标签： iOS，苹果开发文档
- transitionFromViewController:toViewController:duration:options:animations:completion:
Transitions between two of the view controller'��s child view controllers.
Declaration
SWIFT
func transitionFromViewController(_ fromViewController: UIViewController,
toViewController toViewController: UIViewController,
duration duration: NSTimeInterval,
options options: UIViewAnimationOptions,
animations animations: (() -> Void)?,
completion completion: ((Bool) -> Void)?)
OBJECTIVE-C
- (void)transitionFromViewController:(UIViewController * _Nonnull)fromViewController
toViewController:(UIViewController * _Nonnull)toViewController
duration:(NSTimeInterval)duration
options:(UIViewAnimationOptions)options
animations:(void (^ _Nullable)(void))animations
completion:(void (^ _Nullable)(BOOL finished))completion
Parameters
fromViewController
A view controller whose view is currently visible in the parent'��s view hierarchy.
toViewController
A child view controller whose view is not currently in the view hierarchy.
duration
The total duration of the animations, in seconds. If you pass zero, the changes are made without animating them.
options
A mask of options indicating how you want to perform the animations. For a list of valid constants, see UIViewAnimationOptions.
animations
A block object containing the changes to commit to the views. Here you programmatically change any animatable properties of the views in your view hierarchy. This block takes no parameters and has no return value. This parameter must not be NULL.
completion
A block to be called when the animation completes.
The block takes the following parameters:
finished
YES if the animation finished; NO if it was skipped.
Discussion
This method adds the second view controller'��s view to the view hierarchy and then performs the animations defined in your animations block. After the animation completes, it removes the first view controller'��s view from the view hierarchy.
This method is only intended to be called by an implementation of a custom container view controller. If you override this method, you must call super in your implementation.
Availability
Available in iOS 5.0 and later.
1.背景
iOS 5.0 以前 ，我们在一个视图控制器中会用addSubView方法来添加很多子View，并进行对这些子View的控制。
但是，这样做，有一个问题：
一个UIViewController的View可能有很多小的子view。这些子view很多时候被盖在最后，我们在最外层ViewController的viewDidLoad方法中，用addSubview增加了大量的子view。这些子view大多数不会一直处于界面上，只是在某些情况下才会出现，例如登陆失败的提示view，上传附件成功的提示view，网络失败的提示view等。但是虽然这些view很少出现，但是我们却常常一直把它们放在内存中。另外，当收到内存警告时，我们只能自己手工把这些view从super view中去掉。
2.替代方法
聪明的你，也许已经体会到了，该transitionFromViewController方法闪亮登场：
苹果新的API增加了addChildViewController方法，并且希望我们在使用addSubview时，同时调用[self addChildViewController:child]方法将sub view对应的viewController也加到当前ViewController的管理中。
对于那些当前暂时不需要显示的subview，只通过addChildViewController把subViewController加进去；需要显示时再调用transitionFromViewController方法。将其添加进入底层的ViewController中。
这样做的好处：
- 无疑，对页面中的逻辑更加分明了。相应的View对应相应的ViewController。
- 当某个子View没有显示时，将不会被Load，减少了内存的使用。
- 当内存紧张时，没有Load的View将被首先释放，优化了程序的内存释放机制。
3.transitionFromViewController:toViewController:duration:options:animations:completion 方法
- (void)transitionFromViewController:(UIViewController *)fromViewControllertoViewController:(UIViewController *)toViewController duration:(NSTimeInterval)durationoptions:(UIViewAnimationOptions)options animations:(void (^)(void))animations completion:(void (^)(BOOL finished))completion
在两个子视图控制器中转换。支持的iOS 5.0以及以后的版本。
fromViewController：当前显示在父视图控制器中的子视图控制器
toViewController：将要显示的子视图控制器
duration：完成过渡的时间；单位：秒。
options：指定的过渡效果。
animations：转换过程中，的动画。是个Block块操作。
completion：过渡完成后，执行的Block块操作。
该方法，执行完以后，fromViewController指代的视图控制器的View将从界面消失；
toViewController所指代的视图控制器的View将被载入到页面中。
4.使用方法
- 在父ViewController中，使用方法，将各个子添加进来。
\- (void)viewDidLoad{
[super viewDidLoad];
// 对于不显示的子ViewController，要用addChildViewController方法，将其添加到父ViewController中
firstViewController=[[FirstViewController alloc] initWithNibName:@"FirstViewController" bundle:nil];
[self addChildViewController:firstViewController];
secondViewController=[[SecondViewController alloc] initWithNibName:@"SecondViewController"bundle:nil];
[self addChildViewController:secondViewController];
thirdViewController=[[ThirdViewController alloc] initWithNibName:@"ThirdViewController" bundle:nil];
[self addChildViewController:thirdViewController];
// 需要显示的子ViewController，要将其View添加到父View中
[self.view addSubview:thirdViewController.view];
currentViewController=thirdViewController;
}
- 根据按钮事件，来transitionFromViewController方法来切换相应的子View
-(IBAction)onClickbutton:(id)sender
{
if ((currentViewController==firstViewController&&[sender tag]==1)||(currentViewController==secondViewController&&[sender tag]==2) ||(currentViewController==thirdViewController&&[sender tag]==3) ) {
return;
}
UIViewController *oldViewController=currentViewController;
switch ([sender tag]) {
case 1:{
NSLog(@"留言及回复");
[self transitionFromViewController:currentViewController toViewController:firstViewController
duration:1 options:UIViewAnimationOptionTransitionCurlUp
animations:^{
// NOPS；
}
completion:^(BOOL finished) {
if (finished) {
currentViewController=firstViewController;
}else{
currentViewController=oldViewController;
}
}];
}
break;
case 2:{
NSLog(@"生日提醒");
[self transitionFromViewController:currentViewController toViewController:secondViewController
duration:1 options:UIViewAnimationOptionTransitionCurlDown
animations:^{
}
completion:^(BOOL finished) {
if (finished) { currentViewController=secondViewController;
}else{ currentViewController=oldViewController;
}
}];
}
break;
case 3:
{
NSLog(@"好友申请");
[self transitionFromViewController:currentViewController
toViewController:thirdViewController
duration:1
options:UIViewAnimationOptionTransitionCrossDissolve
animations:^{
}
completion:^(BOOL finished) {
if (finished) { currentViewController=thirdViewController;
}else{
currentViewController=oldViewController;
}
}];
}
break;
default:
break;
}
}