页面传值:属性,协议,Block传值

1.属性传值和协议传值

#import "RootViewController.h"
#import "SecondViewController.h"
#warning 第四步:签订协议
@interface RootViewController ()<SecondViewControllerDelegate>
@property(nonatomic,strong)UILabel *showTextLable;
@end

@implementation RootViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view.
    self.view.backgroundColor = [UIColor whiteColor];
    self.navigationItem.title = @"首页";
    //创建UILable用于显示内容
    UILabel *showTextLable = [[UILabel alloc] initWithFrame:CGRectMake(100, 200, 150, 50)];
    showTextLable.backgroundColor = [UIColor yellowColor];
    showTextLable.text = @"美女帅哥";
    showTextLable.textAlignment = NSTextAlignmentCenter;
    [self.view addSubview:showTextLable];
    self.showTextLable = showTextLable;
    
    //创建推出下个界面的UIButton
    UIButton *pushNextBtn = [UIButton buttonWithType:UIButtonTypeCustom];
    pushNextBtn.frame = CGRectMake(100, 300, 150, 50);
    pushNextBtn.backgroundColor = [UIColor magentaColor];
    [pushNextBtn setTitle:@"下一页" forState:UIControlStateNormal];
    [pushNextBtn addTarget:self action:@selector(pushNextController) forControlEvents:UIControlEventTouchUpInside];
    [self.view addSubview:pushNextBtn];
    
    
}
-(void)pushNextController
{
    SecondViewController *secondVC = [[SecondViewController alloc] init];
    //需要把lable的text传给
    //下面这种传值方法是错误的,因为textField还没有创建,还没有加载到视图上,这里是项目期特别容易犯错的地方,必须要考虑视图加载的顺序
    //secondVC.textField.text = self.showTextLable.text;
    //正确的写法应该是直接传送文本内容
    secondVC.content = self.showTextLable.text;
    //
#warning 第五步:指定代理人
    secondVC.secondViewControllerDelegate = self;//指定协议代理人
    [self.navigationController pushViewController:secondVC animated:YES];
}
#warning 第六步:实现协议的方法
-(void)changeValue:(NSString *)text
{
    self.showTextLable.text = text;
}
- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

#import <UIKit/UIKit.h>
#warning 第一步:声明协议
@protocol SecondViewControllerDelegate <NSObject>

-(void)changeValue:(NSString *)text;
@optional//可选的协议方法
-(void)changeColor:(UIColor *)color;

@end
@interface SecondViewController : UIViewController
/**
 *  显示文本输入框的
 */
@property (nonatomic,strong) UITextField *textField;
/**
 *  显示文本输入框的内容文本
 */
@property (nonatomic,strong) NSString *content;
#warning 第二步:声明代理人
/**
 *  第二个Controller中的协议,
    assign避免循环引用
 */
@property (nonatomic,assign)id<SecondViewControllerDelegate>secondViewControllerDelegate;
@end

#import "SecondViewController.h"

@interface SecondViewController ()

@end

@implementation SecondViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view.
    self.view.backgroundColor = [UIColor whiteColor];
    self.navigationItem.title= @"第二页";
    //创建输入文本的文本框
    UITextField *textField = [[UITextField alloc] initWithFrame:CGRectMake(100, 200, 150, 50)];
    textField.placeholder = @"请输入文本内容";
    textField.borderStyle = UITextBorderStyleRoundedRect;
    [self.view addSubview:textField];
    self.textField = textField;
    self.textField.text = self.content;
    
    //创建UIButton用于返回上一个界面
    UIButton *backBtn = [UIButton buttonWithType:UIButtonTypeRoundedRect];
    backBtn.frame = CGRectMake(100, 300, 150, 50);
    [backBtn setTitle:@"返回" forState:UIControlStateNormal];
    backBtn.backgroundColor = [UIColor blackColor];
    [backBtn addTarget:self action:@selector(popButtonAction) forControlEvents:UIControlEventTouchUpInside];
    [self.view addSubview:backBtn];
    
