实现原理

addChildViewController
从使用开始
下载源码下来之后，运行demo
发现Appdelegate的代码如下：

    UINavigationController *navigationController = [[UINavigationController alloc] initWithRootViewController:[[DEMOFirstViewController alloc] init]];
    DEMOLeftMenuViewController *leftMenuViewController = [[DEMOLeftMenuViewController alloc] init];
    DEMORightMenuViewController *rightMenuViewController = [[DEMORightMenuViewController alloc] init];
    
    RESideMenu *sideMenuViewController = [[RESideMenu alloc] initWithContentViewController:navigationController
                                                                    leftMenuViewController:leftMenuViewController
                                                                   rightMenuViewController:rightMenuViewController];
    sideMenuViewController.backgroundImage = [UIImage imageNamed:@"Stars"];
    sideMenuViewController.menuPreferredStatusBarStyle = 1; // UIStatusBarStyleLightContent
    sideMenuViewController.delegate = self;
    sideMenuViewController.contentViewShadowColor = [UIColor blackColor];
    sideMenuViewController.contentViewShadowOffset = CGSizeMake(0, 0);
    sideMenuViewController.contentViewShadowOpacity = 0.6;
    sideMenuViewController.contentViewShadowRadius = 12;
    sideMenuViewController.contentViewShadowEnabled = YES;
    self.window.rootViewController = sideMenuViewController;

包含一个内容控制器navigationController及左视图控制器leftMenuViewController右视图控制器rightMenuViewController

走进初始化方法

- (id)initWithContentViewController:(UIViewController *)contentViewController leftMenuViewController:(UIViewController *)leftMenuViewController rightMenuViewController:(UIViewController *)rightMenuViewController

实现如下：

    self = [self init];
    if (self) {
        _contentViewController = contentViewController;
        _leftMenuViewController = leftMenuViewController;
        _rightMenuViewController = rightMenuViewController;
    }
    return self;

在init中调用commonInit初始化了一堆默认属性。
重写了

@property (strong, readwrite, nonatomic) UIViewController *contentViewController;
@property (strong, readwrite, nonatomic) UIViewController *leftMenuViewController;
@property (strong, readwrite, nonatomic) UIViewController *rightMenuViewController;

这3个属性的set方法。
拿setContentController举例

- (void)setContentViewController:(UIViewController *)contentViewController
{
  //判断如果没有就赋值
    if (!_contentViewController) {
        _contentViewController = contentViewController;
        return;
    }
//赋值之后将页面的所有值清空
    [self hideViewController:_contentViewController];
    _contentViewController = contentViewController;
    //核心代码
   //调用addChildViewController将contentView添加为ResideMenu的子视图
    [self addChildViewController:self.contentViewController];
    self.contentViewController.view.frame = self.view.bounds;
    [self.contentViewContainer addSubview:self.contentViewController.view];
 //添加子视图之后调用，证明已经添加完成
    [self.contentViewController didMoveToParentViewController:self];
    
    [self updateContentViewShadow];
    
    if (self.visible) {
        [self addContentViewControllerMotionEffects];
    }
}

手势添加

    if (self.panGestureEnabled) {
        self.view.multipleTouchEnabled = NO;
        UIPanGestureRecognizer *panGestureRecognizer = [[UIPanGestureRecognizer alloc] initWithTarget:self action:@selector(panGestureRecognized:)];
        panGestureRecognizer.delegate = self;
        [self.view addGestureRecognizer:panGestureRecognizer];
    }

监控每一次手势

- (BOOL)gestureRecognizer:(UIGestureRecognizer *)gestureRecognizer shouldReceiveTouch:(UITouch *)touch

手势滑动触发的回调

//各种操作。。。
- (void)panGestureRecognized:(UIPanGestureRecognizer *)recognizer

//滑动或点击到左右视图后 content的区域为一个button,使用这个button来回去

    self.contentButton = ({
        UIButton *button = [[UIButton alloc] initWithFrame:CGRectNull];
        [button addTarget:self action:@selector(hideMenuViewController) forControlEvents:UIControlEventTouchUpInside];
        button;
    });

实现效果和相关的逻辑判断等有时间再慢慢看。