diff --git a/JTCalendar/JTCalendarDelegate.h b/JTCalendar/JTCalendarDelegate.h
index 9e1348b..6626e24 100644
--- a/JTCalendar/JTCalendarDelegate.h
+++ b/JTCalendar/JTCalendarDelegate.h
@@ -14,6 +14,7 @@
 
 @class JTCalendarManager;
 
+NS_ASSUME_NONNULL_BEGIN
 @protocol JTCalendarDelegate <NSObject>
 
 @optional
@@ -113,3 +114,4 @@
 - (void)calendar:(JTCalendarManager *)calendar didTouchDayView:(UIView<JTCalendarDay> *)dayView;
 
 @end
+NS_ASSUME_NONNULL_END
\ No newline at end of file
diff --git a/JTCalendar/JTCalendarManager.h b/JTCalendar/JTCalendarManager.h
index de5624e..210f6f2 100644
--- a/JTCalendar/JTCalendarManager.h
+++ b/JTCalendar/JTCalendarManager.h
@@ -18,12 +18,13 @@
 #import "JTCalendarDelegateManager.h"
 #import "JTCalendarScrollManager.h"
 
+NS_ASSUME_NONNULL_BEGIN
 @interface JTCalendarManager : NSObject
 
-@property (nonatomic, weak) id<JTCalendarDelegate> delegate;
+@property (nonatomic, weak, nullable) id<JTCalendarDelegate> delegate;
 
-@property (nonatomic, weak) UIView<JTMenu> *menuView;
-@property (nonatomic, weak) UIScrollView<JTContent> *contentView;
+@property (nonatomic, weak, nullable) UIView<JTMenu> *menuView;
+@property (nonatomic, weak, nullable) UIScrollView<JTContent> *contentView;
 
 @property (nonatomic, readonly) JTDateHelper *dateHelper;
 @property (nonatomic, readonly) JTCalendarSettings *settings;
@@ -42,3 +43,4 @@
 
 
 @end
+NS_ASSUME_NONNULL_END
diff --git a/JTCalendar/JTCalendarSettings.h b/JTCalendar/JTCalendarSettings.h
index cabc397..c8d4abd 100644
--- a/JTCalendar/JTCalendarSettings.h
+++ b/JTCalendar/JTCalendarSettings.h
@@ -13,6 +13,7 @@ typedef NS_ENUM(NSInteger, JTCalendarWeekDayFormat) {
     JTCalendarWeekDayFormatFull
 };
 
+NS_ASSUME_NONNULL_BEGIN
 @interface JTCalendarSettings : NSObject
 
 
@@ -38,3 +39,4 @@ typedef NS_ENUM(NSInteger, JTCalendarWeekDayFormat) {
 - (void)commonInit;
 
 @end
+NS_ASSUME_NONNULL_END
\ No newline at end of file
diff --git a/JTCalendar/JTDateHelper.h b/JTCalendar/JTDateHelper.h
index 57d57af..2d37f4a 100644
--- a/JTCalendar/JTDateHelper.h
+++ b/JTCalendar/JTDateHelper.h
@@ -7,21 +7,22 @@
 
 #import <Foundation/Foundation.h>
 
+NS_ASSUME_NONNULL_BEGIN
 @interface JTDateHelper : NSObject
 
 - (NSCalendar *)calendar;
 - (NSDateFormatter *)createDateFormatter;
 
-- (NSDate *)addToDate:(NSDate *)date months:(NSInteger)months;
-- (NSDate *)addToDate:(NSDate *)date weeks:(NSInteger)weeks;
-- (NSDate *)addToDate:(NSDate *)date days:(NSInteger)days;
+- (nullable NSDate *)addToDate:(NSDate *)date months:(NSInteger)months;
+- (nullable NSDate *)addToDate:(NSDate *)date weeks:(NSInteger)weeks;
+- (nullable NSDate *)addToDate:(NSDate *)date days:(NSInteger)days;
 
 // Must be less or equal to 6
 - (NSUInteger)numberOfWeeks:(NSDate *)date;
 
-- (NSDate *)firstDayOfMonth:(NSDate *)date;
-- (NSDate *)firstWeekDayOfMonth:(NSDate *)date;
-- (NSDate *)firstWeekDayOfWeek:(NSDate *)date;
+- (nullable NSDate *)firstDayOfMonth:(NSDate *)date;
+- (nullable NSDate *)firstWeekDayOfMonth:(NSDate *)date;
+- (nullable NSDate *)firstWeekDayOfWeek:(NSDate *)date;
 
