想写一个UINavigationBar的工具类,这个工具类需要传一个ViewController,来执行dismissViewControllerAnimated:YES completion:^{}方法,而我在具体的ViewController中初始化这个工具类的时候传的是self. 
在加上UIBarButtonItem点击事件方法时会报错:*** Terminating app due to uncaught exception “”NSInvalidArgumentException””, reason: “”-[OfflineHistoryViewController backButtonHandler]: unrecognized selector sent to instance 0x7f81e3183440″”
请问问题出在哪里?
 代码如下:
1. 工具类.h 

//
//  TitleBarHelper.h
 
 
//
#import <UIKit/UIKit.h>
#import <Foundation/Foundation.h>
 
@interface TitleBarHelper : NSObject {
}
 
@property(nonatomic, retain) UIViewController *viewController;
 
@property(nonatomic, retain) NSString *titleStr;
 
@property(nonatomic) BOOL needBack;
 
- (id)initWithTitle:(NSString *)title
     ViewController:(UIViewController *)controller
           needBack:(BOOL)needBack;
 
- (UINavigationBar *)getTitleBar;
 
- (void)backButtonHandler;
 
@end

2 工具类.m 

//
//  TitleBarHelper.m
 
 
#import "TitleBarHelper.h"
#import "Public.h"
 
@implementation TitleBarHelper {
 
}
 
 
// 初始化
-(id)initWithTitle:(NSString *)title
    ViewController:(UIViewController *)controller
          needBack:(BOOL) needBack{
    self = [super init];
    if (self) {
        self.viewController = controller;
        self.titleStr = title;
        self.needBack = needBack;
    }
     
    return self;
}
 
 
// 获取titleBar
-(UINavigationBar *) getTitleBar{
 
    UINavigationBar *titleBar = [[UINavigationBar alloc]
                                 initWithFrame:CGRectMake(0, 0, screen_width, Title_Height)];
    [titleBar setBarTintColor:Main_Color];
    [titleBar
     setTitleTextAttributes:[NSDictionary dictionaryWithObjectsAndKeys:
                             [UIColor whiteColor],
                             NSForegroundColorAttributeName,
                             nil]];
    UINavigationItem *titleItem = [[UINavigationItem alloc] initWithTitle:self.titleStr];
     
    if (self.needBack) {
        UIBarButtonItem *leftButton = [UIBarButtonItem new];
        UIButton *btnView = [UIButton buttonWithType:UIButtonTypeCustom];
        [btnView setFrame:CGRectMake(0, 0, 40, 40)];
        [btnView setBackgroundImage:[UIImage imageNamed:@"btn_back.png"]
                           forState:UIControlStateNormal];
        [btnView addTarget:self.viewController
                    action:@selector(backButtonHandler)
          forControlEvents:UIControlEventTouchUpInside];
        [leftButton setCustomView:btnView];
         
        [titleItem setLeftBarButtonItem:leftButton];
    }
     
    [titleBar pushNavigationItem:titleItem animated:NO];
     
    return titleBar;
}
 
 
 
// UIBarButtonItem点击事件
- (void)backButtonHandler {
    [self.viewController dismissViewControllerAnimated:YES completion:^{}];
}
 
@end

3. 使用该工具类的ViewController.m 

//
//  OfflineHistoryViewController.m
 
 
#import "OfflineHistoryViewController.h"
#import "TitleBarHelper.h"
 
@interface OfflineHistoryViewController (){
    UINavigationBar *titleBar;
}
 
@end
 
@implementation OfflineHistoryViewController
 
- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view.
    self.view.backgroundColor = [UIColor grayColor];
     
     
    [self initView];
}
 
- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}
 
 
-(void)initView{
    [self initTitleBar];
}
 
 
-(void)initTitleBar{
    TitleBarHelper * titleBarHelper = [[TitleBarHelper alloc]initWithTitle:@"Title" ViewController:self needBack:YES];
    titleBar = [titleBarHelper getTitleBar];
    [self.view addSubview:titleBar];
}
/*
 
 
@end

        [btnView addTarget:self.viewController
                    action:@selector(backButtonHandler)
          forControlEvents:UIControlEventTouchUpInside];