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使用方法教程

使用方法及教程，查看项目源码github地址：https://github.com/ChenYilong/CYLTabBarController，非常感谢开源的作者，开源促进社区的发展，共建和谐社会😆！

框架全部文件结构

1.CYLTabBarController
2. CYLTabBar
3.CYLPlusButton
4.UIViewController+CYLTabBarControllerExtention
5.UIView+CYLTabBarControllerExtention
6.UITabBarItem+CYLTabBarControllerExtention
7.UIControl+CYLTabBarControllerExtention
8.CYLConstants
8.总结

解读CYLTabBar类文件,在源码中中文注释自己的理解👇

CYLTabBar类文件（.h,.m）

解读CYLTabBar.h, CYLTabBar.m

可能需要理解的知识点：
. sizeThatFits 【 http://www.jianshu.com/p/c9ce5e195a07】
.Block代码块 【 http://www.jianshu.com/p/14efa33b3562】
.KVO设计模式 【 http://www.jianshu.com/p/e59bb8f59302】
.KVC设计模式 【 http://www.jianshu.com/p/45cbd324ea65】

CYLTabBarController.h文件

#import <UIKit/UIKit.h>

@interface CYLTabBar : UITabBar

/*!
 * 让 `TabImageView` 垂直居中时，所需要的默认偏移量。
 * `viewController.tabBarItem.imageInsets = UIEdgeInsetsMake(tabImageViewDefaultOffset, 0, -tabImageViewDefaultOffset, 0);`
 */

//所需要的默认偏移量，在CYLTabBarController第一篇的解读中，通过kvo监听这个属性进行位置调整设置
@property (nonatomic, assign, readonly) CGFloat tabImageViewDefaultOffset;

@end

CYLTabbar.m

#import "CYLTabBar.h"
#import "CYLPlusButton.h"
#import "CYLTabBarController.h"
#import "CYLConstants.h"

//定义一个静态常量，KVO注册监听的标识
static void *const CYLTabBarContext = (void*)&CYLTabBarContext;

@interface CYLTabBar ()

//遵循CYLPlusButtonSubclassing协议的一个凸出按钮
@property (nonatomic, strong) UIButton<CYLPlusButtonSubclassing> *plusButton;
//item的宽度
@property (nonatomic, assign) CGFloat tabBarItemWidth;
//item的数组
@property (nonatomic, copy) NSArray *tabBarButtonArray;

@end

@implementation CYLTabBar

#pragma mark -
#pragma mark - 初始化

- (instancetype)initWithFrame:(CGRect)frame {
    self = [super initWithFrame:frame];
    if (self) {
        self = [self sharedInit];
    }
    return self;
}

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

- (instancetype)sharedInit {
    if (CYLExternPlusButton) {
        self.plusButton = CYLExternPlusButton;
        [self addSubview:(UIButton *)self.plusButton];
    }
    // KVO注册监听（上面自定义的属性tabBarItemWidth）
    _tabBarItemWidth = CYLTabBarItemWidth;
    [self addObserver:self forKeyPath:@"tabBarItemWidth" options:NSKeyValueObservingOptionNew context:CYLTabBarContext];
    return self;
}

//适配iOS11
- (CGSize)sizeThatFits:(CGSize)size {
    CGSize sizeThatFits = [super sizeThatFits:size];
    CGFloat height = [self cyl_tabBarController].tabBarHeight;
    if (height > 0 && !CYL_IS_IPHONE_X && CYL_IS_IOS_11) {
        sizeThatFits.height = [self cyl_tabBarController].tabBarHeight;
    }
    return sizeThatFits;
}

//懒加载，获取元素数组
- (NSArray *)tabBarButtonArray {
    if (_tabBarButtonArray == nil) {
        _tabBarButtonArray = @[];
    }
    return _tabBarButtonArray;
}

//布局控件
- (void)layoutSubviews {
    [super layoutSubviews];
    CGFloat taBarWidth = self.bounds.size.width;
    CGFloat taBarHeight = self.bounds.size.height;
    CYLTabBarItemWidth = (taBarWidth - CYLPlusButtonWidth) / CYLTabbarItemsCount;
    self.tabBarItemWidth = CYLTabBarItemWidth;
    
