错误:-[UIKBBlurredKeyView candidateList]: unrecognized selector sent to instance

错误

app 在线上有个崩溃的问题, crash原因为-[UIKBBlurredKeyView candidateList]: unrecognized selector sent to instance.

原因分析

然后发现是在手写输入的时候会crash，每当提示文字的区域就会crash。这个崩溃是由在UIScrollview的category中重写的三个方法引起的, 代码如下：

- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event {[super touchesBegan:touches withEvent:event];[self.nextResponder touchesBegan:touches withEvent:event];
}- (void)touchesMoved:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event {[super touchesMoved:touches withEvent:event];[self.nextResponder touchesMoved:touches withEvent:event];
}- (void)touchesEnded:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event {[super touchesEnded:touches withEvent:event];[self.nextResponder touchesEnded:touches withEvent:event];
}- (void)touchesCancelled:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event {[super touchesCancelled:touches withEvent:event];[self.nextResponder touchesCancelled:touches withEvent:event];
}

具体原因是由于提示文字区域(Candidate View)点击时, 同样执行上面的代码, 然后事件响应向上传递, 直到出现标题的错误。
再具体些, 就是手写的键盘的提示文字的区域是UIKBCandidateCollectionView类（其父类是UIColloectionView）的实例，这个view的nextResponder是UIKBHandwritingCandidateView类的实例。执行UIKBHandwritingCandidateView的touchesBegan:withEvent:方法后，会使得整个candidate view呈选中状态，而苹果对于手写键盘的提示文字区域, 会避免candidate view呈选中状态的。整个candidate view呈选中状态后再点击键盘的任意地方，本应调用UIKBCandidateView实例的方法candidateList，结果调用了UIKBBlurredKeyView的candidateList方法，导致方法找不到，导致”-[UIKBBlurredKeyView candidateList]: unrecognized selector sent to instance “crash。

解决方案

方案一

摒弃此代码, 选择其他方式代替。

方案二

对于不同的类, 对其进行类型判断, 加强代码的健壮性, 以避免崩溃。比如, UIScrollView中要加入下判断:

- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event {if([self isMemberOfClass:[UIScrollView class]]) {[super touchesBegan:touches withEvent:event];[self.nextResponder touchesBegan:touches withEvent:event];}
}

方案三

使用UITapGestureRecognizer类, 进行用户的点击事件拦截, 且要将tap的cancelsTouchesInView属性设置为NO, 否则会屏蔽到当前View的点击事件。下面以UIScrollView和’UITableView’为例的处理方案:

1.在UIScrollView上面加一个UIView, 通过在view上面的手势来改变键盘

UITapGestureRecognizer *tap = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(hideKeyboard:)];
tap.cancelsTouchesInView = NO;
[backView addGestureRecognizer:tap];

2.在UITableView上改变键盘

UITapGestureRecognizer *tap = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(hideKeyboard:)];
tap.cancelsTouchesInView = NO;
[tableView addGestureRecognizer:tap];