    
}
-(void)popButtonAction
{
#warning 第三步:执行相关的协议方法
    [self.secondViewControllerDelegate changeValue:self.textField.text];
    [self.navigationController popViewControllerAnimated:YES];
}
//总结:属性传值:一般使用从前往后进行传值的情况
//如果从后往前,需要借助其他传值方式
//协议传值方式
/**
 *  实现协议的六个步骤:
 第一步:声明协议
 第二步:声明代理人
 第三步:执行协议方法
 第四步:签订协议
 第五步:指定代理人
 第六步:实现协议方法
 */

2.Block传值

#import "RootViewController.h"
#import "SecondViewController.h"
@interface RootViewController ()
@property(nonatomic,strong)UILabel *showTextLable;
@end

@implementation RootViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view.
    UILabel *showLabel = [[UILabel alloc] initWithFrame:CGRectMake(100, 200, 150, 50)];
    showLabel.backgroundColor = [UIColor redColor];
    showLabel.text = @"美女帅哥";
    showLabel.textAlignment = NSTextAlignmentCenter;
    showLabel.font = [UIFont systemFontOfSize:24];
    [self.view addSubview:showLabel];
    self.showTextLable = showLabel;
    UIButton *nextBtn = [UIButton buttonWithType:UIButtonTypeRoundedRect];
    nextBtn.frame = CGRectMake(100, 300, 150, 50);
    nextBtn.backgroundColor = [UIColor yellowColor];
    [nextBtn setTitle:@"下一页" forState:UIControlStateNormal];
    [nextBtn addTarget:self action:@selector(showNextAction) forControlEvents:UIControlEventTouchUpInside];
    [self.view addSubview:nextBtn];
    
}
-(void)showNextAction
{
    SecondViewController *secondView = [[SecondViewController alloc] init];
    [self.navigationController pushViewController:secondView animated:YES];
    //ARC模式下用__weak修饰可解决内存泄漏问题,MRC模式下用__block
    __weak typeof (self)weakSelf = self;
#warning 第三步:实现Block的内容(实现传递过来的内容)
    secondView.changeValueBlock = ^(NSString *string){
        //下面这种引用容易造成内存泄漏
        //self.showTextLable.text = string;
        weakSelf.showTextLable.text = string;
    };
    //block的核心是:回调,Block作为属性进行传值的时候,一般使用场景是从第二个界面返回到上一个界面,基本步骤:
    //1.在第二个界面中声明一个Block属性
    //2.在第二个界面返回的那句代码之前加上Block需要传递的内容
    //3.在一个界面推出第二个界面那句代码之前,对Block进行实现(即接受Block传递过来的内容)
     secondView.content = self.showTextLable.text;
}

#import <UIKit/UIKit.h>

@interface SecondViewController : UIViewController
@property (nonatomic,strong) NSString *content;
@property (strong,nonatomic) UITextField *textField;
#warning 第一步:声明Block属性,copy是为了解决循环引用的问题
@property (nonatomic,copy) void(^changeValueBlock)(NSString *string);
@end

#import "SecondViewController.h"

@interface SecondViewController ()

@end

@implementation SecondViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view.
    self.view.backgroundColor = [UIColor whiteColor];
    self.view.backgroundColor = [UIColor whiteColor];
    self.navigationItem.title= @"第二页";
    //创建输入文本的文本框
    UITextField *textField = [[UITextField alloc] initWithFrame:CGRectMake(100, 200, 150, 50)];
    textField.placeholder = @"请输入文本内容";
    textField.borderStyle = UITextBorderStyleRoundedRect;
    [self.view addSubview:textField];
    self.textField = textField;
    self.textField.text = self.content;
    
    //创建UIButton用于返回上一个界面
    UIButton *backBtn = [UIButton buttonWithType:UIButtonTypeRoundedRect];
    backBtn.frame = CGRectMake(100, 300, 150, 50);
    [backBtn setTitle:@"返回" forState:UIControlStateNormal];
    backBtn.backgroundColor = [UIColor blackColor];
    [backBtn addTarget:self action:@selector(popButtonAction) forControlEvents:UIControlEventTouchUpInside];
    [self.view addSubview:backBtn];
}
-(void)popButtonAction
{
#warning 第二步:将要传递的内容通过属性block先给它
    self.changeValueBlock(self.textField.text);
  
    [self.navigationController popViewControllerAnimated:YES];
}