iOS实现导航栏透明示例代码

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

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;

}

-(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

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