Question

I use the following codes for showing child form in a MDI parent form. As you know clicking the button will cause a new form to appear. Keep clicking the button and your screen will be filled with blank forms. To stop this from happening, I moved the code that creates the form outside of the button.

Like this:

public partial class Form1 : Form
{
    public Form1()
    {
        InitializeComponent();
    }

    Form2 f2 = new Form2();    

    private void button1_Click(object sender, EventArgs e)
    {
        f2.MdiParent = this;
        f2.Show();
    }

But when I close the child form and want to open it again, it won’t let me.

Please help me to solve this.

Answer 1

You need to keep track of the form state so you know you need to create a new one. Like this:

private Form2 f2;    

private void button1_Click(object sender, EventArgs e)
{
    if (f2 == null) {
       f2 = new Form2();
       f2.MdiParent = this;
       f2.FormClosed += delegate { f2 = null; };
       f2.Show();
    }
    else {
       f2.Activate();
    }
}