[apps/calculation] Move input memoization

Calculation's input is now only saved and restored when the app truly
closes or opens, instead of whenever the EditExpressionController enters
or leaves the responder chain (which also happens when the user switches
to the history or the toolbox, or triggers a syntax error).

Change-Id: I8404f1bc5619bcbc03272b406962d284fe25f7e2

apps/calculation/app.cpp

@@ -71,4 +71,14 @@ bool App::isAcceptableExpression(const Poincare::Expression expression) {
   return !expression.isUninitialized();
 }
 
+void App::didBecomeActive(Window * window) {
+  m_editExpressionController.restoreInput();
+  Shared::ExpressionFieldDelegateApp::didBecomeActive(window);
+}
+
+void App::willBecomeInactive() {
+  m_editExpressionController.memoizeInput();
+  Shared::ExpressionFieldDelegateApp::willBecomeInactive();
+}
+
 }

apps/calculation/app.h

@@ -46,6 +46,8 @@ public:
 private:
   App(Snapshot * snapshot);
   HistoryController m_historyController;
+  void didBecomeActive(Window * window) override;
+  void willBecomeInactive() override;
   EditExpressionController m_editExpressionController;
 };
 

apps/calculation/edit_expression_controller.cpp

@@ -56,14 +56,16 @@ void EditExpressionController::insertTextBody(const char * text) {
 void EditExpressionController::didBecomeFirstResponder() {
   m_contentView.mainView()->scrollToBottom();
   m_contentView.expressionField()->setEditing(true, false);
-  m_contentView.expressionField()->restoreContent(m_cacheBuffer, *m_cacheBufferInformation);
-  clearCacheBuffer();
   Container::activeApp()->setFirstResponder(m_contentView.expressionField());
 }
 
-void EditExpressionController::willExitResponderChain(Responder * nextFirstResponder) {
+void EditExpressionController::restoreInput() {
+  m_contentView.expressionField()->restoreContent(m_cacheBuffer, *m_cacheBufferInformation);
+  clearCacheBuffer();
+}
+
+void EditExpressionController::memoizeInput() {
   *m_cacheBufferInformation = m_contentView.expressionField()->moveCursorAndDumpContent(m_cacheBuffer, k_cacheBufferSize);
-  ::ViewController::willExitResponderChain(nextFirstResponder);
 }
 
 void EditExpressionController::viewWillAppear() {

apps/calculation/edit_expression_controller.h

@@ -27,9 +27,10 @@ public:
 
   View * view() override { return &m_contentView; }
   void didBecomeFirstResponder() override;
-  void willExitResponderChain(Responder * nextFirstResponder) override;
   void viewWillAppear() override;
   void insertTextBody(const char * text);
+  void restoreInput();
+  void memoizeInput();
 
   /* TextFieldDelegate */
   bool textFieldDidReceiveEvent(::TextField * textField, Ion::Events::Event event) override;