How to make a ComboBox with fulltext search autocomplete support in C++Builder?

Question

I try to make a ComboBox with full search autocomplete in C++Builder.

I found a solution in Delphi, but when I try to rewrite it in C++ I get some access error:

How to make a combo box with fulltext search autocomplete support?

Here's my code:

My header file:

class PACKAGE TSmartComboBox : public TComboBox
{
private:
    TStringList* FStoredItems;
    bool dofilter;
    int storeditemindex;
    void FilterItems();
    void __fastcall StoredItemsChange(TObject* Sender);
    void CNCommand(TWMCommand AMessage);
protected:
    DYNAMIC void __fastcall KeyPress(System::WideChar &Key);
    DYNAMIC void __fastcall CloseUp(void);
    DYNAMIC void __fastcall Click(void);
public:
    __fastcall TSmartComboBox(TComponent* Owner);
    __fastcall ~TSmartComboBox();
    void InitSmartCombo();

__published:
    void __fastcall SetStoredItems(TStringList* Value);
    __property TStringList* StoredItems =
    {read = FStoredItems, write = SetStoredItems};
};

And cpp file:

static inline void ValidCtrCheck(TSmartComboBox *)
{
    new TSmartComboBox(NULL);
}
//---------------------------------------------------------------------------
__fastcall TSmartComboBox::TSmartComboBox(TComponent* Owner)
    : TComboBox(Owner)
{
    FStoredItems = new TStringList();
    dofilter = false;
}

__fastcall TSmartComboBox::~TSmartComboBox()
{
    delete FStoredItems;
}

void _fastcall TSmartComboBox::SetStoredItems(TStringList* Value)
{
    if(FStoredItems)
    {
        FStoredItems->Assign(Value);
    } else {
        FStoredItems = Value;
    }
}

void __fastcall TSmartComboBox::KeyPress(System::WideChar &Key)
{
    if(dofilter && (Key >= 13 & Key <= 27))
    {
        if(Items->Count != 0 && DroppedDown)
        {
            SendMessage(Handle, CB_SHOWDROPDOWN, 1, 0);
        }
    }
}

void __fastcall TSmartComboBox::CloseUp(void)
{
    AnsiString x;

    if(dofilter)
    {
        if(Items->Count == 1 && ItemIndex == 0)
        {
            Text = Items->operator [](ItemIndex);
        } else if((Text == "" && ItemIndex != -1 && Text != Items->operator [](ItemIndex)) || (Text == "" && ItemIndex == 0))
        {
            storeditemindex = ItemIndex;
            x = Text;
            ItemIndex = Items->IndexOf(Text);
            if(ItemIndex == -1)
            {
                Text = x;
            }
        } else
        {
            storeditemindex = -1;
        }
    }
}

void __fastcall TSmartComboBox::Click(void)
{
    if(dofilter)
    {
        if(storeditemindex != -1)
        {
            ItemIndex = storeditemindex;
        }
        storeditemindex = -1;
    }
}

void TSmartComboBox::InitSmartCombo()
{
    FStoredItems->OnChange = NULL;
    StoredItems->Assign(Items);
    AutoComplete = false;
    FStoredItems->OnChange = StoredItemsChange;
    dofilter = true;
    storeditemindex = -1;
}

void __fastcall TSmartComboBox::StoredItemsChange(TObject* Sender)
{
    if(FStoredItems)
    {
        FilterItems();
    }
}

void TSmartComboBox::FilterItems()
{
    int i;
    TSelection Selection;

    SendMessage(Handle, CB_GETEDITSEL, WPARAM(Selection.StartPos), LPARAM(Selection.EndPos));

    Items->BeginUpdate();

    if (Text != "")
    {
        Items->Clear();

        for (i = 0; i < FStoredItems->Count - 1; i++)
        {
            if(Pos(UpperCase(Text), UpperCase(FStoredItems->Strings[i])) > 0)
            {
                Items->Add(FStoredItems->Strings[i]);
            }
        }
    } else
    {
        Items->Assign(FStoredItems);
    }

    Items->EndUpdate();

    //SendMessage(Handle, CB_SETEDITSEL, 0, MakeLParam(Selection.StartPos, Selection.EndPos));
}

void TSmartComboBox::CNCommand(TWMCommand AMessage)
{
    if(AMessage.NotifyCode == CBN_EDITUPDATE && dofilter)
    {
        FilterItems();
    }
}

//---------------------------------------------------------------------------
namespace Comboboxsmart
{
    void __fastcall PACKAGE Register()
    {
         TComponentClass classes[1] = {__classid(TSmartComboBox)};
         RegisterComponents(L"polpress", classes, 0);
    }
}

"*I get some access error*" - can you be more specific? What does the error actually say? Which line does it happen on exactly? — Remy Lebeau, Sep 30 '21 at 16:39

Remy Lebeau · Answer 1 · 2021-10-07T00:03:29.237

I see a number of issues with your translation:

CNCommand() is not calling the inherited handler. And it is declared wrong anyway, as it needs to take the TWMCommand by reference instead of by value. Also, you are missing a MESSAGE_MAP to even invoke CNCommand() in the first place.
SetStoredItems() should not be trying to take ownership of the passed TStringList* at all. Not that it matters, since FStoredItems should never be NULL to begin with.
In KeyPress(), you are not calling the inherited handler. Also, you need to use && instead of & when testing 2 separate conditions. In C++, && is LOGICAL AND, whereas & is BITWISE AND. However, you are not actually checking the Key parameter in the same manner that the original Delphi code is.
in fact, a lot of your comparisons are doing the opposite of what the original Delphi code does.
In CloseUp(), you are not calling the inherited handler. Also, you should use (Unicode)String instead of AnsiString. Also, use (*Items)[...] or Items->Strings[...] instead of using Items->operator[](...) explicitly.
In Click(), you are not calling the inherited handler.
In FilterItems(), your parameter values for CB_GETEDITSEL are wrong. They need to be passed by pointer, not by value. Also, your for loop is skipping the last string in FStoredItems. Also, you are missing a try..finally block that is in the original Delphi code.
I would suggest changing the StoredItems property to use TStrings* instead of TStringList*. That will make it more flexible for accepting non-TStringList lists. And SetStoredItems() should not be declared __published. For that matter, does it really make sense to expose the StoredItems property to the Object Inspector at design-time? StoredItems is public in the original Delphi code, not __published.