    //获取根据位置X的大小来排序子视图
    NSArray *sortedSubviews = [self sortedSubviews];
    //从排好序的tabbar子视图数组中，筛选出来UITabBarItem数组
    self.tabBarButtonArray = [self tabBarButtonFromTabBarSubviews:sortedSubviews];
    //遍历TabbarItem的子视图，设置获取偏移，tabImageViewDefaultOffset
    [self setupTabImageViewDefaultOffset:self.tabBarButtonArray[0]];
    if (!CYLExternPlusButton) {
        return;
    }
    //假如有自定义的凸起按钮，设置凸起按钮的center
    CGFloat multiplierOfTabBarHeight = [self multiplierOfTabBarHeight:taBarHeight];
    CGFloat constantOfPlusButtonCenterYOffset = [self constantOfPlusButtonCenterYOffsetForTabBarHeight:taBarHeight];
    self.plusButton.center = CGPointMake(taBarWidth * 0.5, taBarHeight * multiplierOfTabBarHeight + constantOfPlusButtonCenterYOffset);
    NSUInteger plusButtonIndex = [self plusButtonIndex];
    
    //根据凸起按钮的index位置进行遍历修改其他tabbarItem的位置
    [self.tabBarButtonArray enumerateObjectsUsingBlock:^(UIView * _Nonnull childView, NSUInteger buttonIndex, BOOL * _Nonnull stop) {
        //调整UITabBarItem的位置
        CGFloat childViewX;
        if (buttonIndex >= plusButtonIndex) {
            childViewX = buttonIndex * CYLTabBarItemWidth + CYLPlusButtonWidth;
        } else {
            childViewX = buttonIndex * CYLTabBarItemWidth;
        }
        //仅修改childView的x和宽度,yh值不变
        childView.frame = CGRectMake(childViewX,
                                     CGRectGetMinY(childView.frame),
                                     CYLTabBarItemWidth,
                                     CGRectGetHeight(childView.frame)
                                     );
    }];
    //把凸起按钮放到最上层视图
    [self bringSubviewToFront:self.plusButton];
}

#pragma mark -
#pragma mark - Private Methods

+ (BOOL)automaticallyNotifiesObserversForKey:(NSString *)key {
    return NO;
}

// KVO监听执行
- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context {
    if(context != CYLTabBarContext) {
        [super observeValueForKeyPath:keyPath ofObject:object change:change context:context];
        return;
    }
    //发送通知，CYLTabBarItemWidthDidChangeNotification，在CYLTabBarController中定义了
    if(context == CYLTabBarContext) {
        [[NSNotificationCenter defaultCenter] postNotificationName:CYLTabBarItemWidthDidChangeNotification object:self];
    }
}

- (void)dealloc {
    // KVO反注册
    [self removeObserver:self forKeyPath:@"tabBarItemWidth"];
}

- (void)setTabBarItemWidth:(CGFloat )tabBarItemWidth {
    if (_tabBarItemWidth != tabBarItemWidth) {
        [self willChangeValueForKey:@"tabBarItemWidth"];
        _tabBarItemWidth = tabBarItemWidth;
        [self didChangeValueForKey:@"tabBarItemWidth"];
    }
}

- (void)setTabImageViewDefaultOffset:(CGFloat)tabImageViewDefaultOffset {
    if (tabImageViewDefaultOffset != 0.f) {
        [self willChangeValueForKey:@"tabImageViewDefaultOffset"];
        _tabImageViewDefaultOffset = tabImageViewDefaultOffset;
        [self didChangeValueForKey:@"tabImageViewDefaultOffset"];
    }
}

//获取代理中taBarHeight的高度比例
- (CGFloat)multiplierOfTabBarHeight:(CGFloat)taBarHeight {
    CGFloat multiplierOfTabBarHeight;
    if ([[self.plusButton class] respondsToSelector:@selector(multiplierOfTabBarHeight:)]) {
        multiplierOfTabBarHeight = [[self.plusButton class] multiplierOfTabBarHeight:taBarHeight];
    }
    
