标签： objectvie-c Runtime
UIAlertController是在iOS 8.0以后才出现的，用于弹窗提示的视图，在8.0 之前使用的是UIAlertView。UIAlertController有两种模式：Alert和Sheet。只有在Alert模式下，才可以向UIAlertController中添加UITextField，否则会崩溃。默认情况都是点击UIAlertController上的按钮之后，执行相应回调最后dismiss掉。在没有UITextField的时候，这样没有任何问题，但是在UITextField存在的情况下，且需要对输入进行合法性验证，只有输入合法时点击UIAlertController才进行回调处理。按照系统的默认方式在点击UIAlertController按钮时流程为：
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如果输入合法，执行处理回调；如果输入不合法，给出提示，不执行回调。
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UIAlertController dismiss
这里不管输入合法与否，都是会dismiss，如何做到输入不合法，不dismiss，直到输入合法才dismiss。目前能想到的只有两种方法：
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自己重写一个UIAlertController，好处是可以根据实际需求灵活配置，包括大小，颜色之类的，坏处是工作量比较大。
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从系统UIAlertController入手，根据方法调用过程hook相关方法。
在UIAlertController回调里打一个断点，然后查看函数的调用栈：
从函数栈中猜想，系统在这个过程中应该是调用了两个关键方法。首先调用_dismissAnimated:triggeringAction:triggeredByPopoverDimmingView: 将UIAlertController dismiss，接着调用_fireOffActionOnTargetIfValidForAction:来执行回调。
验证：
+ (void)load { static dispatch_once_t onceToken; dispatch_once(&onceToken, ^{ Class class = [self class]; //在iOS 11.0以上UIAlertController的dimiss的私有方法是_dismissAnimated:triggeringAction:triggeredByPopoverDimmingView:dismissCompletion: //iOS 11.0以下是_dismissAnimated:triggeringAction:triggeredByPopoverDimmingView: SEL originalSelectorWitCompletion = NSSelectorFromString(@"_dismissAnimated:triggeringAction:triggeredByPopoverDimmingView:dismissCompletion:"); SEL originalSelector = NSSelectorFromString(@"_dismissAnimated:triggeringAction:triggeredByPopoverDimmingView:"); SEL swizzledSelector = @selector(def_dismissAnimated:triggeringAction:triggeredByPopoverDimmingView:); SEL swizzledSelectorWithCompletion = @selector(def_dismissAnimated:triggeringAction:triggeredByPopoverDimmingView:dismissCompletion:); Method originalMethodWithCompletion = class_getInstanceMethod(class, originalSelec 大专栏 禁止UIAlertController的dimisstorWitCompletion); Method originalMethod = class_getInstanceMethod(class, originalSelector); Method swizzledMethod = class_getInstanceMethod(class, swizzledSelector); Method swizzledMethodWithCompletion = class_getInstanceMethod(class, swizzledSelectorWithCompletion); if (originalMethodWithCompletion) { method_exchangeImplementations(originalMethodWithCompletion, swizzledMethodWithCompletion); } else { method_exchangeImplementations(originalMethod, swizzledMethod); } }); } - (void)def_dismissAnimated:(BOOL)animation triggeringAction:(UIAlertAction *)action triggeredByPopoverDimmingView:(id)view dismissCompletion:(id)handler { if (action.style == UIAlertActionStyleCancel) { [self def_dismissAnimated:animation triggeringAction:action triggeredByPopoverDimmingView:view dismissCompletion:handler]; } else { if (self.validateBlock && self.textFields.count) { self.isDismiss = self.validateBlock(self.textFields.firstObject.text); if (self.isDismiss) { [self def_dismissAnimated:animation triggeringAction:action triggeredByPopoverDimmingView:view dismissCompletion:handler]; } } else { [self def_dismissAnimated:animation triggeringAction:action triggeredByPopoverDimmingView:view dismissCompletion:handler]; } } } - (void)def_dismissAnimated:(BOOL)animation triggeringAction:(UIAlertAction *)action triggeredByPopoverDimmingView:(id)view { if (action.style == UIAlertActionStyleCancel) { [self def_dismissAnimated:animation triggeringAction:action triggeredByPopoverDimmingView:view]; } else { if (self.validateBlock && self.textFields.count) { self.isDismiss = self.validateBlock(self.textFields.firstObject.text); if (self.isDismiss) { [self def_dismissAnimated:animation triggeringAction:action triggeredByPopoverDimmingView:view]; } } else { [self def_dismissAnimated:animation triggeringAction:action triggeredByPopoverDimmingView:view]; } } } - (void)setIsDismiss:(BOOL)isDismiss { objc_setAssociatedObject(self, @selector(isDismiss), @(isDismiss), OBJC_ASSOCIATION_ASSIGN); } - (BOOL)isDismiss { return [(NSNumber *)objc_getAssociatedObject(self, _cmd) boolValue]; } - (void)setValidateBlock:(DEFAlertControllerTextFieldValidateBlock)validateBlock { objc_setAssociatedObject(self, @selector(validateBlock), validateBlock, OBJC_ASSOCIATION_COPY_NONATOMIC); } - (DEFAlertControllerTextFieldValidateBlock)validateBlock { return objc_getAssociatedObject(self, @selector(validateBlock)); } 实际结果表明，上述分析是正确的。有一点需要注意的是，在iOS 11.0以后UIAlertController使用的私有API方法名和11.0以下使用的不一样。