iOS 导航栏透明

在最近一个项目中碰到这样一个场景,在被push进来的一个页面设置导航栏透明,且要求控制对tableview组的头视图进行悬停显示,nav随着tableview偏移量改变透明度,当然这样的需求确实不是什么难事,但是如果当前页面继续push一个不需要此类效果的页面,当在返回当前页面的时候就会出现一个坑,nav的展示很突兀,下面是直接上解决方法...ps:假设A页面为需要设置透明,B页面被Apush且不需要设置透明

A.m

首先在需要设置导航栏透明的页面的viewDidload中写上

self.title = @"Title";
[self.navigationController.navigationBar setBackgroundImage:[UIImage new] forBarMetrics:UIBarMetricsDefault];
    self.navigationController.navigationBar.shadowImage = [UIImage new];
    self.barImageView = self.navigationController.navigationBar.subviews.firstObject;
    self.barImageView.alpha = 0;
    //设置状态栏
    [[UIApplication sharedApplication] setStatusBarStyle:UIStatusBarStyleLightContent];
    //设置标题颜色
    self.navigationController.navigationBar.titleTextAttributes = @{NSForegroundColorAttributeName : [UIColor clearColor]};
   

在scrollViewDidScroll代理方法中

-(void)scrollViewDidScroll:(UIScrollView *)scrollView {
 
    CGFloat offset = scrollView.contentOffset.y;
    //根据自己需要设置(136)的大小
    CGFloat alpha = offset / 136;
    _barImageView.alpha = alpha;
    //记录下当前的透明度,在返回当前页面时需要
    _alpha = alpha;
    [[NSUserDefaults standardUserDefaults] setObject:[NSNumber numberWithFloat:alpha] forKey:@"_alpha"];
    //设置标题的透明度
    self.navigationController.navigationBar.titleTextAttributes = @{NSForegroundColorAttributeName : [UIColor colorWithWhite:0 alpha:alpha]};
}

当前页的viewWillAppear, viewDidAppear, viewWillDisappear

-(void)viewWillAppear:(BOOL)animated
{
    
    [super viewWillAppear:animated];
    self.table.delegate = self;

   BOOL isGesturePop = [[[NSUserDefaults standardUserDefaults] objectForKey:@"isGesturePop"] boolValue];
    self.navigationController.navigationBar.titleTextAttributes = @{NSForegroundColorAttributeName : [UIColor colorWithWhite:0 alpha:_alpha]};
    if (!isGesturePop) {
        [UIView animateWithDuration:0.25 animations:^{
            _barImageView.alpha = _alpha;
            self.navigationController.navigationBar.titleTextAttributes = @{NSForegroundColorAttributeName : [UIColor colorWithWhite:0 alpha:_alpha]};
        }];
    }
}

-(void)viewDidAppear:(BOOL)animated {
    //BOOL isGesturePop = [[[NSUserDefaults standardUserDefaults] objectForKey:@"isGesturePop"] boolValue];
//    if (!isGesturePop) {
   //     _barImageView.alpha = _alpha;
      //  self.navigationController.navigationBar.titleTextAttributes = @{NSForegroundColorAttributeName : [UIColor colorWithWhite:0 alpha:_alpha]};
    //}
    [super viewDidAppear:animated];
}

-(void)viewWillDisappear:(BOOL)animated
{
    [super viewWillDisappear:animated];
    self.table.delegate = nil;
    self.navigationController.navigationBar.titleTextAttributes = @{NSForegroundColorAttributeName : [UIColor blackColor]};
    
    _barImageView.alpha = 1;
    [[NSUserDefaults standardUserDefaults] setObject:[NSNumber numberWithBool:NO] forKey:@"isGesturePop"];
}

那么在我们需要push的下一个页面需要什么操作呢,我们需要在这个页面显示正常的nav并且禁掉系统的手势pop,自己写一个pop手势,以方便我们拿到pop滑动时的偏移量,在做的时候使用了两个类,在最后会有源码贴出

B.m 须遵守UIGestureRecognizerDelegate,并导入NavigationInteractiveTransition.h

全局变量

@property (nonatomic, strong) NavigationInteractiveTransition *navT;

viewDidLoad

self.navigationController.interactivePopGestureRecognizer.enabled = NO;
    
