主要有两个注意事项
1.判断方法是否被交换过，已经交换过就不再重复交换

     if ([delegate respondsToSelector:@selector(secre_webview_webView:decidePolicyForNavigationAction:decisionHandler:)]) {
            TLogD(@"WKNavigationDelegate class %@ has hooked yet.", [NSString stringWithUTF8String:object_getClassName(delegateClass)]);
            return;
        }

2.判断交换的对象为方法实现的类，不要在继承子类中进行方法交换。
原因：
2.1
父类superClass 中实现了methodA
子类selfClass 中没有实现methodA
2.2
如果selfClass中进入hook，那么实际交换的是selfClass中的新方法与superClass中的methodA； 这时selfClass已经hook，但是在superClass中找不过交换的新方法，会再次hook，最终进入死循环crash
2.3
所以，我们需要在selfClass中获取到实现methodA的superClass，直接交换superClass中的methodA，所有的子类方法都能调用到交换后的方法。

        
         //直接交换实现方法的类，避免继承之间循环交换

         //遍历父类找到实现方法的父类
        Class c = [self enumerateClasses:delegateClass];
        if (!c) {
           //如果没有父类方法实现需要交换的方法，就默认交换自己类的方法
            c = delegateClass;  
        }

        [SECREMethodSwizzling swizzleMethod:@selector(webView:decidePolicyForNavigationAction:decisionHandler:) ofClass:c withMethod:@selector(secre_webview_webView:decidePolicyForNavigationAction:decisionHandler:) defaultMethod:@selector(secre_webview_default_webView:decidePolicyForNavigationAction:decisionHandler:) fromClass:WKWebView.class];

以webview为例代码实现

1.方法交换

+ (void)load {
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        // swizzling method
        [SECREMethodSwizzling swizzleMethod:@selector(setNavigationDelegate:) withMethod:@selector(secre_webview_setNavigationDelegate:) ofClass:WKWebView.class];
        TLogD(@"has exchanged setNavigationDelegate: method.");
    });
}

2.交换方法自己与需要添加处理的方法

- (void)secre_webview_setNavigationDelegate:(id<WKNavigationDelegate>)delegate {
    if (delegate) {
        //    NSLog(@"Now is using %s as -[WKWebView setNavigationDelegate:]", __PRETTY_FUNCTION__);
        [self secre_webview_swizzleMethodOfWKNavigationDelegate:delegate];
        [self secre_webview_setNavigationDelegate:delegate];
    }
}

- (void)secre_webview_swizzleMethodOfWKNavigationDelegate:(id<WKNavigationDelegate>)delegate {
    Class delegateClass = delegate.class;
    @synchronized (sc_hookLock) {
        
         //直接交换实现方法的类，避免继承之间循环交换
        Class c = [self enumerateClasses:delegateClass];
        if (!c) {
            c = delegateClass;
        }
        
        if ([delegate respondsToSelector:@selector(secre_webview_webView:decidePolicyForNavigationAction:decisionHandler:)]) {
            TLogD(@"WKNavigationDelegate class %@ has hooked yet.", [NSString stringWithUTF8String:object_getClassName(delegateClass)]);
            return;
        }
        Class wkWebViewClass = WKWebView.class;
        // exchange implementation
        [SECREMethodSwizzling swizzleMethod:@selector(webView:decidePolicyForNavigationAction:decisionHandler:) ofClass:c withMethod:@selector(secre_webview_webView:decidePolicyForNavigationAction:decisionHandler:) defaultMethod:@selector(secre_webview_default_webView:decidePolicyForNavigationAction:decisionHandler:) fromClass:wkWebViewClass];
        // 将hook过的类添加进来
        // [hookedClassNames addObject:NSStringFromClass(delegateClass)];
        TLogD(@"WKNavigationDelegate class %@ has hooked.", [NSString stringWithUTF8String:object_getClassName(delegateClass)]);
    }
}

#pragma mark - helper
//判断页面是否实现了某个sel
- (Class)enumerateClasses:(Class)delegateClass {
    SEL sel = @selector(webView:decidePolicyForNavigationAction:decisionHandler:);
    if ([self isContainSel:sel inClass:[delegateClass class]]) {
        return delegateClass;
    }
    
    Class c = [delegateClass class];
    while (c) {
        c = class_getSuperclass(c);
        if ([self isContainSel:sel inClass:[c class]]) {
            return [c class];
        }
    }
    return nil;
}
- (BOOL)isContainSel:(SEL)sel inClass:(Class)class {
    unsigned int count;
    
    Method *methodList = class_copyMethodList(class,&count);
    for (int i = 0; i < count; i++) {
        Method method = methodList[i];
        NSString *tempMethodString = [NSString stringWithUTF8String:sel_getName(method_getName(method))];
        if ([tempMethodString isEqualToString:NSStringFromSelector(sel)]) {
            return YES;
        }
    }
    return NO;
}

3.默认方法与自己需要添加的实现

#pragma mark - default Methods
- (void)secre_webview_default_webView:(WKWebView *)webView decidePolicyForNavigationAction:(WKNavigationAction *)navigationAction decisionHandler:(void (^)(WKNavigationActionPolicy))decisionHandler {
    decisionHandler(WKNavigationActionPolicyAllow);
}

#pragma mark - swizzling Methods
- (void)secre_webview_webView:(WKWebView *)webView decidePolicyForNavigationAction:(WKNavigationAction *)navigationAction decisionHandler:(void (^)(WKNavigationActionPolicy))decisionHandler {
    TLogD(@"%s: will decide whether can visit url: %@, webview url: %@", __PRETTY_FUNCTION__, navigationAction.request.URL, webView.URL);
    
    NSLog(@"URL :%@", navigationAction.request.URL);
    // do something 
    [self secre_webview_webView:webView decidePolicyForNavigationAction:navigationAction decisionHandler:decisionHandler];
}