Question

This is my code:

namespace Class_Properties {
    public partial class Form1 : Form {
        private string firstHeight1 = "";
        public int firstHeight {
            get {
                        return Convert.ToInt32( firstHeight1 );
            }
        }

        public Form1() {
            InitializeComponent();
        }

        private void button1_Click( object sender, EventArgs e ) {
            firstHeight1 = textBox2.Text;

            Form2 secondForm = new Form2();
            secondForm.Show();
        }
    }
}

and then the other class:

namespace Class_Properties {
    public partial class Form2 : Form {
        public Form2() {
            InitializeComponent();
            Form1 mainWindow = new Form1();
            this.Height = mainWindow.firstHeight;
        }
    }
}

When I run, I type 200 as value for textbox2 and click button1, then Visual Studio says the following exception:

What could I do to solve this error?

Answer 1

This is the failure:

        InitializeComponent();
        Form1 mainWindow = new Form1();
        this.Height = mainWindow.firstHeight;  //<--

No matter what you did on the other Form1, it won’t show up in this one because it’s a new instance so firstHeight == string.Empty and will fail the parse.

You’ll have to send the existing Form1 to Form2:

public Form2(Form1 parent)
{
    this.Height = parent.firstHeight;
}

// called like so from Form1:
var form2 = new Form2(this);

Though admittedly, it would be better to send only what you need:

public Form2(int desiredHeight)
{
    this.Height = desiredHeight;
}

// called like so from Form1:
var form2 = new Form2(this.firstHeight);