Object reference is required for non-static TextBox

Question

C# n00b here. I can't figure out why I get the error on TextBox.text saying:

On googling the error, it seems like it's to do with my TextBox being static..? I can you please explain what this all means? How do I make it non-static? I have a good background in Java, Obj-C, Python and Swift if you can draw any similarities from there.

Code:

namespace WpfApplication2
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
        }

        private void Button(object sender, RoutedEventArgs e)
        {
            // Create OpenFileDialog 
            Microsoft.Win32.OpenFileDialog dlg = new Microsoft.Win32.OpenFileDialog();



            // Set filter for file extension and default file extension 
            dlg.DefaultExt = ".txt";
            dlg.Filter = "Text Files (*.txt)|*.text";


            // Display OpenFileDialog by calling ShowDialog method 
            Nullable<bool> result = dlg.ShowDialog();


            // Get the selected file name and display in a TextBox 
            if (result.HasValue && result.Value)
            {
                // Open document 
                string filename = dlg.FileName;
                TextBox.Text = filename;
            }

        }


    }
}

Change the name of your TextBox to 'txtFileName' and then try 'txtFileName.Text = filename;'. Also, change the name of your function from 'Button' to 'OnButtonClick' — Saagar Elias Jacky, Aug 25 '15 at 01:43
Saagar Elias Jacky is correct. "System.Windows.Forms.TextBox" is a *class*. You need to create an *instance* of that class - for example, "txtFileName", or "textBox1". — paulsm4, Aug 25 '15 at 01:50
`TextBox` and `Button` basically class name, so don't use them as name of your method name or text box name. — NASSER, Aug 25 '15 at 01:53

score 2 · Answer 1 · edited May 23 '17 at 10:26

If you have a TextBox in your xaml, like this:

<TextBox Name="textBox1" Width="100" Height="50" />

you can reference it from the code behind (in your example the MainWindow class) by the name like this:

textBox1.Text = "Hello World";

The class TextBox is not a static class. For more info on static class see this post:

c# What is the different between static class and non-static (I am talking about the class itself not the field)

sstan · Answer 2 · 2015-08-25T02:04:12.453

Text is an instance property. So you need to invoke it using an instance of the TextBox class.

When you do:

TextBox.Text = filename; // "TextBox" is a class, not an instance.

You are trying to invoke Text as if it was a static property, but it isn't.

So I don't know if you do have an instance of a TextBox somewhere in your window. If you added one to your WPF app, by default in VS2015 it will be called textBox (which can easily be confused with TextBox). Whatever it's called, you'll want to use that to set the Text property. Like this:

// consider prefixing with "this" to make sure
// you are using an instance name and not a class name by mistake.
this.textBox.Text = filename;

score 1 · Answer 3 · answered Aug 25 '15 at 01:50

TextBox is a control name and I don't think you can use TextBox.Tex = filename;

You need to give a name to your TextBox control using the Name property in XAML and then assign value to the Text property in your code behind file.

Something like, name your text box as txtFileName and then try assigning value like txtFileName.Text = filename;

Also, giving a name like Button to an event will definitely cause exception. You should better use some name like OnButtonClick to handle the Button Click event, rather than private void Button().

Object reference is required for non-static TextBox

3 Answers3