C# windows form project, public variable in one class gets lost in another class on button click

Question

I declare variable in one class like this:

public ushort variableA = 0;

then I have 2 different buttons, on click I assign

in a first button : variableA =1;

in a second burton: variableA = 2;

then on those buttons click I open a new form.

then I declare in another class in this new form:

First_Form My_variableA= new First_Form();

Then : if (My_variableA.variableA == 1){ do something}

       if (My_variableA.variableA == 2) {do something  }
```I have tested , in MessageBox.Show the value is still 0, even though I make assignment to 1 or 2,

not sure why the public variable value on button click does not get modified???

Get back, thanks in advance.

Answer 1

I understand that you defined the variableA like below:

using System.Windows.Forms;

namespace WindowsFormsApp1
{
    public partial class First_Form : Form
    {
        public ushort variableA = 0;

        public First_Form()
        {
            InitializeComponent();
        }
    }
}

then I declare in another class in this new form:

First_Form My_variableA= new First_Form();

Please note that new First_Form() will create new instance of First_Form class in which the variable variableA is initialized with value of 0.

That's why you observed:

the public variable value on button click does not get modified???

To resolve the issue, I suggest that you change the variableA to static as shown below:

using System.Windows.Forms;

namespace WindowsFormsApp1
{
    public partial class First_Form : Form
    {
        public static ushort variableA = 0;

        public First_Form()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, System.EventArgs e)
        {
            variableA = 1;
            var new_Form = new New_Form();
            new_Form.Show();
        }

        private void button2_Click(object sender, System.EventArgs e)
        {
            variableA = 2;
            var new_Form = new New_Form();
            new_Form.Show();
        }
    }
}

and refer the variableA in new Form as follows:

using System.Windows.Forms;

namespace WindowsFormsApp1
{
    public partial class New_Form : Form
    {
        public New_Form()
        {
            InitializeComponent();

            this.label1.Text = "First_Form.variableA: " + First_Form.variableA;
        }
    }
}

The result is: