Get the value of the textbox on c#

Question

I'm working on a wpf app and i want to get the value of textbox i want to use KeyDown & KeyPress to check if the text is a numeric value but when i write KeyPress the compilator underlined the proprity so i can't use it .

private void sb_KeyDown_1(object sender, System.Windows.Input.KeyEventArgs e)
    {
        nonNumberEntered = false;

        // Determine whether the keystroke is a number from the top of the keyboard.
        if (e.KeyCode < Keys.D0 || e.KeyCode > Keys.D9)
        {
            // Determine whether the keystroke is a number from the keypad.
            if (e.KeyCode < Keys.NumPad0 || e.KeyCode > Keys.NumPad9)
            {
                // Determine whether the keystroke is a backspace.
                if (e.KeyCode != Keys.Back)
                {
                    // A non-numerical keystroke was pressed.
                    // Set the flag to true and evaluate in KeyPress event.
                    nonNumberEntered = true;
                }
            }
        }
        //If shift key was pressed, it's not a number.
        if (Control.ModifierKeys == Keys.Shift)
        {
            nonNumberEntered = true;
        }


    }

and it underlined also e.KeyCode and e.KeyNumPad0 .... what should i do ?

Answer 1

This isn't the right way to handle this in WPF.

Getting the value is simple enough, you just bind to something on your View Model:

<TextBox Text="{Binding Path=MyTextValue}"/>

To get it to update on every character change, set the UpdateSourceTrigger:

<TextBox Text="{Binding Path=MyTextValue, UpdateSourceTrigger=OnPropertyChanged}"/>

Since it looks like you are doing validation, I would suggest looking at the MSDN article on Validation in WPF: Binding Validation

You should (almost) never have to capture actual key-strokes/presses in WPF unless you are writing a game or something similar.

Here is a question on StackOverflow that could also help: WPF TextBox Validation C#

Since you clearly aren't set up for MVVM yet, here is some code you will need:

public class MyViewModel : INotifyPropertyChanged
{
   //Standard INotifyPropertyChanged implementation, pick your favorite

   private String myTextValue;
   public String MyTextValue
   {
      get { return myTextValue; }
      set
      {
          myTextValue = vaule;
          OnPropertyChanged("MyTextValue");
      }
}

Then in your codebehind:

public partial class MainWindow
{
    public MainWindow()
    {
         InitializeComponent();
         DataContext = new MyViewModel();
    }
}

That should be more than enough to get you started (along with the XAML). Let me know if you have any questions!

Answer 2

Bind the Text property of your TextBox in a TwoWay mode and with UpdateSourceTrigger set to PropertyChanged to a public string property supporting change notification in the DataContext (typically a ViewModel ) of your view ( UserControl or Window containing your TextBox ).

Once you do that you'll be able to call a method in your ViewModel every time the TextBox text is changed (every time a key is pressed) and do your TextBox value validation there.