用Visual C#.NET编写服务器日期控件

一、序言

Visual C#.NET是微软公司出品的一种新的编程语言(以下简称C#),它继承了C语言的一些特性,也加入了一些新的元素.以前用过Delphi开发程序的人可能刚开始使用C#的时候,对其有一种似曾相识的感觉(至少包括我).是的,C#语言的创始人正是以前在Borland公司开发出Delphi语言的Anders Hejlsberg.在我开始使用C#开发程序时,就觉得它是一款很棒的开发Windows Form & Web程序的RAD工具.
在开发Web程序方面,C#的出现打破了以前的网页开发模式,实现了与开发Windows

Form程序一样的所见即所得的功能.C#提供了一些常用的Web Form Control供开发人员使用,并且只需将控件拖入页面中即可,非?虻?但有时这些控件也不能满足开发人员的需要,需要开发人员自己编写用户控件(User Control)或自定义控件(Custom Control)来满足需求.在这里,我将讲解如何在C#中开发服务器控件.

    二、预备知识

    在C#中可以开发两种服务器控件,一个是用户控件(User Control)和自定义控件(Custom Control).用户控件的本质与页面文件(aspx文件)差不多,是可被其它aspx页面重复使用的HTML代码段,当然它也包括后台代码(Code-behind),后缀名是ascx.所以在开发一些公用的静态页面时(例如页头,页脚)经常用到,但它的缺点是不易继承,不易分发,无法编译成二进制代码来进行部署.但是自定义控件的功能就强大许多,它可以被编译成二进制代码(DLL文件),可以被扩展、继承、分发.就像Web Form Control一样,其实它们每个控件就是一个DLL文件.

    开发用户控件比较简单,就像编写一个aspx页面一样,在这里就不介绍了.本文对象是自定义控件.服务器控件的基类是System.Web.UI.Control.如果要开发可视化的服务器控件,那我们需要从System.Web.UI.WebControls来继承,否则从System.Web.UI.Control继承.

    服务器控件在设计时以runat=”server”脚本代码嵌入到aspx文件中来表示此控件是在服务器端运行的.在服务器控件所在页面提交回传(PostBack)过程中是依靠ViewState(视图状态)来维护控件状态的.所以我们在设计服务器控件属性时,其值应保存在ViewState中.

    三、代码编写

C#中有一个日历控件Calendar,但是现在我需要一个可以下拉的日历控件,并且初始时不显示日历,当我点击下拉按钮时才弹出,并且当选择了日期,日历会自动隐藏且选择的日期值会显示到相应的输入框中.显然Calendar控件不能满足我的需要,但是稍后我会在我的自定义控件中用到它.

    首先新建项目,在项目类型中选择Visual C#项目,在模板列表中选择Web控件库,输入项目名称AquaCalendar,然后选择项目所在目录,点击【确定】按钮.C#将会生成基本的框架代码.将项目中的类文件和类名改名为DatePicker(即日期控件的类名).由于DatePicker是可视化控件,所以我们必须从System.Web.UI.WebControls继承.并且它包括一个输入框,一个按钮和日历控件,需要在DatePicker类中声明它们.像这种以多个服务器控件组合的控件成为复合控件.代码如下,比较重要的方法和代码在注释中会加以说明：

using System;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.ComponentModel;
using System.Drawing;

namespace AquaCalendar
{
    [DefaultProperty( ), )]
    public class DatePicker : System.Web.UI.WebControls.WebControl , IPostBackEventHandler
    {
        private const string _BUTTONDEFAULTSTYLE = ;
       
       
        private const string _BUTTONDEFAULTTEXT = ;
        private System.Web.UI.WebControls.Calendar _Calendar;
       
        public override ControlCollection Controls
        {
            get
            {
                EnsureChildControls( ); return base.Controls;
            }
        }
       
