Custom textwriter for Console outputstream not working in external classes

Question

I'm trying to forward the Console output to a Windows Forms TextBox control. So I attached a custom TextWriter to the Console which appends the output to the TextBox.

But I think the TextWriter or TextBox is inaccessible from within an external class. How to fix this? Check my code below:

partial class Form1 : Form
{
  public StringWriter _TextWriter;

  public Form1()
  {
    InitializeComponent();

    this._TextWriter = new TextBoxStreamWriter(this.textBox1);
    Console.SetOut(this._TextWriter);

    Console.WriteLine("This text does appear in the TextBox, works perfect.");

    Test ConsoleOutputExternalClass = new Test();
  }
}

public class TextBoxStreamWriter : StringWriter
{
  TextBox _output = null;

  public TextBoxStreamWriter(TextBox output)
  {
    this._output = output;
  }

  public override void WriteLine(string value)
  {
    base.WriteLine(value);
    this._output.AppendText(value.ToString());
  }

  public override Encoding Encoding
  {
    get
    {
      return Encoding.UTF8;
    }
  }
}

private class Test
{
  public Test()
  {
    // HERE I GET AN EXCEPTION ERROR !!
    Console.WriteLine("System.IO.IOException: 'The handle is invalid.'");
  }
}

"But I think the TextWriter or TextBox is inaccessible from within an external class" why do you think so? — styx, Feb 04 '19 at 12:42
Could you show how and where you instantiate and use object of class `Test`? — Alexander, Feb 04 '19 at 12:52
@styx Because I get an Exception, no idea what else it could be. — Bob Vandevliet, Feb 04 '19 at 14:55
@Alexander Of course, forgot that, see my corrected question. — Bob Vandevliet, Feb 04 '19 at 14:56
@BobVandevliet why are you writing an exception to console and not doing anything with your class? — styx, Feb 04 '19 at 15:07
Well, this code works fine for me if i place it in form constructor. Not sure when `WinTool2_Load` event is called. — Alexander, Feb 04 '19 at 15:09
@styx It is just an example string, it is the exception I get. `WinTool_Load` is called by the forms `load` event. Seems strange it doesn't work at my part, will do some more experimenting soon. Thanks! — Bob Vandevliet, Feb 04 '19 at 15:21
I tried my above (generalized) code, and it is indeed working just fine, but in my application it isn't, I'm trying to find out why that is.. — Bob Vandevliet, Feb 05 '19 at 06:37

score 1 · Accepted Answer · answered Feb 05 '19 at 08:46

As I found out after experimenting, the problem had another cause than I expected. In my program I used Console.Clear() to remove all printed lines, but apparently this also destroys the link to the custom set output stream.

And this wouldn't clear the TextBox after all, I should be using TextBox.Clear().

I'm sorry for this, because my question is not to the point in this case, the problem appeared to lie somewhere else. In fact, the code in my question does work perfectly because there is no call to Console.Clear(), but I just didn't find out what really caused the problem yet.

The real question would be: how to "override" Console.Clear() in order to clear the TextBox? But this is for another topic.

Custom textwriter for Console outputstream not working in external classes

1 Answers1