How can I create a new usercontrol inherit from ComboBox? - wpf

Question

I wanna to create a new usercontrol,it is inherit from ComboBox.I will add some new property to it, and rewrite its ControlTemplate.
Here is XAML:
<ComboBox x:Class="Pesticide.CustomUserControls.ComboxUserControl"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:local="clr-namespace:Pesticide.CustomUserControls"
mc:Ignorable="d"
d:DesignHeight="300" d:DesignWidth="300">
<ComboBox.Resources>
<ControlTemplate TargetType="{x:Type ComboBox}" x:Key="{x:Type ComboBox}">
<Grid></Grid>
</ControlTemplate>
</ComboBox.Resources>
</ComboBox>
And here is code behind:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;
namespace Pesticide.CustomUserControls
{
public partial class ComboxUserControl : ComboBox
{
public ComboxUserControl()
{
InitializeComponent();
}
}
}
However,I just wrote these code,but WPF throw an error which is "InvalidCastException: Unable to cast object of type 'System.Windows.Controls.ControlTemplate' to type 'System.Windows.Style'."
What's wrong with my code?Would you please to help me?Thank you.

Answer 1

What's wrong with my code?
Using a type as resource key is the way WPF handles default Styles.
So a resource with
x:Key="{x:Type ComboBox}"
can't be a ControlTemplate. It has to be a Style.
However, it is simpler to directly set the Template property:
<ComboBox ...>
<ComboBox.Template>
<ControlTemplate TargetType="ComboBox">
...
</ControlTemplate>
</ComboBox.Template>
</ComboBox>