggleButton}">
<Border
Background="White"
x:Name="border"
CornerRadius="0,5,5,0"
BorderThickness="0,1,1,1"
BorderBrush="Black">
<ContentPresenter />
</Border>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
<Style x:Key="RoundComboBox" TargetType="{x:Type ComboBox}">
<Setter Property="HorizontalContentAlignment" Value="Center"/>
<Setter Property="VerticalContentAlignment" Value="Center"/>
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type ComboBox}">
<Grid>
<Grid.ColumnDefinitions>
<ColumnDefinition/>
<ColumnDefinition MaxWidth="18"/>
</Grid.ColumnDefinitions>
<TextBox Name="PART_EditableTextBox"
Style="{StaticResource ComboBoxTextBoxStyle}"
Padding="5,0,0,0"
Height="{TemplateBinding Height}"/>
<ToggleButton Grid.Column="1" Margin="0"
Height="{TemplateBinding Height}"
Style="{StaticResource ComboBoxButtonStyle}"
Focusable="False"
IsChecked="{Binding Path=IsDropDownOpen, Mode=TwoWay, RelativeSource={RelativeSource TemplatedParent}}"
ClickMode="Press">
<Path Grid.Column="1"
HorizontalAlignment="Center"
VerticalAlignment="Center"
Data="M 0 0 L 4 4 L 8 0 Z"
Fill="DodgerBlue" />
</ToggleButton>
<ContentPresenter Name="ContentSite"
Content="{TemplateBinding SelectionBoxItem}"
ContentTemplate="{TemplateBinding SelectionBoxItemTemplate}"
ContentTemplateSelector="{TemplateBinding ItemTemplateSelector}"
VerticalAlignment="Center"
HorizontalAlignment="Left"
Margin="5,0,0,0"/>
<Popup Name="Popup"
Placement="Bottom"
IsOpen="{TemplateBinding IsDropDownOpen}"
AllowsTransparency="True"
Focusable="False"
PopupAnimation="Slide">
<Grid Name="DropDown"
SnapsToDevicePixels="True"
MinWidth="{TemplateBinding ActualWidth}"
MaxHeight="{TemplateBinding MaxDropDownHeight}">
<Border
x:Name="DropDownBorder"
BorderThickness="1"
CornerRadius="5"
Background="Azure"
BorderBrush="Black"/>
<ScrollViewer Margin="4,6,4,6" SnapsToDevicePixels="True">
<StackPanel IsItemsHost="True" KeyboardNavigation.DirectionalNavigation="Contained" />
</ScrollViewer>
</Grid>
</Popup>
</Grid>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
UPDATE:
After changing to get my custom version I found out it wasn't the best example to start with (editable combobox, not optimized, missing style etc ...), I found a good example on this website:
http://www.wpfhelper.com/index.php/styles-in-wpf/combobox/15-combobox-style-in-wpf
And here my custom version (to implement in Resources ex: in tag <UserControl.Resources>):
<Style x:Key="ComboBoxToggleButton" TargetType="ToggleButton">
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="ToggleButton">
<Grid>
<Grid.ColumnDefinitions>
<ColumnDefinition />
<ColumnDefinition Width="32" />
</Grid.ColumnDefinitions>
<Border
x:Name="Border"
Grid.ColumnSpan="2"
CornerRadius="8"
Background="{TemplateBinding Background}"
BorderBrush="#F6F6F6"
BorderThickness="1"
/>
<Path
x:Name="Arrow"
Grid.Column="1"
Fill="{TemplateBinding Foreground}"
Stroke="{TemplateBinding Foreground}"
HorizontalAlignment="Center"
VerticalAlignment="Center"
Data="M 0 0 L 4 4 L 8 0 Z"/>
</Grid>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
<ControlTemplate x:Key="ComboBoxTextBox" TargetType="TextBox">
<Border x:Name="PART_ContentHost" Focusable="True" />
</ControlTemplate>
<Style x:Key="theComboBox" TargetType="{x:Type ComboBox}">
<Setter Property="Foreground" Value="#333" />
<Setter Property="BorderBrush" Value="Gray" />
<Setter Property="Background" Value="White" />
<Setter Property="SnapsToDevicePixels" Value="true"/>
<Setter Property="OverridesDefaultStyle" Value="true"/>
<Setter Property="ScrollViewer.HorizontalScrollBarVisibility" Value="Auto"/>
<Setter Property="ScrollViewer.VerticalScrollBarVisibility" Value="Auto"/>
<Setter Property="ScrollViewer.CanContentScroll" Value="true"/>
<Setter Property="FontSize" Value="13" />
<Setter Property="MinWidth" Value="150"/>
<Setter Property="MinHeight" Value="35"/>
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="ComboBox">