    UIGestureRecognizer *gesture = self.navigationController.interactivePopGestureRecognizer;
    gesture.enabled = NO;
    UIView *gestureView = gesture.view;
    
    UIPanGestureRecognizer *popRecognizer = [[UIPanGestureRecognizer alloc] init];
    popRecognizer.delegate = self;
    popRecognizer.maximumNumberOfTouches = 1;
    [gestureView addGestureRecognizer:popRecognizer];
    
    _navT = [[NavigationInteractiveTransition alloc] initWithViewController:self.navigationController];
    [popRecognizer addTarget:_navT action:@selector(handleControllerPop:)];

UIGestureRecognizerDelegate 代理方法gestureRecognizerShouldBegin

- (BOOL)gestureRecognizerShouldBegin:(UIGestureRecognizer *)gestureRecognizer {
    //记录当前是是否是通过手势滑动回去
    [[NSUserDefaults standardUserDefaults] setObject:[NSNumber numberWithBool:YES] forKey:@"isGesturePop"];
    /**
     *  这里有两个条件不允许手势执行,1、当前控制器为根控制器;2、如果这个push、pop动画正在执行(私有属性)
     */
    return self.navigationController.viewControllers.count != 1 && ![[self.navigationController valueForKey:@"_isTransitioning"] boolValue];
}

需要依赖的两个类源码

NavigationInteractiveTransition.h

#import <UIKit/UIKit.h>

@class UIViewController, UIPercentDrivenInteractiveTransition;
@interface NavigationInteractiveTransition : NSObject <UINavigationControllerDelegate>
- (instancetype)initWithViewController:(UIViewController *)vc;
- (void)handleControllerPop:(UIPanGestureRecognizer *)recognizer;
- (UIPercentDrivenInteractiveTransition *)interactivePopTransition;
@end

NavigationInteractiveTransition.m

#import "NavigationInteractiveTransition.h"
#import "PopAnimation.h"

@interface NavigationInteractiveTransition ()
@property (nonatomic, weak) UINavigationController *vc;
@property (nonatomic, strong) UIPercentDrivenInteractiveTransition *interactivePopTransition;
@property(nonatomic, strong) UIImageView *barImageView;
@end

@implementation NavigationInteractiveTransition

- (instancetype)initWithViewController:(UIViewController *)vc
{
    self = [super init];
    if (self) {
        self.vc = (UINavigationController *)vc;
        self.vc.delegate = self;
    }
    return self;
}

/**
 *  我们把用户的每次Pan手势操作作为一次pop动画的执行
 */
- (void)handleControllerPop:(UIPanGestureRecognizer *)recognizer {
    /**
     *  interactivePopTransition就是我们说的方法2返回的对象,我们需要更新它的进度来控制Pop动画的流程,我们用手指在视图中的位置与视图宽度比例作为它的进度。
     */
    CGFloat progress = [recognizer translationInView:recognizer.view].x / recognizer.view.bounds.size.width;
    [self.vc.navigationBar setBackgroundImage:[UIImage new] forBarMetrics:UIBarMetricsDefault];
    self.vc.navigationBar.shadowImage = [UIImage new];
    self.barImageView = self.vc.navigationBar.subviews.firstObject;
    
    CGFloat alpha = [[[NSUserDefaults standardUserDefaults] objectForKey:@"_alpha"] floatValue];
    self.barImageView.alpha = 1 - progress > alpha ? alpha : 1 - progress;
//    NSLog(@"===progress==%.2f",progress);
    /**
     *  稳定进度区间,让它在0.0(未完成)~1.0(已完成)之间
     */
    progress = MIN(1.0, MAX(0.0, progress));
    if (recognizer.state == UIGestureRecognizerStateBegan) {
        /**
         *  手势开始,新建一个监控对象
         */
        self.interactivePopTransition = [[UIPercentDrivenInteractiveTransition alloc] init];
        /**
         *  告诉控制器开始执行pop的动画
         */
        [self.vc popViewControllerAnimated:YES];
    }
    else if (recognizer.state == UIGestureRecognizerStateChanged) {
        
