- (UIPresentationController *)presentationControllerForPresentedViewController:(UIViewController *)presented presentingViewController:(UIViewController *)presenting sourceViewController:(UIViewController *)source{

1.透過if ([presented isKindOfClass:AlbumMenuViewController class])來分別要提供對應PresentationController{
2.建立一個subclass UIPresentationController的class。(怎麼建請看段B)
3.透過UIPresentationController的父方法initWithPresentedViewController...(略)去instance這個PresentationController object。
}

}

- (id<UIViewControllerAnimatedTransitioning> _Nullable)animationControllerForPresentedController:(UIViewController * _Nonnull)presented presentingController:(UIViewController * _Nonnull)presenting sourceController:(UIViewController * _Nonnull)source{

1.用if去知道你等等要回傳那個對應的animator
if([presented isKindOfClass:[HelperTableViewController class]]){
2.SlideMenuAnimator *animator = [[SlideMenuAnimator alloc]init];//製作一個實作UIViewControllerAnimatedTransitioning協議的animator class，怎麼做看段C
3.[animator setPresenting:YES];// 我設計的animator可以同時包含出場與離場的動畫，這樣就不用寫兩個animator了，所以裡面有個參數可以選擇要回傳哪種動畫，這裡是出場就設定YES。
}

}

- (id<UIViewControllerAnimatedTransitioning> _Nullable)animationControllerForDismissedController:(UIViewController * _Nonnull)dismissed{
1.用if去知道你等等要回傳那個對應的animator
if([presented isKindOfClass:[HelperTableViewController class]]){
2.SlideMenuAnimator *animator = [[SlideMenuAnimator alloc]init];//前面解釋過
3.[animator setPresenting:NO];//前面解釋過
}
}

(CGRect)frameOfPresentedViewInContainerView
{
CGRect presentedViewFrame = CGRectZero;//我們要回傳的數值
CGRect containerBounds = [[self containerView] bounds];//得到prestingVC的bounds
// 到這裡你已經可以運加減乘除算出你要顯示的VC的大小，下面示範的是要根據ipad跟iphone做特別處理的做法

if (self.traitCollection.userInterfaceIdiom == UIUserInterfaceIdiomPhone) {
presentedViewFrame.size = CGSizeMake(floorf(containerBounds.size.width * 0.75),
containerBounds.size.height);
}else if(self.traitCollection.userInterfaceIdiom == UIUserInterfaceIdiomPad){
presentedViewFrame.size = CGSizeMake(floorf(300),
containerBounds.size.height);
}

return presentedViewFrame;//最後當然是回傳
}

- (void)presentationTransitionWillBegin {

self.dimmingView = [[UIView alloc]init];
[self.dimmingView setFrame:self.containerView.frame];
[self.dimmingView setBackgroundColor:[UIColor blackColor]];
[self.dimmingView setAlpha:0.3f];

// Add a custom dimming view behind the presented view controller's view
[[self containerView] addSubview:self.dimmingView];
[self.dimmingView addSubview:[[self presentedViewController] view]];

#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Wundeclared-selector"
UITapGestureRecognizer *dimmingViewSingleTap =
[[UITapGestureRecognizer alloc] initWithTarget:self.presentingViewController
action:@selector(handleDimmingViewSingleTap)];
#pragma clang diagnostic pop
[self.dimmingView addGestureRecognizer:dimmingViewSingleTap];

// Fade in the dimming view during the transition.
[self.dimmingView setAlpha:0.0];
// Use the transition coordinator to set up the animations.
[[[self presentingViewController] transitionCoordinator] animateAlongsideTransition:^(id<UIViewControllerTransitionCoordinatorContext>  _Nonnull context) {
[self.dimmingView setAlpha:0.55];
} completion:^(id<UIViewControllerTransitionCoordinatorContext>  _Nonnull context) {

}];
}

- (void)dismissalTransitionWillBegin {
[[[self presentingViewController] transitionCoordinator] animateAlongsideTransition:^(id<UIViewControllerTransitionCoordinatorContext>  _Nonnull context) {
[self.dimmingView setAlpha:0.0];
} completion:^(id<UIViewControllerTransitionCoordinatorContext>  _Nonnull context) {

}];
}

- (void)viewWillTransitionToSize:(CGSize)size withTransitionCoordinator:(id<UIViewControllerTransitionCoordinator>)coordinator 

//製作實作UIViewControllerAnimatedTransitioning協議的animator，系統會去這裡要VC的初始位置跟Final位置，系統再去補齊動畫。
//1 override 下面function來提供動畫內容（兩個位置）
- (void)animateTransition:(id<UIViewControllerContextTransitioning> _Nonnull)transitionContext {
1.// 主畫布
UIView *containerView = [transitionContext containerView];

2.// 對進場來說（toVC是prestedVC），拿到後可以再去拿VC的view
UIViewController *toVC   = [transitionContext
viewControllerForKey:UITransitionContextToViewControllerKey];

3.// 對進場來說（fromVC是prestingVC)，拿到後可以再去拿VC的view
UIViewController *fromVC = [transitionContext
viewControllerForKey:UITransitionContextFromViewControllerKey];

4.//取得view，後面動畫主要就是都在操作這裡
UIView *toView = [transitionContext viewForKey:UITransitionContextToViewKey];
UIView *fromView = [transitionContext viewForKey:UITransitionContextFromViewKey];

5.//取得兩個VC的最終大小，大小是在frameOfPresentedViewInContainerView決定。
// Set up some variables for the animation.
CGRect containerFrame = containerView.frame;
CGRect toViewStartFrame = [transitionContext initialFrameForViewController:toVC];
CGRect fromViewStartFrame = [transitionContext initialFrameForViewController:fromVC];
CGRect toViewFinalFrame = [transitionContext finalFrameForViewController:toVC];
CGRect fromViewFinalFrame = [transitionContext finalFrameForViewController:fromVC];

6.// 開始作畫 Add toVC's view to containerView
// 把toView加進來
[containerView addSubview:toView];

7.//決定一開始的frame
if (self.presenting) {
//這邊直接用預設的
CGSize size = toViewFinalFrame.size;
[toView setFrame:CGRectMake(0, containerFrame.size.height+toViewFinalFrame.size.height, size.width, size.height)];//size一樣。x=0,y=總高度+toView的高
}

//決定最終的frame
if (self.presenting) {
[UIView animateWithDuration:[self transitionDuration:transitionContext] animations:^{
//大小一樣。位置就只要到x=0, y=總高度-toView高度
CGSize size = toViewFinalFrame.size;
CGPoint point = CGPointMake(0, containerFrame.size.height-toViewFinalFrame.size.height);
[toView setFrame:CGRectMake(point.x, point.y, size.width, size.height)];
}completion:^(BOOL finished) {
// 3.Cleaning up and completing the transition.
[transitionContext completeTransition:YES];
}];
}
}

- (NSTimeInterval)transitionDuration:(id<UIViewControllerContextTransitioning> _Nullable)transitionContext {
return 0.2f;
}