Experiment 3 was an application that executed the Select and Focus method on a PictureBox control since that was specifically listed by Microsoft's documentation as not being selectable. The form is shown below:
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The complete code for the program (event parameters are omitted to save space) is shown below:
Public Class Form1
Private Sub SelectPicBox_Click(ByVal ...
PictureBox1.Select()
End Sub
Private Sub FocusPicBox_Click(ByVal ...
PictureBox1.Focus()
End Sub
Private Sub PictureBox1_Click(ByVal ...
Debug.Print("PictureBox1 Click Event")
PictureBox1.BackColor = Color.Blue
End Sub
Private Sub PictureBox1_GotFocus(ByVal ...
Debug.Print("PictureBox1 GotFocus Event")
Debug.Print("Focused property: " & PictureBox1.Focused.ToString)
Debug.Print("ContainsFocus property: " & PictureBox1.ContainsFocus.ToString)
Debug.Print("CanFocus property: " & PictureBox1.CanFocus.ToString)
Debug.Print("CanSelect property: " & PictureBox1.CanSelect.ToString)
PictureBox1.BackColor = Color.Red
End Sub
End Class
This code illustrates one of the two differences I could find between Focus and Select that I could find. Focus has events and properties that are not available for Select such as:
- GotFocus Event
- Focused property
- ContainsFocus property
The goal of the program was the same as before. To see if there was any difference between what Select and Focus did in code. Since Microsoft clearly states that a PictureBox isn't "selectable" I confidently expected to see one. But again ... no difference.
Determined to get to the bottom of this, I created two final experimental programs. One did nothing but Select a PictureBox and the other did nothing but Focus a PictureBox. Then I used the ILDASM utility to examine the actual generated Intermediate Language code generated. The IL code is shown below:
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The IL code only had two differences:
- the actual method called in the System.Windows.Forms.Control object
- the method call returned a void for Select and a bool for Focus
Using Visual Studio's Object Browser confirms this. Select and Focus are shown this way:
System.Windows.Forms.Control.Select()
System.Windows.Forms.Control.Focus() As Boolean
In other words, you can code ...
Dim x As Boolean = PictureBox1.Focus()
... but you can't code ...
Dim x As Boolean = PictureBox1.Select() ' invalid
That's the second difference.
After all this, I have concluded that the moral of this story is, "You can't trust Microsoft to tell you everything. Some things you just have to find out for yourself."
