// 从中间弹出
- (IBAction)centerAlertAction:(id)sender {
NKAlertView *alertView = [[NKAlertView alloc] init];
CenterAlertContentView *customContentView = [[CenterAlertContentView alloc] initWithFrame:CGRectMake(0, 0, 281, 281)];
alertView.contentView = customContentView;
// 点击背景隐藏提示框
alertView.hiddenWhenTapBG = YES;
[alertView show];
}