Change Form 1 Label value using UserControl Window Form-CodePudding

I am new to windows Forms and didn't know about user control. I have a form 1 with a label and want to change the value of the label using user control. I also called user control in form1. I tested the form function using the usercontrol_click event. It shows the message box but not changing the label value.

Form 1 user control name flowLayoutPanel1 user control name ListView

private void ListItem_Click(object sender, EventArgs e)
{
    Form1 a = new Form1();
    //a.emailbody();
    a.label5.Text = "work";
}

public void emailbody()
{
    MessageBox.Show("Welcome");
}

CodePudding user response：

You are creating a new form with Form1 a = new Form1(); in the click event handler, but you never show this form using a.Show(); or a.ShowDialog().

Did you intend to set the label on the current form? If yes, then don't create a new form.

private void ListItem_Click(object sender, EventArgs e)
{
    // Uses label in this form:
    label5.Text = "work";
}

You simply write emailbody(); to call a method on the current form.

If you intended to set the label on another form that was already open, you need a reference to this form. E.g. you can store it in a field in the current form

private Form1 _form1;

private void OpenOtherFormButton_Click(object sender, EventArgs e)
{
    _form1 = new Form1();
    _form1.Show();
}

private void ListItem_Click(object sender, EventArgs e)
{
    if (_form1 is not null) {
        _form1.label5.Text = "work";
    }
}

If you want to change the label of your user control, the label must be public. Assuming that the user control is on your form, do something like this:

myUserControl.label5.Text = "work";

If it is on another form, the user control must be public as well:

_form1.myUserControl.label5.Text = "work";

if the user control is on the panel:

flowLayoutPanel1.myUserControl.label5.Text = "work";

If the user control is on the same form as where the label is and ListItem_Click is in the user control, then you must get reference to the form first.

// In the user control
var form1 = FindForm() as Form1;
if (form1 is not null) {
    form1.label5.Text = "work";
}