iOS开发：UIBarButtonItem的简单用法

用法一：

- (instancetype)initWithTitle:(nullable NSString *)title style:(UIBarButtonItemStyle)style target:(nullable id)target action:(nullable SEL)action;

举例：

self.navigationItem.leftBarButtonItem = [[UIBarButtonItem alloc] initWithTitle:@"取消" style:0 target:self action:@selector(dismiss)];

用法二：

+ (UIBarButtonItem *)barButtonItemWithImage:(UIImage *)image highImage:(UIImage *)highImage target:(id)target action:(SEL)action forControlEvents:(UIControlEvents)controlEvents

举例：

//左边
        viewController.navigationItem.leftBarButtonItem = [UIBarButtonItem barButtonItemWithImage:[UIImage imageNamed:@"navigationbar_back"] highImage:[UIImage imageNamed:@"navigationbar_back_highlighted"] target:self action:@selector(backToPre) forControlEvents:UIControlEventTouchUpInside];

用法三：

- (instancetype)initWithCustomView:(UIView *)customView;

举例：

//right
    UIButton * btn = [UIButton buttonWithType:UIButtonTypeCustom];
    [btn setTitleColor:[UIColor orangeColor] forState:UIControlStateNormal];
    [btn setTitleColor:[UIColor lightGrayColor] forState:UIControlStateDisabled];
    [btn setTitle:@"发送" forState:UIControlStateNormal];
    [btn addTarget:self action:@selector(compose) forControlEvents:UIControlEventTouchUpInside];
    [btn sizeToFit];
    
    UIBarButtonItem * rightBarButton = [[UIBarButtonItem alloc] initWithCustomView:btn];
    rightBarButton.enabled = NO;
    self.navigationItem.rightBarButtonItem = rightBarButton;