Add explanation block to CreatePollBox.

Telegram/Resources/langs/lang.strings

@@ -2223,6 +2223,9 @@ https://github.com/telegramdesktop/tdesktop/blob/master/LEGAL
 "lng_polls_choose_question" = "Please enter a question.";
 "lng_polls_choose_answers" = "Please enter at least two options.";
 "lng_polls_choose_correct" = "Please choose the correct answer.";
+"lng_polls_solution_title" = "Explanation";
+"lng_polls_solution_placeholder" = "Add a Comment (Optional)";
+"lng_polls_solution_about" = "Users will see this comment after choosing a wrong answer, good for educational purposes.";
 
 "lng_polls_poll_results_title" = "Poll results";
 "lng_polls_quiz_results_title" = "Quiz results";

Telegram/SourceFiles/boxes/boxes.style

@@ -800,7 +800,7 @@ themesMenuPosition: point(-2px, 25px);
 
 createPollField: InputField(defaultInputField) {
 	font: boxTextFont;
-	textMargins: margins(0px, 0px, 0px, 0px);
+	textMargins: margins(0px, 4px, 0px, 4px);
 	textAlign: align(left);
 	heightMin: 36px;
 	heightMax: 86px;
@@ -822,6 +822,11 @@ createPollOptionField: InputField(createPollField) {
 	placeholderMargins: margins(2px, 0px, 2px, 0px);
 	heightMax: 68px;
 }
+createPollSolutionField: InputField(createPollField) {
+	textMargins: margins(0px, 4px, 0px, 4px);
+	border: 1px;
+	borderActive: 2px;
+}
 createPollLimitLabel: FlatLabel(defaultFlatLabel) {
 	minWidth: 274px;
 	align: align(topleft);

Telegram/SourceFiles/boxes/create_poll_box.cpp

@@ -794,6 +794,40 @@ not_null<Ui::InputField*> CreatePollBox::setupQuestion(
 	return question;
 }
 
+not_null<Ui::InputField*> CreatePollBox::setupSolution(
+		not_null<Ui::VerticalLayout*> container,
+		rpl::producer<bool> shown) {
+	using namespace Settings;
+
+	const auto outer = container->add(
+		object_ptr<Ui::SlideWrap<Ui::VerticalLayout>>(
+			container,
+			object_ptr<Ui::VerticalLayout>(container))
+	)->setDuration(0)->toggleOn(std::move(shown));
+	const auto inner = outer->entity();
+
+	AddSkip(inner);
+	AddSubsectionTitle(inner, tr::lng_polls_solution_title());
+	const auto solution = inner->add(
+		object_ptr<Ui::InputField>(
+			inner,
+			st::createPollSolutionField,
+			Ui::InputField::Mode::MultiLine,
+			tr::lng_polls_solution_placeholder()),
+		st::createPollFieldPadding);
+	InitField(getDelegate()->outerContainer(), solution, _session);
+	solution->setMaxLength(kQuestionLimit + kErrorLimit);
+
+	inner->add(
+		object_ptr<Ui::FlatLabel>(
+			inner,
+			tr::lng_polls_solution_about(),
+			st::boxDividerLabel),
+		st::createPollFieldTitlePadding);
+
+	return solution;
+}
+
 object_ptr<Ui::RpWidget> CreatePollBox::setupContent() {
 	using namespace Settings;
 
@@ -866,6 +900,11 @@ object_ptr<Ui::RpWidget> CreatePollBox::setupContent() {
 			(_chosen & PollData::Flag::Quiz),
 			st::defaultCheckbox),
 		st::createPollCheckboxMargin);
+
+	const auto explanation = setupSolution(
+		container,
+		rpl::single(quiz->checked()) | rpl::then(quiz->checkedChanges()));
+
 	quiz->setDisabled(_disabled & PollData::Flag::Quiz);
 	if (multiple) {
 		multiple->setDisabled((_disabled & PollData::Flag::MultiChoice)

Telegram/SourceFiles/boxes/create_poll_box.h

@@ -36,7 +36,7 @@ public:
 		PollData::Flags disabled,
 		Api::SendType sendType);
 
-	rpl::producer<Result> submitRequests() const;
+	[[nodiscard]] rpl::producer<Result> submitRequests() const;
 	void submitFailed(const QString &error);
 
 	void setInnerFocus() override;
@@ -54,9 +54,12 @@ private:
 	friend constexpr inline bool is_flag_type(Error) { return true; }
 	using Errors = base::flags<Error>;
 
-	object_ptr<Ui::RpWidget> setupContent();
+	[[nodiscard]] object_ptr<Ui::RpWidget> setupContent();
-	not_null<Ui::InputField*> setupQuestion(
+	[[nodiscard]] not_null<Ui::InputField*> setupQuestion(
 		not_null<Ui::VerticalLayout*> container);
+	[[nodiscard]] not_null<Ui::InputField*> setupSolution(
+		not_null<Ui::VerticalLayout*> container,
+		rpl::producer<bool> shown);
 
 	const not_null<Main::Session*> _session;
 	const PollData::Flags _chosen = PollData::Flags();