Web Browser Combo box Problem

[cigoL..:)]

Greetings,

i'm currently developing a web browser for my school project (i'm kinda new to advance visual basic)... it's 75% complete and the only problem i encountered is that when i enter items for the combo box it accepts duplicate .. for example i entered www.daniweb.com and re-entered it again, two www.daniweb.com will appear in the combo box's item and if i'll enter another url for example www.google.com it must be also added to combo box's item together with the www.daniweb.com and without any duplicates..how will i fix this? how can i remove the duplicate one?
here's the entire code of the system

Dim i As Integer
    Dim int As Integer = 0
  
    Private Sub Loading(ByVal sender As Object, ByVal e As Windows.Forms.WebBrowserProgressChangedEventArgs)
        ToolStripProgressBar1.Maximum = e.MaximumProgress
        ToolStripProgressBar1.Value = e.CurrentProgress
    End Sub

    Private Sub Done(ByVal sender As Object, ByVal e As Windows.Forms.WebBrowserDocumentCompletedEventArgs)
      

        TabControl1.SelectedTab.Text = CType(TabControl1.SelectedTab.Controls.Item(0), WebBrowser).DocumentTitle
        ComboBox1.Text = CType(TabControl1.SelectedTab.Controls.Item(0), WebBrowser).Url.ToString
        ToolStripLabel1.Text = CType(TabControl1.SelectedTab.Controls.Item(0), WebBrowser).Url.AbsoluteUri

        ComboBox1.Items.Add(CType(TabControl1.SelectedTab.Controls.Item(0), WebBrowser).Url.AbsoluteUri)

        ToolStripProgressBar1.Value = ToolStripProgressBar1.Maximum
        Timer1.Stop()
    End Sub


    Private Sub BtnSurf_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button8.Click
        CType(TabControl1.SelectedTab.Controls.Item(0), WebBrowser).Navigate(ComboBox1.Text)

                ComboBox1.Items.Remove(CType(TabControl1.SelectedTab.Controls.Item(0), WebBrowser).Url.AbsoluteUri)

            End If
        Next
    End Sub

    Private Sub Timer1_Tick(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Timer1.Tick
        ToolStripProgressBar1.Increment(1)
    End Sub

    Private Sub RemoveTabBtn_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button7.Click
        If Not TabControl1.TabPages.Count = 1 Then
            TabControl1.TabPages.RemoveAt(TabControl1.SelectedIndex)
            TabControl1.SelectTab(TabControl1.TabPages.Count - 1)
            int = int - 1
        End If
    End Sub

    Private Sub AddTabBtn_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button6.Click
        Dim Browser As New WebBrowser
        TabControl1.TabPages.Add("New Tab")
        TabControl1.SelectTab(int)
        Browser.Name = "Web Browser"
        Browser.Dock = DockStyle.Fill
        TabControl1.SelectedTab.Controls.Add(Browser)
        AddHandler Browser.ProgressChanged, AddressOf Loading
        AddHandler Browser.DocumentCompleted, AddressOf Done
        int = int + 1
        CType(TabControl1.SelectedTab.Controls.Item(0), WebBrowser).GoSearch()

    End Sub

    Private Sub goForwardBtn_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button5.Click
        CType(TabControl1.SelectedTab.Controls.Item(0), WebBrowser).GoForward()
        ToolStripProgressBar1.Value = ToolStripProgressBar1.Minimum
        Timer1.Start()
    End Sub

    Private Sub goBackwardBtn_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button4.Click
        CType(TabControl1.SelectedTab.Controls.Item(0), WebBrowser).GoBack()
        ToolStripProgressBar1.Value = ToolStripProgressBar1.Minimum
        Timer1.Start()

    End Sub

    Private Sub StopBtn_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button3.Click
        CType(TabControl1.SelectedTab.Controls.Item(0), WebBrowser).Stop()
    End Sub

    Private Sub Refresh_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click
        CType(TabControl1.SelectedTab.Controls.Item(0), WebBrowser).Refresh()
        ComboBox1.Text = CType(TabControl1.SelectedTab.Controls.Item(0), WebBrowser).Url.ToString
        ToolStripProgressBar1.Value = ToolStripProgressBar1.Minimum
        Timer1.Start()
    End Sub

    Private Sub GoHomeBtn_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        CType(TabControl1.SelectedTab.Controls.Item(0), WebBrowser).GoHome()
        ToolStripProgressBar1.Value = ToolStripProgressBar1.Minimum
        Timer1.Start()
    End Sub



    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        Dim Browser As New WebBrowser
        TabControl1.TabPages.Add("Untitled")
        Browser.Name = "Web Browser"
        Browser.Dock = DockStyle.Fill
        TabControl1.SelectedTab.Controls.Add(Browser)
        AddHandler Browser.ProgressChanged, AddressOf Loading
        AddHandler Browser.DocumentCompleted, AddressOf Done
        int = int + 1
        CType(TabControl1.SelectedTab.Controls.Item(0), WebBrowser).GoSearch()
    End Sub


    Private Sub TextBox1_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles TextBox1.Click

        TextBox1.Clear()
        TextBox1.Font = New System.Drawing.Font("", 8, Drawing.FontStyle.Regular)
    End Sub

    Private Sub Button9_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button9.Click
        CType(TabControl1.SelectedTab.Controls.Item(0), WebBrowser).Navigate("http://www.google.com/search?sclient=psy&hl=fil&site=&source=hp&q=" & TextBox1.Text)
        ToolStripProgressBar1.Value = ToolStripProgressBar1.Minimum
        Timer1.Start()
    End Sub

Thanks! best regards,
cigoL:)

[Unhnd_Exception]

You can check if a string already exists before adding it with combobox.findstring. Find string will return the index of the first matching item. If -1 the item is not in the combox.

Dim Uri As String = "A Uri"
  If ComboBox1.FindStringExact(Uri) < 0 Then
     'Uri does not exist in the combobox
     ComboBox1.Items.Add(Uri)
  End If

And you should rename your loading and done subs to standard naming convention. With a name and _Underscore with TheEventName it represents. Will make your code easier for someone else to read.

WebBrowser_ProgressChanged
WebBrowser_DocumentComplete

AddHandler Browser.ProgressChanged, AddressOf WebBrowser_ProgressChanged

[cigoL..:)]

You can check if a string already exists before adding it with combobox.findstring. Find string will return the index of the first matching item. If -1 the item is not in the combox.

Dim Uri As String = "A Uri"
  If ComboBox1.FindStringExact(Uri) < 0 Then
     'Uri does not exist in the combobox
     ComboBox1.Items.Add(Uri)
  End If

And you should rename your loading and done subs to standard naming convention. With a name and _Underscore with TheEventName it represents. Will make your code easier for someone else to read.

WebBrowser_ProgressChanged
WebBrowser_DocumentComplete

AddHandler Browser.ProgressChanged, AddressOf WebBrowser_ProgressChanged

Thank you Sir! it works! thank you so much :)