Block傳值

我們先在這裡約定：介面1傳值到介面2為順傳，介面2傳值到介面1為逆傳

一般用Block傳值是為了降低檢視控制器之間的耦合度，和代理傳值類似主要用於逆序傳值。

一. 實現步驟

1. 給介面2定義一個Block屬性；注意：在block傳值中，要傳幾個值，block就有幾個引數，引數要與傳的值對應

2. 在介面2的跳轉方法中檢查block屬性是否有值，有值就執行block，然後介面2出棧

3. 在介面1的跳轉方法中建立介面2，並把要執行的賦值語句儲存到介面2的block變數屬性

二. 具體程式碼

1. AppDelegate類

---------- AppDelegate.m
 
檔案

#import "AppDelegate.h"
#include "OneViewController.h"

@interface AppDelegate ()

@end

@implementation AppDelegate

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

  // 1. 建立視窗
  self.window = [[UIWindow alloc] initWithFrame:[UIScreen mainScreen].bounds
 
];

  // 2. 建立視窗的根控制器
  // 2.1 建立導航控制器的根控制器
  UIViewController *oneVc = [[OneViewController alloc] init];
  // 2.2 建立導航控制器
  UINavigationController *nav = [[UINavigationController alloc] initWithRootViewController:oneVc];
  // 2.3 給視窗設定根控制器
  self.window.rootViewController = nav;

  // 3. 設定視窗為主視窗並顯示視窗
  [self
 
.window makeKeyAndVisible];

  // 隱藏導航控制器的導航條
  nav.navigationBarHidden = YES;

  return YES;
}

@end

2. OneViewController類

---------- OneViewController.m檔案

#import "OneViewController.h"
#import "TwoViewController.h"

@interface OneViewController ()

@property (nonatomic,strong) UITextField *textField;

@end

@implementation OneViewController

- (void)viewDidLoad {
  [super viewDidLoad];

  //設定控制器View的背景顏色
  self.view.backgroundColor = [UIColor greenColor];

  // 建立點選按鈕
  UIButton *clickBtn = [UIButton buttonWithType:UIButtonTypeCustom];
  clickBtn.frame = CGRectMake(10, 100, 80, 40);
  clickBtn.backgroundColor = [UIColor whiteColor];
  [clickBtn setTitle:@"到介面2" forState:UIControlStateNormal];
  [clickBtn setTitleColor:[UIColor blackColor] forState:UIControlStateNormal];
  [clickBtn setTitleColor:[UIColor redColor] forState:UIControlStateHighlighted];
  [clickBtn addTarget:self action:@selector(btnClick) forControlEvents:UIControlEventTouchUpInside];
  [self.view addSubview:clickBtn];

  // 建立文字框
  _textField = [[UITextField alloc] initWithFrame:CGRectMake(10, 150, 250, 40)];
  _textField.borderStyle = UITextBorderStyleRoundedRect;
  _textField.backgroundColor = [UIColor whiteColor];
  [self.view addSubview:_textField];

}

#pragma mark - 點選事件

- (void)btnClick {

  // 建立介面2，並壓入棧
  TwoViewController *twoVc = [[TwoViewController alloc] init];
  [self.navigationController pushViewController:twoVc animated:YES];

  // 給介面的Block設定傳值程式碼塊
  twoVc.twoBlock = ^(NSString *str){
    // 用介面2的值賦給介面1的文字框，這句程式碼是在介面1中執行的
    _textField.text = str;
  };

}

@end

3. TwoViewController類

---------- TwoViewController.h檔案

#import <UIKit/UIKit.h>

// 自定義一個Block變數型別名
typedef void(^TwoViewControllerBlock)(NSString *);

@interface TwoViewController : UIViewController

// Block屬性
@property (nonatomic,strong) TwoViewControllerBlock twoBlock;

@end

---------- TwoViewController.h檔案

#import "TwoViewController.h"

@interface TwoViewController ()

@property (nonatomic,strong) UITextField *textField;

@end

@implementation TwoViewController

- (void)viewDidLoad {
    [super viewDidLoad];

  //設定控制器View的背景顏色
  self.view.backgroundColor = [UIColor yellowColor];

  // 建立點選按鈕
  UIButton *clickBtn = [UIButton buttonWithType:UIButtonTypeCustom];
  clickBtn.frame = CGRectMake(10, 100, 80, 40);
  clickBtn.backgroundColor = [UIColor whiteColor];
  [clickBtn setTitle:@"傳 值" forState:UIControlStateNormal];
  [clickBtn setTitleColor:[UIColor blackColor] forState:UIControlStateNormal];
  [clickBtn setTitleColor:[UIColor redColor] forState:UIControlStateHighlighted];
  [clickBtn addTarget:self action:@selector(btnClick) forControlEvents:UIControlEventTouchUpInside];
  [self.view addSubview:clickBtn];

  // 建立文字框
  _textField = [[UITextField alloc] initWithFrame:CGRectMake(10, 150, 250, 40)];
  _textField.borderStyle = UITextBorderStyleRoundedRect;
  _textField.backgroundColor = [UIColor whiteColor];
  [self.view addSubview:_textField];
}

#pragma mark - 點選事件

- (void)btnClick {

  // 如果Block有值就執行Block
  if (_twoBlock) {
    // 傳入文字框的值傳到介面1
    _twoBlock(_textField.text);
  }

  // 跳轉介面
  [self.navigationController popViewControllerAnimated:YES];

}

@end