How to bind input from user in WPF?

Question

I'm working on this application that gets user's input and puts them into a ListBox and also finds the sum of those numbers(everything works fine). My issue is that every time the user enters a new number that number is being shown in the window(and I don't want that), instead I only want the current sum of all the ListBox numbers to be shown on the window.So if the users enter a new number a new sum should be shown on the window. Please help me. Thank you so much in advanced. Here's my code that runs just fine....

    private void ClickToAddMoreCoins(object sender, RoutedEventArgs e)
    {
        int sum = 0;
        //Hides InputBox and takes input text from user.
        InputBox.Visibility = System.Windows.Visibility.Collapsed;

        // Ensuring that input from user is a integer number
        String input = InputTextBox.Text;
        int result = 0;
        if (int.TryParse(input, out result))
        {
            //Adding number of coins to CoinListBox
            CoinListBox.Items.Add(result);
        }
        else
        {
            MessageBox.Show("Please enter a number of coins");
        }
        sum = CoinListBox.Items.Cast<object>().Sum(x => Convert.ToInt32(x));    
        if(sum > 30)
        {
            //Removing last coin in case number of coins exceeds 30
            CoinListBox.Items.RemoveAt(CoinListBox.Items.Count - 1);
            MessageBoxResult answer = MessageBox.Show("You cannot enter more than 30 coins. Do you want to end?", "Message", MessageBoxButton.YesNo, MessageBoxImage.Question);
            if (answer == MessageBoxResult.Yes)
            {
                Application.Current.Shutdown();
            }
        }

        // Resets InputBox.
        InputTextBox.Text = String.Empty;
    }

Answer 1

1. Slashy's answer is incomplete in that it allows negative number to be added.

2. If you are setting InputTextBox's visibility to Collapsed, then how you are getting user input ? and what's the point of using InputTextBox ?

3. If you want to show only sum, then you can hide the ListBox by setting its visibility to Collapsed. So, now your code should look like :

   ...
   CoinListBox.Visibility = System.Windows.Visibility.Collapsed;
   ...
   sum = CoinListBox.Items.Cast<object>().Sum(x => Convert.ToInt32(x));
               if (sum > 30)
               {
                   sum -= result; // removing excess coin
   
                   //Removing last coin in case number of coins exceeds 30
                   CoinListBox.Items.RemoveAt(CoinListBox.Items.Count - 1);
                   MessageBoxResult answer = MessageBox.Show("You cannot enter more than 30 coins. Do you want to end?", "Message", MessageBoxButton.YesNo, MessageBoxImage.Question);
                   if (answer == MessageBoxResult.Yes)
                   {
                       Application.Current.Shutdown();
                   }
               }
   

4. A better version of your code which should check for negative numbers too would be like :

       List<int> coinList = new List<int>();
       private void ClickToAddMoreCoins2(object sender, RoutedEventArgs e)
       {
           int sum = 0;
   
   //Hides InputBox and takes input text from user.
   //InputTextBox.Visibility = System.Windows.Visibility.Collapsed;
   
   // Ensuring that input from user is a integer number
   String input = InputTextBox.Text;
   int result = 0;
   if (int.TryParse(input, out result) && result > 0)
   {
       //Adding number of coins to CoinListBox
       coinList.Add(result);
   }
   else
   {
       MessageBox.Show("Please enter a valid number of coins");
   }
   sum = coinList.Sum();
   if (sum > 30)
   {
       sum -= result;
       //Removing last coin in case number of coins exceeds 30
       coinList.RemoveAt(coinList.Count - 1);
       MessageBoxResult answer = MessageBox.Show("You cannot enter more than 30 coins. Do you want to end?", "Message", MessageBoxButton.YesNo, MessageBoxImage.Question);
       if (answer == MessageBoxResult.Yes)
       {
           Application.Current.Shutdown();
       }
   }
   
   tbSum.Text = "Sum = " + sum.ToString();
   
   // Resets InputBox.
   InputTextBox.Text = String.Empty;
   
   InputTextBox.Focus();
       }
   

Answer 2

Your main problem was declaring the sum inside the method.

Simply use this:

     int sum = 0;
    private void ClickToAddMoreCoins(object sender, RoutedEventArgs e)
    {
        if (sum+(int) (InputTextBox.Text) > 30)
        {
            //Removing last coin in case number of coins exceeds 30
            CoinListBox.Items.RemoveAt(CoinListBox.Items.Count - 1);
            MessageBoxResult answer = MessageBox.Show("You cannot enter more than 30 coins. Do you want to end?", "Message", MessageBoxButton.YesNo, MessageBoxImage.Question);
            if (answer == MessageBoxResult.Yes)
            {
                Application.Current.Shutdown();
            }
        }     
        //Hides InputBox and takes input text from user.
        InputBox.Visibility = System.Windows.Visibility.Collapsed;

        // Ensuring that input from user is a integer number

        string number = InputTextBox.Text;
        int num;
        if(int.TryParse(number,out num))
        {
            sum += num;
          try { CoinListBox.Items.RemoveAt(0); 
              } catch
       {}
    CoinListBox.Items.Add(sum);
        }

        InputTextBox.Text = string.Empty;

    }

Goodluck.