 - (BOOL)date:(NSDate *)dateA isTheSameMonthThan:(NSDate *)dateB;
 - (BOOL)date:(NSDate *)dateA isTheSameWeekThan:(NSDate *)dateB;
@@ -32,3 +33,4 @@
 - (BOOL)date:(NSDate *)date isEqualOrAfter:(NSDate *)startDate andEqualOrBefore:(NSDate *)endDate;
 
 @end
+NS_ASSUME_NONNULL_END
\ No newline at end of file
diff --git a/JTCalendar/Managers/JTCalendarDelegateManager.h b/JTCalendar/Managers/JTCalendarDelegateManager.h
index 321a343..c9330bf 100644
--- a/JTCalendar/Managers/JTCalendarDelegateManager.h
+++ b/JTCalendar/Managers/JTCalendarDelegateManager.h
@@ -11,9 +11,10 @@
 
 // Provide a default behavior when no delegate are provided
 
+NS_ASSUME_NONNULL_BEGIN
 @interface JTCalendarDelegateManager : NSObject
 
-@property (nonatomic, weak) JTCalendarManager *manager;
+@property (nonatomic, weak, nullable) JTCalendarManager *manager;
 
 // Menu view
 
@@ -46,3 +47,4 @@
 - (void)didTouchDayView:(UIView<JTCalendarDay> *)dayView;
 
 @end
+NS_ASSUME_NONNULL_END
\ No newline at end of file
diff --git a/JTCalendar/Managers/JTCalendarScrollManager.h b/JTCalendar/Managers/JTCalendarScrollManager.h
index b50d812..f7310ea 100644
--- a/JTCalendar/Managers/JTCalendarScrollManager.h
+++ b/JTCalendar/Managers/JTCalendarScrollManager.h
@@ -13,13 +13,13 @@
 #import "JTContent.h"
 
 // Synchronize JTHorizontalCalendarView and JTCalendarMenuView
-
+NS_ASSUME_NONNULL_BEGIN
 @interface JTCalendarScrollManager : NSObject
 
-@property (nonatomic, weak) JTCalendarManager *manager;
+@property (nonatomic, weak, nullable) JTCalendarManager *manager;
 
-@property (nonatomic, weak) UIView<JTMenu> *menuView;
-@property (nonatomic, weak) UIScrollView<JTContent> *horizontalContentView;
+@property (nonatomic, weak, nullable) UIView<JTMenu> *menuView;
+@property (nonatomic, weak, nullable) UIScrollView<JTContent> *horizontalContentView;
 
 - (void)setMenuPreviousDate:(NSDate *)previousDate
                 currentDate:(NSDate *)currentDate
@@ -29,3 +29,4 @@
 - (void)updateHorizontalContentOffset:(CGFloat)percentage;
 
 @end
+NS_ASSUME_NONNULL_END
\ No newline at end of file
diff --git a/JTCalendar/Protocols/JTCalendarDay.h b/JTCalendar/Protocols/JTCalendarDay.h
index 728b225..0db2cdb 100644
--- a/JTCalendar/Protocols/JTCalendarDay.h
+++ b/JTCalendar/Protocols/JTCalendarDay.h
@@ -9,6 +9,7 @@
 
 @class JTCalendarManager;
 
+NS_ASSUME_NONNULL_BEGIN
 @protocol JTCalendarDay <NSObject>
 
 - (void)setManager:(JTCalendarManager *)manager;
@@ -20,3 +21,4 @@
 - (void)setIsFromAnotherMonth:(BOOL)isFromAnotherMonth;
 
 @end
+NS_ASSUME_NONNULL_END
\ No newline at end of file
diff --git a/JTCalendar/Protocols/JTCalendarPage.h b/JTCalendar/Protocols/JTCalendarPage.h
index c4f946e..60db7cb 100644
--- a/JTCalendar/Protocols/JTCalendarPage.h
+++ b/JTCalendar/Protocols/JTCalendarPage.h
@@ -9,6 +9,7 @@
 
 @class JTCalendarManager;
 
+NS_ASSUME_NONNULL_BEGIN
 @protocol JTCalendarPage <NSObject>
 
 - (void)setManager:(JTCalendarManager *)manager;
@@ -19,3 +20,4 @@
 - (void)reload;
 
 @end
+NS_ASSUME_NONNULL_END
\ No newline at end of file
diff --git a/JTCalendar/Protocols/JTCalendarWeek.h b/JTCalendar/Protocols/JTCalendarWeek.h
index 71a97aa..d954ff0 100644
--- a/JTCalendar/Protocols/JTCalendarWeek.h
+++ b/JTCalendar/Protocols/JTCalendarWeek.h
@@ -9,6 +9,7 @@
 
