Block传值

Block简介：

block是存储的数据是一个函数体。使用block是，你可以像调用其他标准函数一样，传入参数数，并得到返回值。
脱字符（^）是块的语法标记。按照我们熟悉的参数语法规约所定义的返回值以及块的主体（也就是可以执行的代码）。

 block的定义：
    //1 定义一个block变量
   
    /*
     * int      返回值类型
     * myBlock  block变量的名称
     * int a,NSString *s 参数
     */
    int (^myBlock)(int a,NSString *s);
//    int (^myBlock)(int ,NSString *);
    // int (^)(int a,NSString *s)[类型]  myblock[变量名]
    //2 创建一个block
    myBlock =^(int a,NSString *s){
        
        //block要调用的代码块
        NSLog(@"myBlock被调用了");
        NSLog(@"a =%d s = %@",a,s);
        
        return a; //和定义的block返回值类型对应.
    };

block最主要的用途就是作为方法的参数在使用的，我们来看看如何使用block在viewcontroller与view上来传递值的吧。

#import <UIKit/UIKit.h>
//创建block的类型与名称。注意ChangeBlock是别名,代替了 void(^)(NSString *text)，ios中规定这么写
typedef void(^ChangeBlock)(NSString *text);

@interface BlockChangeValue : UIView{
    UIButton *button;
}

- (void)changeTextValue:(ChangeBlock)block;
@property(nonatomic,strong)ChangeBlock block;

//
//  BlockChangeValue.m
//  BlockChangeValueandDelegate
//
//  Created by mac on 16/8/2.
//  Copyright © 2016年 mac. All rights reserved.
//

#import "BlockChangeValue.h"

@implementation BlockChangeValue

- (instancetype)initWithFrame:(CGRect)frame{
    
    self = [super initWithFrame:frame];
    if (self != nil) {
        self.backgroundColor = [UIColor orangeColor];
        
        UITextField *textField = [[UITextField alloc] initWithFrame:CGRectMake(20, 20, 200, 80)];
        textField.placeholder = @"请输入";
        textField.layer.cornerRadius = 10;
        textField.textColor = [UIColor blackColor];
        textField.tag = 1000;
        textField.backgroundColor = [UIColor whiteColor];
        [self addSubview:textField];
        
        button = [[UIButton alloc] initWithFrame:CGRectMake((self.frame.size.width - 30)/2, 120, 50, 30)];
        button.backgroundColor = [UIColor blueColor];
        [button setTitle:@"确定" forState:UIControlStateNormal];

        [self addSubview:button];
        
    }
    return self;
}

//使用block方法
- (void)changeTextValue:(ChangeBlock)block {
    self.block = block;
    [button addTarget:self action:@selector(buttnAction:) forControlEvents:UIControlEventTouchUpInside];
    
}
- (void)buttnAction:(UIButton *)button{
    
    UITextField *textFiled = [self viewWithTag:1000];
    //将你需要的值进行传递
    self.block(textFiled.text);
    [self removeFromSuperview];
}
@end

接收方：

    //
//  ViewController.m
//  BlockChangeValueandDelegate
//
//  Created by mac on 16/8/2.
//  Copyright © 2016年 mac. All rights reserved.
//

#import "ViewController.h"
#import "BlockChangeValue.h"
@interface ViewController (){

}

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    //label
    UILabel *label = [[UILabel alloc] initWithFrame:CGRectMake(20, 20, 300, 200)];
    label.backgroundColor = [UIColor grayColor];
    label.textColor = [UIColor whiteColor];
    label.text = @"传值";
    label.textAlignment = NSTextAlignmentCenter;
    label.tag = 1000;

    UIButton *blockBtn = [[UIButton alloc] initWithFrame:CGRectMake(220, 250, 80, 30)];
    [blockBtn setTitle:@"block打开" forState:UIControlStateNormal];
    [blockBtn addTarget:self action:@selector(blockBtnAction:) forControlEvents:UIControlEventTouchUpInside];
    blockBtn.backgroundColor = [UIColor blackColor];
    [self.view addSubview:blockBtn];

    //背景颜色
    self.view.backgroundColor = [UIColor yellowColor];
    [self.view addSubview:label];
}

- (void)blockBtnAction:(UIButton *)button{
  
    BlockChangeValue *blockVC = [[BlockChangeValue alloc] initWithFrame:CGRectMake(0, 0, 300, 200)];
    blockVC.center = self.view.center;
//使用block方法进行值得改变
    [blockVC changeTextValue:^(NSString *text) {
        UILabel *label = [self.view viewWithTag:1000];
        label.text = text;
    }];
    [self.view addSubview:blockVC];
    
}
@end