如何使用try/check for DateTime来防止服务器错误

我正试图编写一个try/catch，但显然失败了。我不确定我是否完全理解try/catch，但我知道我很难理解我需要做什么来验证通过表单提交的日期是否正确。我的意思是，我认为它需要是DateTime格式，而不是字符串，应该是（MM/dd/yyyy），但这种try/check的事情让我陷入了循环。

说明：返回您在frmPersonnel代码并添加带有逻辑的try/catch以防止无效导致服务器错误的日期。

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 frmPersonnel : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        btnSubmit.Click += new EventHandler(this.btnSubmit_Click);//event for button
    }
    private void btnSubmit_Click(object sender, EventArgs e)
    {
//DECLARATIONS
        int count = 0;
        string Msg = "You must enter a value in the following fields: <br/>  ";
        Boolean validatedState = true;
        Boolean validateEntry = false;
        DateTime endDate = new DateTime(2016, 03, 01);
        DateTime startDate = new DateTime(2016, 03, 01);

//BEGIN SERIES OF IF/ELSE FOR CONFIRMING ENTRIES         
        if (Request["txtFirstName"].ToString().Trim() == "")
            {
            //displays yellow bg for missing input
            txtFirstName.BackColor = System.Drawing.Color.Yellow;
            Msg = Msg + "First Name <br/> ";
            }//endif
        else
        {
            txtFirstName.BackColor = System.Drawing.Color.White; 
            count += 1;
        }//end else
        if (Request["txtLastName"].ToString().Trim() == "")
        {
            //displays yellow bg for missing input
            txtLastName.BackColor = System.Drawing.Color.Yellow;
            Msg = Msg + "Last Name <br/> ";
        }//endif
        else
        {
            txtFirstName.BackColor = System.Drawing.Color.White; 
            count += 1;
        }//end else
        if (Request["txtPayRate"].ToString().Trim() == "")
        {
            //displays yellow bg for missing input
            txtPayRate.BackColor = System.Drawing.Color.Yellow;
            Msg = Msg + "Pay Rate <br/>  ";
         }//endif
        else
        {
            txtFirstName.BackColor = System.Drawing.Color.White; 
            count += 1;
        }//end else
        if (Request["txtStartDate"].ToString().Trim() == "")
        {
            //displays yellow bg for missing input
            txtStartDate.BackColor = System.Drawing.Color.Yellow;
            validateEntry = false;
            Msg = Msg + "Start Date <br/>  ";
        }//endif
        else
        {
            try
                {
                //Conversion to DateTime format?
                startDate = DateTime.Parse(Request["txtStartDate"]);
                //How do I write the format I want, and when it should be checked?
                }
            catch (Exception ex)
                {
                //Exception should be caught here, not sure how to write this out though?
                }
            validateEntry = true;
        }//end else
        if (Request["txtEndDate"].ToString().Trim() == "")
        {
            //displays yellow bg for missing input
            txtEndDate.BackColor = System.Drawing.Color.Yellow;
            validateEntry = false;
            Msg = Msg + "End Date <br/>  ";
         }//endif
        else
        {
            try
            {
                //Conversion to DateTime format?
                endDate = DateTime.Parse(Request["txtEndDate"]);
                //How do I write the format I want, and when it should be checked?
            }
            catch (Exception ex)
            {
                //Exception should be caught here, not sure how to write this out though?
            }
            validateEntry = true;
        }//end else
//END SERIES OF IF/ELSE FOR CONFIRMING ENTRIES 
//START IF VALIDATE ENTRY    
        if (validateEntry == true)
        {
            if (DateTime.Compare(startDate, endDate) >= 0)
            {
                txtStartDate.BackColor = System.Drawing.Color.Yellow;
                txtEndDate.BackColor = System.Drawing.Color.Yellow;
                Msg = Msg + "Start Date <br/>" + "End Date <br/> <br/>The end date must be a later date than the start date.";
                //The Msg text will be displayed in lblError.Text after all the error messages are concatenated
                validatedState = false;
                //Boolean value - test each textbox to see if the data entered is valid, if not set validState=false. 
                //If after testing each validation rule, the validatedState value is true, then submit to frmPersonnelVerified.aspx, if not, then display error message
            }
            else //goes to this if dates are correct
            {
                validatedState = true;
                count += 2;
                txtStartDate.BackColor = System.Drawing.Color.White;
                txtEndDate.BackColor = System.Drawing.Color.White;
            }
        }
//END IF VALIDATE ENTRY
//SENDS DATA & ERROR MESSAGES
        if (count == 5 && validatedState == true)
        {
            Session["txtFirstName"] = txtFirstName.Text;
            Session["txtLastName"] = txtLastName.Text;
            Session["txtPayRate"] = txtPayRate.Text;
            Session["txtStartDate"] = txtStartDate.Text;
            Session["txtEndDate"] = txtEndDate.Text;
            Response.Redirect("frmPersonnelVerified.aspx");
            //sends to other page
        }
        else
        {
            //Writes out error messages
            Response.Write("<br/><span style = 'color: red ; position: absolute; top: 360px; left: 90px;'>" + Msg + "</span>");           
        }
//ENDS DATA AND ERROR MESSAGES

    }//end Function: private void BtnSubmit_click...
}