No repetition of values in list (C#)

Question

I created a favorite list box where the user can save text from Textblock in MainPage.xaml

<StackPanel Grid.Row="0" Grid.Column= "0" HorizontalAlignment= "Left" VerticalAlignment= "Top" >
    < Button x:Name= "FavoriteButton" FontFamily= "Segoe MDL2 Assets"
            Content= "&#xE006;" BorderBrush= "Transparent" FontSize= "28"
            Foreground= "{StaticResource PhoneForegroundBrush}"
            Style= "{StaticResource ButtonStyle1}" Click= "FavoriteButton_Click" />
</ StackPanel >

<StackPanel Grid.Row="0" Grid.Column= "2" HorizontalAlignment= "Left" VerticalAlignment= "Top" >
    < Button x:Name= "FavoriteListButton" FontFamily= "Segoe MDL2 Assets"
            Content= "&#xEA55;" BorderBrush= "Transparent" FontSize= "28"
            Foreground= "{StaticResource PhoneForegroundBrush}"
            Style= "{StaticResource ButtonStyle1}" Click= "FavoriteListButton_Click" />
</ StackPanel >

C#

    private void FavoriteButton_Click(object sender, RoutedEventArgs e)
    {

        listobj.Add(new MyData { AnswerName = AnswerTextBlock.Text });


        using (IsolatedStorageFileStream fileStream = Settings1.OpenFile("MyStoreItems", FileMode.Create))
        {
            DataContractSerializer serializer = new DataContractSerializer(typeof(MyDataList));
            serializer.WriteObject(fileStream, listobj);

        }
    }

    private void FavoriteListButton_Click(object sender, RoutedEventArgs e)
    {
        if(FavoriteListBox.Visibility.Equals(Visibility.Collapsed))
        {
            FavoriteListBox.Visibility = Visibility.Visible;
        }
        else if(FavoriteListBox.Visibility.Equals(Visibility.Visible))
        {
            FavoriteListBox.Visibility = Visibility.Collapsed;
        }           
    }

and Listbox

xaml

        <StackPanel Grid.Column="1" Grid.Row="0" HorizontalAlignment="Center" VerticalAlignment="Top">                
            <ListBox x:Name="FavoriteListBox" Visibility="Collapsed" 
                     SelectionChanged="FavoriteListBox_SelectionChanged"
                     HorizontalAlignment="Stretch"
                     VerticalAlignment="Top" Opacity="1"
                     Background="{StaticResource PhoneBackgroundBrush}" Foreground="{StaticResource PhoneForegroundBrush}"
                     Height="300" Width="250">
                <ListBox.ItemTemplate>
                    <DataTemplate>
                        <TextBlock Visibility="Visible" x:Name="FavoriteListBoxTextBlock"  
                                   FontSize="35" Foreground="Black" Text="{Binding AnswerName}"/>
                    </DataTemplate>
                </ListBox.ItemTemplate>
            </ListBox>
        </StackPanel>

C#

public partial class MainPage : PhoneApplicationPage
{
    IsolatedStorageFile Settings1 = IsolatedStorageFile.GetUserStoreForApplication();
    MyDataList listobj = new MyDataList();

    public MainPage()

    {
        InitializeComponent();

        this.Loaded += MainPage_Loaded;

        if (Settings1.FileExists("MyStoreItems"))
        {
            using (IsolatedStorageFileStream fileStream = Settings1.OpenFile("MyStoreItems", FileMode.Open))
            {
                DataContractSerializer serializer = new DataContractSerializer(typeof(MyDataList));
                listobj = (MyDataList)serializer.ReadObject(fileStream);

            }
        }


        FavoriteListBox.ItemsSource = listobj;//binding isolated storage list data



    private void MainPage_Loaded(object sender, RoutedEventArgs e)
    {
        if (Settings1.FileExists("MyStoreItems"))//loaded previous items into list
        {
            using (IsolatedStorageFileStream fileStream = Settings1.OpenFile("MyStoreItems", FileMode.Open))
            {
                DataContractSerializer serializer = new DataContractSerializer(typeof(MyDataList));
                listobj = (MyDataList)serializer.ReadObject(fileStream);

            }
        }
    }

    public class MyData
    {
        public string AnswerName { get; set; }            
    }
    public class MyDataList : ObservableCollection<MyData> //for storing mydata class items with type of list
    {

    }

All text of Textbox which show some text go to isolated storage on favorite button click. but it copies same text again even if that text already exist in the list, so I want when ever user click on favorite button it should check first if text already exist in the list or not, If exist then it should replace or should not copy again. so how to do this.

Answer 1

You can check for duplicates quite easily using a LINQ Any query at the beginning of the FavoriteButton_Click method:

private void FavoriteButton_Click( object sender, RoutedEventArgs e )
{
    //check if there is any item with the same text
    //in which case do not continue
    if ( listobj.Any( l => l.AnswerName == AnswerTextBlock.Text ) ) return;

    listobj.Add( new MyData { AnswerName = AnswerTextBlock.Text } );


    using ( IsolatedStorageFileStream fileStream = Settings1.OpenFile( "MyStoreItems", FileMode.Create ) )
    {
        DataContractSerializer serializer = new DataContractSerializer( typeof( MyDataList ) );
        serializer.WriteObject( fileStream, listobj );

    }
}