Introduce QLayout::indexOf(QLayoutItem *)

This was the missing counter-part to indexOf(QWidget *), which is
sometimes implemented in user code.

Not sure why the original code doesn't use a for-loop and instead accesses
an out-of-bounds element, but I'll preserve the behavior of very old working code.

Change-Id: I7d7fa56b56a4626789774c15c23fdfef41d723e7
Reviewed-by: David Faure <david.faure@kdab.com>
Reviewed-by: Jan Arve Sæther <jan-arve.saether@qt.io>

3 files changed, 41 insertions, 0 deletions

diff --git a/src/widgets/kernel/qlayout.cpp b/src/widgets/kernel/qlayout.cpp
index f3db4f4e2d..64acd8d229 100644
--- a/src/widgets/kernel/qlayout.cpp
+++ b/src/widgets/kernel/qlayout.cpp
@@ -1244,6 +1244,26 @@ int QLayout::indexOf(QWidget *widget) const
 }
 
 /*!
+    \since 5.12
+    Searches for layout item \a layoutItem in this layout (not including child
+    layouts).
+
+    Returns the index of \a layoutItem, or -1 if \a layoutItem is not found.
+*/
+int QLayout::indexOf(QLayoutItem *layoutItem) const
+{
+    int i = 0;
+    QLayoutItem *item = itemAt(i);
+    while (item) {
+        if (item == layoutItem)
+            return i;
+        ++i;
+        item = itemAt(i);
+    }
+    return -1;
+}
+
+/*!
     \enum QLayout::SizeConstraint
 
     The possible values are:
diff --git a/src/widgets/kernel/qlayout.h b/src/widgets/kernel/qlayout.h
index bcc33a0811..616f4e7164 100644
--- a/src/widgets/kernel/qlayout.h
+++ b/src/widgets/kernel/qlayout.h
@@ -122,6 +122,7 @@ public:
     virtual QLayoutItem *itemAt(int index) const = 0;
     virtual QLayoutItem *takeAt(int index) = 0;
     virtual int indexOf(QWidget *) const;
+    QT6_VIRTUAL int indexOf(QLayoutItem *) const;
     virtual int count() const = 0;
     bool isEmpty() const override;
     QSizePolicy::ControlTypes controlTypes() const override;
diff --git a/tests/auto/widgets/kernel/qboxlayout/tst_qboxlayout.cpp b/tests/auto/widgets/kernel/qboxlayout/tst_qboxlayout.cpp
index 2f1a305710..3dfb9c35b3 100644
--- a/tests/auto/widgets/kernel/qboxlayout/tst_qboxlayout.cpp
+++ b/tests/auto/widgets/kernel/qboxlayout/tst_qboxlayout.cpp
@@ -56,6 +56,7 @@ private slots:
     void taskQTBUG_40609_addingWidgetToItsOwnLayout();
     void taskQTBUG_40609_addingLayoutToItself();
     void replaceWidget();
+    void indexOf();
 };
 
 class CustomLayoutStyle : public QProxyStyle
@@ -514,5 +515,24 @@ void tst_QBoxLayout::replaceWidget()
     QCOMPARE(boxLayout->indexOf(replaceTo), 1);
 }
 
+void tst_QBoxLayout::indexOf()
+{
+    QWidget w;
+    auto outer = new QVBoxLayout(&w);
+    auto inner = new QHBoxLayout();
+    outer->addLayout(inner);
+    auto widget1 = new QWidget();
+    QWidget widget2;
+    inner->addWidget(widget1);
+
+    QCOMPARE(inner->indexOf(widget1), 0);
+    QCOMPARE(inner->indexOf(&widget2), -1);
+    QCOMPARE(outer->indexOf(widget1), -1);
+    QCOMPARE(outer->indexOf(&widget2), -1);
+    QCOMPARE(outer->indexOf(outer), -1);
+    QCOMPARE(outer->indexOf(inner), 0);
+    QCOMPARE(inner->indexOf(inner->itemAt(0)), 0);
+}
+
 QTEST_MAIN(tst_QBoxLayout)
 #include "tst_qboxlayout.moc"