2 files changed, 25 insertions, 8 deletions
diff --git a/src/gui/widgets/qabstractbutton.cpp b/src/gui/widgets/qabstractbutton.cpp
index f2a9ceb..1900016 100644
--- a/src/gui/widgets/qabstractbutton.cpp
+++ b/src/gui/widgets/qabstractbutton.cpp
@@ -215,11 +215,8 @@ void QButtonGroup::setExclusive(bool exclusive)
     d->exclusive = exclusive;
 }
 
-/*!
-    Adds the given \a button to the end of the group's internal list of buttons.
 
-    \sa removeButton()
-*/
+// TODO: Qt 5: Merge with addButton(QAbstractButton *button, int id)
 void QButtonGroup::addButton(QAbstractButton *button)
 {
     addButton(button, -1);
@@ -232,8 +229,18 @@ void QButtonGroup::addButton(QAbstractButton *button, int id)
         previous->removeButton(button);
     button->d_func()->group = this;
     d->buttonList.append(button);
-    if (id != -1)
+    if (id == -1) {
+        QList<int> ids = d->mapping.values();
+        if (ids.isEmpty())
+           d->mapping[button] = -2;
+        else {
+            qSort(ids);
+            d->mapping[button] = ids.first()-1;
+        }
+    } else {
         d->mapping[button] = id;
+    }
+
     if (d->exclusive && button->isChecked())
         button->d_func()->notifyChecked();
 }
diff --git a/src/gui/widgets/qbuttongroup.cpp b/src/gui/widgets/qbuttongroup.cpp
index 06bcf1e..ebfafe3 100644
--- a/src/gui/widgets/qbuttongroup.cpp
+++ b/src/gui/widgets/qbuttongroup.cpp
@@ -176,11 +176,21 @@
 */
 
 /*!
-    \fn void QButtonGroup::addButton(QAbstractButton *button, int id = -1);
+    \fn void QButtonGroup::addButton(QAbstractButton *button);
+
+    Adds the given \a button to the end of the group's internal list of buttons.
+    An \a id will be assigned to the button by this QButtonGroup. Automatically
+    assigned ids are guaranteed to be negative, starting with -2. If you are also
+    assigning your own ids, use positive values to avoid conflicts.
+
+    \sa removeButton() buttons()
+*/
+
+/*!
+    \fn void QButtonGroup::addButton(QAbstractButton *button, int id);
 
     Adds the given \a button to the button group, with the given \a
-    id. If \a id is -1 (the default), an id will be assigned to the
-    button by this QButtonGroup.
+    id. It is recommended to assign only positive ids.
 
     \sa removeButton() buttons()
 */