首先在app.xaml文件的下面添加以下样式

 <!--编辑器通用主题样式--> <Style x:Key="nu_editor_style"><Setter Property="Control.Padding" Value="12"></Setter><Setter Property="Control.Background" Value="#FFC1EDF7"></Setter><Setter Property="Control.BorderBrush" Value="#FFA0A2A4"></Setter><Setter Property="Control.BorderThickness" Value="8"></Setter><Setter Property="Control.ClipToBounds" Value="True"></Setter></Style><ControlTemplate x:Key="nu_editor_template" TargetType="{x:Type TextBoxBase}" ><lib:CustomDrawnDecorator BorderBrush="{TemplateBinding BorderBrush}" Background="{TemplateBinding Background}"             BorderThickness="{TemplateBinding BorderThickness}"><ScrollViewer Margin="{TemplateBinding Padding}"HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}"VerticalAlignment="{TemplateBinding VerticalContentAlignment}"x:Name="PART_ContentHost" /></lib:CustomDrawnDecorator></ControlTemplate>

在mainWindow.xaml文件中添加TextBox控件

 <TextBox Width="300" Height="100" Style="{StaticResource nu_editor_style}" Template="{StaticResource nu_editor_template}"     HorizontalAlignment="Left"  Margin="180,0,0,0" TextWrapping="Wrap"  VerticalAlignment="Top" >sdfsd </TextBox>

还有下面是Decorator的代码

using System;
using System.Collections.Generic;
using System.Text;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Controls.Primitives;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Shapes;namespace WpfApp1
{public class CustomDrawnDecorator : Decorator{double arrowLen = 30d;static Thickness defaultBorderThickness = new Thickness(4d);public static  DependencyProperty BorderBrushProperty =DependencyProperty.Register("BorderBrush", typeof(Brush), typeof(CustomDrawnDecorator), new PropertyMetadata(Brushes.Gray));public static  DependencyProperty BorderThicknessProperty =DependencyProperty.Register("BorderThickness", typeof(Thickness), typeof(CustomDrawnDecorator), new   PropertyMetadata(defaultBorderThickness));public static DependencyProperty BackgroundProperty=DependencyProperty.Register("Background", typeof(Brush), typeof(CustomDrawnDecorator), new FrameworkPropertyMetadata(Brushes.RosyBrown));static CustomDrawnDecorator(){}public Brush Background{get{return (Brush)GetValue(BackgroundProperty);}set{SetValue(BackgroundProperty, value);}}public Brush BorderBrush{get{return (Brush)GetValue(BorderBrushProperty);}set{SetValue(BorderBrushProperty, value);}}public Thickness BorderThickness{get { return (Thickness)GetValue(BorderThicknessProperty); }set { SetValue(BorderThicknessProperty, value); }}protected override void OnRender(DrawingContext dc){base.OnRender(dc);Rect bounds = new Rect(0, 0, base.ActualWidth, base.ActualHeight);Pen p = new Pen(BorderBrush,getBorderThickness());//填充背景dc.DrawRectangle(Background, null, bounds);//左长线dc.DrawLine(p, new Point(getBorderThickness() / 2, 0), new Point(getBorderThickness() / 2, ActualHeight));//右长线dc.DrawLine(p, new Point(ActualWidth - getBorderThickness() / 2, 0), new Point(ActualWidth - getBorderThickness() / 2,     ActualHeight));//左上短线dc.DrawLine(p, new Point(0, getBorderThickness() / 2), new Point(arrowLen, getBorderThickness() / 2));//右上短线dc.DrawLine(p, new Point(ActualWidth - arrowLen, getBorderThickness() / 2), new Point(ActualWidth, getBorderThickness() / 2));//左下短线dc.DrawLine(p, new Point(0, ActualHeight - getBorderThickness() / 2), new Point(arrowLen, ActualHeight - getBorderThickness() / 2));//右下短线dc.DrawLine(p, new Point(ActualWidth - arrowLen, ActualHeight - getBorderThickness() / 2), new Point(ActualWidth, ActualHeight - getBorderThickness() / 2));//dc.DrawRectangle(Background, p, bounds);//dc.DrawLine(new Pen(Background, getBorderThickness() / 2), new Point(arrowLen, getBorderThickness() / 4), new //Point(ActualWidth - arrowLen, getBorderThickness() / 4));//dc.DrawLine(new Pen(Background, getBorderThickness() / 2), new Point(arrowLen, ActualHeight - getBorderThickness() / 4), //new Point(ActualWidth - arrowLen, ActualHeight - getBorderThickness() / 4));}private double getBorderThickness(){return BorderThickness.Right != 0 ? BorderThickness.Right : defaultBorderThickness.Right;}}
}

运行结果