asp.net控件开发基础示例(1)-接触自定义控件

本节学习完整实例代码                         返回系列教程目录
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.

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
点击展开
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("&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

点击展开
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>" + CreditCardNoText + "</td>");
      writer.Write("<td><input name=''CreditCardNo'' id=''CreditCardNo'' type=''text'' /></td>");
      writer.Write("</tr>");
      writer.Write("<tr>");
      writer.Write("<td>" + CardholderNameText + "</td>");
      writer.Write("<td><input name=''CardholderName'' id=''CardholderName'' type=''text'' /></td>");
      writer.Write("</tr>");
      writer.Write("<tr>");
      writer.Write("<td>" + ExpirationDateText + "</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("&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=''" + SubmitButtonText + "'' />");
      writer.Write("</td>");
      writer.Write("</tr>");
      writer.Write("</table>");

      base.Render(writer);
    }
  }
}

上面我们接触到了元数据了,意思应该很好理解,为了测试元数据的作用,大家可以新建一个类库项目,然后把写的代码放这个项目里面,接着web网站引用这个项目,成功生成以后,你会发现工具箱已经自动帮你加上了这几个控件


接着你要做的工作就是拖动你需要的控件,然后你会在属性面板看到下图

然后你再结合代码中的元数据,应该就知道大概意思了.(可以根据你的理解结合MSDN看)

三.再次改善,淘汰用Write方法以字符串的方式输出HTML
接着我们继续发现问题,我们发现我们除了定义几个需要自己来修改的属性外,还是要用来大量的字符串用来输出HTML,而且容易输错.所以HtmlTextWriter类提供几个有用的方法用来代替.

(1)AddStyleAttribute方法 为标签添加样式属性
(2)AddAttribute方法 为标签添加属性
(3)RenderBeginTag 开始写入标签头 如<table.>
(4)RenderEndTag 写入标签尾部,如</table>

这里有几点需要特别注意.

一.因为其定义方式跟我们平时定义方式不同,我们平时写HTML时,是先写标签开头,再写标签的属性.如<table borderwidth="0">,然而我们在使用上面几个方法时,需要有先后顺序,我们需要先定义标签的属性和样式,然后再输出标签头.

二.标签头和尾,需一一对应.可以理解为嵌套关系.最好的理解方法就是输出代码后,查看源文件,再结合原来定义的代码来看.

还是看代码比较容易说明,由于CreditCardForm2已经定义了我们需要的属性,而我们现在要做的只是用标签的形式来替代字符串的形式,所以只需要继承CreditCardForm2类,重写Render方法即可

示例三

点击展开
protected override void Render(HtmlTextWriter writer)
    {
      writer.AddStyleAttribute(HtmlTextWriterStyle.BorderWidth, "0");
      writer.RenderBeginTag(HtmlTextWriterTag.Table);
      writer.RenderBeginTag(HtmlTextWriterTag.Tr);
      writer.RenderBeginTag(HtmlTextWriterTag.Td);
      writer.Write("<strong>" + PaymentMethodText + "</strong>");
      writer.RenderEndTag();
      writer.RenderBeginTag(HtmlTextWriterTag.Td);
      writer.AddAttribute(HtmlTextWriterAttribute.Name, "PaymentMethod");
      writer.AddAttribute(HtmlTextWriterAttribute.Id, "PaymentMethod");
      writer.AddStyleAttribute(HtmlTextWriterStyle.Width, "100%");
      writer.RenderBeginTag(HtmlTextWriterTag.Select);

      writer.AddAttribute(HtmlTextWriterAttribute.Value, "0");
      writer.RenderBeginTag(HtmlTextWriterTag.Option);
      writer.Write("Visa");
      writer.RenderEndTag();

      writer.AddAttribute(HtmlTextWriterAttribute.Value, "1");
      writer.RenderBeginTag(HtmlTextWriterTag.Option);
      writer.Write("MasterCard");
      writer.RenderEndTag();

      writer.RenderEndTag();
      writer.RenderEndTag();
      writer.RenderEndTag();

      writer.RenderBeginTag(HtmlTextWriterTag.Tr);
      writer.RenderBeginTag(HtmlTextWriterTag.Td);
      writer.Write("<strong>" + CreditCardNoText + "</strong>");
      writer.RenderEndTag();
      writer.RenderBeginTag(HtmlTextWriterTag.Td);
      writer.AddAttribute(HtmlTextWriterAttribute.Name, "CreditCardNo");
      writer.AddAttribute(HtmlTextWriterAttribute.Id, "CreditCardNo");
      writer.AddAttribute(HtmlTextWriterAttribute.Type, "text");
      writer.RenderBeginTag(HtmlTextWriterTag.Input);
      writer.RenderEndTag();
      writer.RenderEndTag();
      writer.RenderEndTag();

