Question

my code:

in parent_Form:

    public parent_Form()
    {
        InitializeComponent();
    }

    private void button_Click(object sender, EventArgs e)
    {
        child ch = new child();
        ch.MdiParent = this;
        ch.Show();
    }
    public string label
    {
        set
        {
            textBox1.Text = value;
        }
    }

in child form:

    public child()
    {
        InitializeComponent();
    }

    private void write_button_Click(object sender, EventArgs e)
    {
        parent_Form paren = new parent_Form();
        paren.label = "i am vietnamese";
    }

but
“i am vietnamese” doesn’t display on textbox1 (it is on parent winform)

Answer 1

JRoughan’s solution should work. Make sure you have the button click handler properly specified. Set a breakpoint in the handler to make sure it is being executed when you click the button. I tested this and it works.

public child()
{
  InitializeComponent();
}

private void write_button_Click(object sender, EventArgs e)
{
    parent_Form paren = ((parent_Form)MdiParent);
    paren.label = "i am vietnamese";
}