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How to make a combo box with fulltext search autocomplete support?
I would like a user to be able to type in the second or third word from a TComboBoxitem and for that item to appear in the AutoSuggest dropdown options
For example, a combo box contains the items:
- Mr John Brown
- Mrs Amanda Brown
- Mr Brian Jones
- Mrs Samantha Smith
When the user types "Br" the dropdown displays:
- Mr John Brown
- Mrs Amanda Brown
- Mr Brian Jones
and when the user types "Jo" the dropdown displays:
- Mr John Brown
- Mr Brian Jones
The problem is that the AutoSuggest functionality only includes items in the dropdown list that begin with what the user has input and so in the examples above nothing will appear in the dropdown.
Is it possible to use the IAutoComplete interface and/or other related interfaces to get around this issue?
The following example uses the interposed class of the TComboBox component. The main difference from the original class is that the items are stored in the separate StoredItems property instead of
the Items as usually (used because of simplicity).
The StoredItems are being watched by the OnChange event and whenever you change them (for instance by adding or deleting from this string list), the current filter will reflect it even when the combo
list is dropped down.
The main point here is to catch the WM_COMMAND message notification CBN_EDITUPDATE which is being sent whenever the combo edit text is changed but not rendered yet. When it arrives, you just search through the StoredItems list for what you have typed in your combo edit and fill the Items property with matches.
For text searching is used the ContainsText so the search is case insensitive. Forgot to mention,
the AutoComplete feature has to be turned off because it has its own, unwelcomed, logic for this purpose.
unit Unit1;interfaceuses Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms, Dialogs, StdCtrls, StrUtils, ExtCtrls;type TComboBox = class(StdCtrls.TComboBox) private FStoredItems: TStringList; procedure FilterItems; procedure StoredItemsChange(Sender: TObject); procedure SetStoredItems(const Value: TStringList); procedure CNCommand(var AMessage: TWMCommand); message CN_COMMAND; public constructor Create(AOwner: TComponent); override; destructor Destroy; override; property StoredItems: TStringList read FStoredItems write SetStoredItems; end;type TForm1 = class(TForm) ComboBox1: TComboBox; procedure FormCreate(Sender: TObject); private { Private declarations } public { Public declarations } end;var Form1: TForm1;implementation{$R *.dfm}constructor TComboBox.Create(AOwner: TComponent);begin inherited; AutoComplete := False; FStoredItems := TStringList.Create; FStoredItems.OnChange := StoredItemsChange;end;destructor TComboBox.Destroy;begin FStoredItems.Free; inherited;end;procedure TComboBox.CNCommand(var AMessage: TWMCommand);begin // we have to process everything from our ancestor inherited; // if we received the CBN_EDITUPDATE notification if AMessage.NotifyCode = CBN_EDITUPDATE then // fill the items with the matches FilterItems;end;procedure TComboBox.FilterItems;var I: Integer; Selection: TSelection;begin // store the current combo edit selection SendMessage(Handle, CB_GETEDITSEL, WPARAM(@Selection.StartPos), LPARAM(@Selection.EndPos)); // begin with the items update Items.BeginUpdate; try // if the combo edit is not empty, then clear the items // and search through the FStoredItems if Text <> ‘‘ then begin // clear all items Items.Clear; // iterate through all of them for I := 0 to FStoredItems.Count - 1 do // check if the current one contains the text in edit if ContainsText(FStoredItems[I], Text) then // and if so, then add it to the items Items.Add(FStoredItems[I]); end // else the combo edit is empty else // so then we‘ll use all what we have in the FStoredItems Items.Assign(FStoredItems) finally // finish the items update Items.EndUpdate; end; // and restore the last combo edit selection SendMessage(Handle, CB_SETEDITSEL, 0, MakeLParam(Selection.StartPos, Selection.EndPos));end;procedure TComboBox.StoredItemsChange(Sender: TObject);begin if Assigned(FStoredItems) then FilterItems;end;procedure TComboBox.SetStoredItems(const Value: TStringList);begin if Assigned(FStoredItems) then FStoredItems.Assign(Value) else FStoredItems := Value;end;procedure TForm1.FormCreate(Sender: TObject);var ComboBox: TComboBox;begin // here‘s one combo created dynamically ComboBox := TComboBox.Create(Self); ComboBox.Parent := Self; ComboBox.Left := 10; ComboBox.Top := 10; ComboBox.Text := ‘Br‘; // here‘s how to fill the StoredItems ComboBox.StoredItems.BeginUpdate; try ComboBox.StoredItems.Add(‘Mr John Brown‘); ComboBox.StoredItems.Add(‘Mrs Amanda Brown‘); ComboBox.StoredItems.Add(‘Mr Brian Jones‘); ComboBox.StoredItems.Add(‘Mrs Samantha Smith‘); finally ComboBox.StoredItems.EndUpdate; end; // and here‘s how to assign the Items of the combo box from the form // to the StoredItems; note that if you‘ll use this, you have to do // it before you type something into the combo‘s edit, because typing // may filter the Items, so they would get modified ComboBox1.StoredItems.Assign(ComboBox1.Items);end; end.
