The name 'ScriptManager' does not exist in the current context csc

using System;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.ComponentModel;
using System.Collections;
using System.Collections.Specialized;
using System.Text;
 
namespace mm_date
{
    /// <summary>
    /// DatePicker - Generates drop down select objects for date selection
    /// Client side javascript ensures only valid date returned.
    /// </summary>
 
    [DefaultProperty("Text"),
        ToolboxData("<{0}:datepicker runat=server></{0}:datepicker>")]
 
    public class datepicker : System.Web.UI.WebControls.WebControl, System.Web.UI.IPostBackDataHandler
    {
        //Declarations
        private int begyear = 1980;
        private int endyear = System.DateTime.Today.Year;
        private int date_mode = 1;
        private int form_level = 0;
        private DateTime initial_date = System.DateTime.Today;
        private int sel_month = System.DateTime.Today.Month;
        private int sel_day = System.DateTime.Today.Day;
        private int sel_year = System.DateTime.Today.Year;
        private int picked_month = 0;
        private int picked_day = 0;
        private int picked_year = 0;
        private string selected_date;
        private string sel_date_convert;
        private DateTime date_picked;
        private string control = "Datepicker";
 
        //Define Properties
 
        //Control Release & About
        [Bindable(false),
        Category("About"),
        DefaultValue(""),
        Description("Control:  Datepicker\n" +
            "Version:  Ver 1.01 - 12/01/2003\n" +
            "Author:   Michael McLain\n" +
            "Desc:      Date dropdown selection control\n")]
 
        public string Control
        {
            get
            {
                return control;
            }
            set
            {
                control = value;
            }
        }
 
 
        //Posted Date Returned
        [Bindable(true),
        Category("Returned Values"),
        DefaultValue(""),
        Description("Returned date selected (string)")]
        public string Selected_Date
        {
            get
            {
                return selected_date;
            }
            set
            {
                selected_date = value;
            }
        }
 
        public bool LoadPostData(String postDataKey, NameValueCollection values)
        {
            selected_date = values[this.UniqueID.ToString()];
            sel_date_convert = values[this.UniqueID.ToString() + "_conv"];
            date_picked = System.DateTime.Parse(sel_date_convert).Date;
            Month = date_picked.Month;
            Day = date_picked.Day;
            Year = date_picked.Year;
            if (this.EnableViewState)
            {
                this.initial_date = date_picked;
            }
            return false;
        }
 
        public void RaisePostDataChangedEvent()
        {
        }
 
        //Returned date in datetime format
        [Bindable(true),
        Category("Returned Values"),
        DefaultValue(""),
        Description("Returned date selected (datetime)")]
        public DateTime Date_Picked
        {
            get
            {
                return date_picked;
            }
            set
            {
                date_picked = value;
            }
        }
 
        //Returned Month
        [Bindable(false),
        Category("Returned Values"),
        DefaultValue(""),
        Description("Returned month selected (int)")]
        public int Month
        {
            get
            {
                return picked_month;
            }
            set
            {
                picked_month = value;
            }
        }
 
        //Returned Day
        [Bindable(false),
        Category("Returned Values"),
        DefaultValue(""),
        Description("Returned day selected (int)")]
        public int Day
        {
            get
            {
                return picked_day;
            }
            set
            {
                picked_day = value;
            }
        }
 
        //Returned year
        [Bindable(false),
        Category("Returned Values"),
        DefaultValue(""),
        Description("Returned year selected (int)")]
        public int Year
        {
            get
            {
                return picked_year;
            }
            set
            {
                picked_year = value;
            }
        }
 
        //Begin Year
        [Bindable(true),
        Category("Setup Values"),
        DefaultValue(""),
        Description("Beginning Year Select Range")]
        public int YearRange_Start
        {
            get
            {
                return begyear;
            }
 
            set
            {
                begyear = value;
            }
        }
 
        //End Year
        [Bindable(true),
        Category("Setup Values"),
        DefaultValue(""),
        Description("Ending Year Select Range")]
        public int YearRange_End
        {
            get
            {
                return endyear;
            }
 
            set
            {
                endyear = value;
            }
        }
 
        //Initial date selected
        [Bindable(true),
        Category("Setup Values"),
        DefaultValue(""),
        Description("Initial selected date")]
        public DateTime Initial_Date
        {
            get
            {
                return initial_date;
            }
 
