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Saving an array in Session in C#

I have an array that I need to save and retrieve as a session variable.

I initialize and save the array as follows:
g_Move_Direction= new int[40];
for (i=0; i<40; i++)
{g_Move_Direction[i] =2;}
this.Session["Move_Direction"]=g_Move_Direction;

Later I retrieve the array as follows:
int[] g_Move_Direction = (int[]) this.Session["Move_Direction"];

When I try and save a new value to the array using,
g_Move_Direction[g_segment_count]= Convert.ToInt32(this.radio_Direction.SelectedValue);

I get the following error page: [Note I've verified that radio_Direction.SelectedValue is 1 when attempting to save the new value.]
*******************************************************************************************
Object reference not set to an instance of an object.
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: System.NullReferenceException: Object reference not set to an instance of an object.

Source Error:

Line 411: segment_type=this.radio_SegmentType.SelectedValue;
Line 412: //Save segment type, move direction & axis
Line 413: g_Move_Direction[g_segment_count]= Convert.ToInt32(this.radio_Direction.SelectedValue);
Line 414: g_Segment_Type[g_segment_count]=segment_type;
Line 415: g_Segment_Axis[g_segment_count]=this.ddlAxialForceDirection.SelectedValue;

Source File: c:\vsprojects\manhattanapps\actuatordesignersolution\actuatordesigner\complex_move.aspx.cs Line: 413
Stack Trace:

[NullReferenceException: Object reference not set to an instance of an object.]
Actuator1.Complex_Move.btnSaveSegment_Click(Object sender, EventArgs e) in c:\vsprojects\manhattanapps\actuatordesignersolution\actuatordesigner\complex_move.aspx.cs:413
System.Web.UI.WebControls.LinkButton.OnClick(EventArgs e)
System.Web.UI.WebControls.LinkButton.System.Web.UI.IPostBackEventHandler.RaisePostBackEvent(String eventArgument)
System.Web.UI.Page.RaisePostBackEvent(IPostBackEventHandler sourceControl, String eventArgument)
System.Web.UI.Page.RaisePostBackEvent(NameValueCollection postData)
System.Web.UI.Page.ProcessRequestMain()

*******************************************************************************************

Am I saving/retrieving it correctly?

vigrid

Please review and check if these are not null while reading from session:
g_Move_Direction,
g_segment_count

Tell me the exact values these have in line 413 in file "complex_move.aspx.cs" and tell me their exact types too.

RosanneParnell

ASKER

g_Move_Direction is of type int[40] and at this point has <undefined value> in the watch list

g_segment_count is of type int and has the value of 0 (zero).

vigrid

It seems that something happened with the g_Move_Direction meanwhile. Please check if you really got it back correct in line:

int[] g_Move_Direction = (int[]) this.Session["Move_Direction"];

Another thing that pops into my mind is that you can have another variable declared in another scope and you use two different variables, no matter that they have same names?

RosanneParnell

ASKER

I'm new to .Net and C# so the scope is a bit confusing to me right now.

I have g_Move_Direction declared here:
namespace Actuator1
{
      /// <summary>
      /// Summary description for Complex_Move.
      /// </summary>
      public class Complex_Move : System.Web.UI.Page
      {
protected System.Web.UI.HtmlControls.HtmlForm Form1;
.
.
.
int[] g_Move_Direction;

and then in the Page_Load routine (for the first time through the page only - postback=false) I initialize it and save it:
g_Move_Direction= new int[40];
for (i=0; i<40; i++)
{g_Move_Direction[i] =2;}
this.Session["Move_Direction"]=g_Move_Direction;

on a post back to the page I retrieve it using:
int[] g_Move_Direction = (int[]) this.Session["Move_Direction"];

Upon retrieving it (prior to attempting to store a value in it) I did confirm that the array is still set to all 2's.

RosanneParnell

ASKER

Am I defining this variable (g_Move_Direction) in the wrong spot and then the code doesn't see it in the page functions?

SOLUTION

vigrid

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ASKER CERTIFIED SOLUTION

vigrid

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vigrid

And if you would add another method:

public void Test3()
{
myVariable = 3;
Console.WriteLine(myVariable);
}

and changed the Main:

public static void Main()
{
Test1(); // will write 1 (MyNamespace.MyClass.myVariable)
Test2(); // will write 2 (MyNamespace.MyClass.Test2.myVariable)
Test1(); // will write 1 (MyNamespace.MyClass.myVariable)
Test3(); // will write 3 (MyNamespace.MyClass.myVariable!!!, because no variable of the same name is declared)
Test1(); // will write 3 (MyNamespace.MyClass.myVariable)
}

RosanneParnell

ASKER

Thanks! That works!