最直接的教你OC中Block的简单使用场景

场景一： A控制器跳转到B控制器   --   B控制器事件处理通过Block回调给A控制器

A 跳转前界面如下

点击ToB按钮到控制器B

在控制器B中点击按钮返回到A界面如下

                             

不说废话上码！！！！

A-->控制器 .m

#import "ViewControllerA.h"
#import "ViewControllerB.h"

@interface ViewControllerA ()

@property (nonatomic, strong) ViewControllerB *controllerB;

@property (nonatomic, strong) UILabel *testLabel;

@end

@implementation ViewControllerA

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view.
    self.view.backgroundColor = [UIColor whiteColor];

    UIButton *jumpButton = [[UIButton alloc] initWithFrame:CGRectMake(, , , )];
    jumpButton.backgroundColor = [UIColor redColor];
    jumpButton.layer.cornerRadius = ;
    [jumpButton addTarget:self action:@selector(jumpButtonClickAction) forControlEvents:UIControlEventTouchUpInside];
    [jumpButton setTitle:@"ToB" forState:UIControlStateNormal];
    [self.view addSubview:jumpButton];

    _testLabel = [[UILabel alloc] initWithFrame:CGRectMake(, , self.view.frame.size.width - , )];
    _testLabel.center = self.view.center;
    _testLabel.textAlignment = NSTextAlignmentCenter;
    _testLabel.backgroundColor = [UIColor lightGrayColor];
    _testLabel.textColor = [UIColor redColor];
    [self.view addSubview:_testLabel];
}

- (void)jumpButtonClickAction {

    //TODO: 声明weakSelf 在Block中使用 方式Block循环引用
    __weak typeof(self) weakSelf = self;
    _controllerB = [[ViewControllerB alloc] init];

    //TODO: 控制器中点击测试按钮 通过Block的回调实现
    _controllerB.change_controllerA_labelTitleBlock = ^(NSString *title) {
        weakSelf.testLabel.text = [NSString stringWithFormat:@"点击了%@",title];
    };

    [self.navigationController pushViewController:_controllerB animated:YES];
}

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

@end

B--> .h代码

#import <UIKit/UIKit.h>

@interface ViewControllerB : UIViewController

//TODO: 声明用来回调的 Block
@property (nonatomic, copy) void(^change_controllerA_labelTitleBlock)(NSString *title);

@end

B--> .m代码

#import "ViewControllerB.h"

@interface ViewControllerB ()

@end

@implementation ViewControllerB

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view.
    self.view.backgroundColor = [UIColor whiteColor];

    UIButton *buttonLeft = [[UIButton alloc] initWithFrame:CGRectMake(, , , )];
    buttonLeft.backgroundColor = [UIColor blackColor];
    [buttonLeft setTitle:@"buttonLeft" forState:UIControlStateNormal];
    [buttonLeft addTarget:self action:@selector(buttonClickAction:) forControlEvents:UIControlEventTouchUpInside];
    [self.view addSubview:buttonLeft];

    UIButton *buttonRight = [[UIButton alloc] initWithFrame:CGRectMake(CGRectGetMaxX(buttonLeft.frame) + , , , )];
    buttonRight.backgroundColor = [UIColor blackColor];
    [buttonRight setTitle:@"buttonRight" forState:UIControlStateNormal];
    [buttonRight addTarget:self action:@selector(buttonClickAction:) forControlEvents:UIControlEventTouchUpInside];
    [self.view addSubview:buttonRight];

}

- (void)buttonClickAction:(UIButton *)sender {

    //TODO: 判断 self.change_controllerA_labelTitleBlock 是否为空（必写）
    if (self.change_controllerA_labelTitleBlock) {

        //TODO: Block 会调给控制器A 值
        self.change_controllerA_labelTitleBlock(sender.titleLabel.text);
    }
    [self.navigationController popViewControllerAnimated:YES];
}

