asp.net本身提供了很多控件,提供给我们这些比较懒惰的人使用,我认为控件的作用就在此,因为我们不想重复工作,所以要创建它,这个本身便是一个需求的关系,所以学习控件开发很有意思.
wrox网站上有本书
Professional ASP.NET 2.0 Server Control and Component Development 现在还没有出版,但网站上放出了代码,所以正好下载过来学习一下.
我看过前几章代码,环环相扣,作者用不同的知识向我们展示同一个效果,所以循序渐进的学下来很有好处.
虽然自己对控件开发还不是很熟悉，但我感觉以下几点很重要，是我自己总结的
1.了解控件之间的继承关系 最好是先看看看System.Web.UI命名空间
(1)Control 类，所有的控件都共享的一个类，你需要去看下其里面受保护的几个方法和属性，虽然一下看不完，以后会发现常常用到这些方法
大家可以在MSDN看一下其派生类
(2)HtmlTextWriter 类
不得不了解的一个类，主要工作就是我们写的标记字符和文本输出
2.重写方法 (1) 必须继承Control类
(2) 重写Control类的Render方法，这个是必须的，因为其他控件都继承了Control 类类，所以几乎所有控件都有这个方法
3.熟悉元数据 大家都知道asp.net控件属性在编辑器上是分类的，如外观，行为，布局等，每个属性还给出了解释
简单的元数据就是起到这个作用，当然你也可以不加，但使用了元数据让人感到有亲切感，写法如
下
[CategoryAttribute("Appearance")]
要使用元数据，必须引用System.ComponentModel命名控件，一般你如果写组件的话，不可能不用到这样类库。具体的MSDN上有所介绍。
一.输出字符串 说多了没意思，还是来演练吧。首先你得了解HTML。来看下面代码,效果就是输出HTML到客户端
示例一 
using
System;
using
System.Web.UI;
namespace
CustomComponents
{
/**/
///
<summary>
///
Summary description for CreditCardForm
///
</summary>
public
class
CreditCardForm1 : Control
{
protected
override
void
Render(HtmlTextWriter writer)
{
writer.Write(
"
<table style='width:287px;height:124px;border-width:0;'>
"
);
writer.Write(
"
<tr>
"
);
writer.Write(
"
<td><strong>Payment Method</strong></td>
"
);
writer.Write(
"
<td>
"
);
writer.Write(
"
<select name='PaymentMethod' id='PaymentMethod' style='width:100%;'>
"
);
writer.Write(
"
<option value='0'>Visa</option>
"
);
writer.Write(
"
<option value='1'>MasterCard</option>
"
);
writer.Write(
"
</select>
"
);
writer.Write(
"
</td>
"
);
writer.Write(
"
</tr>
"
);
writer.Write(
"
<tr>
"
);
writer.Write(
"
<td><strong>Credit Card No.</strong></td>
"
);
writer.Write(
"
<td><input name='CreditCardNo' id='CreditCardNo' type='text' /></td>
"
);
writer.Write(
"
</tr>
"
);
writer.Write(
"
<tr>
"
);
writer.Write(
"
<td><strong>Cardholder's Name</strong></td>
"
);
writer.Write(
"
<td><input name='CardholderName' id='CardholderName' type='text' /></td>
"
);
writer.Write(
"
</tr>
"
);
writer.Write(
"
<tr>
"
);
writer.Write(
"
<td><strong>Expiration Date</strong></td>
"
);
writer.Write(
"
<td>
"
);
writer.Write(
"
<select name='Month' id='Month'>
"
);
for
(
int
day
=
1
; day
<
13
; day
)
{
if
(day
<
10
)
writer.Write(
"
<option value='
"
day.ToString()
"
'>
"
"
0
"
day.ToString()
"
</option>
"
);
else
writer.Write(
"
<option value='
"
day.ToString()
"
'>
"
day.ToString()
"
</option>
"
);
}
writer.Write(
"
</select>
"
);
writer.Write(
"
&;amp;nbsp
"
);
writer.Write(
"
<select name='Year' id='Year'>
"
);
for
(
int
year
=
2005
; year
<
2015
; year
)
{
writer.Write(
"
<option value='
"
year.ToString()
"
'>
"
year.ToString()
"
</option>
"
);
}
writer.Write(
"
</select>
"
);
writer.Write(
"
</td>
"
);
writer.Write(
"
</tr>
"
);
writer.Write(
"
<tr>
"
);
writer.Write(
"
<td align='center' colspan='2'>
"
);
writer.Write(
"
<input type='submit' value='Submit' />
"
);
writer.Write(
"
</td>
"
);
writer.Write(
"
</tr>
"
);
writer.Write(
"
</table>
"
);
base
.Render(writer);
}
}
}
效果很简单,其实就一直在输出HTML再加几个属性,大家可以直接把代码放在App_Code文件夹里,就可自动编译,当然也可以创建web控件库.
