項(xiàng)目里需要增加強(qiáng)制更新功能，此時(shí)使用的是系統(tǒng)的UIAlertController，結(jié)果點(diǎn)擊跳轉(zhuǎn)到App Store之后，彈框就消失了，這是因?yàn)橄到y(tǒng)默認(rèn)會(huì)自己dismiss，所以需要自己加個(gè)變量可以控制是否dismiss。

@dynamicft_rejectDismiss;

- (void)setFt_rejectDismiss:(BOOL)ft_rejectDismiss {

    objc_setAssociatedObject(self, @selector(ft_rejectDismiss), @(ft_rejectDismiss), OBJC_ASSOCIATION_ASSIGN);

}

- (BOOL)ft_rejectDismiss {

    return [(NSNumber *)objc_getAssociatedObject(self, _cmd) boolValue];

}

+ (void)load {

    static dispatch_once_t onceToken;

    dispatch_once(&onceToken, ^{

        Classclass = [selfclass];

        SEL originalSelector = NSSelectorFromString(@"_dismissAnimated:triggeringAction:triggeredByPopoverDimmingView:dismissCompletion:");

        SELswizzledSelector =@selector(ft_dismissAnimated:

                                         triggeringAction:

                                         triggeredByPopoverDimmingView:

                                         dismissCompletion:);

        MethodoriginalMethod =class_getInstanceMethod(class, originalSelector);

        MethodswizzledMethod =class_getInstanceMethod(class, swizzledSelector);

        // 動(dòng)態(tài)添加方法，如果類(lèi)中不存在這個(gè)方法的實(shí)現(xiàn)，則添加成功

        // 這里 UIAlertController 類(lèi)中存在 originalMethod，所以添加是失敗的

        BOOLdidAddMethod =class_addMethod(class,

                                            originalSelector,

                                            method_getImplementation(swizzledMethod),

                                            method_getTypeEncoding(swizzledMethod));

        if(didAddMethod) {

            // 如果添加成功，則用 originalMethod 替換添加的空方法 originalMethod

            class_replaceMethod(class,

                                swizzledSelector,

                                method_getImplementation(originalMethod),

                                method_getTypeEncoding(originalMethod));

        }else{

            // 交換兩個(gè)方法的實(shí)現(xiàn)

            method_exchangeImplementations(originalMethod, swizzledMethod);

        }

    });

}

- (void)ft_dismissAnimated:(BOOL)animation

          triggeringAction:(UIAlertAction*)action

triggeredByPopoverDimmingView:(id)view

         dismissCompletion:(id)handler {

    // 如果點(diǎn)擊“取消”按鈕或者允許彈框 dismiss，就調(diào)用原來(lái)的方法（originalMethod）

    // 因?yàn)橐呀?jīng)交換了兩個(gè)方法的實(shí)現(xiàn)，所以其實(shí)是調(diào)用 swizzledMethod

    // 所以這里并不會(huì)出現(xiàn)循環(huán)調(diào)用

    // 否則就忽略原來(lái)的方法（originalMethod），直接下一步，掉用后面的方法

    if (action.style == UIAlertActionStyleCancel || self.ft_rejectDismiss == NO) {

        [self ft_dismissAnimated:animation

                triggeringAction:action

   triggeredByPopoverDimmingView:view

               dismissCompletion:handler];

    }else{

        SEL invokeHandler = NSSelectorFromString(@"_invokeHandlersForAction:");

        // 這里如果使用 performSelector 來(lái)調(diào) invokeHandler 這個(gè)方法

        // [self performSelector:invokeHandler withObject:action];

        // 會(huì)報(bào) "PerformSelector may cause a leak because its selector is unknown" 的警告

        // 為消除警告，用下面的方法

        IMPimp = [selfmethodForSelector:invokeHandler];

        void(*func)(id,SEL,UIAlertAction*) = (void*)imp;

        func(self, invokeHandler, action);

    }

}