System.NullReferenceException Handled

Question

Here's code I have written for a simple event based multiplier , this is the error I constantly get: Object reference not set to an instance of an object ath this line: txt3.Text = num3.ToString();.
I am a beginner, so what's my error here? What am I missing? Thanks. All the TextBoxes have value set in XAML.

public partial class MainWindow : Window
{
public MainWindow()
{
InitializeComponent();
}

private void txt2_TextChanged(object sender, TextChangedEventArgs e)
{
int num1, num2, num3;
num1 = int.Parse(txt1.Text);
num2 = int.Parse(txt2.Text);
num3 = num1 * num2;
txt3.Text = num3.ToString();
}
}

Pankaj Pandey · Answer

in above code either txt or txt is blank or get null when you multiplied and num3 value comes null. and when you are converting it to string it show null value exception. you can control this acception by checking null value if( num3 !=null) { txt3.Text = num3.ToString(); } else { txt3.Text=; } try itif any issuethen tell me..i'll suggest you another way to fix it.

Debojyoti Das · Answer

Thank you for your reply already fixed it :) Well num3 can't be null because it's a value type that means that txt3 is null. txtOut is null because the TextChanged event is raised when txtTwo's Text property is set in XAML which likely happens before the txtOut TextBox is created. So the solution is to remove the TextChanged event from XAML and put it in the constructor after InitializeComponent: public MainWindow () { InitializeComponent (); txtTwo . TextChanged += txtTwo_TextChanged ; }