            set
            {
                initial_date = value;
            }
        }
 
        //Date format returned (in string format)
        //Included for backward compatibility to Classic ASP version
        [Bindable(true),
        Category("Setup Values"),
        DefaultValue(""),
        Description("Date format returned in (Selected_Date).\n1 - MM/DD/YYYY\n2 - DD/MM/YYYY\n3 - YYYYMMDD\n4 - universal format")]
        public int Date_Mode
        {
            get
            {
                return date_mode;
            }
 
            set
            {
                date_mode = value;
            }
        }
 
        //Form level index to allow handling multiple forms per page.
        [Bindable(false),
        Category("Setup Values"),
        DefaultValue(""),
        Description("Document form index level")]
        public int Form_Level
        {
            get
            {
                return form_level;
            }
 
            set
            {
                form_level = value;
            }
        }
 
        /// <summary>
        /// Render this control to the output parameter specified.
        /// </summary>
        /// <param name="output"> The HTML writer to write out to </param>
        protected override void Render(HtmlTextWriter output)
        {
            string cid = this.UniqueID.ToString();
            string isSelected = "";
            string docref = "document.forms[" + this.form_level.ToString() + "]." + cid;
            string onchg = " onChange=\"tg_mm_setdays('" + docref + "'," + date_mode.ToString() + ")\"";
            string objinit = "<script language=javascript>tg_mm_setdays('" + docref + "'," + date_mode.ToString() + ")</script>";
 
            //Build control style
            string ostyle = "";
            string c_ostyle = "";
            string ostylevalue = "";
            int stylecount = this.Style.Count;
            foreach (string stmp in this.Style.Keys)
            {
                ostylevalue = this.Style[stmp].ToString();
                c_ostyle = c_ostyle + stmp + ": " + ostylevalue + "; ";
            }
 
            StringBuilder s = new StringBuilder();
 
            //Set component container if applied style
            //Container used to handle grid layout mode
            if (c_ostyle != "")
            {
                s.Append("<div style=\"" + c_ostyle + "\">");
            }
 
            //Build select drop down styles
            string color = "";
            if (!this.ForeColor.IsEmpty)
            {
                color = this.ForeColor.Name;
                if (color != "")
                {
                    if (!this.ForeColor.IsNamedColor && !this.ForeColor.IsSystemColor)
                    {
                        color = "#" + color.Substring(2, 6);
                    }
                }
            }
            string backcolor = "";
            if (!this.BackColor.IsEmpty)
            {
                backcolor = this.BackColor.Name;
                if (backcolor != "")
                {
                    if (!this.BackColor.IsNamedColor && !this.BackColor.IsSystemColor)
                    {
                        backcolor = "#" + backcolor.Substring(2, 6);
                    }
                }
            }
            string fontname = this.Font.Name;
            string fontsize = this.Font.Size.ToString();
            string cssclass = this.CssClass;
            bool fontstyle = this.Font.Italic;
            bool fontbold = this.Font.Bold;
            bool underline = this.Font.Underline;
            bool overline = this.Font.Overline;
            bool strikeout = this.Font.Strikeout;
            string textdecoration = "";
 
            //TEXT-DECORATION: underline overline line-through
            if (underline || overline || strikeout)
            {
                textdecoration = "TEXT-DECORATION: ";
                if (underline)
                {
                    textdecoration = textdecoration + "underline ";
                }
                if (overline)
                {
                    textdecoration = textdecoration + "overline ";
                }
                if (strikeout)
                {
                    textdecoration = textdecoration + "strikeout ";
                }
                textdecoration = textdecoration + ";";
            }
 
            if (cssclass != "")
            {
                cssclass = " class=\"" + cssclass + "\"";
            }
            ostyle = " style=\"";
            if (fontname != "")
            {
                ostyle = ostyle + "FONT-FAMILY: " + fontname + ";";
            }
            if (fontsize != "")
            {
                ostyle = ostyle + "FONT-SIZE: " + fontsize + ";";
            }
            if (fontstyle)
            {
                ostyle = ostyle + "FONT-STYLE: italic;";
            }
            if (fontbold)
            {
                ostyle = ostyle + "FONT-WEIGHT: bold;";
            }
 
            if (color != "")
            {
                ostyle = ostyle + "COLOR: " + color + ";";
            }
 
            if (backcolor != "")
            {
                ostyle = ostyle + "BACKGROUND-COLOR: " + backcolor + ";";
            }
 
            if (textdecoration != "")
            {
                ostyle = ostyle + textdecoration;
            }
            ostyle = ostyle + "\"" + cssclass;
 
