iOS: delay callbacks to UITextInput to avoid recursion

If the application calls "reset" or "commit" on the input
method (or forces active focus on some other item) from a text
changed or key pressed handler, iOS will sometimes throw
an exception. It does so because we try to change the state
of UITextInput (by calling textDidChange) while processing a
callback from the same place (insertText).

Optimally this should not happen since we would normally
post such events to Qt, not send them directly. But with
text input we cannot do this since UITextInput expects us
to update immediately upon receiving text input callbacks.
If not, word completion and spell checking will stop working.

This change will guard against recursive callbacks by delaying
callbacks to UITextInput when text/selection/first responder
changes.

Change-Id: I099f30adf1c5aba241fc833a45b423016f4ed8d0
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@digia.com>

src/plugins/platforms/ios/qiosinputcontext.mm

@@ -54,7 +54,6 @@
     QIOSInputContext *m_context;
     BOOL m_keyboardVisible;
     BOOL m_keyboardVisibleAndDocked;
-    BOOL m_ignoreKeyboardChanges;
     BOOL m_touchPressWhileKeyboardVisible;
     BOOL m_keyboardHiddenByGesture;
     QRectF m_keyboardRect;
@@ -74,7 +73,6 @@
         m_context = context;
         m_keyboardVisible = NO;
         m_keyboardVisibleAndDocked = NO;
-        m_ignoreKeyboardChanges = NO;
         m_touchPressWhileKeyboardVisible = NO;
         m_keyboardHiddenByGesture = NO;
         m_duration = 0;
@@ -160,7 +158,7 @@
 
 - (void) keyboardWillShow:(NSNotification *)notification
 {
-    if (m_ignoreKeyboardChanges)
+    if ([QUIView inUpdateKeyboardLayout])
         return;
     // Note that UIKeyboardWillShowNotification is only sendt when the keyboard is docked.
     m_keyboardVisibleAndDocked = YES;
@@ -175,7 +173,7 @@
 
 - (void) keyboardWillHide:(NSNotification *)notification
 {
-    if (m_ignoreKeyboardChanges)
+    if ([QUIView inUpdateKeyboardLayout])
         return;
     // Note that UIKeyboardWillHideNotification is also sendt when the keyboard is undocked.
     m_keyboardVisibleAndDocked = NO;
@@ -407,11 +405,7 @@ void QIOSInputContext::update(Qt::InputMethodQueries query)
 
 void QIOSInputContext::reset()
 {
-    // Since the call to reset will cause a 'keyboardWillHide'
-    // notification to be sendt, we block keyboard nofifications to avoid artifacts:
-    m_keyboardListener->m_ignoreKeyboardChanges = true;
     [m_focusView reset];
-    m_keyboardListener->m_ignoreKeyboardChanges = false;
 }
 
 void QIOSInputContext::commit()

src/plugins/platforms/ios/quiview.h

@@ -75,4 +75,5 @@
 - (void)updateInputMethodWithQuery:(Qt::InputMethodQueries)query;
 - (void)reset;
 - (void)commit;
++ (bool)inUpdateKeyboardLayout;
 @end

src/plugins/platforms/ios/quiview_textinput.mm

@@ -45,9 +45,12 @@ class StaticVariables
 {
 public:
     QInputMethodQueryEvent inputMethodQueryEvent;
+    bool inUpdateKeyboardLayout;
     QTextCharFormat markedTextFormat;
 
-    StaticVariables() : inputMethodQueryEvent(Qt::ImQueryInput)
+    StaticVariables()
+        : inputMethodQueryEvent(Qt::ImQueryInput)
+        , inUpdateKeyboardLayout(false)
     {
         // There seems to be no way to query how the preedit text
         // should be drawn. So we need to hard-code the color.
@@ -152,6 +155,47 @@ Q_GLOBAL_STATIC(StaticVariables, staticVariables);
     return [super resignFirstResponder];
 }
 
