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how to retain a static class across forms

Posted on 2011-02-14
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Last Modified: 2013-12-27
I am developing a windows mobile application with 5 input forms. As the data is entered into the form, i am writing it to a static class. After all 5 forms are entered, I save the data to the database. However, when I close form1 to load form2, the static class is getting reinitialized. How can I carry forward the same class, so the data is persistent. I tried it in a winform application and it worked but in the net CF application something is different, the class is getting destroyed everytime I call form.close event.
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Question by:tornadog
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11 Comments
 
LVL 24

Expert Comment

by:alexey_gusev
ID: 34889386
how and where do you declare it?
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Expert Comment

by:hjgode
ID: 34890564
Declare the class var outside the form code, for example in program.cs

namespace TestStatic
{
      class MainClass
      {
            public class staticDataClass{
                  public static int iData = 0;
                  public static string sData = "";
            }
            public staticDataClass staticData = new staticDataClass();
            public static void Main (string[] args)
            {
                  MainClass.staticDataClass.sData="start";
                  WinForm form = new WinForm ();
                  Application.Run (form);
                  //Console.WriteLine("Hello World!");
            }
      }
      public class WinForm : Form
      {
            public WinForm ()
            {
                  InitializeComponent ();
                  
                  TestStatic.MainClass.staticDataClass.sData ="new value";
            }
...

Does this meet your need?

~Josef
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Author Comment

by:tornadog
ID: 34890953
I want to keep the class static, so I dont have to instantiate it with each form load.. So I declared the class

as

public static class TestClass{
public static string data1 {get; set;}
public static string data2 {get; set;}
public static string data3 {get; set;}
}

And in my form1 , I have a Fill method that saves all the textbox data into TestClass as;

TestClass.data1 = TextBox1.Text;
and so on

Then form1 is closed on button click and in form2, something like
TestClass.data2 = TextBox1.Text;
lbl1.Text = TestClass.data1;  //data passed from form1 but I get a null reference exception here.

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LVL 24

Expert Comment

by:alexey_gusev
ID: 34891111
what happens if you remove "static" in the class definition? this way you get the same functionality but framework doesn't try to control when it loads it
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LVL 16

Expert Comment

by:hjgode
ID: 34891840
Do you pass the static class by reference from form1 to form2? Otherwise you get a new class instance.

change the constructor of form2 to accept your static class as argument. Soemthing like this:

public class Form2{
     private TestClass myTestClass;
     Form2(ref Testclass testClass){
         this.myTestClass = testClass;
     ...
anywhere else, where you call Form2 include a reference of the TestClass
...
    Form2 _form2 = new Form2(ref myFirstTestClass);

But I would go with my first tipp and declare TestClass once globally ouside any Form code before the first form is instanciated.

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Author Comment

by:tornadog
ID: 34892389
but if its a static class I cannot create a new instance like you do. Is that right?

for eg:

private TestClass myTestClass will be invalid if MyTestClass is a static class.
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Expert Comment

by:alexey_gusev
ID: 34892432
why should you??? MyTestClass.data1 is available from anywhere MyTestClass is visible from
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Author Comment

by:tornadog
ID: 34892600
thats what I thought, but I am getting an empty string when I try to access data1 on form2. This whole thing works great in a simple winform application, but in a windows mobile application, it does not. The data is getting reset when I close the form.
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Expert Comment

by:alexey_gusev
ID: 34892621
no no, I mean without word "static" in the class definition
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Author Comment

by:tornadog
ID: 34892820
yes I tried that too. Only the members are defined as static, the class itself is public.
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Accepted Solution

by:
alexey_gusev earned 2000 total points
ID: 34892872
that is true, but you can keep it 'sealed' if you define private constructor.

I reckon it does what you need, apart from being non-static in a sense?
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