With that said, try this instead:

class PACKAGE TSmartComboBox : public TComboBox
{
    typedef TComboBox inherited;

private:
    TStrings* FStoredItems;
    bool dofilter;
    int storeditemindex;
    void __fastcall FilterItems();
    void __fastcall StoredItemsChange(TObject* Sender);
    void __fastcall SetStoredItems(TStrings* Value);
    void __fastcall CNCommand(TWMCommand& AMessage);
protected:
    DYNAMIC void __fastcall KeyPress(WideChar &Key);
    DYNAMIC void __fastcall CloseUp();
    DYNAMIC void __fastcall Click();
public:
    __fastcall TSmartComboBox(TComponent* Owner);
    __fastcall ~TSmartComboBox();
    void __fastcall InitSmartCombo();

    BEGIN_MESSAGE_MAP
        VCL_MESSAGE_HANDLER(CN_COMMAND, TWMCommand, CNCommand)
    END_MESSAGE_MAP(TComboBox)
    
__published:
    __property TStrings* StoredItems = {read = FStoredItems, write = SetStoredItems};
};

static inline void ValidCtrCheck(TSmartComboBox *)
{
    new TSmartComboBox(NULL);
}
//---------------------------------------------------------------------------
__fastcall TSmartComboBox::TSmartComboBox(TComponent* Owner)
    : TComboBox(Owner)
{
    FStoredItems = new TStringList;
    dofilter = false;
}

__fastcall TSmartComboBox::~TSmartComboBox()
{
    delete FStoredItems;
}

void _fastcall TSmartComboBox::SetStoredItems(TStrings* Value)
{
    FStoredItems->Assign(Value);
}

void __fastcall TSmartComboBox::KeyPress(WideChar &Key)
{
    inherited::KeyPress(Key);
    if (dofilter && (Key != 13 && Key != 27))
    {
        if (Items->Count != 0 && !DroppedDown)
        {
            SendMessage(Handle, CB_SHOWDROPDOWN, 1, 0);
        }
    }
}

void __fastcall TSmartComboBox::CloseUp()
{
    if (dofilter)
    {
        if(Items->Count == 1 && ItemIndex == 0)
        {
            Text = Items->Strings[ItemIndex];
        }
        else if ((Text != _D("") && ItemIndex != -1 && Text != Items->Strings[ItemIndex]) || (Text == _D("") && ItemIndex == 0))
        {
            storeditemindex = ItemIndex;
            String x = Text;
            ItemIndex = Items->IndexOf(Text);
            if(ItemIndex == -1)
            {
                Text = x;
            }
        }
        else
        {
            storeditemindex = -1;
        }
    }
    inherited::CloseUp();
}

void __fastcall TSmartComboBox::Click()
{
    if (dofilter)
    {
        if (storeditemindex != -1)
        {
            ItemIndex = storeditemindex;
            storeditemindex = -1;
        }
    }
    inherited::Click();
}

void __fastcall TSmartComboBox::InitSmartCombo()
{
    static_cast<TStringList*>(FStoredItems)->OnChange = NULL;
    FStoredItems->Assign(Items);
    AutoComplete = false;
    static_cast<TStringList*>(FStoredItems)->OnChange = &StoredItemsChange;
    dofilter = true;
    storeditemindex = -1;
}

void __fastcall TSmartComboBox::StoredItemsChange(TObject* Sender)
{
    FilterItems();
}

void TSmartComboBox::FilterItems()
{
    DWORD StartPos, EndPos;

    SendMessage(Handle, CB_GETEDITSEL, reinterpret_cast<WPARAM>(&StartPos), reinterpret_cast<LPARAM>(&EndPos));

    Items->BeginUpdate();
    try
    {
        if (Text != _D(""))
        {
            Items->Clear();

            for (int i = 0; i < FStoredItems->Count; ++i)
            {
                if (UpperCase(Text).Pos(UpperCase(FStoredItems->Strings[i])) > 0)
                {
                    Items->Add(FStoredItems->Strings[i]);
                }
            }
        }
        else
        {
            Items->Assign(FStoredItems);
        }
    }
    __finally
    {
        Items->EndUpdate();
    }

    SendMessage(Handle, CB_SETEDITSEL, 0, MAKELPARAM(StartPos, EndPos));
}

void TSmartComboBox::CNCommand(TWMCommand AMessage)
{
    TComboBox::Dispatch(&AMessage);
    if (AMessage.NotifyCode == CBN_EDITUPDATE && dofilter)
    {
        FilterItems();
    }
}

//---------------------------------------------------------------------------
namespace Comboboxsmart
{
    void __fastcall PACKAGE Register()
    {
         TComponentClass classes[1] = {__classid(TSmartComboBox)};
         RegisterComponents(L"polpress", classes, 0);
    }
}

You appear to be basing your C++ code on this Delphi code, but you have not incorporated any of the additional fixes provided by this Delphi code. Just saying...

How to make a ComboBox with fulltext search autocomplete support in C++Builder?

1 Answers1