关于UIAlertView和UIAlertController

写在前边：
一个视图控制器仅能使用presentViewController模态方法弹出一个控制器;
如果想在模态方法弹出第二个视图控制器，可以使用已弹出的alert1来弹出.

UIAlertView 用法

- (void)showAlertView {
    UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"提示" message:@"UIAlertView is deprecated. Use UIAlertController with a preferredStyle of UIAlertControllerStyleAlert instead, ios(2.0, 9.0)" delegate:self cancelButtonTitle:@"取消" otherButtonTitles:@"确认", nil];
    
    [self presentViewController:alert animated:true completion:nil];
}

#pragma mark - UIAlertViewDelegate
-(void)alertView:(UIAlertView *)alertView clickedButtonAtIndex:(NSInteger)buttonIndex {
    printf("%ld",buttonIndex);
}

上面使用UIAlertView 需要使用代理处理自定义事件；

UIAlertController 用法

- (void)showAlert:(NSString *)title {
    UIAlertController *alert = [UIAlertController alertControllerWithTitle:[NSString stringWithFormat:@"提示%@",title] message:nil preferredStyle:UIAlertControllerStyleAlert];
    UIAlertAction *confirm = [UIAlertAction actionWithTitle:@"确定" style:UIAlertActionStyleDefault handler:nil];
    [alert addAction:confirm];
    [self presentViewController:alert animated:true completion:nil];
}

与UIAlertView相比直观的赶脚是代码量上减少了;

关于alert ，随着业务不断的递增，屏幕上展示的alert提示框个数和样式也在不断的增加，直接导致体验不友好，UIAlertController就是苹果为了规范提示框新增的API，但是这里需要注意，如果使用上面的- (void)showAlert:(NSString *)title 可能会出现和UIAlertView一样一次展示多个提示的问题；在网上参考了大家的分享，总结如下：

- (void)showAlert:(NSString *)title {
    UIAlertController *alert = [UIAlertController alertControllerWithTitle:[NSString stringWithFormat:@"提示%@",title] message:nil preferredStyle:UIAlertControllerStyleAlert];
    UIAlertAction *confirm = [UIAlertAction actionWithTitle:@"确定" style:UIAlertActionStyleDefault handler:nil];
    [alert addAction:confirm];
    //两种方式不一样
    //方式一：类似 UIAlertView  可以同时展示几个
    [[LBAlertViewController topViewController] presentViewController:alert animated:true completion:nil];
    //方式二：
//    [self presentViewController:alert animated:true completion:nil];
}

+ (UIViewController *)getCurrentVC {
    //1. 先找到KeyWindow
    UIWindow * window = [[UIApplication sharedApplication] keyWindow];
    //2. 正常情况下KeyWindow应该是在UIWindowLevelNormal,有Alert的时候KeyWindow就是Alert框
    if (window.windowLevel != UIWindowLevelNormal)
    {
        //3. 如果不是UIWindowLevelNormal,那么找到UIWindowLevelNormal级别的Window
        // 这里有个缺陷,因为UIWindowLevelNormal的不一定只有一个,虽然正常情况下只有一个
        NSArray *windows = [[UIApplication sharedApplication] windows];
        for(UIWindow * tmpWin in windows)
        {
            if (tmpWin.windowLevel == UIWindowLevelNormal)
            {
                //找到了UIWindowLevelNormal的Window
                window = tmpWin;
                break;
            }
        }
    }
    //4. 判断RootViewController不是TabBarVC和NaviVC,且是ViewController
    id result = window.rootViewController;
    BOOL isViewController = ![result isKindOfClass:[UITabBarController class]] && ![result isKindOfClass:[UINavigationController class]] && [result isKindOfClass:[UIViewController class]];
    //5. 进入递归循环,排除TabBarVC和NaviVC,以及进入PresentedVC继续递归
    while (!isViewController) {
        while ([result isKindOfClass:[UITabBarController class]]) {
            UITabBarController *tempVC = result;
            result = [tempVC selectedViewController];
        }
        while ([result isKindOfClass:[UINavigationController class]]) {
            UINavigationController *tempVC = result;
            result = [tempVC.viewControllers lastObject];
        }
        
        //MARK: 重点是这里  如果上一个是present  则会直接返回上一个alert
        id presentedVC = [result presentedViewController];
        if (presentedVC) {
            result = presentedVC;
        }
        //MARK:---- 注释上部分则会present一次
        
        isViewController = ![result isKindOfClass:[UITabBarController class]] && ![result isKindOfClass:[UINavigationController class]] && [result isKindOfClass:[UIViewController class]];
    }

    return result;
}

注意理解开头提到的，就会明白怎么才会只提示一次alert！当然如果注释相关代码也会如UIAlertView一样alert满天飞！！！