Disable AutoSelect behavior for System.Window.Forms.ComboBox (C #)

Question

Background:

I have Forms.ComboBox with DropDownStyle = DropDown .

I do not use AutoComplete , but I implemented something similar, which not only filters the beginning of the text, but also uses a regular expression and shows all the elements that match the entered text. It works great.

However, when I type the first letter of the corresponding element, the ComboBox returns to its original behavior and sets DroppedDown = true and automatically selects the first record and completes the text according to the selected element (similar to AutoCompleteMode Add). I want there to be no automatic selection and no automatic completion.

What I have found so far is that I somehow have to prevent SendMessage() from CB_FINDSTRING to call and replace CB_FINDSTRING with CB_FINDSTRINGEXACT ( MSDN link ).

I think I need to extend the ComboBox class, but I'm not sure which methods I need to override. I am working with C # .NET Framework v3.5.

Questions:

• How to extend Windows.Forms.ComboBox to prevent automatic selection behavior?

References:

How to prevent automatic selection in ComboBox from the drop-down list, except for exact matches? (didn't help me)

Answer 1

Try the following:

 using System; using System.Collections.Generic; using System.Runtime.InteropServices; using System.Windows.Forms; using Opulos.Core.Win32; namespace Opulos.Core.UI { // Extension class to disable the auto-select behavior when a combobox is in DropDown mode. public static class ComboBoxAutoSelectEx { public static void AutoSelectOff(this ComboBox combo) { Data.Register(combo); } public static void AutoSelectOn(this ComboBox combo) { Data data = null; if (Data.dict.TryGetValue(combo, out data)) { data.Dispose(); Data.dict.Remove(combo); } } private class Data { // keep a reference to the native windows so they don't get disposed internal static Dictionary<ComboBox, Data> dict = new Dictionary<ComboBox, Data>(); // a ComboBox consists of 3 windows (combobox handle, text edit handle and dropdown list handle) ComboBox combo; NW nwList = null; // handle to the combobox dropdown list NW2 nwEdit = null; // handle to the edit window internal void Dispose() { dict.Remove(this.combo); this.nwList.ReleaseHandle(); this.nwEdit.ReleaseHandle(); } public static void Register(ComboBox combo) { if (dict.ContainsKey(combo)) return; // already registered Data data = new Data() { combo = combo }; Action assign = () => { if (dict.ContainsKey(combo)) return; // already assigned COMBOBOXINFO info = COMBOBOXINFO.GetInfo(combo); // new COMBOBOXINFO(); //info.cbSize = Marshal.SizeOf(info); //COMBOBOXINFO2.SendMessageCb(combo.Handle, 0x164, IntPtr.Zero, out info); dict[combo] = data; data.nwList = new NW(combo, info.hwndList); data.nwEdit = new NW2(info.hwndEdit); }; if (!combo.IsHandleCreated) combo.HandleCreated += delegate { assign(); }; else assign(); combo.HandleDestroyed += delegate { data.Dispose(); }; } } private class NW : NativeWindow { ComboBox combo; public NW(ComboBox combo, IntPtr handle) { this.combo = combo; AssignHandle(handle); } private const int LB_FINDSTRING = 0x018F; private const int LB_FINDSTRINGEXACT = 0x01A2; protected override void WndProc(ref Message m) { if (m.Msg == LB_FINDSTRING) { m.Msg = LB_FINDSTRINGEXACT; } base.WndProc(ref m); if (m.Msg == LB_FINDSTRINGEXACT) { String find = Marshal.PtrToStringAuto(m.LParam); for (int i = 0; i < combo.Items.Count; i++) { Object item = combo.Items[i]; if (item.Equals(find)) { m.Result = new IntPtr(i); break; } } } } } private class NW2 : NativeWindow { public NW2(IntPtr handle) { AssignHandle(handle); } private const int EM_SETSEL = 0x00B1; private const int EM_GETSEL = 0x00B0; protected override void WndProc(ref Message m) { if (m.Msg == EM_SETSEL) { // if this code is not here, then the entire combobox text is selected // which looks ugly, especially when there are multiple combo boxes. // // if this method returns immediately, then the caret position is set // to (0, 0). However, it seems that calling EM_GETSEL has a side effect // that the caret position is mostly maintained. Sometimes it slips back // to (0, 0). SendMessage(Handle, EM_GETSEL, IntPtr.Zero, IntPtr.Zero); //int selStart = (sel & 0x00ff); //int selEnd = (sel >> 16) & 0x00ff; //Debug.WriteLine("EM_GETSEL: " + selStart + " nEnd: " + selEnd); return; } base.WndProc(ref m); } [DllImportAttribute("user32.dll", SetLastError=true)] private static extern int SendMessage(IntPtr hWnd, int msg, IntPtr wParam, IntPtr lParam); } } [StructLayout(LayoutKind.Sequential)] public struct COMBOBOXINFO { public Int32 cbSize; public RECT rcItem; public RECT rcButton; public int buttonState; public IntPtr hwndCombo; public IntPtr hwndEdit; public IntPtr hwndList; public static COMBOBOXINFO GetInfo(ComboBox combo) { COMBOBOXINFO info = new COMBOBOXINFO(); info.cbSize = Marshal.SizeOf(info); SendMessageCb(combo.Handle, 0x164, IntPtr.Zero, out info); return info; } [DllImport("user32.dll", EntryPoint = "SendMessageW", CharSet = CharSet.Unicode)] private static extern IntPtr SendMessageCb(IntPtr hWnd, int msg, IntPtr wp, out COMBOBOXINFO lp); } //[StructLayout(LayoutKind.Sequential)] //public struct RECT { // public int Left; // public int Top; // public int Right; // public int Bottom; //} }