MHGSwipeNavigationController.h

//
//  MHGSwipeNavigationController.h
//  SwipeNavigationController
//
//  Created by 缪和光 on 28/12/2013.
//  Copyright (c) 2013 Hokuang. All rights reserved.
//

#import <UIKit/UIKit.h>

@interface MHGSwipeNavigationController : UINavigationController

@property (nonatomic, strong, readonly) UIPanGestureRecognizer *mhg_popGestureRecognizer;

@end

MHGSwipeNavigationController.m

//
//  MHGSwipeNavigationController.m
//  SwipeNavigationController
//
//  Created by 缪和光 on 28/12/2013.
//  Copyright (c) 2013 Hokuang. All rights reserved.
//

#import "MHGSwipeNavigationController.h"

#define KEY_WINDOW  [[UIApplication sharedApplication] keyWindow]
#define TOP_VIEW    (KEY_WINDOW.rootViewController.view)

@interface MHGSwipeNavigationController ()

@property (nonatomic, strong) NSMutableArray *snapshotStack;
@property (nonatomic, strong) UIImageView *snapshotImageView;

@property (nonatomic, assign) CGFloat lastTouchX;

@end

@implementation MHGSwipeNavigationController

- (id)initWithCoder:(NSCoder *)aDecoder {
    self = [super initWithCoder:aDecoder];
    if (self) {
        [self commonInit];
    }
    return self;
}

- (id)initWithRootViewController:(UIViewController *)rootViewController {
    self = [super initWithRootViewController:rootViewController];
    if (self) {
        [self commonInit];
    }
    return self;
}

- (id)init {
    self = [super init];
    if (self) {
        [self commonInit];
    }
    return self;
}

- (void)commonInit {
    if ([self respondsToSelector:@selector(interactivePopGestureRecognizer)]) {
        self.interactivePopGestureRecognizer.enabled = NO;
    }
}


- (void)viewDidLoad
{
    [super viewDidLoad];
    UIPanGestureRecognizer *panGestureRecognizer = [[UIPanGestureRecognizer alloc] initWithTarget:self action:@selector(handlePanGesture:)];
    [self.view addGestureRecognizer:panGestureRecognizer];
    _mhg_popGestureRecognizer = panGestureRecognizer;
}

- (void)viewWillAppear:(BOOL)animated
{
    [self addShadowForView];
}

#pragma mark - capture last view's snapshot

- (UIImage *)takeSnapshot
{
    UIGraphicsBeginImageContextWithOptions(TOP_VIEW.bounds.size, TOP_VIEW.opaque, 0.0);
    [TOP_VIEW.layer renderInContext:UIGraphicsGetCurrentContext()];
    UIImage *snapshot = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    
    return snapshot;
}

#pragma mark - override push

- (void)pushViewController:(UIViewController *)viewController animated:(BOOL)animated
{
    if (!self.snapshotStack) {
        self.snapshotStack = [[NSMutableArray alloc] initWithCapacity:5];
    }
    
    UIImage *snapshot = [self takeSnapshot];
    if (snapshot) [self.snapshotStack addObject:snapshot];
    
    [super pushViewController:viewController animated:animated];
}

- (UIViewController *)popViewControllerAnimated:(BOOL)animated
{
    [self.snapshotStack removeLastObject];
    return [super popViewControllerAnimated:animated];
}

#pragma mark - handlePanGesture

- (void)handlePanGesture:(UIPanGestureRecognizer *)panGestureRecognizer
{
    if (self.viewControllers.count <= 1) return ;
    
    CGPoint point = [panGestureRecognizer locationInView:KEY_WINDOW];
    
    if (panGestureRecognizer.state == UIGestureRecognizerStateBegan) {
        [self initSnapshot];
        self.snapshotImageView.image = [self.snapshotStack lastObject];
        self.snapshotImageView.hidden = NO;
        [TOP_VIEW.superview insertSubview:self.snapshotImageView belowSubview:TOP_VIEW];
        self.lastTouchX = point.x;
//        [self addShadowForView];
    } else if (panGestureRecognizer.state == UIGestureRecognizerStateChanged) {
        CGRect frame = TOP_VIEW.frame;
        CGFloat newX = (point.x - self.lastTouchX) + frame.origin.x;
        if (newX < 0) {
            return;
        }
        frame.origin.x = newX;
        TOP_VIEW.frame = frame;
        self.lastTouchX = point.x;
        [self offsetImageViewForX:newX];
    } else {
        [self judgeToPushOrPop];
    }
}

- (void)initSnapshot
{
    if (!self.snapshotImageView) {
        self.snapshotImageView = [[UIImageView alloc] initWithFrame:TOP_VIEW.bounds];
    }
    CGRect imageViewFrame = TOP_VIEW.bounds;
    imageViewFrame.origin.x = -TOP_VIEW.bounds.size.width / 3 * 2;
    self.snapshotImageView.frame = imageViewFrame;
}

#pragma mark - judgeToPushOrPop

- (void)judgeToPushOrPop
{
    __block CGRect frame = TOP_VIEW.frame;
    if (frame.origin.x > (frame.size.width / 3)) {
        [UIView animateWithDuration:0.3 animations:^{
            frame.origin.x = frame.size.width;
            TOP_VIEW.frame = frame;
            [self offsetImageViewForX:frame.origin.x];
        } completion:^(BOOL finished) {
            [self popViewControllerAnimated:NO];
            self.snapshotImageView.hidden = YES;
            frame.origin.x = 0;
            TOP_VIEW.frame = frame;
        }];
    } else {
        [UIView animateWithDuration:0.3 animations:^{
            frame.origin.x = 0;
            TOP_VIEW.frame = frame;
            [self offsetImageViewForX:frame.origin.x];
        } completion:^(BOOL finished) {
            self.snapshotImageView.hidden = YES;
        }];
    }
}

- (void)offsetImageViewForX:(CGFloat)x {
    CGFloat imageViewX = x / 3 * 2  -TOP_VIEW.bounds.size.width / 3 * 2;
    CGRect imageViewFrame = self.snapshotImageView.frame;
    imageViewFrame.origin.x = imageViewX;
    self.snapshotImageView.frame = imageViewFrame;
}

- (void)addShadowForView {
    UIView *shadowedView = self.view;
    UIBezierPath* newShadowPath = [UIBezierPath bezierPathWithRect:shadowedView.bounds];
    shadowedView.layer.masksToBounds = NO;
    shadowedView.layer.shadowRadius = 10;
    shadowedView.layer.shadowOpacity = 1;
    shadowedView.layer.shadowColor = [[UIColor blackColor] CGColor];
    shadowedView.layer.shadowOffset = CGSizeZero;
    shadowedView.layer.shadowPath = [newShadowPath CGPath];
}
@end