1.场景描述

在iOS开发过程中，一般都是UIViewController来控制UIView的行为，一般很少方向交互，即UIView的特性变化后调用UIViewController的相应的方法，在遇到这种情况，大多数都采用了在UIView的子类中放一个UIViewController的指针，当UIView需要调用UIViewController的方法的时候，就可以通过这个指针来实现了。

2.解决方案

这种方法是有效的（C/C++常用哦），但总是觉得不够优雅，有没有其他办法来实现呢，答案是肯定的，估计很多人都已经想到了，那就是委托（Delegate），其实iOS中很多界面元素都使用这种方式与UIViewController交互，这种方式给人的感觉更“Apple化"一些！

3.主要知识点

委托模式能够起到两方面的作用：

第一：委托协助对象主体完成某项操作，将需要定制化的操作通过委托对象来自定义实现，达到和子类化对象主体同样的作用。
第二：事件监听，委托对象监听对象主体的某些重要事件，对事件做出具体响应或广播事件交给需要作出响应的对象。

个人理解采用委托模式的好处在于：

A、避免子类化带来的过多的子类以及子类与父类的耦合
B、通过委托传递消息机制实现分层解耦

4.请看代码

4.1实现委托前的代码

//
//  MainViewController.h
//  WellLogGraph
//
//  Created by wanglei on 13-8-23.
//  Copyright (c) 2013年 wanglei. All rights reserved.
//

#import <UIKit/UIKit.h>

@interface MainViewController : UIViewController


@end

4.1.2 MainViewController.m

//
//  MainViewController.m
//  WellLogGraph
//
//  Created by wanglei on 13-8-23.
//  Copyright (c) 2013年 wanglei. All rights reserved.
//

#import "MainViewController.h"

#import "WellLogMapView.h"


@interface MainViewController ()

@end

@implementation MainViewController

- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
    self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
    if (self) {
        // Custom initialization
    }
    return self;
}

- (void)viewDidLoad
{
    [super viewDidLoad];
	// Do any additional setup after loading the view.
    
    
}

-(void)viewWillAppear:(BOOL)animated
{
    WellLogMapView* v = (WellLogMapView*)self.view;
    
    [v setNeedsDisplay];
}

- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}


@end

4.1.3 WellLogMapView.h

//
//  WellLogMapView.h
//  WellLogGraph
//
//  Created by wanglei on 13-8-24.
//  Copyright (c) 2013年 wanglei. All rights reserved.
//

#import <UIKit/UIKit.h>



@interface WellLogMapView : UIView
{
        
}


@end

4.1.4 WellLogMapView.m

//
//  WellLogMapView.m
//  WellLogGraph
//
//  Created by wanglei on 13-8-24.
//  Copyright (c) 2013年 wanglei. All rights reserved.
//

#import "WellLogMapView.h"


@implementation WellLogMapView


- (id)initWithFrame:(CGRect)frame
{
    self = [super initWithFrame:frame];
    if (self) {
        // Initialization code
    }
    return self;
}



// Only override drawRect: if you perform custom drawing.
// An empty implementation adversely affects performance during animation.
- (void)drawRect:(CGRect)rect
{
    // Drawing code
    
    
}


-(void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
    
    
}

-(void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event
{
    //UITouch *touch = [touches anyObject];
    
    // 希望在这里告诉MainViewController做一些活动，也就是如何调用MainViewController的方法
    

}


@end

4.2实现委托后的代码

4.2.1 MainViewController.h

//
//  MainViewController.h
//  WellLogGraph
//
//  Created by wanglei on 13-8-23.
//  Copyright (c) 2013年 wanglei. All rights reserved.
//

#import <UIKit/UIKit.h>

@protocol WellLogMapViewDelegate

-(void)onSelectionChanged:(id)selection;

@end

@interface MainViewController : UIViewController<WellLogMapViewDelegate>

-(void)onSelectionChanged:(id)selection;

@end

4.2.2 MainViewController.m

//
//  MainViewController.m
//  WellLogGraph
//
//  Created by wanglei on 13-8-23.
//  Copyright (c) 2013年 wanglei. All rights reserved.
//

#import "MainViewController.h"

#import "WellLogMapView.h"


@interface MainViewController ()

@end

@implementation MainViewController

- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
    self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
    if (self) {
        // Custom initialization
    }
    return self;
}

- (void)viewDidLoad
{
    [super viewDidLoad];
// Do any additional setup after loading the view.
    
    self.navigationItem.rightBarButtonItem.title = @"添加分栏";
    [self.navigationItem.rightBarButtonItem initWithBarButtonSystemItem:UIBarButtonSystemItemUndo
                                                                 target:self
                                                                 action:@selector(myAction)];
    
    WellLogMapView* view = (WellLogMapView*)self.view;
    [view setDelegate:self];
}

-(void)viewWillAppear:(BOOL)animated
{
    WellLogMapView* v = (WellLogMapView*)self.view;
    
    [v setNeedsDisplay];
}

- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

-(void)onSelectionChanged:(id)selection
{
    //do something
}

@end

4.2.3 WellLogMapView.h

//
//  WellLogMapView.h
//  WellLogGraph
//
//  Created by wanglei on 13-8-24.
//  Copyright (c) 2013年 wanglei. All rights reserved.
//

#import <UIKit/UIKit.h>

#import "MainViewController.h"

@interface WellLogMapView : UIView
{
    id<WellLogMapViewDelegate> delegate;
}

@property (nonatomic, retain) id delegate;

@end

4.2.4 WellLogMapView.m

//
//  WellLogMapView.m
//  WellLogGraph
//
//  Created by wanglei on 13-8-24.
//  Copyright (c) 2013年 wanglei. All rights reserved.
//

#import "WellLogMapView.h"

@implementation WellLogMapView

@synthesize delegate;

- (id)initWithFrame:(CGRect)frame
{
    self = [super initWithFrame:frame];
    if (self) {
        // Initialization code
    }
    return self;
}



// Only override drawRect: if you perform custom drawing.
// An empty implementation adversely affects performance during animation.
- (void)drawRect:(CGRect)rect
{
    // Drawing code
    
}

-(void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event
{
    //UITouch *touch = [touches anyObject];

    [delegate onSelectionChanged:nil];
    
}


@end

iOS技巧篇之UIViewController与UIView的双向交互