将Windows窗体中的文本框值传递给类

Question

I am learning C# and have run into an interesting issue to me. I have a class variable defined as public and I instantiate a new instance of my form in my class and access the value of the public variable it is always null.

To further explain my issue - this syntax prints the appropriate value

System.Diagnostics.Debug.WriteLine(tboxvalue.ToString());

However, this syntax is always outputting a 0

System.Diagnostics.Debug.WriteLine(f1.tboxvalue.ToString());

How do I need to alter my syntax so that the correct value is passed to the class Functions ?

public partial class Form1 : Form
{

    public double tboxvalue;
    private string exportdata;

    public Form1()
    {
        InitializeComponent();
    }

    private void btnClicker_Click(object sender, EventArgs e)
    {
        Functions.EE();
    }
    private void txtData_CheckedChanged(object sender, EventArgs e)
    {
        bool @checked = ((CheckBox)sender).Checked;

        if (@checked.ToString() == "True")
        {
            exportdata = "Yes";
            tboxvalue = Convert.ToDouble(this.txtData.Text);
            System.Diagnostics.Debug.WriteLine(tboxvalue.ToString());
        }
        else
            exportdata = "No";
    }
}
class Functions
{
    public static void EE()
    {
        Form1 f1 = new Form1();
        System.Diagnostics.Debug.WriteLine(f1.tboxvalue.ToString());
    }
}

Answer 1

To access properties of the form, you need to change two Things. First you have to pass the form to the 'EE' method, then you can access the form's properties. Second, don't create a new form in 'EE' method.

public partial class Form1 : Form
{

    public double tboxvalue;
    private string exportdata;

    public Form1()
    {
        InitializeComponent();
    }

    private void btnClicker_Click(object sender, EventArgs e)
    {
        Functions.EE(this);
    }
    private void txtData_CheckedChanged(object sender, EventArgs e)
    {
        bool @checked = ((CheckBox)sender).Checked;

        if (@checked.ToString() == "True")
        {
            exportdata = "Yes";
            tboxvalue = Convert.ToDouble(this.txtData.Text);
            System.Diagnostics.Debug.WriteLine(tboxvalue.ToString());
        }
        else
            exportdata = "No";
    }
}
class Functions
{
    public static void EE(Form1 f1)
    {
        System.Diagnostics.Debug.WriteLine(f1.tboxvalue.ToString());
    }
}

Answer 2

If i understood your question i guess you are recreated Form1 with own textbox or labels when you click btnClicker button. You can reassign your form objects where you created it.

Answer 3

You might add static Form1 object and Setter routine to Functions class:

    private static Form1 _form;

    public static void SetForm(Form1 form)
    {
        _form = form;
    }

and pass the form to the class in Form_Load event-click on the form twice:

private void Form1_Load(object sender, EventArgs e)
    {
        Functions.SetForm(this);
    }

Then you can play with the form in Functions class using the object _form
good luck!