c#鼠标点击TextBox控件后清空默认字体

方案（一）

脚本：

<script type="text/javascript" language="javascript">
        //得到焦点时触发事件
        function onFocusFun(element, elementValue) {
            if (element.value == elementValue) {
                element.value = "";
                element.style.color = "";
            }

}
        //离开输入框时触发事件
        function onblurFun(element, elementValue) {

if (element.value == '') {
                element.style.color = "#808080";
                element.value = elementValue;
            }

}
</script>

调用示例：

<tr align="center">
                  <td style="background-image:url('bg03.gif');background-position:center;background-repeat:no-repeat;height:69px">
                     <span style="color: #000000; font-family: 黑体;"><strong>用户名:</strong></span><asp:textbox id="UserName" Text="请输入用户名" runat="server" Width="100px" Height="20px" ForeColor="#808080"
                                            OnFocus="onFocusFun(this,'请输入用户名')"
                                            OnBlur="onblurFun(this,'请输入用户名')"></asp:textbox>             
                     <br />
                     <span style="color: #000000; font-family: 黑体;"><strong>密&nbsp;&nbsp;码:</strong></span><asp:textbox id="UserPass" runat="server" Width="100px" TextMode="Password" Height="20px"></asp:textbox>             
                  </td>
              </tr>

--------------------------------------------------------------------------------------------------------------------------------------------

方案（二）

[ 方法一]

前台代码：

<div>
    <asp:TextBox ID="txtName" runat="server"></asp:TextBox>
    <asp:TextBox ID="txtPwd" runat="server"></asp:TextBox>
    <asp:Button ID="btnLongin" runat="server" Text="提交" />
</div>

后台代码：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;

public partial class _Default : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        //用户输入
        txtName.Attributes.Add("Value", "请输入用户名");
        txtName.Attributes.Add("OnFocus", "if(this.value=='请输入用户名') {this.value=''}");
        txtName.Attributes.Add("OnBlur", "if(this.value==''){this.value='请输入用户名'}");
        //密码输入
        txtPwd.Attributes.Add("Value", "请输入密码");
        txtPwd.Attributes.Add("OnFocus", "if(this.value=='请输入密码'){this.value=''}");
        txtPwd.Attributes.Add("OnBlur", "if(this.value==''){this.value='请输入密码'}");

//
        if (!IsPostBack)
        {
            //内容
        }
    }
}

[ 方法二]

前台文本框里添加下面2个事件属性：

OnFocus="javascript:if(this.value=='提示文字') {this.value=''}"

OnBlur="javascript:if(this.value=='') {this.value='提示文字'}"

-----------------------------------例-----------------------------------------

<asp:TextBox ID="txtName" runat="server" Text="请输入用户名"

OnFocus="javascript:if(this.value=='请输入用户名') {this.value=''}"

OnBlur="javascript:if(this.value==''){this.value='请输入用户名'}">

</asp:TextBox>

<asp:TextBox ID="txtPwd" runat="server" Text="请输入密码"

OnFocus="javascript:if(this.value=='请输入密码') {this.value=''}"

OnBlur="javascript:if(this.value==''){this.value='请输入密码'}">

</asp:TextBox>