水印文本框

　　先看下效果：

　　流程：

　　1.新建watermarktextbox类，继承自textbox。添加依赖项属性watermark(水印)、watermarkforeground(水印前景色)。

 1     public class watermarktextbox : textbox
 2     {
 3         #region dependencyproperties
 4         public string watermark
 5         {
 6             get { return (string)getvalue(watermarkproperty); }
 7             set { setvalue(watermarkproperty, value); }
 8         }
 9 
10         // using a dependencyproperty as the backing store for watermark.  this enables animation, styling, binding, etc...
11         public static readonly dependencyproperty watermarkproperty =
12             dependencyproperty.register("watermark", typeof(string), typeof(watermarktextbox), new propertymetadata(default(string)));
13 
14         public brush watermarkforeground
15         {
16             get { return (brush)getvalue(watermarkforegroundproperty); }
17             set { setvalue(watermarkforegroundproperty, value); }
18         }
19 
20         // using a dependencyproperty as the backing store for watermarkforeground.  this enables animation, styling, binding, etc...
21         public static readonly dependencyproperty watermarkforegroundproperty =
22             dependencyproperty.register("watermarkforeground", typeof(brush), typeof(watermarktextbox), new propertymetadata(new solidcolorbrush(colors.gray)));
23 
24         #endregion
25 
26         static watermarktextbox()
27         {
28             defaultstylekeyproperty.overridemetadata(typeof(watermarktextbox), new frameworkpropertymetadata(typeof(watermarktextbox)));
29         }
30     }

　　2.编写watermarktextbox样式。

 1             <style x:key="watermarktextboxstyle" targettype="{x:type local:watermarktextbox}">
 2                 <setter property="snapstodevicepixels" value="true" />
 3                 <setter property="horizontalcontentalignment" value="left" />
 4                 <setter property="verticalcontentalignment" value="center" />
 5                 <setter property="borderthickness" value="1" />
 6                 <setter property="borderbrush" value="black" />
 7                 <setter property="padding" value="4,2" />
 8                 <setter property="template">
 9                     <setter.value>
10                         <controltemplate targettype="{x:type local:watermarktextbox}">
11                             <border background="{templatebinding background}" borderbrush="{templatebinding borderbrush}" borderthickness="{templatebinding borderthickness}" snapstodevicepixels="{templatebinding snapstodevicepixels}">
12                                 <grid>
13                                     <scrollviewer name="part_contenthost" focusable="false" horizontalscrollbarvisibility="hidden" verticalscrollbarvisibility="hidden" />
14                                     <textblock x:name="part_watermark"
15                                                margin="{templatebinding padding}"
16                                                horizontalalignment="{templatebinding horizontalcontentalignment}"
17                                                verticalalignment="{templatebinding verticalcontentalignment}"
18                                                fontfamily="{templatebinding fontfamily}"
19                                                fontsize="{templatebinding fontsize}"
20                                                fontweight="{templatebinding fontweight}"
21                                                foreground="{templatebinding watermarkforeground}"
22                                                text="{templatebinding watermark}"
23                                                visibility="collapsed" />
24                                 </grid>
25                             </border>
26                             <controltemplate.triggers>
27                                 <multitrigger>
28                                     <multitrigger.conditions>
29                                         <condition property="isfocused" value="false" />
30                                         <condition property="text" value="" />
31                                     </multitrigger.conditions>
32                                     <setter targetname="part_watermark" property="visibility" value="visible" />
33                                 </multitrigger>
34                                 <trigger property="ismouseover" value="true">
35                                     <setter property="borderbrush" value="#ff7eb4ea" />
36                                 </trigger>
37                                 <trigger property="iskeyboardfocused" value="true">
38                                     <setter property="borderbrush" value="#ff569de5" />
39                                 </trigger>
40                                 <trigger property="isenabled" value="false">
41                                     <setter property="opacity" value="0.56" />
42                                 </trigger>
43                             </controltemplate.triggers>
44                         </controltemplate>
45                     </setter.value>
46                 </setter>
47             </style>

　　3.界面引用。

1         <stackpanel horizontalalignment="center" verticalalignment="center" orientation="horizontal">
2             <local:watermarktextbox x:name="txt"
3                                     width="200" height="28"
4                                     style="{staticresource watermarktextboxstyle}"
5                                     watermark="请输入..." />
6             <button width="60" height="28"
7                     margin="10,0,0,0"
8                     click="btnconfirm_click" content="确定" />
9         </stackpanel>