iOS基础 - 动作目标机制

▶ target-action

目标是动作消息的接收者，一个控件或更为常见的是它的单元，以插座变量的形式保有其他动作消息的目标

动作是控件发送给目标的消息，从目标角度看，它是目标为了响应动作而实现的方法。程序需要某些机制来进行事件和指令的翻译，这个机制就是目标-动作机制

如何使用 target-action？下面代码中会分别采用枚举、动作目标两种方式！采取枚举方式的会在视图 TouchView 内部响应用户操作；而采用动作目标方式的则在目标对象 ViewController 中进行响应

// - TouchView.h

#import <UIKit/UIKit.h>
typedef enum{
    TouchViewTypeChangeColor,
    TouchViewTypeChangeFrame,
    TouchViewTypeChangeBounds
}TouchViewType;

@interface TouchView : UIView{
    TouchViewType _type;
}

// 枚举
- (id)initWithFrame:(CGRect)frame type:(TouchViewType )aType;

// target-action
@property(nonatomic,assign)NSObject *target; // 建议使用 id型
@property(nonatomic,assign)SEL action;
- (id)initWithTarget:(NSObject *)aTarget action:(SEL)aAction;

@end

// - TouchView.m

#import "TouchView.h"
@implementation TouchView

// 枚举
- (id)initWithFrame:(CGRect)frame type:(TouchViewType )aType{
    self = [super initWithFrame:frame];
    if (self) {
        _type = aType;
    }
    return self;
}

// target - action
- (id)initWithTarget:(NSObject *)aTarget action:(SEL)aAction{
    self = [super init];
    if (self) {
        _target = aTarget;
        _action = aAction;
    }
    return self;
}

// 点击视图
-(void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event{

    //----------------------- 枚举 --------------------------
    // 我们要清楚 View 的作用只是负责展示内容和响应用户的点击
    // 如果点击完视图后还要把将要做的事情写进自身视图内部，无疑是一个高耦合状态
    
    switch (_type) {
        case TouchViewTypeChangeColor:{
            self.backgroundColor = [UIColor colorWithRed:arc4random()%256/255.0 green:arc4random()%256/255.0 blue:arc4random()%256/255.0 alpha:1.0];
        }
            break;
        case TouchViewTypeChangeBounds:{
            self.transform = CGAffineTransformScale(self.transform, 1, 2);// 纵向伸缩
        }
        default:
            break;
    }

    //-----------------Target - Action----------------------
    // 我们完全可以利用 Target - Action：当视图被点击的时
    // 这样视图不做任何处理，而是通知某对象执行某个方法
    [_target performSelector:_action withObject:self afterDelay:0.1];
}

@end

// - ViewController.m

#import "ViewController.h"
#import "TouchView.h"
@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];

    // --------------使用枚举----------------
    // 改变颜色
    TouchView *touchView01 = [[TouchView alloc] initWithFrame:CGRectMake(50, 50, 100, 100) type:TouchViewTypeChangeColor];
    touchView01.backgroundColor = [UIColor orangeColor];
    [self.view addSubview:touchView01];

    // 改变尺寸
    TouchView *touchView02 = [[TouchView alloc] initWithFrame:CGRectMake(220, 100, 50, 50) type:TouchViewTypeChangeBounds];
    touchView02.backgroundColor = [UIColor purpleColor];
    [self.view addSubview:touchView02];

    //---------------------- target - action：----------------------
    // 方式一：直接通过成员变量赋值
    TouchView *touchView03 = [[TouchView alloc] initWithTarget:self action:@selector(changeColor:)];
    touchView03.frame = CGRectMake(50, 200, 100, 100);
    touchView03.backgroundColor = [UIColor redColor];
    [self.view addSubview: touchView03];

    TouchView *touchView04 = [[TouchView alloc] initWithTarget:self action:@selector(changeFrame:)];
    touchView04.frame = CGRectMake(220, 250, 50, 50);
    touchView04.backgroundColor = [UIColor orangeColor];
    [self.view addSubview:touchView04];

    // 方式二：通过属性赋值
    TouchView *touchView05 = [[TouchView alloc] initWithFrame:CGRectMake(50, 400, 50, 50)];
    touchView05.target = self;
    touchView05.action = @selector(changeFrame:);
    touchView05.backgroundColor = [UIColor blackColor];
    [self.view addSubview:touchView05];

}

// frame
-(void)changeFrame:(TouchView *)touchView{
    touchView.frame = CGRectMake(arc4random()%220, arc4random()%486, 80, 80);
}

// Color
- (void)changeColor:(TouchView *)touchView{
    touchView.backgroundColor = [UIColor colorWithRed:arc4random()%256/255.0 green:arc4random()%256/255.0 blue:arc4random()%256/255.0 alpha:1.0];
}

@end