QIOSTextResponder: recreate responder upon reset

Apple introduced UITextInteraction in iOS 13, which
caused issues with our text handling, and resulted in
e00d888daefb. This, again, seems to be the reason why
UIKit in some cases simply removes the input delegate
from our text responder. This typically happens after
a QPlatformInputContext::reset(), and then when the
next character is typed on the input panel (and hence,
leaves no informative stack trace).

The result of removing the input delegate, which is the
interface that let's Qt communicate IM changes back to
UIKit, leads Qt and the UIKit out of IM sync. E.g for a
japanese keyboard, after a QPlatformInputContext::reset(),
the Qt input field would remove the marked text, but
UIKit would still show japanese characters
based on what used to be marked text.

To work around this issue, this patch will therefore
recreate the text responder when Qt tells us to reset.
This will cause the first responder to change, which will
apparently also reset the UIKit IM state.

Fixes: QTBUG-102960
Pick-to: 6.3 6.2 5.15
Change-Id: I00901e980874fae819cc7d89a68fa34ae44808c2
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>

1 files changed, 16 insertions, 3 deletions

diff --git a/src/plugins/platforms/ios/qiosinputcontext.mm b/src/plugins/platforms/ios/qiosinputcontext.mm
index 1ae7f953b2..5aba4278c7 100644
--- a/src/plugins/platforms/ios/qiosinputcontext.mm
+++ b/src/plugins/platforms/ios/qiosinputcontext.mm
@@ -735,11 +735,24 @@ bool QIOSInputContext::inputMethodAccepted() const
 */
 void QIOSInputContext::reset()
 {
-    qImDebug("updating Qt::ImQueryAll and unmarking text");
+    qImDebug("releasing text responder");
+
+    // UIKit will sometimes, for unknown reasons, unset the input delegate on the
+    // current text responder. This seems to happen as a result of us calling
+    // [self.inputDelegate textDidChange:self] from [m_textResponder reset].
+    // But it won't be set to nil directly, only after a character is typed on
+    // the input panel after the reset. This strange behavior seems to be related
+    // to us overriding [QUIView setInteraction] to ignore UITextInteraction. If we
+    // didn't do that, the delegate would be kept. But not overriding that function
+    // has its own share of issues, so it seems better to keep that way for now.
+    // Instead, we choose to recreate the text responder as a brute-force solution
+    // until we have better knowledge of what is going on (or implement the new
+    // UITextInteraction protocol).
+    [m_textResponder reset];
+    [m_textResponder autorelease];
+    m_textResponder = nullptr;
 
     update(Qt::ImQueryAll);
-
-    [m_textResponder reset];
 }
 
 /*!