 @class JTCalendarManager;
 
+NS_ASSUME_NONNULL_BEGIN
 @protocol JTCalendarWeek <NSObject>
 
 - (void)setManager:(JTCalendarManager *)manager;
@@ -17,3 +18,4 @@
 - (void)setStartDate:(NSDate *)startDate updateAnotherMonth:(BOOL)enable monthDate:(NSDate *)monthDate;
 
 @end
+NS_ASSUME_NONNULL_END
diff --git a/JTCalendar/Protocols/JTCalendarWeekDay.h b/JTCalendar/Protocols/JTCalendarWeekDay.h
index 4bf951d..0beacf2 100644
--- a/JTCalendar/Protocols/JTCalendarWeekDay.h
+++ b/JTCalendar/Protocols/JTCalendarWeekDay.h
@@ -9,6 +9,7 @@
 
 @class JTCalendarManager;
 
+NS_ASSUME_NONNULL_BEGIN
 @protocol JTCalendarWeekDay <NSObject>
 
 - (void)setManager:(JTCalendarManager *)manager;
@@ -16,3 +17,4 @@
 - (void)reload;
 
 @end
+NS_ASSUME_NONNULL_END
\ No newline at end of file
diff --git a/JTCalendar/Protocols/JTContent.h b/JTCalendar/Protocols/JTContent.h
index d37d5dc..c9ada28 100644
--- a/JTCalendar/Protocols/JTContent.h
+++ b/JTCalendar/Protocols/JTContent.h
@@ -9,6 +9,7 @@
 
 @class JTCalendarManager;
 
+NS_ASSUME_NONNULL_BEGIN
 @protocol JTContent <NSObject>
 
 - (void)setManager:(JTCalendarManager *)manager;
@@ -23,3 +24,4 @@
 - (void)loadNextPageWithAnimation;
 
 @end
+NS_ASSUME_NONNULL_END
\ No newline at end of file
diff --git a/JTCalendar/Protocols/JTMenu.h b/JTCalendar/Protocols/JTMenu.h
index 8237751..8c90510 100644
--- a/JTCalendar/Protocols/JTMenu.h
+++ b/JTCalendar/Protocols/JTMenu.h
@@ -9,6 +9,7 @@
 
 @class JTCalendarManager;
 
+NS_ASSUME_NONNULL_BEGIN
 @protocol JTMenu <NSObject>
 
 - (void)setManager:(JTCalendarManager *)manager;
@@ -22,3 +23,4 @@
 - (UIScrollView *)scrollView;
 
 @end
+NS_ASSUME_NONNULL_END
diff --git a/JTCalendar/Views/JTCalendarDayView.h b/JTCalendar/Views/JTCalendarDayView.h
index 06ace2b..f4207e6 100644
--- a/JTCalendar/Views/JTCalendarDayView.h
+++ b/JTCalendar/Views/JTCalendarDayView.h
@@ -9,9 +9,10 @@
 
 #import "JTCalendarDay.h"
 
+NS_ASSUME_NONNULL_BEGIN
 @interface JTCalendarDayView : UIView<JTCalendarDay>
 
-@property (nonatomic, weak) JTCalendarManager *manager;
+@property (nonatomic, weak, nullable) JTCalendarManager *manager;
 
 @property (nonatomic) NSDate *date;
 
@@ -30,3 +31,4 @@
 - (void)commonInit;
 
 @end
+NS_ASSUME_NONNULL_END
diff --git a/JTCalendar/Views/JTCalendarMenuView.h b/JTCalendar/Views/JTCalendarMenuView.h
index f6dfb9b..cdd46bc 100644
--- a/JTCalendar/Views/JTCalendarMenuView.h
+++ b/JTCalendar/Views/JTCalendarMenuView.h
@@ -9,9 +9,10 @@
 
 #import "JTMenu.h"
 
+NS_ASSUME_NONNULL_BEGIN
 @interface JTCalendarMenuView : UIView<JTMenu, UIScrollViewDelegate>
 
-@property (nonatomic, weak) JTCalendarManager *manager;
+@property (nonatomic, weak, nullable) JTCalendarManager *manager;
 
 @property (nonatomic) CGFloat contentRatio;
 
@@ -23,3 +24,4 @@
 - (void)commonInit;
 
