WinForms RichTextBox Append Log and UIThread extensions

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Turn any RichTextBox in winforms to a log view. Just call rtxt.AppendLog("someString"); and it will append that to a new line in the richtextbox. And scroll it to view.

public static void AppendLog(this RichTextBox rtxt, string s)
{
 rtxt.UIThread(() =>
 {
  rtxt.AppendText($"{s}{Environment.NewLine}");
  rtxt.SelectionLength = 0;
  if (rtxt.Lines.Length > 10000)
  {
   rtxt.Lines = rtxt.Lines.Skip(5000).ToArray();
  }
  rtxt.SelectionStart = rtxt.TextLength;
  rtxt.ScrollToCaret();
 });
}

The above snippet of code requires the following to function correctly.

static public void UIThread(this Control control, Action code)
{
 if (control.InvokeRequired)
 {
  control.BeginInvoke(code);
  return;
 }
 code.Invoke();
}

I can't take credit, found it years ago on some forum somewhere. But here it is anyway. It makes a call to a winforms control synschronize with the GUI thread so that no cross-threading exceptions is thrown. GUI items can only be modified from the GUI thread and this ensures just that.

The exception thrown if correct thread synchronization is not used is: 

System.InvalidOperationException was unhandled
  HResult=-2146233079
  Message=Cross-thread operation not valid: Control 'rtxtOutput' accessed from a thread other than the thread it was created on.
  Source=System.Windows.Forms
  StackTrace:
       at System.Windows.Forms.Control.get_Handle()
       at System.Windows.Forms.TextBoxBase.GetSelectionStartAndLength(Int32& start, Int32& length)
       at System.Windows.Forms.TextBoxBase.set_SelectionLength(Int32 value)
       at System.Windows.Forms.RichTextBox.set_SelectionLength(Int32 value)
       at ave.dev.winform.Form1.ticker_Tick(Object sender, EventArgs e) in C:\tfs\YYY\Form1.cs:line 54
       at ave.dev.winform.Form1._loggerHook_NewLogLine(String s) in C:\tfs\YYY\Form1.cs:line 38

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SGEN: Could not load file or assembly 'xxx' or one of its dependencies. Operation is not supported. (Exception from HRESULT: 0x80131515)

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Always nice to see our old friend HRESULT in an error message.

Ran into this today when converting some .NET3.5 projects to .NET4.0 and at the same time upgrading some 3rd party libraries.

Seems that downloaded files get a blocked attribute set on them that prevents the usage of them. In Visual Studio 2010, the HRESULT: 0x80131515 is shown when linking to dll’s that are blocked.

To come around this, open Windows Explorer, navigate to the folder hosting the dll. Right click on it and select properties. There should be a Unblock button in the dialog window. Click on it and SGEN should stop complaining.

Hope this helps : )