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Wdeprecated-declarations"
    else if ([[self.plusButton class] respondsToSelector:@selector(multiplerInCenterY)]) {
        multiplierOfTabBarHeight = [[self.plusButton class] multiplerInCenterY];
    }
#pragma clang diagnostic pop
    
    else {
        CGSize sizeOfPlusButton = self.plusButton.frame.size;
        CGFloat heightDifference = sizeOfPlusButton.height - self.bounds.size.height;
        if (heightDifference < 0) {
            multiplierOfTabBarHeight = 0.5;
        } else {
            CGPoint center = CGPointMake(self.bounds.size.height * 0.5, self.bounds.size.height * 0.5);
            center.y = center.y - heightDifference * 0.5;
            multiplierOfTabBarHeight = center.y / self.bounds.size.height;
        }
    }
    return multiplierOfTabBarHeight;
}

//获取代理中偏移常量，通过该常量进行调整凸起按钮的位置
- (CGFloat)constantOfPlusButtonCenterYOffsetForTabBarHeight:(CGFloat)taBarHeight {
    CGFloat constantOfPlusButtonCenterYOffset = 0.f;
    if ([[self.plusButton class] respondsToSelector:@selector(constantOfPlusButtonCenterYOffsetForTabBarHeight:)]) {
        constantOfPlusButtonCenterYOffset = [[self.plusButton class] constantOfPlusButtonCenterYOffsetForTabBarHeight:taBarHeight];
    }
    return constantOfPlusButtonCenterYOffset;
}

//获取凸起按钮的index位置
- (NSUInteger)plusButtonIndex {
    NSUInteger plusButtonIndex;
    if ([[self.plusButton class] respondsToSelector:@selector(indexOfPlusButtonInTabBar)]) {
        //根据代理获取凸起按钮的index位置
        plusButtonIndex = [[self.plusButton class] indexOfPlusButtonInTabBar];
        //仅修改self.plusButton的x,ywh值不变
        self.plusButton.frame = CGRectMake(plusButtonIndex * CYLTabBarItemWidth,
                                           CGRectGetMinY(self.plusButton.frame),
                                           CGRectGetWidth(self.plusButton.frame),
                                           CGRectGetHeight(self.plusButton.frame)
                                           );
    } else {
        if (CYLTabbarItemsCount % 2 != 0) {
            [NSException raise:@"CYLTabBarController" format:@"If the count of CYLTabbarControllers is odd,you must realizse `+indexOfPlusButtonInTabBar` in your custom plusButton class.【Chinese】如果CYLTabbarControllers的个数是奇数，你必须在你自定义的plusButton中实现`+indexOfPlusButtonInTabBar`，来指定plusButton的位置"];
        }
        //设置默认在中间
        plusButtonIndex = CYLTabbarItemsCount * 0.5;
    }
    CYLPlusButtonIndex = plusButtonIndex;
    return plusButtonIndex;
}

//根据位置x排序视图得到视图数组
- (NSArray *)sortedSubviews {
    NSArray *sortedSubviews = [self.subviews sortedArrayUsingComparator:^NSComparisonResult(UIView * formerView, UIView * latterView) {
        CGFloat formerViewX = formerView.frame.origin.x;
        CGFloat latterViewX = latterView.frame.origin.x;
        return  (formerViewX > latterViewX) ? NSOrderedDescending : NSOrderedAscending;
    }];
    return sortedSubviews;
}

//从排好序的tabbar子视图数组中，筛选出来UITabBarItem数组
- (NSArray *)tabBarButtonFromTabBarSubviews:(NSArray *)tabBarSubviews {
    NSMutableArray *tabBarButtonMutableArray = [NSMutableArray arrayWithCapacity:tabBarSubviews.count - 1];
    [tabBarSubviews enumerateObjectsUsingBlock:^(UIView * _Nonnull obj, NSUInteger idx, BOOL * _Nonnull stop) {
        //遍历排好序的子视图，假如是uicontrol对象，再判断是不是tabbar前缀的对象如UITabBarItem
        if ([obj cyl_isTabButton]) { //假如是UITabBarItem对象类型，
            [tabBarButtonMutableArray addObject:obj];
        }
    }];
    //假如存在自定义视图（凸起按钮视图），需要删除对应位置的元素
    if (CYLPlusChildViewController) {
        [tabBarButtonMutableArray removeObjectAtIndex:CYLPlusButtonIndex];
    }
    return [tabBarButtonMutableArray copy];
}