注意要继承Control类,重写Render方法,用HtmlTextWriter类的Write输出HTML
使用控件 (1).需要先注册一下
<%@ Register TagPrefix="custom" Namespace="CustomComponents" %>
(2) 然后就使用标签输出效果
<custom:CreditCardForm1 runat="server" ID="ccf" />
下为效果图
二.改善,加入属性和元数据 可能上面做出的 控件毫无用处,但却可以让你熟悉一下步骤,上面的控件定的很死,没有定义任何属性,用处不大,下面来改造
我们来定义常用属性,然后再输出,这样我们就可以修改控件的属性了,
示例二 using
System;
using
System.Web.UI;
using
System.ComponentModel;
namespace
CustomComponents
{
[DefaultPropertyAttribute(
"
CardholderNameText
"
)]
[ToolboxData(
@"
<{0}:CreditCardForm2
PaymentMethodText='信用卡类型' CreditCardNoText='信用卡卡号'
CardholderNameText='信用卡持有者姓名' SubmitButtonText = '提交'
runat='server'></{0}:CreditCardForm2>
"
)
]
public
class
CreditCardForm2 : Control
{
private
string
paymentMethodText
=
"
信用卡类型
"
;
private
string
creditCardNoText
=
"
信用卡卡号
"
;
private
string
cardholderNameText
=
"
信用卡持有者姓名
"
;
private
string
expirationDateText
=
"
最后使用时间
"
;
private
string
submitButtonText
=
"
提交
"
;
[BrowsableAttribute(
true
)]
[DescriptionAttribute(
"
获取和设置信用卡类型
"
)]
[DefaultValueAttribute(
"
信用卡类型
"
)]
[CategoryAttribute(
"
Appearance
"
)]
public
virtual
string
PaymentMethodText
{
get
{
return
this
.paymentMethodText; }
set
{
this
.paymentMethodText
=
value; }
}
[BrowsableAttribute(
true
)]
[DescriptionAttribute(
"
获取或设置信用卡卡号
"
)]
[DefaultValueAttribute(
"
信用卡卡号
"
)]
[CategoryAttribute(
"
Appearance
"
)]
public
virtual
string
CreditCardNoText
{
get
{
return
this
.creditCardNoText; }
set
{
this
.creditCardNoText
=
value; }
}
[BrowsableAttribute(
true
)]
[DescriptionAttribute(
"
获取或设置信用卡持有者姓名
"
)]
[DefaultValueAttribute(
"
信用卡持有者姓名
"
)]
[CategoryAttribute(
"
Appearance
"
)]
public
virtual
string
CardholderNameText
{
get
{
return
this
.cardholderNameText; }
set
{
this
.cardholderNameText
=
value; }
}
[BrowsableAttribute(
true
)]
[DescriptionAttribute(
"
获取或设置最后使用时间
"
)]
[DefaultValueAttribute(
"
最后使用时间
"
)]
[CategoryAttribute(
"
Appearance
"
)]
public
virtual
string
ExpirationDateText
{
get
{
return
this
.expirationDateText; }
set
{
this
.expirationDateText
=
value; }
}
[BrowsableAttribute(
true
)]
[DescriptionAttribute(
"
获取或设置按钮标签
"
)]
[DefaultValueAttribute(
"
提交
"
)]
[CategoryAttribute(
"
Appearance
"
)]
public
virtual
string
SubmitButtonText
{
get
{
return
this
.submitButtonText; }
set
{
this
.submitButtonText
=
value; }
}
protected
override
void
Render(HtmlTextWriter writer)
{
writer.Write(
"
<table style='width:287px;height:124px;border-width:0;'>
"
);
writer.Write(
"
<tr>
"
);
writer.Write(
"
<td>
"
PaymentMethodText
"
</td>
"
);
writer.Write(
"
<td>
"
);
writer.Write(
"
<select name='PaymentMethod' id='PaymentMethod' style='width:100%;'>
"
);
writer.Write(
"
<option value='0'>Visa</option>
"
);
writer.Write(
"
<option value='1'>MasterCard</option>
"
);
writer.Write(
"
</select>
"
);
writer.Write(
"
</td>
"
);
writer.Write(
"
</tr>
"
);
writer.Write(
"
<tr>
"
);
writer.Write(
"
<td>
"
&
