iOS 导航栏自定义返回按钮

方法一：
// 缺陷是图片显示成纯色的
// 设置全局导航栏返回按钮指示图
UINavigationBar *navBar = [UINavigationBar appearance];
UIImage *image = [UIImage imageNamed:@"back"];
//如下两个必须同时设置
navBar.backIndicatorImage = image;
navBar.backIndicatorTransitionMaskImage = image;

//在viewController里面将backItem的title设成"", 主要做用是没有显示内容
UIBarButtonItem *backItem = [[UIBarButtonItem alloc] init];
backItem.title = @"";
self.navigationItem.backBarButtonItem = backItem;

方法二：
// 缺陷是向左滑动时不能做为返回操做使用
// 设置viewController的 leftBarButtonItem
UIButton *btn = [UIButton buttonWithType:UIButtonTypeCustom];
UIImage *backImage = [UIImage imageNamed:@"back"];
[btn setImage:backImage forState:UIControlStateNormal];
[btn addTarget:self action:@selector(btnBackClick) forControlEvents:UIControlEventTouchUpInside];
self.navigationItem.leftBarButtonItem = [[UIBarButtonItem alloc] initWithCustomView:btn];

//以上方法，返回按钮不太靠边，可使用重写如下方法达到效果
//.h文件
@interface UINavigationItem (DM)

@end

//.m文件
@implementation UINavigationItem (DM)

- (void)setLeftBarButtonItem:(UIBarButtonItem *)leftBarButtonItem
{
    if (iOS7UP && leftBarButtonItem.customView)
    {
        UIBarButtonItem *negativeSeperator = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemFixedSpace target:nil action:nil];
        
        negativeSeperator.width = -7.0;//此处修改到边界的距离
        
        if (leftBarButtonItem) 
        {
            [self setLeftBarButtonItems:@[negativeSeperator, leftBarButtonItem]];
        } 
        else 
        {
            [self setLeftBarButtonItems:@[negativeSeperator]];
        }
    } 
    else 
    {
        [self setLeftBarButtonItem:leftBarButtonItem animated:NO];
    }
}

- (void)setRightBarButtonItem:(UIBarButtonItem *)rightBarButtonItem
{
    if (iOS7UP && rightBarButtonItem.customView) 
    {
        UIBarButtonItem *negativeSeperator = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemFixedSpace target:nil action:nil];
        negativeSeperator.width = -7.0;//此处修改到边界的距离
        if (rightBarButtonItem) 
        {
            [self setRightBarButtonItems:@[negativeSeperator, rightBarButtonItem]];
        } 
        else 
        {
            [self setRightBarButtonItems:@[negativeSeperator]];
        }
    } 
    else 
    {
        [self setRightBarButtonItem:rightBarButtonItem animated:NO];
    }
}

@end

方法三：
// 继承导航栏，将导航栏隐藏，自定义导航栏