WinForm : Make control unfocusable - winforms

Question

My winform contains a TextBox that is the main control of the form. When I do CtrL + C, and often end up with an empty clipboard because for some reason the ActiveControl of the form is set to another control, like for instance the TabControl, the SplitContainer, etc. I tried to set those control TabStop = fasle, but to avail. Is there a way to prevent all controls from getting focus ? Not only regarding the mouse clicks, but also the tab keys.

Answer 1

I can imagine trying with some native windows messages like WM_SetFocus, or some native windows styles like WS_TABSTOP, or some control styles like ControlStyles.Selectable, or ControlStyles.UserMouse, but I'd say you cannot find a generic solution which handles all controls.
What I'm proposing here (according to your comments, looking for a better way of handling focus rather than trying to make things focusable, which makes more sense in UX point of view as well) is handling TabControl and SplitterContainer focus related events:
Tab control: Handle SelectedIndexChanged, and then move the focus to the first focusable control of the tab.
Splitter container: Handle MouseDown to trap the start of splitting, then store the active panel; later handle SplitterMoved and move the focus to he first focusable control of the active panel.
Here is what worked for me:
SplitterPanel activePanel;
private void splitContainer1_SplitterMoved(object sender, SplitterEventArgs e)
{
splitContainer1.SelectNextControl(activePanel,
forward: true, tabStopOnly: true, nested: true, wrap: true);
}
private void splitContainer1_MouseDown(object sender, MouseEventArgs e)
{
activePanel = splitContainer1.Panel1.ContainsFocus ? splitContainer1.Panel1 :
splitContainer1.Panel2.ContainsFocus ? splitContainer1.Panel2 : null;
}
private void tabControl1_SelectedIndexChanged(object sender, EventArgs e)
{
var page = this.tabControl1.SelectedTab;
page.SelectNextControl(null,
forward: true, tabStopOnly: true, nested: true, wrap: true);
}

Answer 2

Instead of preventing focus, which might cause problems for those trying to navigate your app using only the keyboard, implement the IMessageFilter interface and trap Ctrl-C for your whole app. Then you can simply put the contents of your "main textbox" on the clipboard manually:
public partial class Form1 : Form, IMessageFilter
{
public Form1()
{
InitializeComponent();
Application.AddMessageFilter(this);
}
bool IMessageFilter.PreFilterMessage(ref Message m)
{
if (m.Msg == 0x0100 &&
(Keys)m.WParam.ToInt32() == Keys.C &&
ModifierKeys == Keys.Control)
{
Console.WriteLine("Ctrl-C Trapped!");
if (textBox1.SelectionLength > 0)
{
Clipboard.SetText(textBox1.SelectedText);
}
else
{
Clipboard.SetText(textBox1.Text);
}
return true;
}
return false;
}
}