++ (bool)inUpdateKeyboardLayout
+{
+    return staticVariables()->inUpdateKeyboardLayout;
+}
+
+- (void)updateKeyboardLayout
+{
+    if (![self isFirstResponder])
+        return;
+
+    // There seems to be no API to inform that the keyboard layout needs to update.
+    // As a work-around, we quickly resign first responder just to reassign it again.
+    QScopedValueRollback<bool> rollback(staticVariables()->inUpdateKeyboardLayout);
+    staticVariables()->inUpdateKeyboardLayout = true;
+    [super resignFirstResponder];
+    [self updateTextInputTraits];
+    [super becomeFirstResponder];
+}
+
+- (void)updateUITextInputDelegate:(NSNumber *)intQuery
+{
+    // As documented, we should not report textWillChange/textDidChange unless the text
+    // was changed externally. That will cause spell checking etc to fail. But we don't
+    // really know if the text/selection was changed by UITextInput or Qt/app when getting
+    // update calls from Qt. We therefore use a less ideal approach where we always assume
+    // that UITextView caused the change if we're currently processing an event sendt from it.
+    if (m_inSendEventToFocusObject)
+        return;
+
+    Qt::InputMethodQueries query = Qt::InputMethodQueries([intQuery intValue]);
+    if (query & (Qt::ImCursorPosition | Qt::ImAnchorPosition)) {
+        [self.inputDelegate selectionWillChange:id<UITextInput>(self)];
+        [self.inputDelegate selectionDidChange:id<UITextInput>(self)];
+    }
+
+    if (query & Qt::ImSurroundingText) {
+        [self.inputDelegate textWillChange:id<UITextInput>(self)];
+        [self.inputDelegate textDidChange:id<UITextInput>(self)];
+    }
+}
+
 - (void)updateInputMethodWithQuery:(Qt::InputMethodQueries)query
 {
     Q_UNUSED(query);
@@ -160,26 +204,13 @@ Q_GLOBAL_STATIC(StaticVariables, staticVariables);
     if (!focusObject)
         return;
 
-    if (!m_inSendEventToFocusObject) {
-        if (query & (Qt::ImCursorPosition | Qt::ImAnchorPosition))
-            [self.inputDelegate selectionWillChange:id<UITextInput>(self)];
-        if (query & Qt::ImSurroundingText)
-            [self.inputDelegate textWillChange:id<UITextInput>(self)];
-    }
-
     // Note that we ignore \a query, and instead update using Qt::ImQueryInput. This enables us to just
     // store the event without copying out the result from the event each time. Besides, we seem to be
     // called with Qt::ImQueryInput when only changing selection, and always if typing text. So there would
     // not be any performance gain by only updating \a query.
     staticVariables()->inputMethodQueryEvent = QInputMethodQueryEvent(Qt::ImQueryInput);
     QCoreApplication::sendEvent(focusObject, &staticVariables()->inputMethodQueryEvent);
-
-    if (!m_inSendEventToFocusObject) {
-        if (query & (Qt::ImCursorPosition | Qt::ImAnchorPosition))
-            [self.inputDelegate selectionDidChange:id<UITextInput>(self)];
-        if (query & Qt::ImSurroundingText)
-            [self.inputDelegate textDidChange:id<UITextInput>(self)];
-    }
+    [self updateUITextInputDelegate:[NSNumber numberWithInt:int(query)]];
 }
 
 - (void)sendEventToFocusObject:(QEvent &)e
@@ -189,35 +220,31 @@ Q_GLOBAL_STATIC(StaticVariables, staticVariables);
         return;
 
     // While sending the event, we will receive back updateInputMethodWithQuery calls.
-    // To not confuse iOS, we cannot not call textWillChange/textDidChange at that
-    // point since it will cause spell checking etc to fail. So we use a guard.
+    // Note that it would be more correct to post the event instead, but UITextInput expects
+    // callbacks to take effect immediately (it will query us for information after a callback).
+    QScopedValueRollback<BOOL> rollback(m_inSendEventToFocusObject);
     m_inSendEventToFocusObject = YES;
     QCoreApplication::sendEvent(focusObject, &e);
-    m_inSendEventToFocusObject = NO;
 }
 
 - (void)reset
 {
-    [self.inputDelegate textWillChange:id<UITextInput>(self)];
     [self setMarkedText:@"" selectedRange:NSMakeRange(0, 0)];
     [self updateInputMethodWithQuery:Qt::ImQueryInput];
-
-    if ([self isFirstResponder]) {
-        // There seem to be no way to inform that the keyboard needs to update (since
-        // text input traits might have changed). As a work-around, we quickly resign
-        // first responder status just to reassign it again:
-        [super resignFirstResponder];
-        [self updateTextInputTraits];
-        [super becomeFirstResponder];
-    }
-    [self.inputDelegate textDidChange:id<UITextInput>(self)];
+    // Guard agains recursive callbacks by posting calls to UITextInput
+    [self performSelectorOnMainThread:@selector(updateKeyboardLayout) withObject:nil waitUntilDone:NO];
+    [self performSelectorOnMainThread:@selector(updateUITextInputDelegate:)
+      withObject:[NSNumber numberWithInt:int(Qt::ImQueryInput)]
+      waitUntilDone:NO];
 }
 
 - (void)commit
 {
-    [self.inputDelegate textWillChange:id<UITextInput>(self)];
     [self unmarkText];
-    [self.inputDelegate textDidChange:id<UITextInput>(self)];
+    // Guard agains recursive callbacks by posting calls to UITextInput
+    [self performSelectorOnMainThread:@selector(updateUITextInputDelegate:)
+      withObject:[NSNumber numberWithInt:int(Qt::ImSurroundingText)]
+      waitUntilDone:NO];
 }
 
 - (QVariant)imValue:(Qt::InputMethodQuery)query