Add gtk_widget_remove_css_classes_by_prefix() helper

src/gtkhelper.c

@@ -24,3 +24,16 @@ void gtk_grid_set_spacing(GtkGrid *grid, int spacing) {
   gtk_grid_set_row_spacing(grid, spacing);
   gtk_grid_set_column_spacing(grid, spacing);
 }
+
+void gtk_widget_remove_css_classes_by_prefix(
+  GtkWidget  *w,
+  const char *prefix
+) {
+  char **classes = gtk_widget_get_css_classes(w);
+
+  for (char **i = classes; *i != NULL; i++)
+    if (strncmp(*i, prefix, strlen(prefix)) == 0)
+      gtk_widget_remove_css_class(w, *i);
+
+  g_strfreev(classes);
+}

src/gtkhelper.h

@@ -9,3 +9,4 @@ void gtk_widget_set_margin(GtkWidget *w, int margin);
 void gtk_widget_set_expand(GtkWidget *w, gboolean expand);
 void gtk_widget_set_align(GtkWidget *w, GtkAlign x, GtkAlign y);
 void gtk_grid_set_spacing(GtkGrid *grid, int spacing);
+void gtk_widget_remove_css_classes_by_prefix(GtkWidget *w, const char *prefix);

src/widget-drop-down.c

@@ -3,6 +3,7 @@
 
 #include <ctype.h>
 
+#include "gtkhelper.h"
 #include "widget-drop-down.h"
 
 struct drop_down {
@@ -14,16 +15,6 @@ struct drop_down {
   int                 fixed_text;
 };
 
-static void remove_selected_classes(GtkWidget *widget) {
-  char **classes = gtk_widget_get_css_classes(widget);
-
-  for (char **i = classes; *i != NULL; i++)
-    if (strncmp(*i, "selected-", 9) == 0)
-      gtk_widget_remove_css_class(widget, *i);
-
-  g_strfreev(classes);
-}
-
 static void sanitise_class_name(char *s) {
   char *dst = s;
 
@@ -120,7 +111,7 @@ static void drop_down_updated(
   int value = alsa_get_elem_value(elem);
   gtk_single_selection_set_selected(data->selection, value);
 
-  remove_selected_classes(data->button);
+  gtk_widget_remove_css_classes_by_prefix(data->button, "selected-");
   add_class(data->button, alsa_get_item_name(elem, value));
 
   if (data->fixed_text)