自定义控件，重写 TextBox 实例

项目中可能会遇到重写控件的情况，特此记录下：

<Window x:Class="WpfApp6.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:WpfApp6"
        mc:Ignorable="d"
        Title="MainWindow" Height="157" Width="287">
    <Window.Resources>
        <Style TargetType="local:CustomTextBox">
            <Setter Property="Template">
                <Setter.Value>
                    <ControlTemplate>
                        <Grid>
                            <Grid.ColumnDefinitions>
                                <ColumnDefinition />
                                <ColumnDefinition Width="auto" />
                            </Grid.ColumnDefinitions>
                            <TextBox VerticalContentAlignment="Center" 
                                     Padding="5"
                                     Text="{Binding RelativeSource={RelativeSource TemplatedParent},Path=Text}"/>
                            <Button x:Name="btnclear" Grid.Column="1" Width="30" Margin="3" Content="清空" />
                        </Grid>
                    </ControlTemplate>
                </Setter.Value>
            </Setter>
        </Style>
    </Window.Resources>
    <Grid>
        <StackPanel>
            <local:CustomTextBox Text="852"/>
        </StackPanel>
    </Grid>
</Window>

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 WpfApp6
{
    /// <summary>
    /// MainWindow.xaml 的交互逻辑
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
        }
    }


    public class CustomTextBox : TextBox
    {
        public override void OnApplyTemplate()
        {
            base.OnApplyTemplate();

            var btnclear = GetTemplateChild("btnclear") as Button;
            btnclear.Click += Btnclear_Click;
        }

        private void Btnclear_Click(object sender, RoutedEventArgs e)
        {
            Text = string.Empty;
        }
    }
}