       
        protected override void CreateChildControls( )
        {
            Controls.Clear( );
            _Calendar = new Calendar( );
            _Calendar.ID = MyCalendarID;
            _Calendar.SelectedDate = DateTime.Parse( Text );
            _Calendar.TitleFormat = TitleFormat.MonthYear;
            _Calendar.NextPrevFormat = NextPrevFormat.ShortMonth;
            _Calendar.CellSpacing = 0;
            _Calendar.Font.Size = FontUnit.Parse( );
            _Calendar.Font.Name = ;
            _Calendar.SelectedDayStyle.BackColor = ColorTranslator.FromHtml( );
            _Calendar.SelectedDayStyle.ForeColor = ColorTranslator.FromHtml( );
            _Calendar.DayStyle.BackColor = ColorTranslator.FromHtml( );
            _Calendar.TodayDayStyle.BackColor = ColorTranslator.FromHtml( );
            _Calendar.TodayDayStyle.ForeColor = ColorTranslator.FromHtml( );
            _Calendar.DayHeaderStyle.Font.Size = FontUnit.Parse( );
            _Calendar.DayHeaderStyle.Font.Bold = true;
            _Calendar.DayHeaderStyle.Height = Unit.Parse( );
            _Calendar.DayHeaderStyle.ForeColor = ColorTranslator.FromHtml( );
            _Calendar.NextPrevStyle.Font.Size = FontUnit.Parse( );
            _Calendar.NextPrevStyle.Font.Bold = true;
            _Calendar.NextPrevStyle.ForeColor = ColorTranslator.FromHtml( );
            _Calendar.TitleStyle.Font.Size = FontUnit.Parse( );
            _Calendar.TitleStyle.Font.Bold = true;
            _Calendar.TitleStyle.Height = Unit.Parse( );
            _Calendar.TitleStyle.ForeColor = ColorTranslator.FromHtml( );
            _Calendar.TitleStyle.BackColor = ColorTranslator.FromHtml( );
            _Calendar.OtherMonthDayStyle.ForeColor = ColorTranslator.FromHtml( );
            _Calendar.NextPrevFormat = NextPrevFormat.CustomText;
            _Calendar.NextMonthText = ;
            _Calendar.PrevMonthText = ;
            _Calendar.Style.Add( , ); new EventHandler( _Calendar_SelectionChanged );
            this.Controls.Add( _Calendar );
        }
        [
        Category( ), )
       
        public string Text
        {
            get
            {
                EnsureChildControls( );
                return ( ViewState[] == null )?System.DateTime.Today.ToString( ):ViewState[].ToString( );
            }
            set
            {
                EnsureChildControls( );
                DateTime dt = System.DateTime.Today;
                try
                {
                    dt = DateTime.Parse( value );
                }
                catch
                {
                    throw new ArgumentOutOfRangeException( );
                }
               
                ViewState[] = DateFormat == CalendarEnum.LongDateTime?dt.ToString( ):dt.ToString( );
            }
        }
       
       
        public override bool Enabled
        {
            get
            {
                EnsureChildControls( );
                return ViewState[] == null?true:( bool )ViewState[];
            }
            set
            {
                EnsureChildControls( );
                ViewState[] = value;
            }
        }
       
        public string ButtonStyle
        {
            get
            {
                EnsureChildControls( );
                object o = ViewState[];
                return ( o == null )?_BUTTONDEFAULTSTYLE:o.ToString( );
            }
            set
            {
                EnsureChildControls( );
                ViewState[] = value;
            }
        }
       
        [
        DefaultValue( CalendarEnum.LongDateTime ),
        ]
       
        public CalendarEnum DateFormat
        {
            get
            {
                EnsureChildControls( );
                object format = ViewState[];
                return format == null?CalendarEnum.LongDateTime:( CalendarEnum )format;
            }
            set
            {
                EnsureChildControls( );
                ViewState[] = value;
                DateTime dt = DateTime.Parse( Text );
                Text=DateFormat == CalendarEnum.LongDateTime?dt.ToString( ):dt.ToString( );
            }
        }
       
        [
        Browsable( false ),
        DesignerSerializationVisibility( DesignerSerializationVisibility.Hidden )
        ]
       
        public string MyCalendarID
            get
            {
                EnsureChildControls( );
                return this.ClientID+;
            }
        }
       
        [
        Browsable( false ),
        DesignerSerializationVisibility( DesignerSerializationVisibility.Hidden )
        ]
       
        public string MyCalendarName
            get
            {
                EnsureChildControls( );
                return this.UniqueID+;
            }
        }
       
        [
        Browsable( false ),
        DesignerSerializationVisibility( DesignerSerializationVisibility.Hidden )
        ]
       
        public string DatePickerInputID
            get
            {
                EnsureChildControls( );
                return this.ClientID+;
            }
        }
       
        [
        Browsable( false ),
        DesignerSerializationVisibility( DesignerSerializationVisibility.Hidden )
        ]
       
        public string DatePickerInputName
            get
            {
                EnsureChildControls( );
                return this.UniqueID+;
            }
        }
       
        [
        Browsable( false ),
        DesignerSerializationVisibility( DesignerSerializationVisibility.Hidden )
        ]
       
        public string DatePickerButtonID
            get
            {
                EnsureChildControls( );
                return this.ClientID+;
            }
        }
       
        [
        Browsable( false ),
        DesignerSerializationVisibility( DesignerSerializationVisibility.Hidden )
        ]
       
        public string DatePickerButtonName
            get
            {
                EnsureChildControls( );
                return this.UniqueID+;
            }
        }
       
        public string ButtonText
        {
            get
            {
                EnsureChildControls( );
                return ViewState[] == null?_BUTTONDEFAULTTEXT:( string )ViewState[];
            }
            set
            {
                EnsureChildControls( );
                ViewState[] = value;
            }
        }
       
