Dialogs: allow preventing processing of standard buttons

Add an actionChosen() signal to DefaultDialogWrapper, allowing the
developer to stop further processing of the event by setting the
"accepted" field to false. This is especially useful when some
validation on the dialog contents need to take place before the dialog
can be accepted.

[ChangeLog][Dialogs] Add a signal to the Dialog class to allow the
client to intercept the button presses and optionally prevent further
processing of the event. This allows performing some validation on the
fields before dismissing the dialog.

Task-number: QTBUG-69095
Change-Id: I19bca0bd9fcbafc72d337a5870776a96634ba748
Reviewed-by: Mitch Curtis <mitch.curtis@qt.io>

2 files changed, 76 insertions, 15 deletions

diff --git a/src/dialogs/DefaultDialogWrapper.qml b/src/dialogs/DefaultDialogWrapper.qml
index b446c3162..3ca030c4c 100644
--- a/src/dialogs/DefaultDialogWrapper.qml
+++ b/src/dialogs/DefaultDialogWrapper.qml
@@ -47,6 +47,9 @@ import "qml"
 AbstractDialog {
     id: root
     default property alias data: defaultContentItem.data
+
+    signal actionChosen(var action)
+
     onVisibilityChanged: if (visible && contentItem) contentItem.forceActiveFocus()
 
     Rectangle {
@@ -63,19 +66,7 @@ AbstractDialog {
             defaultContentItem.implicitWidth, buttonsRowImplicitWidth, Screen.pixelDensity * 50) + outerSpacing * 2)
         color: palette.window
         Keys.onPressed: {
-            event.accepted = true
-            switch (event.key) {
-                case Qt.Key_Escape:
-                case Qt.Key_Back:
-                    reject()
-                    break
-                case Qt.Key_Enter:
-                case Qt.Key_Return:
-                    accept()
-                    break
-                default:
-                    event.accepted = false
-            }
+            event.accepted = handleKey(event.key)
         }
 
         SystemPalette { id: palette }
@@ -109,7 +100,7 @@ AbstractDialog {
                 id: buttonsLeftRepeater
                 Button {
                     text: (buttonsLeftRepeater.model && buttonsLeftRepeater.model[index] ? buttonsLeftRepeater.model[index].text : index)
-                    onClicked: root.click(buttonsLeftRepeater.model[index].standardButton)
+                    onClicked: content.handleButton(buttonsLeftRepeater.model[index].standardButton)
                 }
             }
 
@@ -136,9 +127,54 @@ AbstractDialog {
                 // TODO maybe: insert gaps if the button requires it (destructive buttons only)
                 Button {
                     text: (buttonsRightRepeater.model && buttonsRightRepeater.model[index] ? buttonsRightRepeater.model[index].text : index)
-                    onClicked: root.click(buttonsRightRepeater.model[index].standardButton)
+                    onClicked: content.handleButton(buttonsRightRepeater.model[index].standardButton)
+                }
+            }
+        }
+
+        function handleButton(button) {
+            var action = {
+                "button": button,
+                "key": 0,
+                "accepted": true,
+            }
+            root.actionChosen(action)
+            if (action.accepted) {
+                click(button)
+            }
+        }
+
+        function handleKey(key) {
+            var button = 0
+            switch (key) {
+                case Qt.Key_Escape:
+                case Qt.Key_Back:
+                    button = StandardButton.Cancel
+                    break
+                case Qt.Key_Enter:
+                case Qt.Key_Return:
+                    button = StandardButton.Ok
+                    break
+                default:
+                    return false
+            }
+            var action = {
+                "button": button,
+                "key": key,
+                "accepted": true,
+            }
+            root.actionChosen(action)
+            if (action.accepted) {
+                switch (button) {
+                    case StandardButton.Cancel:
+                        reject()
+                        break
+                    case StandardButton.Ok:
+                        accept()
+                        break
                 }
             }
+            return true
         }
     }
     function setupButtons() {
diff --git a/src/dialogs/qquickdialog.cpp b/src/dialogs/qquickdialog.cpp
index 485eeb437..ef6a9a1f2 100644
--- a/src/dialogs/qquickdialog.cpp
+++ b/src/dialogs/qquickdialog.cpp
@@ -154,6 +154,31 @@ QT_BEGIN_NAMESPACE
 */
 
 /*!
+    \qmlsignal Dialog::actionChosen(var action)
+
+    This signal is emitted when the user has pressed any button or a key
+    associated with some role (such as the Enter or Escape keys). The \a
+    action parameter carries information about the event:
+
+    \list
+    \li StandardButton button - The role of the button which was pressed. If a
+        key was pressed instead, this will be \c StandardButton.Ok if accepted
+        and \c StandardButton.Cancel if rejected.
+    \li Qt.Key key - The key which was pressed, or \c 0 if none
+    \li bool accepted - Set this to \c false to stop the event from triggering
+        its predefined action
+    \endlist
+
+    By handling this signal and setting the \c action.accepted field to \c
+    false, it's possible to implement some validation on the dialog contents
+    before accepting it, for example.
+
+    The corresponding handler is \c onActionChosen.
+
+    \since QtQuick.Controls 1.8
+*/
+
+/*!
     \qmlproperty bool Dialog::visible
 
     This property holds whether the dialog is visible. By default this is