Method Combo

src/imgui/imgui_widgets.cpp:2126–2171

Old API, prefer using BeginCombo() nowadays if you can.

// Old API, prefer using BeginCombo() nowadays if you can.
bool ImGui::Combo(const char* label, int* current_item, const char* (*getter)(void* user_data, int idx), void* user_data, int items_count, int popup_max_height_in_items)
{
    ImGuiContext& g = *GImGui;

    // Call the getter to obtain the preview string which is a parameter to BeginCombo()
    const char* preview_value = NULL;
    if (*current_item >= 0 && *current_item < items_count)
        preview_value = getter(user_data, *current_item);

    // The old Combo() API exposed "popup_max_height_in_items". The new more general BeginCombo() API doesn't have/need it, but we emulate it here.
    if (popup_max_height_in_items != -1 && !(g.NextWindowData.HasFlags & ImGuiNextWindowDataFlags_HasSizeConstraint))
        SetNextWindowSizeConstraints(ImVec2(0, 0), ImVec2(FLT_MAX, CalcMaxPopupHeightFromItemCount(popup_max_height_in_items)));

    if (!BeginCombo(label, preview_value, ImGuiComboFlags_None))
        return false;

    // Display items
    bool value_changed = false;
    ImGuiListClipper clipper;
    clipper.Begin(items_count);
    clipper.IncludeItemByIndex(*current_item);
    while (clipper.Step())
        for (int i = clipper.DisplayStart; i < clipper.DisplayEnd; i++)
        {
            const char* item_text = getter(user_data, i);
            if (item_text == NULL)
                item_text = "*Unknown item*";

            PushID(i);
            const bool item_selected = (i == *current_item);
            if (Selectable(item_text, item_selected) && *current_item != i)
            {
                value_changed = true;
                *current_item = i;
            }
            if (item_selected)
                SetItemDefaultFocus();
            PopID();
        }

    EndCombo();
    if (value_changed)
        MarkItemEdited(g.LastItemData.ID);

    return value_changed;
}

// Combo box helper allowing to pass an array of strings.
bool ImGui::Combo(const char* label, int* current_item, const char* const items[], int items_count, int height_in_items)