       
       
       
        > 要写出到的 HTML 编写器 </param>
       
        protected override void Render( HtmlTextWriter output )
        {
            );
            output.AddAttribute( HtmlTextWriterAttribute.Border, );
            output.AddAttribute( HtmlTextWriterAttribute.Cellpadding, );
           
            output.AddStyleAttribute( , this.Style[] );
            output.AddStyleAttribute( , this.Style[] );
            output.AddStyleAttribute( , );
           
            if ( Width != Unit.Empty )
            {
                output.AddStyleAttribute( HtmlTextWriterStyle.Width, Width.ToString( ) );
            }
            else
            {
                output.AddStyleAttribute( HtmlTextWriterStyle.Width, );
            }
           
            output.RenderBeginTag( HtmlTextWriterTag.Table ); );
            output.RenderBeginTag( HtmlTextWriterTag.Td );
           
           
            if ( !Enabled )
            {
                output.AddAttribute( HtmlTextWriterAttribute.ReadOnly, );
            }
           
            output.AddAttribute( HtmlTextWriterAttribute.Type, );
            output.AddAttribute( HtmlTextWriterAttribute.Id, DatePickerInputID );
            output.AddAttribute( HtmlTextWriterAttribute.Name, DatePickerInputName );
            output.AddAttribute( HtmlTextWriterAttribute.Value, Text );
            output.AddStyleAttribute( HtmlTextWriterStyle.Width, );
            output.AddStyleAttribute( HtmlTextWriterStyle.Height, );
            output.AddStyleAttribute( HtmlTextWriterStyle.FontFamily, Font.Name );
            output.AddStyleAttribute( HtmlTextWriterStyle.FontSize, Font.Size.ToString( ) );
            output.AddStyleAttribute( HtmlTextWriterStyle.FontWeight, Font.Bold?: );
            output.RenderBeginTag( HtmlTextWriterTag.Td );
           
           
            if ( !Enabled )
            {
                output.AddAttribute( HtmlTextWriterAttribute.Disabled, );
            }
           
            output.AddAttribute( HtmlTextWriterAttribute.Type, );
            output.AddAttribute( HtmlTextWriterAttribute.Id, DatePickerButtonID );
            output.AddAttribute( HtmlTextWriterAttribute.Name, DatePickerButtonName );
            output.AddAttribute( HtmlTextWriterAttribute.Value, ButtonText );
            output.AddStyleAttribute( HtmlTextWriterStyle.Width, );
            output.AddAttribute( HtmlTextWriterAttribute.Onclick, Page.GetPostBackEventReference( this ) );
            output.AddAttribute( HtmlTextWriterAttribute.Style, ButtonStyle );
            output.RenderBeginTag( HtmlTextWriterTag.Input );
            output.RenderEndTag( );
           
            output.RenderEndTag( );
            output.RenderBeginTag( HtmlTextWriterTag.Tr );
            output.AddAttribute( HtmlTextWriterAttribute.Colspan, );
            output.RenderBeginTag( HtmlTextWriterTag.Td );
            _Calendar.RenderControl( output );
            output.RenderEndTag( );
            output.RenderEndTag( );
        }
       
       
        public void RaisePostBackEvent( string eventArgument )
        {
            OnClick( EventArgs.Empty );
        }
       
        protected virtual void OnClick( EventArgs e )
        {
            if ( _Calendar.Attributes[] != DateTime.Parse( Text );
                _Calendar.Style.Add( ,private void _Calendar_SelectionChanged( object sender, EventArgs e )
        {
           
            _Calendar.Style.Add( , );
        }
    }
}

在上面的代码中,需要注意以下几点：

    ·如果你想将此控件的某些属性供重载,则在声明属性前加上virtual关键字;

    ·在页面输出此控件时(即在Render事件中),是先定义子控件的样式或属性,然后再产生子控件;

    ·在隐藏日历子控件时,建议不要使用Visible属性来显示/隐藏,使用Visible=false隐藏时服务器端将不会将日历控件HTML代码发送给客户端,会导致复合控件装载日历控件的表格会空白一块出来,影响页面的布局.所以使用样式display=none设置来使日历控件在客户端隐藏,但是HTML代码依然存在于页面中;




    四、结束语

    在编写服务器控件时,需要一定的HTML语言基?惨宄?NET程序的请求处理方式.服务器控件封装了客户端行为及逻辑判断,无需开发者添加更多代码.当然,有些地方使用服务器控件可以带来方便,但是也增加了服务器的负荷.有时适当的结合javascript使一些代码在客户端运行,可提高WEB应用程序效率