Working with ListBox and ComboBox

Both the ListBox and ComboBox are useful controls for displaying lists. They are commonly used when you want users to choose from several predefined items instead of typing everything manually.

The main difference is how they show the list:

• ListBox displays many or all items at once.
• ComboBox usually displays one item first.
• The ComboBox reveals more items when the user clicks the drop-down arrow.
• Both controls can be updated at design time or at runtime.

The function of a ListBox in Visual Basic 2015 is to display a list of items so that the user can select one or more items from that list. Items can be added when designing the form or while the program is running.

To add items at design time, insert a list box on the form, open the Properties window, and click the collection editor for the Items property. Then type the items one by one.

In Visual Basic 2015, you can also add items to the ListBox while the program is running by using the Items.Add() method.

Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
    ListBox1.Items.Add("Visual Studio 2015")
End Sub

The code above adds a new item to the end of the ListBox when the form loads. This is very useful when the list depends on conditions or user input.

You can also allow the user to add their own items by using an InputBox. Add a button to the form, change its text to Add Item, and use code like this:

Private Sub BtnAdd_Click(sender As Object, e As EventArgs) Handles Button1.Click
    Dim myitem
    myitem = InputBox("Enter your Item")
    ListBox1.Items.Add(myitem)
End Sub

When the user clicks the button, an input box appears. Whatever the user types will be added to the list.

To delete an item at runtime, use the Remove() method:

Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
    ListBox1.Items.Remove("Visual Basic 6")
End Sub

You can also let the user choose which item to delete by using another input box:

Private Sub BtnDelete_Click(sender As Object, e As EventArgs) Handles Button1.Click
    Dim myitem
    myitem = InputBox("Enter your Item for Deletion")
    ListBox1.Items.Remove(myitem)
End Sub

To remove all items from the ListBox at once, use the Clear() method:

Private Sub Button3_Click(sender As Object, e As EventArgs) Handles Button2.Click
    ListBox1.Items.Clear()
End Sub

In Visual Basic 2015, the ComboBox also presents a list of items for selection. However, unlike the ListBox, it shows only one item at first and hides the rest until the user clicks the drop-down arrow on the right side.

You can add items to the ComboBox at design time using the same String Collection Editor, and you can also specify a default displayed text.

You may also use the Items.Add() method to add items at runtime:

Private Sub BtnAdd_Click(sender As Object, e As EventArgs) Handles Button1.Click
    ComboBox1.Items.Add("Visual Studio 2015")
End Sub

To let the user add their own item:

Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
    Dim myitem
    myitem = InputBox("Enter your Item")
    ComboBox1.Items.Add(myitem)
End Sub

To remove an item:

Private Sub Delete_Click(sender As Object, e As EventArgs) Handles Button2.Click
    ComboBox1.Items.Remove("Visual Basic 6")
End Sub

To clear all items:

Private Sub Btn_Clr_Click(sender As Object, e As EventArgs) Handles Button2.Click
    ComboBox1.Items.Clear()
End Sub