//TODO: Block Set方法(必写)
- (void)setChange_controllerA_labelTitleBlock:(void (^)(NSString *))change_controllerA_labelTitleBlock {
    _change_controllerA_labelTitleBlock = change_controllerA_labelTitleBlock;
}

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

@end

场景二：A控制器中添加子View 子View中的事件回调

截图如下

A --> .m

#import "ViewControllerA.h"
#import "TestBlockView.h"

@interface ViewControllerA ()

@property (nonatomic, strong) TestBlockView *testBlockView;

@property (nonatomic, strong) UILabel *testLabel;

@end

@implementation ViewControllerA

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view.
    self.view.backgroundColor = [UIColor whiteColor];

    _testLabel = [[UILabel alloc] initWithFrame:CGRectMake(20, 70, self.view.frame.size.width - 40, 40)];
    _testLabel.textAlignment = NSTextAlignmentCenter;
    _testLabel.backgroundColor = [UIColor lightGrayColor];
    _testLabel.textColor = [UIColor redColor];
    [self.view addSubview:_testLabel];

    __weak typeof(self) weakSelf = self;
    _testBlockView = [[TestBlockView alloc] initWithFrame:CGRectMake(0, 0, self.view.frame.size.width - 100, self.view.frame.size.width - 100) testBlock:^(NSString *title) {
        weakSelf.testLabel.text = [NSString stringWithFormat:@"点击了%@",title];
    }];

    _testBlockView.center = self.view.center;
    _testBlockView.backgroundColor = [UIColor yellowColor];
    [self.view addSubview:_testBlockView];
}

@end

TestBlockView --> .h

#import <UIKit/UIKit.h>

//TODO: 声明Block的第二种写法

typedef void(^TestBlock)(NSString *title);

@interface TestBlockView : UIView

@property (nonatomic, copy) TestBlock testBlock1;

//TODO: 重写init方法 加上Block回调处理
- (instancetype)initWithFrame:(CGRect)frame testBlock:(TestBlock)testBlock1;
@end

TestBlockView --> .m

#import "TestBlockView.h"

@implementation TestBlockView

//TODO: 重写init方法 加上Block回调处理
- (instancetype)initWithFrame:(CGRect)frame testBlock:(TestBlock)testBlock1 {
    if (self = [super initWithFrame:frame]) {
        _testBlock1 = testBlock1;
        [self addTestButton];
    }
    return self;
}

- (void)addTestButton {
    UIButton *testButton1 = [[UIButton alloc] initWithFrame:CGRectMake(, , , )];
    testButton1.layer.cornerRadius = ;
    testButton1.backgroundColor = [UIColor lightGrayColor];
    [testButton1 setTitle:@"testButton1" forState:UIControlStateNormal];
    [testButton1 addTarget:self action:@selector(testButtonClick:) forControlEvents:UIControlEventTouchUpInside];
    [self addSubview:testButton1];

    UIButton *testButton2 = [[UIButton alloc] initWithFrame:CGRectMake(CGRectGetMaxX(testButton1.frame) + , CGRectGetMinY(testButton1.frame), , )];
    testButton2.layer.cornerRadius = ;
    testButton2.backgroundColor = [UIColor lightGrayColor];
    [testButton2 setTitle:@"testButton2" forState:UIControlStateNormal];
    [testButton2 addTarget:self action:@selector(testButtonClick:) forControlEvents:UIControlEventTouchUpInside];
    [self addSubview:testButton2];
}

- (void)testButtonClick:(UIButton *)sender {
    if (self.testBlock1) {
        self.testBlock1(sender.titleLabel.text);
    }
}

/*
// Only override drawRect: if you perform custom drawing.
// An empty implementation adversely affects performance during animation.
- (void)drawRect:(CGRect)rect {
    // Drawing code
}
*/

@end

以上是我简单直接的介绍了项目中常用的两种Block的使用，自我感觉比起通知代理要方便的多，有疑问的小伙伴可以留言问我。