            //Build Month Dropdown
            sel_month = initial_date.Month;
            sel_day = initial_date.Day;
            sel_year = initial_date.Year;
 
            //Determine days in Month
            DateTime wrkdate = initial_date.Date;
            int daysinmonth = 0;
            while (sel_month == wrkdate.Month)
            {
                daysinmonth = wrkdate.Day;
                wrkdate = wrkdate.AddDays(1);
            }
            s.Append("\n<select name=\"" + cid + "_month\"" + onchg + ostyle + ">\n");
            isSelected = checkselected(1, sel_month);
            s.Append("<option value=1" + isSelected + ">Jan</option>\n");
            isSelected = checkselected(2, sel_month);
            s.Append("<option value=2" + isSelected + ">Feb</option>\n");
            isSelected = checkselected(3, sel_month);
            s.Append("<option value=3" + isSelected + ">Mar</option>\n");
            isSelected = checkselected(4, sel_month);
            s.Append("<option value=4" + isSelected + ">Apr</option>\n");
            isSelected = checkselected(5, sel_month);
            s.Append("<option value=5" + isSelected + ">May</option>\n");
            isSelected = checkselected(6, sel_month);
            s.Append("<option value=6" + isSelected + ">Jun</option>\n");
            isSelected = checkselected(7, sel_month);
            s.Append("<option value=7" + isSelected + ">Jul</option>\n");
            isSelected = checkselected(8, sel_month);
            s.Append("<option value=8" + isSelected + ">Aug</option>\n");
            isSelected = checkselected(9, sel_month);
            s.Append("<option value=9" + isSelected + ">Sep</option>\n");
            isSelected = checkselected(10, sel_month);
            s.Append("<option value=10" + isSelected + ">Oct</option>\n");
            isSelected = checkselected(11, sel_month);
            s.Append("<option value=11" + isSelected + ">Nov</option>\n");
            isSelected = checkselected(12, sel_month);
            s.Append("<option value=12" + isSelected + ">Dec</option>\n");
            s.Append("</select>\n");
 
            //Build Day Dropdown
            s.Append("\n<select name=\"" + cid + "_day\"" + onchg + ostyle + ">\n");
            int i;
            string lc_i;
            for (i = 1; i < daysinmonth + 1; i++)
            {
                lc_i = i.ToString();
                if (lc_i.Length == 1)
                {
                    lc_i = "0" + lc_i;
                }
                isSelected = checkselected(i, sel_day);
                s.Append("<option value=" + i.ToString() + isSelected + ">" + lc_i + "</option>\n");
            }
            s.Append("</select>\n");
 
            //Build Year Dropdown
            s.Append("\n<select name=\"" + cid + "_year\"" + onchg + ostyle + ">\n");
            for (i = begyear; i <= endyear; i++)
            {
                lc_i = i.ToString();
                isSelected = checkselected(i, sel_year);
                s.Append("<option value=" + i.ToString() + isSelected + ">" + i.ToString() + "</option>\n");
            }
            s.Append("</select>\n");
 
            //Build hidden input type to hold current date
            s.Append("\n<input type=hidden name=\"" + cid + "\">\n");
            s.Append("\n<input type=hidden name=\"" + cid + "_conv\">\n");
 
            //Close container for applied styles
            if (c_ostyle != "")
            {
                s.Append("</div>");
            }
 
            //Add in object initialization for Netscape inline script bug
            s.Append(objinit);
 
            //Render control
            output.Write(s.ToString());
        }
 
        protected string checkselected(int current_selection, int compair_selection)
        {
            if (current_selection == compair_selection)
            {
                return " SELECTED";
            }
            return "";
        }
 
