ASP.Net - code behind

Can separate HTML and Code parts of an ASP.NET web form - this is called "code-behind" because the code is not on the .aspx page (but somewhere in the background "behind" the .aspx page)
Basically the code that would appear in between the <script> and </script> tags is placed a separate file.
1. Create a CS file containing event handlers, helper methods, and other code—everything that would normally appear between <script> and </script> tags in an ASPX file. Make each of these source code elements members of a class derived from System.Web.UI.Page.
2. In your Page-derived class, declare protected fields whose names mirror the IDs of the controls declared in the ASPX file. For example, if the Web form includes a pair of TextBox controls whose IDs are UserName and Password, include the following statements in your class declaration:
```
protected TextBox UserName;
protected TextBox Password;
```
  Without these fields, the CS file won’t compile because references to UserName and Password are unresolvable. At run time, ASP.NET maps these fields to the controls of the same name so that reading UserName.Text, for example, reads the text typed into the TextBox control named UserName.
  Code Behind class is the base class of the code generated by the .aspx page
3. Compile the CS file into a DLL and place the DLL in a subdirectory named bin in the virtual directory that holds the ASPX file.
4. Place the HTML portion of the Web form—everything between the <html> and </html> tags—in an ASPX file. Include in the ASPX file an @ Page directive containing an Inherits attribute that identifies the Page-derived class in the DLL.

Code Behind Example - Lunar Lander

<%@ Page Inherits="LanderPage" %> 

<html>
  <body>
    <h1>Lunar Lander</h1>
    <form runat="server">
      <hr>
      <table cellpadding="8"> 
        <tr>
          <td>Altitude (m):</td>
          <td><asp:Label ID="Altitude" Text="15200.0"
            RunAt="Server" /></td>
        </tr>
        <tr>
          <td>Velocity (m/sec):</td>
          <td><asp:Label ID="Velocity" Text="0.0"
            RunAt="Server" /></td>
        </tr>
        <tr>
          <td>Acceleration (m/sec2):</td>
          <td><asp:Label ID="Acceleration" Text="-1.6"
            RunAt="Server" /></td>
        </tr>
        <tr>
          <td>Fuel (kg):</td>
          <td><asp:Label ID="Fuel" Text="8165.0" RunAt="Server" /></td>
        </tr>
        <tr>
          <td>Elapsed Time (sec):</td>
          <td><asp:Label ID="ElapsedTime" Text="0.0"
            RunAt="Server" /></td>
        </tr>
        <tr>	
          <td>Throttle (%):</td>
          <td><asp:TextBox ID="Throttle" RunAt="Server" /></td>
        </tr>
        <tr>	
          <td>Burn Time (sec):</td>
          <td><asp:TextBox ID="Seconds" RunAt="Server" /></td>
        </tr>
      </table>
      <br>
      <asp:Button Text="Calculate" OnClick="OnCalculate"
        RunAt="Server" />
      <br><br>
      <hr>
      <h3><asp:Label ID="Output" RunAt="Server" /></h3>
    </form>
  </body>
</html>

Here is the Code Behind this page

using System;
using System.Web.UI;
using System.Web.UI.WebControls;

public class LanderPage : Page 
{
    const double gravity = 1.625;      // Lunar gravity
    const double landermass = 17198.0; // Lander mass

    protected Label Altitude; 
    protected Label Velocity;
    protected Label Acceleration;
    protected Label Fuel;
    protected Label ElapsedTime;
    protected Label Output;
    protected TextBox Throttle;
    protected TextBox Seconds;

    public void OnCalculate (Object sender, EventArgs e)
    {
        double alt1 = Convert.ToDouble (Altitude.Text);

        if (alt1 > 0.0)  {
            // Check for blank input fields
            if (Throttle.Text.Length == 0) {
                Output.Text = "Error: Required field missing";
                return;
            }

            if (Seconds.Text.Length == 0) {
                Output.Text = "Error: Required field missing";
                return;
            }

            // Extract and validate user input
            double throttle;
            double sec;

            try {
                throttle = Convert.ToDouble (Throttle.Text);
                sec = Convert.ToDouble (Seconds.Text);
            }
            catch (FormatException) {
                Output.Text = "Error: Invalid input";
                return;
            }

            if (throttle < 0.0 || throttle > 100.0) {
                Output.Text = "Error: Invalid throttle value";
                return;
            }

            if (sec <= 0.0) {
                Output.Text = "Error: Invalid burn time";
                return;
            }

            // Extract flight parameters from the Label controls
            double vel1 = Convert.ToDouble (Velocity.Text);
            double fuel1 = Convert.ToDouble (Fuel.Text);
            double time1 = Convert.ToDouble (ElapsedTime.Text);

            // Compute thrust and remaining fuel
            double thrust = throttle * 1200.0;
            double fuel = (thrust * sec) / 2600.0;
            double fuel2 = fuel1 - fuel;

            // Make sure there's enough fuel
            if (fuel2 < 0.0) {
                Output.Text = "Error: Insufficient fuel";
                return;
            }
				
            // Compute new flight parameters
            Output.Text = "";
            double avgmass = landermass + ((fuel1 + fuel2) / 2.0);
            double force = thrust - (avgmass * gravity);
            double acc = force / avgmass;

            double vel2 = vel1 + (acc * sec);
            double avgvel = (vel1 + vel2) / 2.0;
            double alt2 = alt1 + (avgvel * sec);
            double time2 = time1 + sec;

            // If altitude <= 0, then we've landed
            if (alt2 <= 0.0) {
                double mul = alt1 / (alt1 - alt2);
                vel2 = vel1 - ((vel1 - vel2) * mul);
                alt2 = 0.0;
                fuel2 = fuel1 - ((fuel1 - fuel2) * mul);
                time2 = time1 - ((time1 - time2) * mul);

                if (vel2 >= -4.0)
                    Output.Text = "The Eagle has landed";
                else
                    Output.Text = "Kaboom!";
            }			

            // Update the Labels to show latest flight parameters
            Altitude.Text = alt2.ToString ("f1"); 
            Velocity.Text = vel2.ToString ("f1");
            Acceleration.Text = acc.ToString ("f1");
            Fuel.Text = fuel2.ToString ("f1");
            ElapsedTime.Text = time2.ToString ("f1");
        }
    }
}

Windows Systems Programming: Spring 2004

ASP.Net - Part 2

Code Behind

Code Behind Example - Lunar Lander

Here is the Code Behind this page

Copyright chris wild 1999-2004.
For problems or questions regarding this web contact [Dr. Wild].
Last updated: February 09, 2004.

Windows Systems Programming: Spring 2004

ASP.Net - Part 2

Code Behind

Code Behind Example - Lunar Lander

Here is the Code Behind this page

Copyright chris wild 1999-2004. For problems or questions regarding this web contact [Dr. Wild]. Last updated: February 09, 2004.

Copyright chris wild 1999-2004.
For problems or questions regarding this web contact [Dr. Wild].
Last updated: February 09, 2004.