How to validate .NET dialog items when using automatic DialogResult?

Question

At the moment I have setup a custom ok cancel dialog with a drop down in c#. The ok and cancel buttons use the DialogResult property so no code behind it. What I now need to do is validate the drop down to check it isn't left empty before posting back a dialogresult.

Is this possible?

Answer 1

From here

Double-click the Closing field, and implement it as follows:

private void Second_Closing(object sender, 
        System.ComponentModel.CancelEventArgs e)
{
    // When the user attempts to close the form, don't close it...
    e.Cancel = (dropdown.selecteditemindex >= 0);
}

Answer 2

Disable your OK button until the combobox is changed to a valid value.

Answer 3

If you want check for something, you allways need some code behind the designer. For your case, you can use a "Closing" event in the form, check what you need and if you want, set "e.Cancel = true;" - then form will not be closed.

Answer 4

What I have done for this is to not set the DialogResult on the OK button, but put some code behind the button.

private void OkButton_Clicked(object sender, EventArgs e)
{
    this.DialogResult = ValueComboBox.SelectedIndex >= 0
        ? DialogResult.Ok
        : DialogResult.None;
}

Answer 5

You can keep using the OK and Cancel button functionality of dialogs, and then put this code in the Clicked handler for the OK button:

private void OkButton_Clicked(object sender, EventArgs e)
{
    if (!IsValid()) {
        this.DialogResult = System.Windows.Forms.DialogResult.None;
    }
}

In the code above, IsValid() is a method you have to implement, that validates the input fields on the dialog.