UITabViewController点击tab的一个转场动画

在一些老项目中,看到了一个点击UITabViewController的tab,左右滑动出现子控制器的转场动画.
虽然是OC写的,但是代码写的还算精简,也比较好用,就先放着这里吧.

.h文件

#import <UIKit/UIKit.h>

@interface Transformer : NSObject <UITabBarControllerDelegate, UIViewControllerAnimatedTransitioning>
@property (assign, nonatomic) NSInteger preIndex;
@property (assign, nonatomic) NSInteger selectedIndex;
@end

.m文件

#import "Transformer.h"
#import "TabBarController.h"

static CGFloat const kPadding  = 10;
static CGFloat const kDamping  = 0.75;
static CGFloat const kVelocity = 2;

@implementation Transformer

- (instancetype)init {
    self = [super init];
    if (self) {
        _preIndex = 0;
        _selectedIndex = 0;
    }
    return self;
}

#pragma mark- UITabBarControllerDelegate
- (id<UIViewControllerAnimatedTransitioning>)tabBarController:(UITabBarController *)tabBarController animationControllerForTransitionFromViewController:(UIViewController *)fromVC toViewController:(UIViewController *)toVC {
    TabBarController *tabVC = (TabBarController *)tabBarController;
    return tabVC.transform;
}

#pragma mark- UIViewControllerAnimatedTransitioning
- (NSTimeInterval)transitionDuration:(id<UIViewControllerContextTransitioning>)transitionContext {
    return 0.5;
}

- (void)animateTransition:(id<UIViewControllerContextTransitioning>)transitionContext {
    NSLog(@"Animation begin... ... ");
    
    UIViewController *toViewController = [transitionContext viewControllerForKey:UITransitionContextToViewControllerKey];
    UIViewController *fromViewController = [transitionContext viewControllerForKey:UITransitionContextFromViewControllerKey];
    UIView *containerView = [transitionContext containerView];
    
    CGFloat translation = containerView.bounds.size.width + kPadding;
    CGAffineTransform transform = CGAffineTransformMakeTranslation(_preIndex > _selectedIndex ? translation : -translation, 0);
    toViewController.view.transform = CGAffineTransformInvert(transform);
    [containerView addSubview:toViewController.view];
    
    [UIView animateWithDuration:[self transitionDuration:transitionContext] delay:0 usingSpringWithDamping:kDamping initialSpringVelocity:kVelocity options:UIViewAnimationOptionCurveEaseInOut animations:^{
        fromViewController.view.transform = transform;
        toViewController.view.transform = CGAffineTransformIdentity;
    } completion:^(BOOL finished) {
        fromViewController.view.transform = CGAffineTransformIdentity;
        [transitionContext completeTransition:![transitionContext transitionWasCancelled]];
    }];
}

@end

使用
在UITabViewController的子类中
.h文件

#import <UIKit/UIKit.h>
@class Transformer;
@interface TabBarController : UITabBarController
@property (nonatomic, strong) UIView *snapShot;
@property (strong, nonatomic) Transformer *transform;
@end

.m文件

#import "TabBarController.h"
#import "AppDelegate.h"
#import "Transformer.h"

@interface TabBarController ()

@end

@implementation TabBarController

- (void)viewDidLoad {
    [super viewDidLoad];
    
    // 添加转场动画的代理
    self.transform = [[Transformer alloc] init];
    self.delegate = self.transform;
}

- (void)viewWillAppear:(BOOL)animated {
    [super viewWillAppear:animated];
    
    weakifySelf
    self.snapShot.frame = self.view.bounds;
    [self.view addSubview:self.snapShot];
    [UIView animateWithDuration:1 animations:^{
        strongifySelf
        self.snapShot.transform = CGAffineTransformScale(CGAffineTransformIdentity, 5, 5);
        self.snapShot.alpha = 0;
    } completion:^(BOOL finished) {
        strongifySelf
        [self.snapShot removeFromSuperview];
        
    }];
}

- (void)viewDidAppear:(BOOL)animated {
    [super viewDidAppear:animated];
    
    // 用于设置tabbar itemz中的tag
    for (NSInteger i = 0; i < self.childViewControllers.count; i++) {
        [self.tabBar.items[i] setTag:i];
    }
    
    AppDelegate *appDelegate = (AppDelegate *)[UIApplication sharedApplication].delegate;
    [[NSUserDefaults standardUserDefaults] setBool:true forKey:@"didShowTab"];
    [[NSUserDefaults standardUserDefaults] synchronize];
    [appDelegate startTimer];
}

#pragma mark- UITabBarDelegate
- (void)tabBar:(UITabBar *)tabBar didSelectItem:(UITabBarItem *)item {
    self.transform.selectedIndex = item.tag;
    self.transform.preIndex = self.selectedIndex;
}

@end