Question

Inside my Main method I’m instantiating the UpdateDialog class inside which based on if the user presses a button or not I need to call function1() from Main. Here is the code:

public partial class Main : Form
{
  public void function1()
  {
    doing_stuff_here();
  }

  private void button1_Click(Object sender, EventArgs e)
  {
    var update = new UpdateDialog();
    update.ShowDialog();
  } 
}

public partial class UpdateDialog : Form
{
  private void button2_Click(object sender, EventArgs e)
  {
    //call here function1() from Main
  }
}

What should I do to be able to call function1() from Main inside the partial class UpdateDialog?

LE: although the method suggested by Styxxy seems right it doesn’t work well in my app because of cross-thread invalid operation so I ended up using the delegate workaround suggested by Cuong Le.

Answer 1

You’ll have to have an instance of the Main form in your UpdateDialog form. As you say that UpdateDialog is a child form of your Main form, I guess that you create the UpdateDialog in your Main form and do a show there. Before showing that form, you could assign the Parent property.

var updateDialog = new UpdateDialog();
// Or use "UpdateDialog updateDialog = new UpdateDialog();" as people like Andreas Johansson don't like the "var" keyword
// Do other stuff here as well
updateDialog.Parent = this;
// Or use Show() for non modal window
updateDialog.ShowDialog();

You get the error ArgumentException: Top-level control cannot be added to a control.. Now this can be solved in two ways.

1. You can set the TopLevel property to false on your Main form (I’m not a huge fan of this).
2. You can use the Owner property to your Main form (this). Below two ways of doing it.

You can set the Owner manually:

updateDialog.Owner = this;

Or you can add this as parameter to the Show(owner) or ShowDialog(owner) methods; this way, the Owner is also being set.

updateDialog.Show(this);
// or
updateDialog.ShowDialog(this);

“Full” code makes this:

var updateDialog = new UpdateDialog();
// Do other stuff here as well
updateDialog.Owner= this;
updateDialog.ShowDialog(); // or use .Show()
// or
updateDialog.ShowDialog(this); // or use .Show(this)