Autocompletebox with long lists for windows phone 7

I recently was working with a list of American cities which has around 19000 cities in WP7 application. I wanted to use the autocompletebox which will be helpful to find a name fast. However, the autocompletebox was sluggish. Hence I created a list of lists. The lists where for each alphabet which reduced the list sizes to reasonable size. I also used LINQ to get the city name.

When I tested in WP7 I got all searches under 100 milliseconds and most of them around 2 to 30 milliseconds.

Another thing I found out is the autocompletebox does not like Pivot control. The selection list offsets to the top of the screen with the first selection completely masked!

See the reference below

http://www.jeff.wilcox.name/2011/03/acb-in-pivot/

The XAML and the code are given below. This also used the textbox substitution to make sure the initial display did not have the drop down of the autocompletebox as per this forum discussion which I initiated:

AutoCompleteBox initial value in Windows Phone 7

 <StackPanel Grid.Row="0" Orientation="Horizontal"   HorizontalAlignment="Stretch">
 <toolkit:AutoCompleteBox   ItemsSource="{Binding}"       x:Name="City_Name_TextBox"   ValueMemberPath="CityName"
 Width="370" Visibility="Collapsed"  MinimumPopulateDelay="200"                                                      <toolkit:AutoCompleteBox.ItemTemplate>
 <DataTemplate   >
 <StackPanel VerticalAlignment="Stretch"    >
 <TextBlock   Text="{Binding CityName}"      />
   </StackPanel>
  </DataTemplate>
   </toolkit:AutoCompleteBox.ItemTemplate>
     </toolkit:AutoCompleteBox>
   <TextBox  Width="300"  x:Name="City_Name_TextBox_Init"  Visibility="Visible" Text="Palo Alto" MouseLeftButtonDown="City_Name_TextBox_Init_MouseLeftButtonDown"></TextBox>
 <Button x:Name="Go_Button" Width="100"  Content="GO" Click="Go_Button_Click"  ></Button>
</StackPanel>

 private void City_Name_TextBox_Init_MouseLeftButtonDown(object sender, MouseButtonEventArgs e)
        {
            City_Name_TextBox_Init.Visibility = System.Windows.Visibility.Collapsed;
            City_Name_TextBox.Visibility = System.Windows.Visibility.Visible;
            City_Name_TextBox.Text = "";
            City_Name_TextBox.Focus();
            // City_Name_TextBox.Focus();
        } 

 public void Load_City_Alpha()
        {
            string[] abclist = new[] { "a", "b", "c","d","e","f","g","h","i","j",
                                       "k","l","m","n","o","p","q","r","s","t",
                                       "u","v","w","x","y","z"};
             int salphaselectormax=26;
             DateTime dtstart = DateTime.Now ;
            
             for ( int salphaselector = 0; salphaselector < salphaselectormax; salphaselector++)
            {
                string salpha = abclist[salphaselector];
                city_list_abc.Add( (from n in  citylist
                                         where n.CityName.ToLower().StartsWith(salpha)
                                         select n).ToList());
               
                
            }
             //List<string> testlistlength = new List<string>();
             //for (int i = 0; i < 26; i++)
             //{
             //    testlistlength.Add(abclist[i]+"--" + city_list_abc[i].Count.ToString());
             //}
             DateTime dtend = DateTime.Now;
             int  dtduration = (dtend - dtstart).Milliseconds;
                 
        }

  private void City_Name_TextBox_Populating(object sender, PopulatingEventArgs e)
        {
            // Allow us to wait for the response
            DateTime dtstart = DateTime.Now;
            e.Cancel = true;
            //only query web service if more than 3 chars
            
            if (City_Name_TextBox.Text.Length >= 3)
            {
                // Create a request for suggestion
                int listindex = Array.IndexOf(abclist, City_Name_TextBox.Text.ToLower().Substring(0,1));
                List<City> results = (from n in (Application.Current as App).city_list_abc[listindex]
                                      where n.CityName.ToLower().StartsWith(City_Name_TextBox.Text.ToLower())
                                      select n).ToList();  
                City_Name_TextBox.ItemsSource = results;
                City_Name_TextBox.PopulateComplete();
            }
            DateTime dtend = DateTime.Now;
            int dtduration = (dtend - dtstart).Milliseconds;
            Timer_TextBox.Text = dtduration.ToString();
        }