How can I allow ctrl+a with TextBox in winform?

I'm asking the question already asked (and even answered) here: https://stackoverflow.com/questions/5885739/why-are-some-textboxes-not-accepting-control-a-shortcut-to-select-all-by-defau

But that answer doesn't work for me. I have this code:

public class LoginForm : Form
{
    private TextBox tbUsername;
    
    public LoginForm()
    {
        tbUsername = new TextBox();
        tbUsername.ShortcutsEnabled = true;
        tbUsername.Multiline = false;
        Controls.Add(tbUsername);
    }
}

The textbox shows up, I can write on it, I can cut, copy and paste text on it without any problems. But when I try to press Ctrl+A I only hear a "bling" similar to the bling that you hear if you try to erase text from an empty textbox (try it with your browser's address bar).

Like other answers indicate, Application.EnableVisualStyles() should be called. Also the TextBox.ShortcutsEnabled should be set to true. But if your TextBox.Multiline is enabled then Ctrl+A will not work (see MSDN documentation). Using RichTextBox instead will get around the problem.

Just create a keydown event for that TextBox in question and include this code:

private void tbUsername_KeyDown(object sender, KeyEventArgs e)
{
    if (e.Control && e.KeyCode == Keys.A)
    {
        if (sender != null)
            ((TextBox)sender).SelectAll();
    }
}

You could always override the process command keys to get the desired result

protected override bool ProcessCmdKey(ref Message msg, Keys keyData)
{
    const int WM_KEYDOWN = 0x100;
    var keyCode = (Keys) (msg.WParam.ToInt32() &
                          Convert.ToInt32(Keys.KeyCode));
    if ((msg.Msg == WM_KEYDOWN && keyCode == Keys.A) 
        && (ModifierKeys == Keys.Control) 
        && tbUsername.Focused)
    {
        tbUsername.SelectAll();
        return true;
    }            
    return base.ProcessCmdKey(ref msg, keyData);
}

Quick answer is that if you are using multiline true you have to explicitly call the select all.

private void tbUsername_KeyDown(object sender, KeyEventArgs e)
{
    if (e.KeyCode == Keys.A && e.Control)
    {
        tbUsername.SelectAll();
    }
}

This happened to me once too, I'm assuming you removed the call for Application.EnableVisualStyles(); from your program? Add it back to the Main() function and everything should work fine.

Textbox has a method SelectAll() and worked well for me. (.net 4.5)

No need to handle WM_KEYDOWN! I know that most examples here (and CodeProject and many other places) all say there is, but it does not cure the beep that results whenever a WM_CHAR arises that is not handled.

Instead, try this:

LRESULT CALLBACK Edit_Prc(HWND hwnd,UINT msg,WPARAM wParam,LPARAM lParam){
  if(msg==WM_CHAR&&wParam==1){SendMessage(hwnd,EM_SETSEL,0,-1); return 1;}
  else return CallWindowProc((void*)WPA,hwnd,msg,wParam,lParam);
}

Remember to subclass the EDIT control to this Edit_Prc() using WPA=SetWindowLong(...) where WPA is the window procedure address for CallWindowProc(...)

I figured this out by experiment, after finding that all the answers I found online insisted on handling WM_KEYDOWN, using GetKeyState(), and ended up with bigger code that failed to stop that annoying beep!

While this answer doesn't deal with dotnet, in cases like this it's usually better to cut to the chase and solve it rather than agonise over which version of a large code wrapper system may or may not do it for you, especially if you want to avoid the risk of fighting against inbuilt behaviour.

Throwing in my two cents. Calling this under keypress is just another option.

private void TxtBox_KeyPress(object sender, KeyPressEventArgs e)
{
    if (e.KeyChar == '\x1')
    {
        TxtBox.SelectAll();
        e.Handled = true;
    }
}

This is my code, it is working fine

private void mainSimPlus_KeyDown(object sender, KeyEventArgs e)
            {
                e.Handled = true;
                if (e.Control == true && e.KeyCode == Keys.A)
                {
                    if (SelectAllTextBox(txt1))
                        return;
                    if (SelectAllTextBox(txt2))
                        return;
                }
            }
            private bool SelectAllTextBox(TextBox txt)
            {
                if (txt.Focused)
                {
                    txt.SelectAll();
                    return true;
                }
                else
                    return false;
            }