CATransition过渡

开发中，我们都希望能通过属性动画对一些比较难做动画的布局做变化，而属性动画只对图层的可动画属性起作用，所以要改变一个不能动画的属性或者从当前界面移除，属性动画将不起作用。

为了解决上面的问题，才有了过渡动画，过渡动画不像属性动画那样很平滑的从一个值过渡到另一个值，而是先出现上一个图形的轮廓外观，然后在两者之间进行交换，替换。

要是用过渡动画就要使用CATransition，它有type和subType两个属性来控制变化的效果：
type的属性是一个NSString类型，有下面几个值：

 kCATransitionFade
 kCATransitionMoveIn
 kCATransitionPush
 kCATransitionReveal

subType来控制滑入的方向：

kCATransitionFromRight
kCATransitionFromLeft
kCATransitionFromTop
kCATransitionFromBottom

下面简单写了个Demo，先看效果图：

很明显两者的变化是有区别的。

//
//  ViewController.m
//  CATransition过渡
//
//  Created by 刘浩浩 on 16/6/27.
//  Copyright © 2016年 CodingFire. All rights reserved.
//

#import "ViewController.h"

@interface ViewController ()
{
    UIImageView *imageView;
     NSArray *images;
}
@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
    imageView=[[UIImageView alloc]initWithFrame:CGRectMake(80, 80, 150, 150)];
    [self.view addSubview:imageView];
    images = @[[UIImage imageNamed:@"1"],
                    [UIImage imageNamed:@"2"],
                    [UIImage imageNamed:@"3"],
                    [UIImage imageNamed:@"4"]];
    UIButton *btn = [UIButton buttonWithType:UIButtonTypeRoundedRect];
    btn.frame = CGRectMake(20, 568-100, 280, 40);
    [btn setTitle:@"Switch 突兀" forState:UIControlStateNormal];
    btn.layer.cornerRadius=5;
    btn.layer.borderWidth=1;
    btn.layer.borderColor = [UIColor blackColor].CGColor;
    [btn addTarget:self action:@selector(switchImage) forControlEvents:UIControlEventTouchUpInside];
    [self.view addSubview:btn];

    UIButton *btn1 = [UIButton buttonWithType:UIButtonTypeRoundedRect];
    btn1.frame = CGRectMake(20, 568-50, 280, 40);
    [btn1 setTitle:@"Switch 平滑" forState:UIControlStateNormal];
    btn1.layer.cornerRadius=5;
    btn1.layer.borderWidth=1;
    btn1.layer.borderColor = [UIColor blackColor].CGColor;
    [btn1 addTarget:self action:@selector(switchImage1) forControlEvents:UIControlEventTouchUpInside];
    [self.view addSubview:btn1];


}
-(void)switchImage
{
    UIImage *currentImage = imageView.image;
    NSUInteger index = [images indexOfObject:currentImage];
    index = (index + 1) % [images count];
    imageView.image = images[index];
}
- (void)switchImage1
{
    //set up crossfade transition
    CATransition *transition = [CATransition animation];
    //切换模式
    transition.type = kCATransitionFade;
    //apply transition to imageview backing layer
    [imageView.layer addAnimation:transition forKey:nil];
    //cycle to next image
    UIImage *currentImage = imageView.image;
    NSUInteger index = [images indexOfObject:currentImage];
    index = (index + 1) % [images count];
    imageView.image = images[index];
}
- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

@end

Demo下载地址：https://github.com/codeliu6572/CATransition