//遍历TabbarItem的子视图，找到imageView视图，根据这个视图进行设置赋值图片的偏移属性tabImageViewDefaultOffset
- (void)setupTabImageViewDefaultOffset:(UIView *)tabBarButton {
    __block BOOL shouldCustomizeImageView = YES;
    __block CGFloat tabImageViewHeight = 0.f;
    __block CGFloat tabImageViewDefaultOffset = 0.f;
    CGFloat tabBarHeight = self.frame.size.height;
    [tabBarButton.subviews enumerateObjectsUsingBlock:^(__kindof UIView * _Nonnull obj, NSUInteger idx, BOOL * _Nonnull stop) {
        if ([obj cyl_isTabLabel]) {
            shouldCustomizeImageView = NO;
        }
        tabImageViewHeight = obj.frame.size.height;
        //假如是tabbarItem的ImageView
        BOOL isTabImageView = [obj cyl_isTabImageView];
        if (isTabImageView) {
            tabImageViewDefaultOffset = (tabBarHeight - tabImageViewHeight) * 0.5 * 0.5;
        }
        if (isTabImageView && tabImageViewDefaultOffset == 0.f) {
            shouldCustomizeImageView = NO;
        }
    }];
    if (shouldCustomizeImageView && !CYL_IS_IPHONE_X) {
        self.tabImageViewDefaultOffset = tabImageViewDefaultOffset;
    }
}

/*!
 *  Capturing touches on a subview outside the frame of its superview.
 */
- (UIView *)hitTest:(CGPoint)point withEvent:(UIEvent *)event {
    //1. 边界情况：不能响应点击事件
    
    BOOL canNotResponseEvent = self.hidden || (self.alpha <= 0.01f) || (self.userInteractionEnabled == NO);
    if (canNotResponseEvent) {
        return nil;
    }
    
    //2. 优先处理 PlusButton （包括其突出的部分）、TabBarItems 未凸出的部分
    //这一步主要是在处理只有两个 TabBarItems 的场景。
    // 2.1先考虑clipsToBounds情况：子view超出部分没有显示出来
    if (self.clipsToBounds && ![self pointInside:point withEvent:event]) {
        return nil;
    }
    
    if (CYLExternPlusButton) {
        CGRect plusButtonFrame = self.plusButton.frame;
        BOOL isInPlusButtonFrame = CGRectContainsPoint(plusButtonFrame, point);
        if (isInPlusButtonFrame) {
            return CYLExternPlusButton;
        }
    }
    NSArray *tabBarButtons = self.tabBarButtonArray;
    if (self.tabBarButtonArray.count == 0) {
        tabBarButtons = [self tabBarButtonFromTabBarSubviews:self.subviews];
    }
    for (NSUInteger index = 0; index < tabBarButtons.count; index++) {
        UIView *selectedTabBarButton = tabBarButtons[index];
        CGRect selectedTabBarButtonFrame = selectedTabBarButton.frame;
        BOOL isTabBarButtonFrame = CGRectContainsPoint(selectedTabBarButtonFrame, point);\
        if (isTabBarButtonFrame) {
            return selectedTabBarButton;
        }
    }
    
    //3. 最后处理 TabBarItems 凸出的部分、添加到 TabBar 上的自定义视图、点击到 TabBar 上的空白区域
    
    UIView *result = [super hitTest:point withEvent:event];
    if (result) {
        return result;
    }
    
    for (UIView *subview in self.subviews.reverseObjectEnumerator) {
        CGPoint subPoint = [subview convertPoint:point fromView:self];
        result = [subview hitTest:subPoint withEvent:event];
        if (result) {
            return result;
        }
    }
    return nil;
}

@end

总结：

通过继承系统的UITabbar控件，自定义了CYLTabbar类，这个类是是通过KVC替换UITabbarController中的系统UITabbar,替换为CYLTabbar

主要功能：
1、根据遍历tabbar中的子视图，给每个Item对象的图片做偏移量设置处理，设置每个item的宽度，并且KVO进行监听item的宽度变化，发出通知
2、通过获取凸起按钮的代理设置的偏移常量，高度比例因子，凸起按钮的index位置，进行布局更新每个item的位置，并且设置处理好凸起按钮的位置。
3、通过对点击视图的方法进行改写，进行凸起按钮的点击事件处理，保证点击按钮凸出部分可以响应点击事件