iOS11 UIBarButtonItem无法偏移问题

1、创建UINavigationItem Category

@implementation UINavigationItem (SXFixSpace)

+(void)load {
    [self swizzleMethod:@selector(setLeftBarButtonItem:)
                                 swizzledSelector:@selector(sx_setLeftBarButtonItem:)];
    [self swizzleMethod:@selector(setRightBarButtonItem:)
                                 swizzledSelector:@selector(sx_setRightBarButtonItem:)];
}

-(void)sx_setLeftBarButtonItem:(UIBarButtonItem *)leftBarButtonItem{
    if (leftBarButtonItem.customView) {
        if ([[[UIDevice currentDevice] systemVersion] floatValue] >= 11) {
            UIView *customView = leftBarButtonItem.customView;
            BarView *barView = [[BarView alloc]initWithFrame:customView.bounds];
            [barView addSubview:customView];
            customView.center = barView.center;
            [barView setPosition:SXBarViewPositionLeft];
            [self setLeftBarButtonItems:nil];
            [self sx_setLeftBarButtonItem:[[UIBarButtonItem alloc]initWithCustomView:barView]];
        }else {
            [self sx_setLeftBarButtonItem:nil];
            [self setLeftBarButtonItems:@[[self fixedSpaceWithWidth:-20], leftBarButtonItem]];
        }
    }else {
        [self setLeftBarButtonItems:nil];
        [self sx_setLeftBarButtonItem:leftBarButtonItem];
    }
}

-(void)sx_setRightBarButtonItem:(UIBarButtonItem *)rightBarButtonItem{
    if (rightBarButtonItem.customView) {
        if ([[[UIDevice currentDevice] systemVersion] floatValue] >= 11) {
            UIView *customView = rightBarButtonItem.customView;
            BarView *barView = [[BarView alloc]initWithFrame:customView.bounds];
            [barView addSubview:customView];
            customView.center = barView.center;
            [barView setPosition:SXBarViewPositionRight];
            [self setRightBarButtonItems:nil];
            [self sx_setRightBarButtonItem:[[UIBarButtonItem alloc]initWithCustomView:barView]];
        } else {
            [self sx_setRightBarButtonItem:nil];
            [self setRightBarButtonItems:@[[self fixedSpaceWithWidth:-20], rightBarButtonItem]];
        }
    }else {
        [self setRightBarButtonItems:nil];
        [self sx_setRightBarButtonItem:rightBarButtonItem];
    }
}

-(UIBarButtonItem *)fixedSpaceWithWidth:(CGFloat)width {
    UIBarButtonItem *fixedSpace = [[UIBarButtonItem alloc]initWithBarButtonSystemItem:UIBarButtonSystemItemFixedSpace
                                                                               target:nil
                                                                               action:nil];
    fixedSpace.width = width;
    return fixedSpace;
}

@end

2、创建UIView

typedef NS_ENUM(NSInteger, SXBarViewPosition) {
    SXBarViewPositionLeft,
    SXBarViewPositionRight
};
@interface BarView : UIView
@property (nonatomic, assign) SXBarViewPosition position;
@property (nonatomic, assign) BOOL applied;
@end

@implementation BarView

- (void)layoutSubviews {
    [super layoutSubviews];
    if (self.applied || [[[UIDevice currentDevice] systemVersion] floatValue]  < 11) return;
    UIView *view = self;
    while (![view isKindOfClass:UINavigationBar.class] && view.superview) {
        view = [view superview];
        if ([view isKindOfClass:UIStackView.class] && view.superview) {
            if (self.position == SXBarViewPositionLeft) {
                for (NSLayoutConstraint *constraint in view.superview.constraints) {
                    if (([constraint.firstItem isKindOfClass:UILayoutGuide.class] &&
                         constraint.firstAttribute == NSLayoutAttributeTrailing)) {
                        [view.superview removeConstraint:constraint];
                    }
                }
                [view.superview addConstraint:[NSLayoutConstraint constraintWithItem:view
                                                                           attribute:NSLayoutAttributeLeading
                                                                           relatedBy:NSLayoutRelationEqual
                                                                              toItem:view.superview
                                                                           attribute:NSLayoutAttributeLeading
                                                                          multiplier:1.0
                                                                            constant:0]];
                self.applied = YES;
            } else if (self.position == SXBarViewPositionRight) {
                for (NSLayoutConstraint *constraint in view.superview.constraints) {
                    if (([constraint.firstItem isKindOfClass:UILayoutGuide.class] &&
                         constraint.firstAttribute == NSLayoutAttributeLeading)) {
                        [view.superview removeConstraint:constraint];
                    }
                }
                [view.superview addConstraint:[NSLayoutConstraint constraintWithItem:view
                                                                           attribute:NSLayoutAttributeTrailing
                                                                           relatedBy:NSLayoutRelationEqual
                                                                              toItem:view.superview
                                                                           attribute:NSLayoutAttributeTrailing
                                                                          multiplier:1.0
                                                                            constant:0]];
                self.applied = YES;
            }
            break;
        }
    }
}

@end

3、自定义view添加到leftBarButtonItem

        self.navigationItem.leftBarButtonItem = [[[UIBarButtonItem alloc] initWithCustomView:[UIView alloc] init]];

坑

按钮需要在viewWillAppear中进行添加按钮

- (void)viewWillAppear:(BOOL)animated {
}

未知情况，在viewDidLoad设置，页面再次出现时无法渲染