combobox = textbox

See if that works:

Prerequisites:
2 Forms
1 TextBox
1 ComboBox
1 Button

Go to the form where you placed the Button (and the TextBox) and make sure the form's code is the same as below:

Public Class Form2

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Form1.ComboBox1.Items.Add(TextBox1.Text)
    End Sub
End Class

This should work. If not, reply to this post so I can further help you.

it work..but after i relaunch application, item in combobox is not there..

After closing the forms you will lose all data because all that data was just saved in memory therefore its only temporary. What you want to do is save that data into a database

After closing the forms you will lose all data because all that data was just saved in memory therefore its only temporary. What you want to do is save that data into a database

The other option is to save the information to a CSV file or XML file as to hold the information. Then use a subroutine to load the information on FORM LOAD. This is easy to implement and there are multiple threads in this forum that cover this same information. There is other methods to do this. But a file is easy to deploy and does not need admin privileges to implement. If your issues are resolved please mark the thread as solved.

is there any procedure in vb.net for listing the items as dropdownlist in a textbox