        //		protected void Write_Client_Scripts()
        /// <summary> 
        ///    Add date validation JavaScript to the Page 
        /// </summary> 
        /// <param name="e"></param> 
        override protected void OnPreRender(EventArgs e)
        {
            StringBuilder s = new StringBuilder();
            s.Append("\n<SCRIPT LANGUAGE=javascript>\n");
            s.Append("function tg_mm_daysinmonth(lnMonth,lnYear) {\n");
            s.Append("var dt1, cmn1, cmn2, dtt, lflag, dycnt, lmn\n");
            s.Append("lmn = lnMonth-1\n");
            s.Append("dt1 = new Date(lnYear,lmn,1)\n");
            s.Append("cmn1 = dt1.getMonth()\n");
            s.Append("dtt=dt1.getTime()+2332800000\n");
            s.Append("lflag = true\n");
            s.Append("dycnt=28\n");
            s.Append("while (lflag) {\n");
            s.Append("   dtt = dtt + 86400000\n");
            s.Append("   dt1.setTime(dtt)\n");
            s.Append("   cmn2 = dt1.getMonth()\n");
            s.Append("   if (cmn1!=cmn2) {\n");
            s.Append("      lflag = false }\n");
            s.Append("   else {dycnt = dycnt + 1}}\n");
            s.Append("if (dycnt > 31) {dycnt = 31}\n");
            s.Append("return dycnt\n");
            s.Append("}\n");
            s.Append("\n");
            s.Append("function tg_mm_setdays(sobjname, datemode){\n");
            s.Append("var dobj = eval(sobjname + \"_day\")\n");
            s.Append("var mobj = eval(sobjname + \"_month\")\n");
            s.Append("var yobj = eval(sobjname + \"_year\")\n");
            s.Append("var hobj = eval(sobjname)\n");
            s.Append("var hobjconv = eval(sobjname + \"_conv\")\n");
            s.Append("var monthdays = tg_mm_daysinmonth(mobj.options[mobj.selectedIndex].value,yobj.options[yobj.selectedIndex].value)\n");
            s.Append("var selectdays = dobj.length\n");
            s.Append("var curdy = dobj.options[dobj.selectedIndex].value\n");
            s.Append("if (curdy.length==1) {curdy = \"0\"+curdy}\n");
            s.Append("var curmn = mobj.options[mobj.selectedIndex].value\n");
            s.Append("if (curmn.length==1) {curmn = \"0\"+curmn}\n");
            s.Append("var curyr = yobj.options[yobj.selectedIndex].value\n");
            s.Append("if (selectdays > monthdays) {\n");
            s.Append("   for (var dlp=selectdays; dlp > monthdays; dlp--) {\n");
            s.Append("       dobj.options[dlp-1] = null }}\n");
            s.Append("else if (monthdays > selectdays) {\n");
            s.Append("   for (var dlp=selectdays; dlp < monthdays; dlp++) {\n");
            s.Append("       dobj.options[dlp] = new Option(dlp+1,dlp+1) }}\n");
            s.Append("if (curdy > monthdays) {\n");
            s.Append("   dobj.options[monthdays-1].selected = true\n");
            s.Append("   curdy = monthdays }\n");
            s.Append("var curdateconv = curmn+\"/\"+curdy+\"/\"+curyr\n");
            s.Append("if (datemode==1) {\n");
            s.Append("   var curdate = curmn+\"/\"+curdy+\"/\"+curyr }\n");
            s.Append("else if (datemode==2) {\n");
            s.Append("   var curdate = curdy+\"/\"+curmn+\"/\"+curyr }\n");
            s.Append("else if (datemode==3) {\n");
            s.Append("   var curdate = curyr+curmn+curdy }\n");
            s.Append("else if (datemode==4) {\n");
            s.Append("   var cdate = new Date(curyr,curmn-1,curdy)\n");
            s.Append("   var curdate = cdate.toGMTString() }\n");
            s.Append("hobj.value = curdate\n");
            s.Append("hobjconv.value = curdateconv\n");
            s.Append("}\n");
            s.Append("</SCRIPT>\n");
            s.Append("\n");
	
	    string CloseWindow;
 
            CloseWindow = "alert('Hello World')";
 
            ScriptManager.RegisterStartupScript(this,this.GetType(), "CloseWindow", CloseWindow, true);
 
            // Add the Script to the Page 
          //  this.Page.ClientScript.RegisterClientScriptBlock("mm_datepicker", s.ToString());
        
        }
 
    }
}

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