title: Showing an alert with Cocoa
body: <p>I have been using VB.NET for a while and I switched to Xcode 4.</p>
  
  <p>In the VB.NET environment, I used to type the following command in a button:</p>
  
  <pre><code>if TextBox1.text="" then
      MessageBox.Show("You can't leave the textbox empty!, "Error!")
  else
      Label1.text = TextBox1.text
  </code></pre>
  
  <p>That is just an example. In Xcode, I want to do the same thing except for I want to have a Pop-Up Alert (in the iPhone) instead of the MessageBox in VB.NET.</p>
  
  <p>Any Ideas?</p>