仿新浪微博 UINavigationController 向左滑动时显示上一个控制器的View.

实现原理,UINavigationController 的 self.view显示时把当前显示的view截图下来，保存到一个数组中。当push一个view时把上一个view的截图放到self.view后面,当self.view向右拖动时显示上一个view。

NavigationController.m

#import "NavigationController.h"

@interface NavigationController ()

/** 存放每个控制器的全屏截图 */

@property (nonatomic, strong) NSMutableArray *images;

@property (nonatomic, strong) UIImageView *lastVcView;

@property (nonatomic, strong) UIView *cover;

@end

@implementation NavigationController

- (UIImageView *)lastVcView

{

    if (!_lastVcView) {

        UIWindow *window = [UIApplication sharedApplication].keyWindow;

        UIImageView *lastVcView = [[UIImageView alloc] init];

        lastVcView.frame = window.bounds;

        self.lastVcView = lastVcView;

    }

    return _lastVcView;

}

- (UIView *)cover

{

    if (!_cover) {

        UIWindow *window = [UIApplication sharedApplication].keyWindow;

        UIView *cover = [[UIView alloc] init];

        cover.backgroundColor = [UIColor blackColor];

        cover.frame = window.bounds;

        cover.alpha = 0.5;

        self.cover = cover;

    }

    return _cover;

}

- (NSMutableArray *)images

{

    if (!_images) {

        self.images = [[NSMutableArray alloc] init];

    }

    return _images;

}

- (void)viewDidLoad {

    [super viewDidLoad];

    // 拖拽手势

    UIPanGestureRecognizer *recognizer = [[UIPanGestureRecognizer alloc] initWithTarget:self action:@selector(dragging:)];

    [self.view addGestureRecognizer:recognizer];

}

- (void)dragging:(UIPanGestureRecognizer *)recognizer

{

    // 假设仅仅有1个子控制器,停止拖拽

    if (self.viewControllers.count <= 1) return;

    // 在x方向上移动的距离

    CGFloat tx = [recognizer translationInView:self.view].x;

    if (tx < 0) return;

    if (recognizer.state == UIGestureRecognizerStateEnded || recognizer.state == UIGestureRecognizerStateCancelled) {

        // 决定pop还是还原

        CGFloat x = self.view.frame.origin.x;

        if (x >= self.view.frame.size.width * 0.5) {

            [UIView animateWithDuration:0.25 animations:^{

                self.view.transform = CGAffineTransformMakeTranslation(self.view.frame.size.width, 0);

            } completion:^(BOOL finished) {

                [self popViewControllerAnimated:NO];

                [self.lastVcView removeFromSuperview];

                [self.cover removeFromSuperview];

                self.view.transform = CGAffineTransformIdentity;

                [self.images removeLastObject];

            }];

        } else {

            [UIView animateWithDuration:0.25 animations:^{

                self.view.transform = CGAffineTransformIdentity;

            }];

        }

    } else {

        // 移动view

        self.view.transform = CGAffineTransformMakeTranslation(tx, 0);

        UIWindow *window = [UIApplication sharedApplication].keyWindow;

        // 加入截图到最后面

        self.lastVcView.image = self.images[self.images.count - 2];

        [window insertSubview:self.lastVcView atIndex:0];

        [window insertSubview:self.cover aboveSubview:self.lastVcView];

    }

}

/**

 *  产生截图

 */

- (void)createScreenShot

{

    UIGraphicsBeginImageContextWithOptions(self.view.frame.size, YES, 0.0);

    [self.view.layer renderInContext:UIGraphicsGetCurrentContext()];

    UIImage *image = UIGraphicsGetImageFromCurrentImageContext();

    [self.images addObject:image];

}

- (void)viewDidAppear:(BOOL)animated

{

    [super viewDidAppear:animated];

    if (self.images.count > 0) return;

    [self createScreenShot];

}

- (void)pushViewController:(UIViewController *)viewController animated:(BOOL)animated

{

    [super pushViewController:viewController animated:animated];

    [self createScreenShot];

}

@end