        /**
         *  更新手势的完成进度
         */
        [self.interactivePopTransition updateInteractiveTransition:progress];
    }
    else if (recognizer.state == UIGestureRecognizerStateEnded || recognizer.state == UIGestureRecognizerStateCancelled) {
        
        /**
         *  手势结束时如果进度大于一半,那么就完成pop操作,否则重新来过。
         */
        if (progress > 0.5) {
            [self.interactivePopTransition finishInteractiveTransition];
            self.barImageView.alpha = 0;;
        }
        else {
            [self.interactivePopTransition cancelInteractiveTransition];
        }

        self.interactivePopTransition = nil;
    }
    
}

- (id<UIViewControllerAnimatedTransitioning>)navigationController:(UINavigationController *)navigationController
                                  animationControllerForOperation:(UINavigationControllerOperation)operation
                                               fromViewController:(UIViewController *)fromVC
                                                 toViewController:(UIViewController *)toVC {
    /**
     *  方法1中判断如果当前执行的是Pop操作,就返回我们自定义的Pop动画对象。
     */
    if (operation == UINavigationControllerOperationPop)
        return [[PopAnimation alloc] init];

    return nil;
}

- (id<UIViewControllerInteractiveTransitioning>)navigationController:(UINavigationController *)navigationController
                         interactionControllerForAnimationController:(id<UIViewControllerAnimatedTransitioning>)animationController {

    /**
     *  方法2会传给你当前的动画对象animationController,判断如果是我们自定义的Pop动画对象,那么就返回interactivePopTransition来监控动画完成度。
     */
    if ([animationController isKindOfClass:[PopAnimation class]])
        return self.interactivePopTransition;

    return nil;
}

@end

PopAnimation.h

#import <Foundation/Foundation.h>
#import <UIKit/UIKit.h>

@interface PopAnimation : NSObject <UIViewControllerAnimatedTransitioning>

@end

PopAnimation.m

#import "PopAnimation.h"

@interface PopAnimation ()
@property (nonatomic, strong) id <UIViewControllerContextTransitioning> transitionContext;
@end

@implementation PopAnimation

- (NSTimeInterval)transitionDuration:(id <UIViewControllerContextTransitioning>)transitionContext {
    //这个方法返回动画执行的时间
    return 0.25;
}

/**
 *  transitionContext你可以看作是一个工具,用来获取一系列动画执行相关的对象,并且通知系统动画是否完成等功能。
 */
- (void)animateTransition:(id <UIViewControllerContextTransitioning>)transitionContext {
    /**
     *  获取动画来自的那个控制器
     */
    UIViewController *fromViewController = [transitionContext viewControllerForKey:UITransitionContextFromViewControllerKey];
    /**
     *  获取转场到的那个控制器
     */
    UIViewController *toViewController = [transitionContext viewControllerForKey:UITransitionContextToViewControllerKey];
    
    /**
     *  转场动画是两个控制器视图时间的动画,需要一个containerView来作为一个“舞台”,让动画执行。
     */
    UIView *containerView = [transitionContext containerView];
    [containerView insertSubview:toViewController.view belowSubview:fromViewController.view];
    
    NSTimeInterval duration = [self transitionDuration:transitionContext];

    /**
     *  执行动画,我们让fromVC的视图移动到屏幕最右侧
     */
    [UIView animateWithDuration:duration animations:^{
        fromViewController.view.transform = CGAffineTransformMakeTranslation([UIScreen mainScreen].bounds.size.width, 0);
    }completion:^(BOOL finished) {
        /**
         *  当你的动画执行完成,这个方法必须要调用,否则系统会认为你的其余任何操作都在动画执行过程中。
         */
        [transitionContext completeTransition:!transitionContext.transitionWasCancelled];
    }];

}

- (void)animationDidStop:(CATransition *)anim finished:(BOOL)flag {
    [_transitionContext completeTransition:!_transitionContext.transitionWasCancelled];
}
@end

ps:如果是自定义view设置nav或者是直接隐藏nav可以参考我的另一篇简书http://www.jianshu.com/p/b46166b05f02
备注:还有些许不足请各位见谅指正

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