      writer.RenderBeginTag(HtmlTextWriterTag.Tr);
      writer.RenderBeginTag(HtmlTextWriterTag.Td);
      writer.Write("<strong>" + CardholderNameText + "</strong>");
      writer.RenderEndTag();
      writer.RenderBeginTag(HtmlTextWriterTag.Td);
      writer.AddAttribute(HtmlTextWriterAttribute.Name, "CardholderName");
      writer.AddAttribute(HtmlTextWriterAttribute.Id, "CardholderName");
      writer.AddAttribute(HtmlTextWriterAttribute.Type, "text");
      writer.RenderBeginTag(HtmlTextWriterTag.Input);
      writer.RenderEndTag();
      writer.RenderEndTag();
      writer.RenderEndTag();

      writer.RenderBeginTag(HtmlTextWriterTag.Tr);
      writer.RenderBeginTag(HtmlTextWriterTag.Td);
      writer.Write("<strong>" + ExpirationDateText + "</strong>");
      writer.RenderEndTag();
      writer.RenderBeginTag(HtmlTextWriterTag.Td);
      writer.AddAttribute(HtmlTextWriterAttribute.Name, "Month");
      writer.AddAttribute(HtmlTextWriterAttribute.Id, "Month");
      writer.RenderBeginTag(HtmlTextWriterTag.Select);

      for (int day = 1; day < 13; day++)
      {
        writer.AddAttribute(HtmlTextWriterAttribute.Value, day.ToString());
        writer.RenderBeginTag(HtmlTextWriterTag.Option);

        if (day < 10)
          writer.Write("0" + day.ToString());
        else
          writer.Write(day);

        writer.RenderEndTag();
      }

      writer.RenderEndTag();
      writer.Write("&nbsp;");

      writer.AddAttribute(HtmlTextWriterAttribute.Name, "Year");
      writer.AddAttribute(HtmlTextWriterAttribute.Id, "Year");
      writer.RenderBeginTag(HtmlTextWriterTag.Select);

      for (int year = 2005; year < 2015; year++)
      {
        writer.AddAttribute(HtmlTextWriterAttribute.Value, year.ToString());
        writer.RenderBeginTag(HtmlTextWriterTag.Option);
        writer.Write(year);
        writer.RenderEndTag();
      }

      writer.RenderEndTag();

      writer.RenderEndTag();
      writer.RenderEndTag();

      writer.RenderBeginTag(HtmlTextWriterTag.Tr);
      writer.AddAttribute(HtmlTextWriterAttribute.Align, "center");
      writer.AddAttribute(HtmlTextWriterAttribute.Colspan, "2");
      writer.RenderBeginTag(HtmlTextWriterTag.Td);
      writer.AddAttribute(HtmlTextWriterAttribute.Type, "submit");
      writer.AddAttribute(HtmlTextWriterAttribute.Value, SubmitButtonText);
      writer.RenderBeginTag(HtmlTextWriterTag.Input);
      writer.RenderEndTag();
      writer.RenderEndTag();
      writer.RenderEndTag();
      writer.RenderEndTag();
    }

实现的效果虽然一样,但上面的代码是不是漂亮很多,而且不容易输错.这也是所提倡的做法

四.未使用视图状态的后果
还是视图状态,关于视图状态大家可以参考MSDN和相关文章
看以下的示例,还是CreditCardForm3这个控件

if (!IsPostBack)
    {
      creditcardform.CardholderNameText = "Full Name";
      creditcardform.CreditCardNoText = "CreditCardNo";
      creditcardform.ExpirationDateText = "ExpirationDate";
      creditcardform.PaymentMethodText = "Payment Options";
      creditcardform.SubmitButtonText = "Send";
    }

首次加载效果

点击按钮以后

 五.使用视图状态改善效果
前提条件是你未禁用视图状态
继承CreditCardForm3,改写每个属性

点击展开
public override string PaymentMethodText
    {
        get { return ViewState["PaymentMethodText"] != null ? (string)ViewState["PaymentMethodText"] : "信用卡类型"; }
      set { ViewState["PaymentMethodText"] = value; }
    }

    public override string CreditCardNoText
    {
        get { return ViewState["CreditCardNoText"] != null ? (string)ViewState["CreditCardNoText"] : "信用卡卡号"; }
      set { ViewState["CreditCardNoText"] = value; }
    }

    public override string CardholderNameText
    {
        get { return ViewState["CardholderNameText"] != null ? (string)ViewState["CardholderNameText"] : "信用卡持有者姓名"; }
      set { ViewState["CardholderNameText"] = value; }
    }

    public override string ExpirationDateText
    {
        get { return ViewState["ExpirationDateText"] != null ? (string)ViewState["ExpirationDateText"] : "最后使用时间"; }
      set { ViewState["ExpirationDateText"] = value; }
    }

    public override string SubmitButtonText
    {
        get { return ViewState["SubmitButtonText"] != null ? (string)ViewState["SubmitButtonText"] : "提交"; }
      set { ViewState["SubmitButtonText"] = value; }
    }