我们平时自定义WPF控件的方法有：Style，DataTemplate，ControlTemplate， DependencyProperty， CustomControl等几个方法。
按照优先顺序应该是从左到右。 （所谓Style，这里仅包括Setter）


对于搜索框，其组成也就是TextBox+Button（清空），这里我们用CustomControl的方法比较合适。

1.创建SearchBox继承于TextBox，并声明2个Part属性， 表明此控件组成 
     [TemplatePart(Name = "PART_SearchTextBox", Type = typeof(TextBox))]
     [TemplatePart(Name = "PART_ClearButton", Type = typeof(Button))]
      public class SearchBox : TextBox
 2.创建2个子控件的Style， 注意ControlTemplate中的子控件命名和上述属性声明一致 
<Style TargetType="{x:Type local:SearchBox}">
      <Setter Property="Template">   
         <Setter.Value>                
               <ControlTemplate TargetType="{x:Type local:SearchBox}">
                    
               
          
      
 3.如果在当前程序集里，必须放在.\Themes文件夹下; 必须在程序集的AssemblyInfo.cs里指定ThemeInfo（用来指定控件默认Style）
 [assembly: ThemeInfo(     ResourceDictionaryLocation.None, //where theme specific resource dictionaries are located     //(used if a resource is not found in the page,      // or application resource dictionaries)     ResourceDictionaryLocation.SourceAssembly //where the generic resource dictionary is located     //(used if a resource is not found in the page,      // app, or any theme specific resource dictionaries) )] 
4.在自定义控件的实现中注册路由事件等等其它逻辑处理
 比如：对子元素Clear按钮进行处理 
       public override void OnApplyTemplate()
         {             base.OnApplyTemplate();               Button btnClear = base.GetTemplateChild("PART_ClearButton") as Button;             if (btnClear != null)
             {                btnClear.Click += new RoutedEventHandler(OnClearButton_Click);
             }         }           private void OnClearButton_Click(Object sender, RoutedEventArgs e)
         {             TextBox txtSearch = base.GetTemplateChild("PART_SearchTextBox") as TextBox;               if (txtSearch!= null)
             {                txtSearch.Text = String.Empty;
                txtSearch.Focus();
             }         }