Expose QQuickCheckBox::nextCheckState() to QML

[ChangeLog][Controls][CheckBox] Made it possible to implement
nextCheckState() in QML.

Task-number: QTBUG-63238
Change-Id: I9ca27409efcaf546f557b974563ba598658fe694
Reviewed-by: Mitch Curtis <mitch.curtis@qt.io>

src/quicktemplates2/qquickcheckbox.cpp

@@ -38,6 +38,7 @@
 #include "qquickabstractbutton_p_p.h"
 
 #include <QtGui/qpa/qplatformtheme.h>
+#include <QtQml/qjsvalue.h>
 
 QT_BEGIN_NAMESPACE
 
@@ -107,10 +108,20 @@ public:
     {
     }
 
+    void setNextCheckState(const QJSValue &callback);
+
     bool tristate;
     Qt::CheckState checkState;
+    QJSValue nextCheckState;
 };
 
+void QQuickCheckBoxPrivate::setNextCheckState(const QJSValue &callback)
+{
+    Q_Q(QQuickCheckBox);
+    nextCheckState = callback;
+    emit q->nextCheckStateChanged();
+}
+
 QQuickCheckBox::QQuickCheckBox(QQuickItem *parent)
     : QQuickAbstractButton(*(new QQuickCheckBoxPrivate), parent)
 {
@@ -194,10 +205,45 @@ void QQuickCheckBox::buttonChange(ButtonChange change)
         QQuickAbstractButton::buttonChange(change);
 }
 
+/*!
+    \since QtQuick.Controls 2.4 (Qt 5.11)
+    \qmlproperty function QtQuick.Controls::CheckBox::nextCheckState
+
+    This property holds a callback function that is called to determine
+    the next check state whenever the checkbox is interactively toggled
+    by the user via touch, mouse, or keyboard.
+
+    By default, a normal checkbox cycles between \c Qt.Unchecked and
+    \c Qt.Checked states, and a tri-state checkbox cycles between
+    \c Qt.Unchecked, \c Qt.PartiallyChecked, and \c Qt.Checked states.
+
+    The \c nextCheckState callback function can override the default behavior.
+    The following example implements a tri-state checkbox that can present
+    a partially checked state depending on external conditions, but never
+    cycles to the partially checked state when interactively toggled by
+    the user.
+
+    \code
+    CheckBox {
+        tristate: true
+        checkState: allChildrenChecked ? Qt.Checked :
+                       anyChildChecked ? Qt.PartiallyChecked : Qt.Unchecked
+
+        nextCheckState: function() {
+            if (checkState === Qt.Checked)
+                return Qt.Unchecked
+            else
+                return Qt.Checked
+        }
+    }
+    \endcode
+*/
 void QQuickCheckBox::nextCheckState()
 {
     Q_D(QQuickCheckBox);
-    if (d->tristate)
+    if (d->nextCheckState.isCallable())
+        setCheckState(static_cast<Qt::CheckState>(d->nextCheckState.call().toInt()));
+    else if (d->tristate)
         setCheckState(static_cast<Qt::CheckState>((d->checkState + 1) % 3));
     else
         QQuickAbstractButton::nextCheckState();
@@ -211,3 +257,5 @@ QAccessible::Role QQuickCheckBox::accessibleRole() const
 #endif
 
 QT_END_NAMESPACE
+
+#include "moc_qquickcheckbox_p.cpp"

src/quicktemplates2/qquickcheckbox_p.h

@@ -59,6 +59,7 @@ class Q_QUICKTEMPLATES2_PRIVATE_EXPORT QQuickCheckBox : public QQuickAbstractBut
     Q_OBJECT
     Q_PROPERTY(bool tristate READ isTristate WRITE setTristate NOTIFY tristateChanged FINAL)
     Q_PROPERTY(Qt::CheckState checkState READ checkState WRITE setCheckState NOTIFY checkStateChanged FINAL)
+    Q_PRIVATE_PROPERTY(QQuickCheckBox::d_func(), QJSValue nextCheckState MEMBER nextCheckState WRITE setNextCheckState NOTIFY nextCheckStateChanged FINAL REVISION 4)
 
 public:
     explicit QQuickCheckBox(QQuickItem *parent = nullptr);
@@ -72,6 +73,7 @@ public:
 Q_SIGNALS:
     void tristateChanged();
     void checkStateChanged();
+    Q_REVISION(4) void nextCheckStateChanged();
 
 protected:
     QFont defaultFont() const override;

tests/auto/controls/data/tst_checkbox.qml

@@ -494,4 +494,51 @@ TestCase {
         verify(control)
         compare(control.baselineOffset, control.contentItem.y + control.contentItem.baselineOffset)
     }
+
+    Component {
+        id: nextCheckStateBox
+        CheckBox {
+            tristate: true
+            nextCheckState: function() {
+                if (checkState === Qt.Checked)
+                    return Qt.Unchecked
+                else
+                    return Qt.Checked
+            }
+        }
+    }
+
+    function test_nextCheckState_data() {
+        return [
+            { tag: "unchecked", checkState: Qt.Unchecked, expectedState: Qt.Checked },
+            { tag: "partially-checked", checkState: Qt.PartiallyChecked, expectedState: Qt.Checked },
+            { tag: "checked", checkState: Qt.Checked, expectedState: Qt.Unchecked }
+        ]
+    }
+
+    function test_nextCheckState(data) {
+        var control = createTemporaryObject(nextCheckStateBox, testCase)
+        verify(control)
+
+        // mouse
+        control.checkState = data.checkState
+        compare(control.checkState, data.checkState)
+        mouseClick(control)
+        compare(control.checkState, data.expectedState)
+
+        // touch
+        control.checkState = data.checkState
+        compare(control.checkState, data.checkState)
+        var touch = touchEvent(control)
+        touch.press(0, control).commit().release(0, control).commit()
+        compare(control.checkState, data.expectedState)
+
+        // keyboard
+        control.forceActiveFocus()
+        tryCompare(control, "activeFocus", true)
+        control.checkState = data.checkState
+        compare(control.checkState, data.checkState)
+        keyClick(Qt.Key_Space)
+        compare(control.checkState, data.expectedState)
+    }
 }