Thanks for the heart! With a little reworking, I think that is quite right.
unit Unit1;interfaceuses Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms, Dialogs, StdCtrls, StrUtils, ExtCtrls;type TComboBox = class(StdCtrls.TComboBox) private FStoredItems: TStringList; procedure FilterItems; procedure StoredItemsChange(Sender: TObject); procedure SetStoredItems(const Value: TStringList); procedure CNCommand(var AMessage: TWMCommand); message CN_COMMAND; protected public constructor Create(AOwner: TComponent); override; destructor Destroy; override; property StoredItems: TStringList read FStoredItems write SetStoredItems; end;type TForm1 = class(TForm) procedure FormCreate(Sender: TObject); private public end;var Form1: TForm1;implementation{$R *.dfm}{}constructor TComboBox.Create(AOwner: TComponent); begin inherited; AutoComplete := False; FStoredItems := TStringList.Create; FStoredItems.OnChange := StoredItemsChange; end;{}destructor TComboBox.Destroy; begin FStoredItems.Free; inherited; end;{}procedure TComboBox.CNCommand(var AMessage: TWMCommand); begin // we have to process everything from our ancestor inherited; // if we received the CBN_EDITUPDATE notification if AMessage.NotifyCode = CBN_EDITUPDATE then begin // fill the items with the matches FilterItems; end; end;{}procedure TComboBox.FilterItems; type TSelection = record StartPos, EndPos: Integer; end; var I: Integer; Selection: TSelection; xText: string; begin // store the current combo edit selection SendMessage(Handle, CB_GETEDITSEL, WPARAM(@Selection.StartPos), LPARAM(@Selection.EndPos)); // begin with the items update Items.BeginUpdate; try // if the combo edit is not empty, then clear the items // and search through the FStoredItems if Text <> ‘‘ then begin // clear all items Items.Clear; // iterate through all of them for I := 0 to FStoredItems.Count - 1 do begin // check if the current one contains the text in edit // if ContainsText(FStoredItems[I], Text) then if Pos( Text, FStoredItems[I])>0 then begin // and if so, then add it to the items Items.Add(FStoredItems[I]); end; end; end else begin // else the combo edit is empty // so then we‘ll use all what we have in the FStoredItems Items.Assign(FStoredItems) end; finally // finish the items update Items.EndUpdate; end; // and restore the last combo edit selection xText := Text; SendMessage(Handle, CB_SHOWDROPDOWN, Integer(True), 0); if (Items<>nil) and (Items.Count>0) then begin ItemIndex := 0; end else begin ItemIndex := -1; end; Text := xText; SendMessage(Handle, CB_SETEDITSEL, 0, MakeLParam(Selection.StartPos, Selection.EndPos)); end;{}procedure TComboBox.StoredItemsChange(Sender: TObject); begin if Assigned(FStoredItems) then FilterItems; end;{}procedure TComboBox.SetStoredItems(const Value: TStringList); begin if Assigned(FStoredItems) then FStoredItems.Assign(Value) else FStoredItems := Value; end;//====================================================================={}procedure TForm1.FormCreate(Sender: TObject); var ComboBox: TComboBox; xList:TStringList; begin // here‘s one combo created dynamically ComboBox := TComboBox.Create(Self); ComboBox.Parent := Self; ComboBox.Left := 8; ComboBox.Top := 8; ComboBox.Width := Width-16;// ComboBox.Style := csDropDownList; // here‘s how to fill the StoredItems ComboBox.StoredItems.BeginUpdate; try xList:=TStringList.Create; xList.LoadFromFile(‘list.txt‘); ComboBox.StoredItems.Assign( xList); finally ComboBox.StoredItems.EndUpdate; end; ComboBox.DropDownCount := 24; // and here‘s how to assign the Items of the combo box from the form // to the StoredItems; note that if you‘ll use this, you have to do // it before you type something into the combo‘s edit, because typing // may filter the Items, so they would get modified ComboBox.StoredItems.Assign(ComboBox.Items); end;end.
How to make a combo box with fulltext search autocomplete support?
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