Odd error in TextChanged Event in C#

Question

So I have a combobox:

<ComboBox IsEditable="True" TextBoxBase.TextChanged="textBox_Changed"/>

When the text in the combobox changes, it fires off the textBox_changed function:

private void textBox_Changed(object sender, RoutedEventArgs e)
{
    LinearGradientBrush gradient = new LinearGradientBrush(Colors.MistyRose, Colors.SandyBrown, new Point(0, 0), new Point(0, 1));
    this.saveButton.Background = gradient;
}

What this function does is change the background color of a button elsewhere on the window. So far this works perfectly. The issue appears when I try to use this same function with a TextBox instead of a Combobox:

<TextBox TextChanged="textBox_Changed"/>

When I run the application, I get the following error:

Object reference not set to an instance of an object.

Very bizarre error that I can't figure out.

[What is a NullReferenceException and how do I fix it?](http://stackoverflow.com/questions/4660142/what-is-a-nullreferenceexception-and-how-do-i-fix-it) — Soner Gönül, Oct 01 '14 at 10:36
I don't understand how that exception applies however. The object clearly exists as I use it with the ComboBox. — Jason Axelrod, Oct 01 '14 at 10:38
Have a look at the stacktrace if you can figure out at what point the error is caused, also try to to run the application with Step debugging by using the F10 or F11 keys. — Bernd Linde, Oct 01 '14 at 10:44
Do you have any default value for the TextBox ? My guess is that the event is triggered when the form is initializing and saveButton was not yet initialized. — Adrian Fâciu, Oct 01 '14 at 10:50
Thank you Adrian Faciu; that was the issue. I removed the default value from the text box and now its working fine. — Jason Axelrod, Oct 01 '14 at 11:07

score 0 · Accepted Answer · answered Oct 01 '14 at 20:42

0

Issue solved! The event was getting triggered when the form was initializing, but saveButton was not initialized yet. I removed the default values of the field and all is well.

answered Oct 01 '14 at 20:42

Jason Axelrod

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Hey man. I know this answer was posted a long time ago, but what values did you remove to get it working? I'm having the same issues at the moment. – CareTaker22 Apr 03 '16 at 10:08

Odd error in TextChanged Event in C#

1 Answers1