block 代碼塊 反向傳值，block代碼傳值

block 代碼塊 反向傳值，block代碼傳值

block 代碼塊 也稱作閉包 與C語言函數類似  具有反向傳值、回調的功能

block公式分兩種:

   ①聲明和實現寫到一塊的公式

   傳回值類型(^block名字)(參數列表 參數類型 參數名) = ^(參數列表 參數類型 參數名){

        實現代碼(如果有傳回值 需要return 傳回值類型的值)

   };

　調用:block名字(參數);

 

  ②聲明和實現分開寫的公式

     (1)聲明

     傳回值類型(^block名字)(參數列表);

     (2)實現

     block名字 = ^(參數列表){

        實現代碼(如果有傳回值 需要return 傳回值類型的值)

     };

　　(3)調用

     block名字(實參);

　　注⃝ 在調用之前必須有實現的方法   

 

今天在這裡主要將一下block的方向傳值（方向傳值就是在回調的時候給他一個值）,通過button的樣本來講一下block怎麼反向傳值。

具體代碼如下:

在AppDelegate.m中建立帶導覽列的視窗

#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檔案裡面建立兩個button,並且建立一個繼承於UIViewController名叫BlockViewController類,匯入ViewController.m檔案裡面

#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{      //放圖片的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];       //用於點擊的按鈕     UIButton *button = [UIButton buttonWithType:UIButtonTypeCustom];     button.frame = CGRectMake(100, 250, 200, 50);     [button setTitle:@"進入下一頁" forState:UIControlStateNormal];     button.backgroundColor = [UIColor brownColor];     button.layer.cornerRadius = 6;     [button addTarget:self action:@selector(clickButton) forControlEvents:UIControlEventTouchUpInside];     [self.view addSubview:button];  } //按鈕的觸發事件 - (void)clickButton{     BlockViewController *block = [[BlockViewController alloc]init];     //block的實現     block.buttonBlock = ^(UIImage *image){         [testButton setImage:image forState:UIControlStateNormal];     };     [self presentViewController:block animated:YES completion:nil];   } @end

在自己建立的BlockViewController.h檔案中聲明block的方法並且把block當屬性使用

#import <UIKit/UIKit.h>@interface BlockViewController : UIViewController//block的聲明 這裡把block當做屬性@property(nonatomic,copy)void(^buttonBlock)(UIImage *image);@end

在BlockViewController.m檔案中實現block的回調

#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:@"頭像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:@"返回上一頁" 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的回調    self.buttonBlock([UIImage imageNamed:@"頭像3.jpg"]);　  //返回到上一頁    [self dismissViewControllerAnimated:YES completion:nil];}@end