菜鸟与事件； 击中F5后引起动作

Question

So yes I'm very new to creating my own custom events. I can do the basics when I put controls on a form but this one is a little more complex. I have an application that reads in a .TSV and populates a form with controls based on the number of objects it "reads." So for instance: I have a file that contains 10 people objects and my code populates a form with controls for each person. Easy stuff!

Now lets say I have a ComboBox with the items: "Alive", "Deceased", "Unborn". Right next to this I have a textbox for age. Now originally, this textbox is not enabled because the default value for the ComboBox is "Unborn". But lets say when the user selects "Alive", I want that textbox to become enabled so an age can be entered.

Obviously from me asking this and the title of this question, I don't know how to go about doing this. I don't really understand events and I learn by example but the MSDN examples don't quite cut it.

Any help (especially an awesome Step-by-Step guide) would be greatly appreciated.

Answer 1

From what I gather from the comments, you want to add events to a form object that is created at runtime. Use the AddHandler command to the object. Something to the effect of:

AddHandler NameOfFormObject.TypeOfAction, AddressOf HowToHandle

Private Sub HowToHandle(ByVal sender as System.Object, ByVal e As System.EventArgs)
   DropDownMenu.enabled = True
End Sub

Doing it this way, you will be able to modify the events of an object created at runtime. In your case, it sounds like you'll want to use the action that Josaph recommended, and end up incorporating both solutions offered, like so

AddHandler ComboBox1.SelectedIndexChanged, AddressOf HowToHandle

Private Sub HowToHandle(ByVal sender as System.Object, ByVal e As System.EventArgs)

    If DirectCast(sender, ComboBox).SelectedIndex = 0 'Alive 
        DirectCast(DirectCast(sender, ComboBox).Tag, TextBox).enabled = True
    Else
        DirectCast(DirectCast(sender, ComboBox).Tag, TextBox).enabled = False
    End If
End Sub

Answer 2

You will want to use the ComboBox_SelectedIndexChanged() event to capture that the combo box item has been changed. At that point, you will need to check to see which combo box item has been selected and make a decision as to whether the TextBox should be enabled or not. Here is an example. Note: This example assumes that "Alive" is the first item in your combobox at the 0 index.

    Private Sub ComboBox1_SelectedIndexChanged(ByVal sender As System.Object, ByVal e As System.EventArgs)
        If ComboBox1.SelectedIndex = 0 Then 'Alive 
            TextBox1.Enabled = True
        Else
            TextBox1.Enabled = False
        End If
    End Sub

Dynamically generate the combobox and add handler.

Dim cmb as New ComboBox
AddHandler cmb.SelectedIndexChanged, AddressOf ComboBox1_SelectedIndexChanged
Me.Controls.Add(cmb)

Answer 3

I suppose that as you will have 10 comboboxes... in the same way you'll have 10 textboxes.

In that case... once you attach and handle the event as AndyPerfect and Joseph... in that method you will need code something to know which of the Textboxs you need to enable/disable.

First you need to know which combobox triggered the event: this is done using the "sender" parameter. ctype(sender, Combobox) to access the methods and properties of the ComboBox.

Once you know which combo, you need to activate/deactivate the correct textbox. To accomplish this, you'll need to add a reference to the TextBox in the "TAG" property of the Combobox at the moment of creating it.

Dim txt as new TextBox
Dim cmb as new ComboBox
cmb.Tag = txt

Then... you simple use:

ctype(ctype(sender, Combobox).Tag, TextBox).Enable = true

Answer 4

Here is how I ended up writing it in the end. I appreciate all the help! Thank you!

    If DirectCast(sender, ComboBox).SelectedIndex = 2 Then
        DirectCast(Me.Controls.Item(DirectCast(sender, ComboBox).Tag), TextBox).Enabled = True
    Else
        DirectCast(Me.Controls.Item(DirectCast(sender, ComboBox).Tag), TextBox).Enabled = False
    End If