前言
使用 UIAlertController 弹出对话框时，想支持用户点击空白处能自动隐藏对话框。UIAlertControllerStyleActionSheet添加cancel按钮即可实现。同样的，UIAlertControllerStyleAlert即使添加cancel按钮也不行，下面，我们使用分类给它添加自动隐藏功能。

UIAlertController+HLTapDismiss.h

#import <UIKit/UIKit.h>
@interface UIAlertController (HLTapDismiss)

/// 弹窗点击dismiss 
- (void)alertTapDismiss;
@end

UIAlertController+HLTapDismiss.m

#import "UIAlertController+HLTapDismiss.h"

@interface UIAlertController ()<UIGestureRecognizerDelegate>

@end

@implementation UIAlertController (HLTapDismiss)

- (void)alertTapDismiss {
    
    NSArray * arrayViews = [UIApplication sharedApplication].keyWindow.subviews;
    if (arrayViews.count>0) {
        //array会有两个对象，一个是UILayoutContainerView，另外一个是UITransitionView，我们找到最后一个
        UIView * backView = arrayViews.lastObject;

        backView.userInteractionEnabled = YES;
        UITapGestureRecognizer *tap = [[UITapGestureRecognizer alloc]initWithTarget:self action:@selector(tap)];
        tap.delegate = self;
        [backView addGestureRecognizer:tap];
    }
    
}

- (void)tap {
    [self dismissViewControllerAnimated:YES completion:nil];
}

#pragma mark - UIGestureRecognizerDelegate
- (BOOL)gestureRecognizer:(UIGestureRecognizer *)gestureRecognizer shouldReceiveTouch:(UITouch *)touch {
    
    UIView *tapView = gestureRecognizer.view;
    CGPoint point = [touch locationInView:tapView];
    CGPoint conPoint = [self.view convertPoint:point fromView:tapView];
    BOOL isContains = CGRectContainsPoint(self.view.bounds, conPoint);
    if (isContains) {
        // 单击点包含在alert区域内 不响应tap手势
        return NO;
    }
    return YES;
}

@end

栗子

UIAlertController *alert = [UIAlertController alertControllerWithTitle:@"测试" message:@"测试一下" preferredStyle:UIAlertControllerStyleAlert];
[alert addAction:[UIAlertAction actionWithTitle:@"cancel" style:UIAlertActionStyleCancel handler:^(UIAlertAction * _Nonnull action) {
    NSLog(@"取消");
}]];
[alert addAction:[UIAlertAction actionWithTitle:@"sure" style:UIAlertActionStyleDefault handler:^(UIAlertAction * _Nonnull action) {
    NSLog(@"确定");
}]];
[self presentViewController:alert animated:YES completion:^{
    // 添加点击空白隐藏手势
    [alert alertTapDismiss]; 
}];