这可能看起来像以前提出的问题( PageViewController delegate functions called twice ),但问题是我无法将该解决方案应用于我的问题。
您可能会注意到,我正在开发一个日历应用程序并使用 UIPageViewController 来管理我的年度日历显示。正如您所看到的,我正在使用 UIPageViewControllerTransitionStylePageCurl,当用户 curl 页面(向前/向后)时,他们各自的委托(delegate)将被调用两次,这根据执行的委托(delegate)给我 2 年的增量或减量。现在我需要找出导致此问题的原因并阻止它执行两次。
我知道在那些提供下一页或上一页的委托(delegate)中返回一个 viewController 非常重要,因此我只是刷新 viewController 的 View ,以便我可以使用新数据渲染 View 。我还尝试了另一个名为 willTransitionToViewControllers 的委托(delegate),但不会让我到任何地方,因为 willTransitionToViewControllers 只会在之后执行 viewControllerAfterViewController 和 viewControllerBeforeViewController。
有人帮助我理解并解决这个问题。
- (void)addCalendarViews
{
CGRect frame = CGRectMake(0., 0., self.view.frame.size.width, self.view.frame.size.height);
pageViewController = [[UIPageViewController alloc] initWithTransitionStyle:UIPageViewControllerTransitionStylePageCurl
navigationOrientation:UIPageViewControllerNavigationOrientationHorizontal
options:[NSDictionary dictionaryWithObject:[NSNumber numberWithInt:UIPageViewControllerSpineLocationNone] forKey:UIPageViewControllerOptionSpineLocationKey]];
pageViewController.doubleSided = YES;
pageViewController.delegate = self;
pageViewController.dataSource = self;
YearCalendarViewController *yearController = [[YearCalendarViewController alloc] init];
NSArray *viewControllers = [NSArray arrayWithObject:yearController];
[self.pageViewController setViewControllers:viewControllers
direction:UIPageViewControllerNavigationDirectionReverse
animated:YES
completion:nil];
[self addChildViewController:pageViewController];
[self.view addSubview:pageViewController.view];
[pageViewController didMoveToParentViewController:self];
CGRect pageViewRect = yearController.view.bounds;
self.pageViewController.view.frame = pageViewRect;
viewCalendarMonth = [[SGMonthCalendarView alloc] initWithFrame:frame];
[self.view addSubview:viewCalendarMonth];
arrayCalendars = @[pageViewController.view, viewCalendarMonth];
}
-(UIViewController*)pageViewController:(UIPageViewController *)pageViewController viewControllerAfterViewController:(UIViewController *)viewController
{
NSDate *currentDate = [[SGSharedDate sharedManager] currentDate];
NSDateComponents *currentDateComp = [NSDate returnDateComponentsForDate:currentDate];
self.nextDate = [NSDate dateWithYear:currentDateComp.year+1 month:currentDateComp.month day:currentDateComp.day];
[[SGSharedDate sharedManager] setCurrentDate:nextDate];
{
//I m reloading viewController's view here to display the new set of data for the increamented date.
}
NSLog(@"After Dates====>%@", nextDate);
return viewController;
}
-(UIViewController*)pageViewController:(UIPageViewController *)pageViewController viewControllerBeforeViewController:(UIViewController *)viewController
{
NSDate *currentDate = [[SGSharedDate sharedManager] currentDate];
NSDateComponents *currentDateComp = [NSDate returnDateComponentsForDate:currentDate];
nextDate = [NSDate dateWithYear:currentDateComp.year-1 month:currentDateComp.month day:currentDateComp.day];
[[SGSharedDate sharedManager] setCurrentDate:nextDate];
{
//I m reloading viewController's view here to display the new set of data for the decremented date.
}
NSLog(@"Before Dates====>%@", nextDate);
return viewController;
}
最佳答案
UIPageController
倾向于提前(和向后)缓存,因此当您从 View Controller N
向前滑动时,N+1
会加载,但是默默地执行N+2
,因此如果您滑动两次,您的内容就已经加载了。
但是由于委托(delegate)方法中有一个不可见的副作用(递增日期),因此您会受到此影响。
我的建议是从委托(delegate)中删除约会副作用,并以某种方式将日期代码绑定(bind)到呈现的 View Controller (委托(delegate)或属性),然后捕获 pageController 的 didFinishAnimating 方法。
- (void)pageViewController:(UIPageViewController *)pageViewController didFinishAnimating:(BOOL)finished previousViewControllers:(NSArray *)previousViewControllers transitionCompleted:(BOOL)completed {
if (completed) {
if ([[self.pageViewController.viewControllers firstObject] isKindOfClass:[MyCalenderViewController class]]) {
currentDate = [self workOutCurrentDateForVC:[self.pageViewController.viewControllers firstObject]];
}
}
}
副作用是代码味道。尝试并避免。
编辑
我刚刚注意到您正在回收 View Controller 并使用新的日期点重新加载它。不要这样做。您需要将 View Controller 视为书籍的单个页面。因此,生成一个新的并设置该月...
简单举个例子...
@interface YearViewController : UIViewController
@property NSDate *focusedYear;
-(instancetype)initWithYear:(NSDate)adate;
@end
@implementation YearViewController
-(instancetype)initWithYear:(NSDate)adate {
self = [super initWithNibName:nil bundle:nil];
if(self) {
self.focusedYear = adate;
....
}
}
@end
因此,在页面 Controller 委托(delegate)中,您只需根据前一个页面的日期(以及您分页的方向)提供一个新的“页面”
-(UIViewController*)pageViewController:(UIPageViewController *)pageViewController viewControllerAfterViewController:(UIViewController *)viewController
{
YearViewController *yvc = (YearViewController *)viewController;
NSDate *currentDate = yvc.focusedYear;
NSDateComponents *currentDateComp = [NSDate returnDateComponentsForDate:currentDate];
NSDate *nextDate = [NSDate dateWithYear:currentDateComp.year+1 month:currentDateComp.month day:currentDateComp.day];
YearViewController *freshYVC = [[YearViewController alloc] initWithDate:nextDate];
return freshYVC;
}
关于副作用的评论仍然有效。
关于ios - UIPageViewController 的 DataSource 委托(delegate)在单次滑动中连续被调用 2 次,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/24998102/