iOS-拦截导航栏backBarButtonItem事件

╰半夏微凉° 2021-09-20 03:26 368阅读 0赞

[2019独角兽企业重金招聘Python工程师标准>>> ][2019_Python_] ![hot3.png][]

前言

我们很熟悉也很普通的场景：用户在当前页面填写信息，当点击backBarButtonItem回退按钮准备返回上一界面时，弹出提示框是否放弃此次的输入；如果确定放弃返回上一界面，否则保留在当前界面。自定义回退事件可以解决这个问题，本篇文章主要是讲通过拦截系统自带的back按钮实现该效果。

解决方案；

1、创建UINavigationController控制器分类，通过runtime交换navigationBar:shouldPopItem:方法（该方法决定是否pop上一界面）；

2、实现交换后的方法- (BOOL)test\_navigationBar:(UINavigationBar \*)navigationBar shouldPopItem:(UINavigationItem \*)item；

#import "UINavigationController+navigationPopBack.h"
    #import "UIViewController+BackButtonEvent.h"
    #import <objc/runtime.h>
    
    static void * const interactivePopGestureDelegate = "interactivePopGestureDelegate";
    @implementation UINavigationController (navigationPopBack)
    
    + (void)load {
        
        static dispatch_once_t onceToken;
        dispatch_once(&onceToken, ^{
            
            [self test_swizzleOriginSel:@selector(navigationBar:shouldPopItem:) withSwizzleSel:@selector(test_navigationBar:shouldPopItem:)];
            
            [self test_swizzleOriginSel:@selector(viewDidLoad) withSwizzleSel:@selector(test_viewDidLoad)];
        });
    }
    
    + (void)test_swizzleOriginSel:(SEL)originSel withSwizzleSel:(SEL)swizzleSel {
        
        Class curClass = self.class;
        
        Method originMethod = class_getInstanceMethod(curClass, originSel);
        Method swizzleMethod = class_getInstanceMethod(curClass, swizzleSel);
        
        BOOL didAddMethod = class_addMethod(curClass,
                                            originSel,
                                            method_getImplementation(swizzleMethod),
                                            method_getTypeEncoding(swizzleMethod));
        if (didAddMethod) {
            class_replaceMethod(curClass,
                                swizzleSel,
                                method_getImplementation(originMethod),
                                method_getTypeEncoding(originMethod));
        } else {
            
            method_exchangeImplementations(originMethod, swizzleMethod);
        }
    }
    
    - (void)test_viewDidLoad {
        
        [self test_viewDidLoad];
        
        objc_setAssociatedObject(self, interactivePopGestureDelegate, self.interactivePopGestureRecognizer.delegate, OBJC_ASSOCIATION_ASSIGN);
        self.interactivePopGestureRecognizer.delegate = (id<UIGestureRecognizerDelegate>)self;
    }
    
    - (BOOL)test_navigationBar:(UINavigationBar *)navigationBar shouldPopItem:(UINavigationItem *)item {
        
        UIViewController *vc = self.topViewController;
        
        if (item != vc.navigationItem) {
            
            // 当使用popViewControllerAnimated进行pop时，会进入此处，返回YES，即self.topViewController获取的是pop之后的vc。
            return YES;
        }
        
        if ([vc conformsToProtocol:@protocol(BackButtonHandler)] && [vc respondsToSelector:@selector(test_navigationShouldPopOnBackButton)]) {
            
            if ([vc test_navigationShouldPopOnBackButton]) {
                
                return [self test_navigationBar:navigationBar shouldPopItem:item];
                
            } else {
                
                for (UIView *subview in [navigationBar subviews]) {
                    
                    if (subview.alpha > 0. && subview.alpha < 1.) {
                        
                        [UIView animateWithDuration:.25 animations:^{
                            
                            subview.alpha = 1.;
                        }];
                    }
                }
                
                return NO;
            }
            
        } else {
            
            return [self test_navigationBar:navigationBar shouldPopItem:item];
        }
        
        return NO;
    }
    
    // 拦截侧滑返回事件
    - (BOOL)gestureRecognizerShouldBegin:(UIGestureRecognizer *)gestureRecognizer
    {
        if (gestureRecognizer == self.interactivePopGestureRecognizer) {
            
