1、导航栏返回按钮无文字设置：

用的下面方法设置的导致按钮向下偏移的

[[UIBarButtonItem appearance] setBackButtonTitlePositionAdjustment:UIOffsetMake(0,-60) forBarMetrics:UIBarMetricsDefault];

解决办法：

[[UIBarButtonItem appearance] setBackButtonTitlePositionAdjustment:UIOffsetMake(-200, 0) forBarMetrics:UIBarMetricsDefault];

2、使用tableView时，状态栏空出20像素

解决办法：

self.extendedLayoutIncludesOpaqueBars = YES;

if (@available(iOS 11.0, *)) {

self.tableView.contentInsetAdjustmentBehavior = UIScrollViewContentInsetAdjustmentNever;

} else {

self.automaticallyAdjustsScrollViewInsets = NO;

}

3、自定义导航栏返回按钮，UIBarButtonSystemItemFixedSpace失效

解决办法：

UIBarButtonItem *leftItem = [[UIBarButtonItem alloc]initWithImage:[UIImage imageNamed:@"back"] style:UIBarButtonItemStyleDone target:self action:@selector(backBtnClick)];

if (@available(ios 11.0,*)) {

leftItem.imageInsets = UIEdgeInsetsMake(0, -10, 0, 0);

self.navigationItem.leftBarButtonItem = leftItem;

} else {

UIBarButtonItem *negativeSpacer = [[UIBarButtonItem alloc]initWithBarButtonSystemItem:UIBarButtonSystemItemFixedSpace target:nil action:nil];

negativeSpacer.width = -10;

self.navigationItem.leftBarButtonItems = [NSArray arrayWithObjects:negativeSpacer, leftItem, nil];

}