How do I check if all fields are filled in

How would I check if certain fields are incomplete?

I wan开发者_如何学JAVAt it so that whenever somebody clicks my button called "ADD?" that a messagebox will appear if required fields have not been properly filled out.

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In your event handler for the "Add" button, just check to see if the "field" has been filled in, and if not, don't continue:

void buttonAdd_Click(object sender, EventArgs e)
{
    if (string.IsNullOrWhiteSpace(textBoxField.Text))
    {
         // Show message?
         MessageBox.Show(....);

         return; // Don't process
    }

    // Field has a value, do your thing here...

}

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Use a errorprovider component, or simply check the input text length if it is 0 throw up a message

If (myTextBox.Text.Length == 0)
 {
   //throw up message box
   MessageBox.Show("You forgot to fill in this field!");
   return;
 }