            // 解决根视图侧滑导致push卡死的问题
            if (self.viewControllers.count == 1) {
                return NO;
            }
            
            // 当前视图不是根视图，执行popBack操作
            UIViewController *vc = self.topViewController;
            if([vc respondsToSelector:@selector(test_navigationShouldPopOnBackButton)]) {
                
                return [vc test_navigationShouldPopOnBackButton];
            }
            
            id<UIGestureRecognizerDelegate> originDelegate = objc_getAssociatedObject(self, interactivePopGestureDelegate);
            return [originDelegate gestureRecognizerShouldBegin:gestureRecognizer];
        }
        
        return YES;
    }
    
    @end

使用场景；

1、控制器中实现TestDelegate协议，也就是点击backBarButtonItem按钮后弹出提示框，让用户决定是否放弃。点击确认按钮后返回上一界面。

#import <UIKit/UIKit.h>
    #import "UIViewController+BackButtonEvent.h"
    
    @interface ThirdViewController : UIViewController
    
    @end
    
    
    #import "ThirdViewController.h"
    
    @interface ThirdViewController () <UIAlertViewDelegate>
    
    @end
    
    @implementation ThirdViewController
    
    - (void)viewDidLoad {
        [super viewDidLoad];
        // Do any additional setup after loading the view.
        self.view.backgroundColor = [UIColor whiteColor];
        
        self.title = @"胜多负少绝地反击是读后感多个";
        
        UIButton *backButton = [UIButton buttonWithType:UIButtonTypeCustom];
        [backButton setTitle:@"返回" forState:UIControlStateNormal];
        [backButton setTitleColor:[UIColor blackColor] forState:UIControlStateNormal];
        backButton.frame = CGRectMake(0, 0, 200, 40);
        backButton.center = self.view.center;
        [backButton addTarget:self action:@selector(backVC) forControlEvents:UIControlEventTouchUpInside];
        
        [self.view addSubview:backButton];
    }
    
    - (void)didReceiveMemoryWarning {
        [super didReceiveMemoryWarning];
        // Dispose of any resources that can be recreated.
    }
    
    - (void)backVC {
        
        [self.navigationController popViewControllerAnimated:YES];
    }
    
    - (BOOL)test_navigationShouldPopOnBackButton {
        
        UIAlertView *alertView = [[UIAlertView alloc] initWithTitle:@"温馨提示" message:@"当前数据尚未保存是否放弃本次操作？" delegate:self cancelButtonTitle:@"取消" otherButtonTitles:@"确定", nil];
        [alertView show];
        
        return NO;
    }
    
    
    - (void)alertView:(UIAlertView *)alertView clickedButtonAtIndex:(NSInteger)buttonIndex {
        
        if (buttonIndex == 0) {
            
        } else {
            
            [self.navigationController popViewControllerAnimated:YES];
        }
    }
    
    @end

需要注意的地方；

1、其实我们可以发现执行backBarButtonItem的逻辑和通过代码执行popViewControllerAnimated方法的逻辑是不一样的，也就是说backBarButtonItem获取到的topViewController是pop前的VC而popViewControllerAnimated获取到的topViewController是pop后的VC，因此item != vc.navigationItem主要判断是否点击backBarButtonItem按钮。

2、侧滑返回与点击backBarButtonItem按钮返回逻辑一致。

3、但按钮被点击后箭头会变灰（alpha值被改变），需要通过遍历navigationBar的子view改变其alpha值（IOS7.1以上）；

for (UIView \*subview in \[navigationBar subviews\]) \{

if (subview.alpha < 1.) \{

\[UIView animateWithDuration:.25 animations:^\{

subview.alpha = 1.;

\}\];

转载于:https://my.oschina.net/u/1450995/blog/868465

[2019_Python_]: https://my.oschina.net/u/2663968/blog/3061697
[hot3.png]: /images/20210726/977ded38f851497ba7fd01420964b06c.png