Combobox too slow on Linux with too many entries - alternatives?

[tmssngr]

If one sets a combobox several hundred entries or more, the whole UI freezes for a long time trying to show it. What alternative do you suggest to use instead - a text field to filter and a list/table to show the found entries?

[merks]

Is that a problem for org.eclipse.swt.widgets.Combo and org.eclipse.swt.custom.CCombo?

[tmssngr]

It is about Combo. Hence I don't know whether this is a GTK or SWT problem.

[vogella]

Snippet147 starts super fast, even if I add hundreds of entries to the Combo.

combo.setLayoutData(new GridData(GridData.FILL_HORIZONTAL));
for (int i = 0; i < 500; i++) {
combo.add("Item " + i);
}

[HeikoKlare]

I can confirm this (for Windows). I've added 50k entries and it's still super fast.

[laeubi]

I can confirm this (for Windows)

Windows has other controls that become slow:

• [win] Scale with large maximum freeze UI #1325

In any case one might question that a combo with that many items is really the right UI anyways, what is "the best" depends of course on the use-case.

[tmssngr]

Please try that again with 5,000 or 10,000 items. On my machine (Linux Mint Debian Edition) launching takes much longer (78ms for 500, 6.8s for 5,000 items, 37s for 10,000 items). When clicking the Down-button of the combobox with 5,000 items the first time, it took on my machine 18s until the popup occurred.

[tmssngr]

@laeubi What alternative do you suggest? In our Git client we want to use it to let the user select branches or tags.

[laeubi]

You can take a look how EGit is doing it when switching branches (spoiler: it only shows a limited set of recently used branches in popups/menus and have a dialog with search capability if you do not find it in the list).

Also Nebula TableCombo Widget is quite neat, you can simulate something similar with an editable Combo if you require native L&F when you use the currently entered text as a filter.

[tmssngr]

This is a GTK problem:

• create combo-test.c:

#include <gtk/gtk.h>

#define editable true

int main(int argc, char *argv[]) {
    gtk_init(&argc, &argv);

    GtkWidget *window = gtk_window_new(GTK_WINDOW_TOPLEVEL);
    gtk_window_set_title(GTK_WINDOW(window), "Combo Test");
    gtk_window_set_default_size(GTK_WINDOW(window), 200, 50);

    g_signal_connect(window, "destroy", G_CALLBACK(gtk_main_quit), NULL);

    GtkWidget *combo =
#ifdef editable
        gtk_combo_box_text_new_with_entry();
#elif
        gtk_combo_box_text_new();
#endif
    for (int i = 0; i < 500; i++) {
        char buf[32];
        g_snprintf(buf, sizeof(buf), "Item %d", i);
#ifdef editable
        gtk_combo_box_text_append_text(GTK_COMBO_BOX_TEXT(combo), buf);
#elif
        gtk_combo_box_text_append(GTK_COMBO_BOX_TEXT(combo), NULL, buf);
#endif
    }

    gtk_container_add(GTK_CONTAINER(window), combo);
    gtk_widget_show_all(window);

    gtk_main();
    return 0;
}

• install libgtk-3.0 package
• create following script for compilation:

#!/bin/bash

CFLAGS=$(pkg-config --cflags gtk+-3.0)
LIBS=$(pkg-config --libs gtk+-3.0)
echo CFLAGS: $CFLAGS
echo LIBS: $LIBS
gcc combo-test.c -o combo-test $CFLAGS $LIBS

• run that script and then the application

With 500 items it is acceptable, with 5000 items it also takes several seconds to launch for my machine. The usability of the GTK combobox is also not good because it does not have a scrollbar. So it should not be used for large amount of items.

[vogella]

@tmssngr based on an analysis from Gemini CLI, here is the recommendation:

Recommendations for large datasets:

• Use CCombo: For applications requiring thousands of items in a combo-like widget, the recommended approach in SWT is to use org.eclipse.swt.custom.CCombo. CCombo uses a standard SWT List (which is a
  GtkTreeView) in its popup. GtkTreeView is virtual and handles thousands of items nearly instantaneously because it only creates widgets for the visible rows.
• Batch Updates: Always use setItems(String[]) instead of calling add(String) in a loop, as setItems is now much more efficient and avoids multiple Java array re-allocations.

I also tested with CCombo with 5000 Items and it is really fast.