Declare textbox event in XAML

Question

How do I declare the Keypresseventargs event from a textbox to work with this event in Code Behind? The code to run the event I have, I just can’t declare the event, as I do with Click, for example. That I can. I thought for keypress, keydown, it was not necessary to declare, but when I create my event in Code Behind, gives me error in textbox. Look at my codes. XAML:

<TextBox x:Name="txtTara" HorizontalAlignment="Left" Height="23" Margin="161,130,0,0" TextWrapping="Wrap" Text="0" VerticalAlignment="Top" Width="120"/>

Code Behind:

private void txtTara(object sender, KeyPressEventArgs e)
{
    if (e.KeyChar == '.' || e.KeyChar == ',')
    {
        //troca o . pela virgula
        e.KeyChar = ',';

        //Verifica se já existe alguma vírgula na string
        if (txtTara.Text.Contains(","))
        {
            e.Handled = true; // Caso exista, aborte 
        }
    }

    //aceita apenas números, tecla backspace.
    else if (!char.IsNumber(e.KeyChar) && !(e.KeyChar == (char)Keys.Back))
    {
        e.Handled = true;
    }
}

That code I copied here on Sopt.

Answer 1

You’re making a huge mess.

First of all, KeyPressEventArgs is not a event is only one class used to pass parameters for the KeyPress.

So, this does not exist. This class comes from Windows Forms, it makes no sense to try to use it because its element is not of this namespace.

For WPF what is used is KeyEventArgs.

private void txtTara_KeyPress(object sender, KeyEventArgs e) { }

Second, there is no event KeyPress in WPF, you will have to use the KeyDown.

Third, change the method name to txtTara_KeyPress. Because: 1) there is already an element with this name (the component itself); and 2) this is the C nomenclature standard#.

And finally, it is necessary to link the event to the visual element. Somehow the visual needs to know that there is an event triggered, there is no magic to figure it out.

To link an event to a componenen, it is necessary to declare in XAML.

For example:

<TextBox x:Name="txtTara" 
         HorizontalAlignment="Left" Height="23" Margin="161,130,0,0"  
         TextWrapping="Wrap" Text="0" VerticalAlignment="Top" 
         Width="120" KeyDown="txtTara_KeyPress"/>