UIViewController 方法调配不起作用

Question

我在 UIViewController 上使用一个类别来调配 viewWillAppear: 跨多个 ViewController 的方法。

@implementation UIViewController (Tracking)

+(void)load
{
    static dispatch_once_t onceToken;

    dispatch_once(&onceToken, ^{
        Class class = [self class];

        SEL originalSelector = @selector(viewWillAppear:);
        SEL swizzledSelector = @selector(xx_viewWillAppear:);

        Method originalMethod = class_getInstanceMethod(class, originalSelector);
        Method swizzledMethod = class_getInstanceMethod(class, swizzledSelector);

        BOOL didAddMethod = class_addMethod(class, originalSelector, method_getImplementation(swizzledMethod), method_getTypeEncoding(swizzledMethod));

        if (didAddMethod)
        {
            class_replaceMethod(class, swizzledSelector, method_getImplementation(originalMethod), method_getTypeEncoding(originalMethod));
        }else{
            method_exchangeImplementations(originalMethod, swizzledMethod);
        }

    });
}

-(void)xx_viewWillAppear:(BOOL)animated
{
    [self xx_viewWillAppear:animated];

    NSLog(@"VC loaded");
}

@end

当我从 Storyboard 加载初始 VC 时，从未调用 swizzled 方法。只有在 VC 中的 viewWillAppear 方法被注释掉时才会调用它。但是，当我删除类别并将代码移动到个人 VC 时，这两种方法都会被调用。

#import "ViewController.h"
#import "UIViewController+Tracking.h"

@interface ViewController ()
@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
}

-(void)viewWillAppear:(BOOL)animated
{
    NSLog(@"Inside Controller1");
}

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

@end

是否可以在 VC 中实现 viewWillAppear，如果它要被 swizzled？如果不是，如果我需要在 VC 的 viewWillAppear 中编写一些代码，我该如何处理？

Answer 1

您需要从 ViewController 中调用 viewWillAppear: 中的 super，否则基础 class (UIViewController) 中的方法将不会执行, 那就是你调配的那个。

viewWillAppear: 的以下版本应该会给您预期的结果：

-(void)viewWillAppear:(BOOL)animated
{
    [super viewWillAppear:animated];
    NSLog(@"Inside Controller1");
}

UIViewController 方法调配不起作用

UIViewController method swizzling not working

objective-c

ios

method-swizzling