無限滾動UIPageViewController

Question

我試圖設置一個UIPageViewController，它可以通過NSUrlConnection數據拉動動態加載頁面瀏覽量來無限滾動。我從3個視角開始：prev，curr，next;並在達到pageData陣列中的第一個或最後一個視圖時加載附加視圖。

問題是我在viewControllerBeforeViewController或viewControllerAfterViewController中加載了額外的視圖。看起來這些方法在頁面之間進行一次滑動時可以調用2-3次。它們也可以在半滑動過程中調用，從不完成頁面轉換。這可能意味着多個預加載開始過早完成。然後以某種方式pageViewController忘記當前的位置。

[self.pageViewController setViewControllers:@[[self.pageData objectAtIndex:gotoIdx]] direction:direction animated:NO completion:nil]; 

這條線以下用於用信號在pageViewController加法數據，並且去誒相應的視圖。當我開始使用它時，不用通過滑動進入prev/next視圖，它開始跳轉到看起來隨機的視圖。一旦我開始向前滑動時向後滑動...

是否有一個更合適的地方做預加載，只在頁面轉換完成後調用一次？而且，是否必須調用上面的行，或者有更可靠的方法來確保它進入正確的頁面？試圖在這裏進行聯繫感到沮喪。

// the init line, somewhere early on. uses Scoll style 
self.pageViewController = [[UIPageViewController alloc] initWithTransitionStyle:UIPageViewControllerTransitionStyleScroll navigationOrientation:UIPageViewControllerNavigationOrientationVertical options:nil]; 

- (UIViewController *)pageViewController:(UIPageViewController *)pageViewController viewControllerBeforeViewController:(UIViewController *)viewController { 
    NSUInteger index = [self.pageData indexOfObject:viewController]; 
    if(index == 1){ 
     // if loading last one on start, preload one more in advance 
     [self loadSecondaryCalData:-1 endView:[[self viewControllerAtIndex:index-1] retain]]; 
    } else if ((index == 0) || (index == NSNotFound)) { 
     return nil; 
    } 

    index--; 
    return [self viewControllerAtIndex:index]; 
} 

- (UIViewController *)pageViewController:(UIPageViewController *)pageViewController viewControllerAfterViewController:(UIViewController *)viewController { 

    NSUInteger index = [self.pageData indexOfObject:viewController]; 
    if(index == [self.pageData count]-2){ 
     [self loadSecondaryCalData:1 endView:[[self viewControllerAtIndex:index+1] retain]]; // if last one, preload one more in advance 
    } else if (index == NSNotFound) { 
     return nil; 
    } 

    index++; 
    if (index == [self.pageData count]) { 
     return nil; 
    } 
    return [self viewControllerAtIndex:index]; 
}  


- (void)loadSecondaryCalData:(int)howMany endView:(CalendarViewController*)endView { 
    // initiate NSURLConnection async request for view data 
} 

- (void)loadSecondaryCals: (NSDictionary*)data { 
    // callback for async request 

    // ... process view, cal 

    // add new object to page data, at start or end 
    if(next){ 
     [self.pageData addObject:cal]; 
     gotoIdx = [self.pageData count]-2; 
     direction = UIPageViewControllerNavigationDirectionForward; 
    } else { 
     [self.pageData insertObject:cal atIndex:0]; 
     gotoIdx = 1; 
     direction = UIPageViewControllerNavigationDirectionReverse; 
    } 

    [self.pageViewController setViewControllers:@[[self.pageData objectAtIndex:gotoIdx]] direction:direction animated:NO completion:nil]; 

// alternate method to above line 
/* 
__block CalendarPageViewViewController *blocksafeSelf = self; 
__block int blocksafeGotoIdx = gotoIdx; 
__block UIPageViewControllerNavigationDirection blocksafeDirection = direction; 
[self.pageViewController setViewControllers:@[[self.pageData objectAtIndex:gotoIdx]] direction:direction animated:YES completion:^(BOOL finished){ 
    if(finished) 
    { 
     dispatch_async(dispatch_get_main_queue(), ^{ 
      [blocksafeSelf.pageViewController setViewControllers:@[[blocksafeSelf.pageData objectAtIndex:blocksafeGotoIdx]] direction:blocksafeDirection animated:NO completion:nil]; 
     }); 
    } 
}]; 
*/ 


} 

UPDATE：

由於下面的快速響應，引用一個偉大的功能，我不知道的。這是預加載方法，完成後只需調用一次即可完成轉換。這似乎很大程度上清除了不可靠的意見跳動和忘記位置。謝謝@sha！

// function to detect if we've reached the first or last item in views 
// detects for full completion only 
- (void)pageViewController:(UIPageViewController *)pageViewController didFinishAnimating:(BOOL)finished previousViewControllers:(NSArray *)previousViewControllers transitionCompleted:(BOOL)completed { 

    if(completed == TRUE && [previousViewControllers count] > 0 && [pageData count] > 1){ 
     CalendarViewController *firstCal = [pageData objectAtIndex:0]; 
     CalendarViewController *lastCal = [pageData objectAtIndex:([pageData count]-1)]; 

     CalendarViewController *prevCal = [previousViewControllers objectAtIndex:0]; 
     CalendarViewController *currCal = [[pageViewController viewControllers] objectAtIndex:0]; 

     NSLog(@"transition completed: %@ -> %@", prevCal.week_day_date, currCal.week_day_date); 
     if(currCal == firstCal){ 
      // preload on begining 
      [self loadSecondaryCalData:-1 endView:firstCal]; 
     } else if(currCal == lastCal){ 
      // preload to end 
      [self loadSecondaryCalData:1 endView:lastCal]; 
     } 
    } 
} 

Answer 1

我想你需要在pageViewController:didFinishAnimating:previousViewControllers:transitionCompleted:處理程序中做你的加載調用。當動畫完成並且新的ViewController變成活動的時候，這個方法將被調用。