iOS 多界面传值之--Block(代码块)传值

Block传值

一般应用于逆向传值,即第二界面向第一界面传值,我们需要记住的两点:
1.要在第二个界面(SecondViewController.h)定义一个Block:
2.在第一个界面(ViewController.m)跳转第二个界面的方法中我们为block属性赋值完成block传值:

3.首先来到SecondViewController.h定义一个代码块

#import <UIKit/UIKit.h>//定义Blocktypedef void (^PushBlock)(NSString *);//声明Block属性@interface SecondViewController : UIViewController@property (nonatomic,strong) PushBlock pushValueString;@end

4.在SecondViewController,m里面设置UITextField 和 UIbutton 成为属性,然后在viewDidLoad 方法里面分别创建一个textField 和 一个button

#import "SecondViewController.h"@interface SecondViewController ()@property (nonatomic,strong) UITextField *textF;@property (nonatomic,strong) NSString *textString;@end@implementation SecondViewController- (void)viewDidLoad {    [super viewDidLoad];    self.view.backgroundColor = [UIColor yellowColor];    _textF = [[UITextField alloc]initWithFrame:CGRectMake(0, 250, self.view.bounds.size.width, 50)];    _textF.borderStyle = UITextBorderStyleRoundedRect;    [self.view addSubview:_textF];    UIButton *btn = [UIButton buttonWithType:UIButtonTypeRoundedRect];    btn.frame = CGRectMake(20, 350, self.view.bounds.size.width-40, 50);    btn.backgroundColor = [UIColor purpleColor];    btn.titleLabel.font = [UIFont systemFontOfSize:25.0];    btn.tintColor = [UIColor whiteColor];    [btn setTitle:@"Back" forState:UIControlStateNormal];    [btn addTarget:self action:@selector(backAction:) forControlEvents:UIControlEventTouchUpInside];    [self.view addSubview:btn];}

5.实现button里面的点击事件的方法,并且在这方法里面实现Block的核心代码

-(void)backAction:(UIButton *)sender{//    核心代码    _pushValueString (_textF.text);    [self dismissViewControllerAnimated:YES completion:nil];}

6.回到ViewController里面,首先我们需要导入一下头文件#import “SecondViewController.h”,并且创建一个UITextField 和 UIbutton

#import "ViewController.h"#import "SecondViewController.h"@interface ViewController ()@property (nonatomic,strong)UITextField *textField;@end@implementation ViewController- (void)viewDidLoad {    [super viewDidLoad];    /**     *  block传值(场景)一般用于逆向传值,即第二个界面传值给第一个界面        1.要在第二个界面(SecondViewController.h)定义一个Block:        2.要在第一个界面(ViewController.m)跳转第二个界面的方法中我们为block属性赋值完成block传值:     */    self.view.backgroundColor = [UIColor greenColor];    self.title = @"Block传值";     _textField = [[UITextField alloc]initWithFrame:CGRectMake(0, 250, self.view.bounds.size.width, 50)];    _textField.borderStyle = UITextBorderStyleRoundedRect;    [self.view addSubview:_textField];    UIButton *btn = [UIButton buttonWithType:UIButtonTypeRoundedRect];    btn.frame = CGRectMake(20, 350, self.view.bounds.size.width-40, 50);    btn.titleLabel.font = [UIFont systemFontOfSize:25.0];    btn.backgroundColor = [UIColor blueColor];    btn.tintColor = [UIColor whiteColor];    [btn setTitle:@"Next" forState:UIControlStateNormal];    [btn addTarget:self action:@selector(nextAction:) forControlEvents:UIControlEventTouchUpInside];    [self.view addSubview:btn];}

7.实现一下button的点击事件的方法,并在这个方法里面实现跳转界面和block的核心代码属性赋值

-(void)nextAction:(UIButton *)sender{    SecondViewController *secondVC = [[SecondViewController alloc]init];//    核心代码为block属性赋值    secondVC.pushValueString = ^(NSString *string){        _textField.text = string;    };    [self presentViewController:secondVC animated:YES completion:nil];}

8.由于我们用的是模态视图进行页面之间的跳转,所以就不需要去创建UINavigationController了.模拟器运行效果如下