 @end
+NS_ASSUME_NONNULL_END
\ No newline at end of file
diff --git a/JTCalendar/Views/JTCalendarPageView.h b/JTCalendar/Views/JTCalendarPageView.h
index 0ba3f30..84b4f43 100644
--- a/JTCalendar/Views/JTCalendarPageView.h
+++ b/JTCalendar/Views/JTCalendarPageView.h
@@ -9,9 +9,10 @@
 
 #import "JTCalendarPage.h"
 
+NS_ASSUME_NONNULL_BEGIN
 @interface JTCalendarPageView : UIView<JTCalendarPage>
 
-@property (nonatomic, weak) JTCalendarManager *manager;
+@property (nonatomic, weak, nullable) JTCalendarManager *manager;
 
 @property (nonatomic) NSDate *date;
 
@@ -21,3 +22,4 @@
 - (void)commonInit;
 
 @end
+NS_ASSUME_NONNULL_END
\ No newline at end of file
diff --git a/JTCalendar/Views/JTCalendarWeekDayView.h b/JTCalendar/Views/JTCalendarWeekDayView.h
index b0ea796..0da374a 100644
--- a/JTCalendar/Views/JTCalendarWeekDayView.h
+++ b/JTCalendar/Views/JTCalendarWeekDayView.h
@@ -9,11 +9,12 @@
 
 #import "JTCalendarWeekDay.h"
 
+NS_ASSUME_NONNULL_BEGIN
 @interface JTCalendarWeekDayView : UIView<JTCalendarWeekDay>
 
-@property (nonatomic, weak) JTCalendarManager *manager;
+@property (nonatomic, weak, nullable) JTCalendarManager *manager;
 
-@property (nonatomic, readonly) NSArray *dayViews;
+@property (nonatomic, readonly) NSArray<UILabel *> *dayViews;
 
 /*!
  * Must be call if override the class
@@ -26,3 +27,4 @@
 - (void)reload;
 
 @end
+NS_ASSUME_NONNULL_END
diff --git a/JTCalendar/Views/JTCalendarWeekView.h b/JTCalendar/Views/JTCalendarWeekView.h
index 35e7497..832e2cb 100644
--- a/JTCalendar/Views/JTCalendarWeekView.h
+++ b/JTCalendar/Views/JTCalendarWeekView.h
@@ -9,9 +9,10 @@
 
 #import "JTCalendarWeek.h"
 
+NS_ASSUME_NONNULL_BEGIN
 @interface JTCalendarWeekView : UIView<JTCalendarWeek>
 
-@property (nonatomic, weak) JTCalendarManager *manager;
+@property (nonatomic, weak, nullable) JTCalendarManager *manager;
 
 @property (nonatomic, readonly) NSDate *startDate;
 
@@ -21,3 +22,4 @@
 - (void)commonInit;
 
 @end
+NS_ASSUME_NONNULL_END
\ No newline at end of file
diff --git a/JTCalendar/Views/JTHorizontalCalendarView.h b/JTCalendar/Views/JTHorizontalCalendarView.h
index faf8339..b9a79e6 100644
--- a/JTCalendar/Views/JTHorizontalCalendarView.h
+++ b/JTCalendar/Views/JTHorizontalCalendarView.h
@@ -9,9 +9,10 @@
 
 #import "JTContent.h"
 
+NS_ASSUME_NONNULL_BEGIN
 @interface JTHorizontalCalendarView : UIScrollView<JTContent>
 
-@property (nonatomic, weak) JTCalendarManager *manager;
+@property (nonatomic, weak, nullable) JTCalendarManager *manager;
 
 @property (nonatomic) NSDate *date;
 
@@ -21,3 +22,4 @@
 - (void)commonInit;
 
 @end
+NS_ASSUME_NONNULL_END
diff --git a/JTCalendar/Views/JTVerticalCalendarView.h b/JTCalendar/Views/JTVerticalCalendarView.h
index c70a2d1..70f059f 100644
--- a/JTCalendar/Views/JTVerticalCalendarView.h
+++ b/JTCalendar/Views/JTVerticalCalendarView.h
@@ -9,9 +9,10 @@
 
 #import "JTContent.h"
 
+NS_ASSUME_NONNULL_BEGIN
 @interface JTVerticalCalendarView : UIScrollView<JTContent>
 
-@property (nonatomic, weak) JTCalendarManager *manager;
+@property (nonatomic, weak, nullable) JTCalendarManager *manager;
 
 @property (nonatomic) NSDate *date;
 
@@ -21,3 +22,4 @@
 - (void)commonInit;
 
 @end
+NS_ASSUME_NONNULL_END