提交表单期间如何修改表单字段值？

Question

I'm developing a form using ASP.NET form controls. One of the form fields is Date of Birth. The date format is in dd/mm/yyyy. What I need to do is actually convert this form field to mm/dd/yyyy once the user submits the form but before the data goes to the server because the system the form data is going to is forcing US date formats (mm/dd/yyyy) which I can't control, hence all date formats in dd/mm/yyyy will be reversed so they will be incorrect. So I need to actually switch it before hand, so its actually reversed back to the correct format. Here's what I've wrote in order to switch the value.

string userDOB = Request.Form["txtDOB2"];
DateTime convertedDOB = Convert.ToDateTime(userDOB);
txtDOB2.Text = convertedDOB.ToString("MM/dd/yyyy");

Note: I am checking to make sure the Date of Birth field not null or empty etc, just posting the specific code related to my question.

I'm running this in code behind via a submit button click action. So far, a test label just appends the switched date format value to confirm its working. However I'm unsure how to switch the form value itself so it ends up in the actual posted form data. Request.Form is read only, so I don't know how to assign the modified date to the form field value.

Another potential problem is the form action is to an external source, outside of the domain the form is running on.

Answer 1

This would be how I'd attack it:

FormatDatesModule.cs

public class FormatDatesModule : IHttpModule
{
    private static readonly Regex dateFilter = new Regex(@"^(?<d>\d{2})\/(?<m>\d{2})\/(?<y>\d{4})$", RegexOptions.Compiled);

    public void Init(HttpApplication context)
    {
        context.BeginRequest += (sender,e) => {
            HttpRequest request = ((HttpApplication)sender).Request;

            if (request.QueryString.Count > 0)
            {
                this.FormatDatesInCollection(request.QueryString);
            }

            if (request.HttpMethod == "POST" && request.Form.Count > 0)
            {
                this.FormatDatesInCollection(request.Form);
            }
        };
    }

    private static void FormatDatesInCollection(NameValueCollection parameters)
    {
        // Bypass readonly
        PropertyInfo isReadOnly = parameters.GetType().GetProperty("IsReadOnly", BindingFlags.Instance | BindingFlags.NonPublic);
        isReadOnly.SetValue(parameters, false, null);

        for (var i = 0; i < parameters.Count; i++)
        {
            Match dateMatch = dateFilter.Match(parameters[i]);
            if (dateMatch.Success)
            {
                parameters[i] = String.Join("/", dateMatch.Groups["m"].Value, dateMatch.Groups["d"].Value, dateMatch.Groups["y"].Value);
            }
        }

        isReadOnly.SetValue(parameters, true, null);
    }

    public void Dispose()
    {
    }
}

web.config

<configuration>
    <system.web>
        <httpModules>
            <add name="FormatDatesModule" type="FormatDatesModule"/>
        </httpModules>
    </system.web>
    <system.webServer> <!-- IIS 7 Integrated Mode -->
        <modules>
            <add name="FormatDatesModule" type="FormatDatesModule"/>
        </modules>
    </system.webServer>
</configuration>

Answer 2

You can write this code on button click event. for eg

    textBox1.Text="31/03/2014"

then

   Button_click()
   {
        DateTime MyDateTime = new DateTime();
        MyDateTime = DateTime.ParseExact(textBox1.Text, "MM/dd/yyyy", null);
        textBox2.Text = MyDateTime.ToString("dd/MM/yyyy");
   }

OR Directly you can use

   textBox2.Text=(DateTime.ParseExact(textBox1.Text, "MM/dd/yyyy",null).ToString("dd/MM/yyyy"));

First you have to Convert it to DateTime format, then again in string. Hope that would be helpful for you.

Answer 3

After reviewing everything I've decided to use a WebRequest:

http://msdn.microsoft.com/en-us/library/debx8sh9.aspx

With the form action being an external URL (not on the same domain) I have come to the conclusion I am unable to modify the form data. However, by allowing the form to postback and specifying the form action and everything else in code behind I'm able to specify the DOB value to send, using Himanshu's DOB conversion method, I was able to POST a form with the DOB switched.