How to pass a value from one Class file to another Class ???

Hi

I have same problem .thanks for code now it will help me to solve my issue of o pass a value from one Class file to another Class.

Yes thanks a lot. Now i am able to access the value without declaring variable as static.

From the code in classB you will get the product id as "APB12345".

I am not getting the value. :(.
Is there any option to avoid same static property object shared between the request... ?

Yes i can avoid the null ref exception as you mentioned.  but as per my requirement i want to update the productId from the classB method. So ClassA.ProductId should not be null object when i call from ClassB.
If i declaring this ProductId as static variable the object exist.  So i can able to update my productId as per my wish.

so same like this i want to retain the object without declaring property as static.(the reason for avoiding static variable - if i am declaring property as static, the same object shared with all request. So i want to avoid that....)

I will explain my requirement clearly.
My aspx:
       string Userid = string.Empty;
        ClassA objClassA = new ClassA();
         objClassA.GetDetails(Userid);
       
---------------
class ClassA
{
    private string _ProductId;
    public string ProductId
    {
        get
        { return _ProductId; }
        set
        { _ProductId = value; }
    }
    public void GetDetails(string Userid)
    {
        if (Userid.Equals(string.Empty))
        {
            _ProductId = "APB12345";
        }
        ClassB objClassB = new ClassB();
        objClassB.CheckConstraint(Userid);
    }
}
--------------------------
class ClassB
{
    public void CheckConstraint(string Userid)
    {
        ClassA objClassA = new ClassA();
        if (objClassA.ProductId.Equals(string.Empty))
        {
            objClassA.ProductId = "APB12341";
        }
    }
}------------
when my breakpoint reaches the ClassA.ProductId its returning with Null refer exeception. If i declare the ProductId as static it will work but i dont want that....
Please suggest me how to get the object without using static declartion?
 
 
 
 

Use properties with get set to access the values between the class.
check the sample

class Class1
    {
        private int ProductId = 20;
        public int intPublicProperty
        {
            get
            {return ProductId;}
            set
            { ProductId = value;}
        }
    }
class class2
    {
        public void Checkvalue()
         {
             Class1 objClass1 = new Class1();
             MessageBox.Show("Showing in Class Two : " + objClass1.intPublicProperty);
         }
    }