<Grid>
<ToggleButton
Cursor="Hand"
Name="ToggleButton"
BorderBrush="{TemplateBinding BorderBrush}"
Background="{TemplateBinding Background}"
Foreground="{TemplateBinding Foreground}"
Style="{StaticResource ComboBoxToggleButton}"
Grid.Column="2"
Focusable="false"
IsChecked="{Binding Path=IsDropDownOpen,Mode=TwoWay,RelativeSource={RelativeSource TemplatedParent}}"
ClickMode="Press"/>
<ContentPresenter
Name="ContentSite"
IsHitTestVisible="False"
Content="{TemplateBinding SelectionBoxItem}"
ContentTemplate="{TemplateBinding SelectionBoxItemTemplate}"
ContentTemplateSelector="{TemplateBinding ItemTemplateSelector}"
Margin="10,3,30,3"
VerticalAlignment="Center"
HorizontalAlignment="Left" />
<TextBox x:Name="PART_EditableTextBox"
Style="{x:Null}"
Template="{StaticResource ComboBoxTextBox}"
HorizontalAlignment="Left"
VerticalAlignment="Center"
Margin="3,3,23,3"
Focusable="True"
Visibility="Hidden"
IsReadOnly="{TemplateBinding IsReadOnly}"/>
<Popup
Name="Popup"
Placement="Bottom"
IsOpen="{TemplateBinding IsDropDownOpen}"
AllowsTransparency="True"
Focusable="False"
PopupAnimation="Slide">
<Grid
Name="DropDown"
SnapsToDevicePixels="True"
MinWidth="{TemplateBinding ActualWidth}"
MaxHeight="{TemplateBinding MaxDropDownHeight}">
<Border
CornerRadius="8"
x:Name="DropDownBorder"
Background="White"
BorderThickness="1"
BorderBrush="#F6F6F6"
/>
<ScrollViewer Margin="4,6,4,6" SnapsToDevicePixels="True">
<StackPanel IsItemsHost="True" KeyboardNavigation.DirectionalNavigation="Contained" />
</ScrollViewer>
</Grid>
</Popup>
</Grid>
<ControlTemplate.Triggers>
<Trigger Property="HasItems" Value="false">
<Setter TargetName="DropDownBorder" Property="MinHeight" Value="95"/>
</Trigger>
<Trigger Property="IsGrouping" Value="true">
<Setter Property="ScrollViewer.CanContentScroll" Value="false"/>
</Trigger>
<Trigger Property="IsEditable" Value="true">
<Setter Property="IsTabStop" Value="false"/>
<Setter TargetName="PART_EditableTextBox" Property="Visibility" Value="Visible"/>
<Setter TargetName="ContentSite" Property="Visibility" Value="Hidden"/>
</Trigger>
</ControlTemplate.Triggers>
</ControlTemplate>
</Setter.Value>
</Setter>
<Style.Triggers>
</Style.Triggers>
</Style>
<Style x:Key="theComboBoxItem" TargetType="{x:Type ComboBoxItem}">
<Setter Property="SnapsToDevicePixels" Value="true" />
<Setter Property="HorizontalAlignment" Value="Stretch" />
<Setter Property="VerticalAlignment" Value="Stretch" />
<Setter Property="FontSize" Value="13" />
<Setter Property="OverridesDefaultStyle" Value="true"/>
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="ComboBoxItem">
<Border
Name="Border"
Padding="5"
Margin="2"
BorderThickness="2,0,0,0"
CornerRadius="0"
Background="Transparent"
BorderBrush="Transparent">
<TextBlock TextAlignment="Left">
<ContentPresenter />
</TextBlock>
</Border>
<ControlTemplate.Triggers>
<Trigger Property="IsHighlighted" Value="true">
<Setter TargetName="Border" Property="BorderBrush" Value="#B3CB37"/>
<Setter TargetName="Border" Property="Background" Value="#F8FAEB"/>
</Trigger>
</ControlTemplate.Triggers>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
And here the Combobox and style implementation:
<ComboBox
FontSize="13"
Style="{DynamicResource theComboBox}"
Padding="15,5,15,5"
HorizontalContentAlignment="Left"
VerticalAlignment="Center"
MinWidth="100"
MaxWidth="375"
Grid.Row="1"
Grid.Column="1"
ItemContainerStyle="{DynamicResource theComboBoxItem}"
>
<ComboBoxItem>Available</ComboBoxItem>
<ComboBoxItem>Busy</ComboBoxItem>
<ComboBoxItem>On Duty</ComboBoxItem>
<ComboBoxItem>On Meeting</ComboBoxItem>
<ComboBoxItem>On Vacation</ComboBoxItem>
<ComboBoxItem>On Weekend</ComboBoxItem>
</ComboBox>

Answer 3

Add a ComboBox in your WPF project, right click on it and select EditTemplate> Edit a copy...
Choose a name for style and click ok.
vs create a ComboBoxTemplate for ComboBox.
now you can add a border and set desired CornerRadius to ComboBoxTemplate.