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C#: Copy to clipboard Exception

On my form I have a CopyBTN this Copies the contents of a RichTextBox to the clipboard any suggestions why it sometimes fails yet if in debug you can just continue for it to work
How do I capture this exception?
FYI there is lines of text in ResultsRTB.Text

        private void CopyBTN_Click(object sender, EventArgs e)
        {
            Clipboard.SetText(ResultsRTB.Text);
        }

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Error

System.Runtime.InteropServices.ExternalException was unhandled
  ErrorCode=-2147221040
  HResult=-2147221040
  Message=Requested Clipboard operation did not succeed.
  Source=System.Windows.Forms
  StackTrace:
       at System.Windows.Forms.Clipboard.ThrowIfFailed(Int32 hr)
       at System.Windows.Forms.Clipboard.SetDataObject(Object data, Boolean copy, Int32 retryTimes, Int32 retryDelay)
       at System.Windows.Forms.Clipboard.SetText(String text, TextDataFormat format)
       at System.Windows.Forms.Clipboard.SetText(String text)
       at Trevor.Form1.CopyBTN_Click(Object sender, EventArgs e) in D:\Vb\Trevor\Trevor\Form1.cs:line 265
       at System.Windows.Forms.Control.OnClick(EventArgs e)
       at System.Windows.Forms.Button.OnClick(EventArgs e)
       at System.Windows.Forms.Button.OnMouseUp(MouseEventArgs mevent)
       at System.Windows.Forms.Control.WmMouseUp(Message& m, MouseButtons button, Int32 clicks)
       at System.Windows.Forms.Control.WndProc(Message& m)
       at System.Windows.Forms.ButtonBase.WndProc(Message& m)
       at System.Windows.Forms.Button.WndProc(Message& m)
       at System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m)
       at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m)
       at System.Windows.Forms.NativeWindow.DebuggableCallback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)
       at System.Windows.Forms.UnsafeNativeMethods.DispatchMessageW(MSG& msg)
       at System.Windows.Forms.Application.ComponentManager.System.Windows.Forms.UnsafeNativeMethods.IMsoComponentManager.FPushMessageLoop(IntPtr dwComponentID, Int32 reason, Int32 pvLoopData)
       at System.Windows.Forms.Application.ThreadContext.RunMessageLoopInner(Int32 reason, ApplicationContext context)
       at System.Windows.Forms.Application.ThreadContext.RunMessageLoop(Int32 reason, ApplicationContext context)
       at System.Windows.Forms.Application.Run(Form mainForm)
       at Trevor.Program.Main() in D:\Vb\Trevor\Trevor\Program.cs:line 19
       at System.AppDomain._nExecuteAssembly(RuntimeAssembly assembly, String[] args)
       at System.AppDomain.ExecuteAssembly(String assemblyFile, Evidence assemblySecurity, String[] args)
       at Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly()
       at System.Threading.ThreadHelper.ThreadStart_Context(Object state)
       at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
       at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
       at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
       at System.Threading.ThreadHelper.ThreadStart()
  InnerException:

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gr8gonzo

My guess is that something had the clipboard open when you tried to access it. The Windows clipboard is basically one central location, and when you get or set the text, it's like you're opening a file, getting/setting the content, and then closing the file. And if something else still has the clipboard open when you try to get/set the content, you'll get an error.

trevor1940

ASKER

So how would I program this, put it in a try catch finally block with a delay on the exception?

something like this??

        private void CopyBTN_Click(object sender, EventArgs e)
        {
            try
              {
                 Clipboard.SetText(ResultsRTB.Text);
              }
           catch  (Exception e)
              {
                    int milliseconds = 500;
                    Thread.Sleep(milliseconds);
              }
            finally
              {
                 Clipboard.SetText(ResultsRTB.Text);
              }

        }

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ASKER CERTIFIED SOLUTION

gr8gonzo

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kaufmed

The "finally" clause runs at the end, no matter what,

Errrr... almost no matter what.

https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/try-finally

Within a handled exception, the associated finally block is guaranteed to be run. However, if the exception is unhandled, execution of the finally block is dependent on how the exception unwind operation is triggered. That, in turn, is dependent on how your computer is set up.

For all practical purposes, it runs no matter what.

gr8gonzo

Good point. :)

trevor1940

ASKER

Thank you
i'm sure this technique will come in handy again
Didn't quite understand kaufmed point

Other than The "finally" clause runs at the end so don't attempt to run code here that could fail / or be the the cause of an exception

gr8gonzo

kaufmed was pointing out that there are times where the "finally" clause won't run. These situations are pretty rare, and the vast majority are related to a scenario where your app is pretty much going to crash or shutdown in some way, and there's no avoiding it. I can't think of any common situation where this isn't the case (where you wouldn't hit the finally block but your app would keep running afterwards).

One example would be a stack overflow exception. An example would be like this:

        public Form1()
        {
            InitializeComponent();
            InfinitelyRecursingMethod();
        }

        private void InfinitelyRecursingMethod()
        {
            try
            {
                // Recursing infinitely will eventually result in a stack overflow
                InfinitelyRecursingMethod();
            }
            catch(Exception ex)
            {
                Console.WriteLine("Exception caught");
            }
            finally
            {
                Console.WriteLine("FINALLY!");
            }
        }

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If you attach a debugger and break on the catch and finally lines, you'll notice they're not hit - the stack overflow pretty much says, "Sorry - I'm outta room to do anything more!" and exits.