block 代码块 反向传值

block 代码块 也称作闭包 与C语言函数类似  具有反向传值、回调的功能

block公式分两种:

①声明和实现写到一块的公式

返回值类型(^block名字)(参数列表 参数类型 参数名) = ^(参数列表 参数类型 参数名){

实现代码(如果有返回值 需要return 返回值类型的值)

};

　调用:block名字(参数);

②声明和实现分开写的公式

(1)声明

返回值类型(^block名字)(参数列表);

(2)实现

block名字 = ^(参数列表){

实现代码(如果有返回值 需要return 返回值类型的值)

};

　　(3)调用

block名字(实参);

　　注? 在调用之前必须有实现的方法

今天在这里主要将一下block的方向传值（方向传值就是在回调的时候给他一个值）,通过button的示例来讲一下block怎么反向传值。

具体代码如下:

在AppDelegate.m中创建带导航栏的窗口

#import "AppDelegate.h"
#import "ViewController.h"

@interface AppDelegate ()

@end

@implementation AppDelegate

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {

    self.window = [[UIWindow alloc]initWithFrame:[UIScreen mainScreen].bounds];

    self.window.rootViewController = [[UINavigationController alloc]initWithRootViewController:[[ViewController alloc]init]];

    [self.window makeKeyAndVisible];

    return YES;

}

@end

在ViewController.m文件里面创建两个button,并且创建一个继承于UIViewController名叫BlockViewController类,导入ViewController.m文件里面

#import "ViewController.h"
#import "BlockViewController.h"

@interface ViewController ()
{

    UIButton *testButton;

}
@end

@implementation ViewController

- (void)viewDidLoad {

    [super viewDidLoad];

    self.view.backgroundColor = [UIColor whiteColor];

    [self createButton]; 

}

- (void)createButton{ 

    //放图片的button

    testButton = [UIButton buttonWithType:UIButtonTypeCustom];

    testButton.frame = CGRectMake(150, 100, 100, 100);

    testButton.backgroundColor = [UIColor brownColor];

    testButton.layer.cornerRadius = 50;

    testButton.layer.masksToBounds = YES;

    [self.view addSubview:testButton];

     //用于点击的按钮

    UIButton *button = [UIButton buttonWithType:UIButtonTypeCustom];

    button.frame = CGRectMake(100, 250, 200, 50);

    [button setTitle:@"进入下一页" forState:UIControlStateNormal];

    button.backgroundColor = [UIColor brownColor];

    button.layer.cornerRadius = 6;

    [button addTarget:self action:@selector(clickButton) forControlEvents:UIControlEventTouchUpInside];

    [self.view addSubview:button];

}

//按钮的触发事件

- (void)clickButton{

    BlockViewController *block = [[BlockViewController alloc]init];

    //block的实现

    block.buttonBlock = ^(UIImage *image){

        [testButton setImage:image forState:UIControlStateNormal];

    };

    [self presentViewController:block animated:YES completion:nil];  

}

@end

在自己创建的BlockViewController.h文件中声明block的方法并且把block当属性使用

#import <UIKit/UIKit.h>

@interface BlockViewController : UIViewController

//block的声明 这里把block当做属性

@property(nonatomic,copy)void(^buttonBlock)(UIImage *image);

@end

在BlockViewController.m文件中实现block的回调

#import "BlockViewController.h"

@interface BlockViewController ()

{

    UIButton *testButton;

}

@end

@implementation BlockViewController

- (void)viewDidLoad {

    [super viewDidLoad];

    self.view.backgroundColor = [UIColor whiteColor];

    [self backButton];

}

- (void)backButton{

    testButton = [UIButton buttonWithType:UIButtonTypeCustom];

    testButton.frame = CGRectMake(150, 100, 100, 100);

    [testButton setImage:[UIImage imageNamed:@"头像3.jpg"] forState:UIControlStateNormal];

    testButton.backgroundColor = [UIColor brownColor];

    testButton.layer.cornerRadius = 50;

    [self.view addSubview:testButton];

    UIButton *button = [UIButton buttonWithType:UIButtonTypeCustom];

    button.frame = CGRectMake(100, 250, 200, 50);

    [button setTitle:@"返回上一页" forState:UIControlStateNormal];

    button.backgroundColor = [UIColor brownColor];

    button.layer.cornerRadius = 6;

    [button addTarget:self action:@selector(clickButton) forControlEvents:UIControlEventTouchUpInside];

    [self.view addSubview:button];

}

- (void)clickButton{

    //block的回调

    self.buttonBlock([UIImage imageNamed:@"头像3.jpg"]);

　  //返回到上一页

    [self dismissViewControllerAnimated:YES completion:nil];

}

@end