block传值

到目前为止，有4中传值方法

1.属性传值

2.代理传值

3.单例 传值

4.block传值

block传值，是在一个类A里面，把block设定为属性，在另一个类B中包含这个类。在B中创建一个A的对象，使用block。这里是block的实现。

在A类里面创建一个B对象，使用block。这里是block的调用。

A类为RootViewController,B类为FirstViewController.

把A类中的按钮的颜色传到B类中

RootViewController.h

#import <UIKit/UIKit.h>

//将void(^)(UIColor *)重名为BLOCK
typedef void(^BLOCK)(UIColor *);

@interface RootViewController : UIViewController

//①.将block声明为属性，因为其他页面会用的到
@property(nonatomic,copy)BLOCK block;

@end

RootViewController.m

#import "RootViewController.h"

#import "FirstViewController.h"

@interface RootViewController ()

@end

@implementation RootViewController

- (void)viewDidLoad {
[super viewDidLoad];

self.view.backgroundColor = [UIColor yellowColor];

#pragma mark --------------创建rightBarButtonItem

[self createBarButtonItems];

[self createButton];

// Do any additional setup after loading the view.
}

-(void)createButton{
UIButton *button = [UIButton buttonWithType:UIButtonTypeCustom];

button.backgroundColor = [UIColor redColor];

button.frame = CGRectMake(100, 100, 60, 40);

[button addTarget:self action:@selector(didClickButton:) forControlEvents:UIControlEventTouchUpInside];
[self.view addSubview:button];

}

-(void)didClickButton:(UIButton *)button{

FirstViewController *firstVC = [[FirstViewController alloc]init];

[self.navigationController pushViewController:firstVC animated:YES];

//当点击button按钮的时候，调用block，调用的形式：block变量名（实参列表）

[firstVC view];

_block(button.backgroundColor);

[firstVC release];
}

-(void)createBarButtonItems{

UIBarButtonItem *rightButtonItem = [[UIBarButtonItem alloc]initWithTitle:@"PUSH" style:UIBarButtonItemStylePlain target:self action:@selector(clickToPush:)];

self.navigationItem.rightBarButtonItem= rightButtonItem;

}

-(void)clickToPush:(UIBarButtonItem *)button{
///推出下一级页面

FirstViewController *firstVC = [[FirstViewController alloc]init];

[self.navigationController pushViewController:firstVC animated:YES];

}

FirstViewController.m中的代码，.h中基本没有代码，所以就不列举了

#import "FirstViewController.h"

#import "RootViewController.h"

typedef int(^Block)(int ,int );

@interface FirstViewController ()

@end

@implementation FirstViewController

- (void)viewDidLoad {
[super viewDidLoad];

self.view.backgroundColor = [UIColor cyanColor];

self.view.backgroundColor = _block;

//匿名函数
//    int (int a ,int b);
//    int (int a ,int b){
//
//        return a + b;
//
//    }

//定义block变量 , 分三部分

//1. 类型 ： int (^)(int , int )

//2.变量名:block

//3.初值：^(int a,int b){ return a + b; };

Block block = ^int (int a,int b){

return a+b;
};

//二，如何使用block 形式：block变量名（实参列表）

int a = block(3, 5);

NSLog(@"%d",a);

//使用block实现对两个整数求积

Block mutiBlock = ^int (int a ,int b){

return a*b;
};

int  b = mutiBlock(3,5);

NSLog(@"%d",b);

//获得上一个页面对应的视图控制器对象

RootViewController *controller =(RootViewController *)self.navigationController.viewControllers[0];

controller.block = ^void(UIColor *color){

self.view.backgroundColor = color;

};