Block传值

typedef void(^DemoBlock)();
typedef void(^INTBlock)(int a, int b);

@property(nonatomic,assign)DemoBlock demoBlock;
@property(nonatomic,assign)INTBlock  initBlock;

-(void)creatdemoBlock:(DemoBlock)demoBlock InitBlock:(INTBlock)initBlock{
    demoBlock();
    initBlock(10,20);
}

    [self creatdemoBlock:^{

        NSLog(@"hehehe");

    }InitBlock:^(int a, int b) {
        NSLog(@"%d",a+b);//30
    }];

　　

   int (^Myblock)(int,int) = ^(int a , int b){
        return a+b;
    };

    int(^Myblock2)() = ^(){
        return 10;
    };

    int (^Myblock3)() =^{
        return 20;
    };

    NSLog(@"%d",Myblock(10,20));//30
    NSLog(@"%d",Myblock2());//10
    NSLog(@"%d",Myblock3());//20

    self.memberVariable = ;
    //    NSInteger outsideVariable = 20;//如果不添加_block则block会捕获该值
    //添加了_block则会跳过获取后面的值，如果没有则显示此值。
    __block NSInteger outsideVariable = ;
    NSMutableArray * outsideArray = [[NSMutableArray alloc] init];

    void (^blockObject)(void) = ^(void){
        NSInteger insideVariable = ;//不会变
        NSLog(@"  > member variable = %ld", (long)self.memberVariable);//
        NSLog(@"  > outside variable = %ld", (long)outsideVariable);//有_block:30?20
        NSLog(@"  > inside variable = %ld", (long)insideVariable);//
        [outsideArray addObject:@"AddedInsideBlock"];
    };

    outsideVariable = ;
    self.memberVariable = ;

    blockObject();

    NSLog(@"  > %lu items in outsideArray", (unsigned long)[outsideArray count]);

1、在需要回调的B界面：.h

//1、定义一个Block 返回字符串
typedef void(^ReturnTextStr)(NSString*str);
//2、声明一个Block
@property(nonatomic,strong)ReturnTextStr returnStrBlock;
//3、声明一个Block方法
-(void)returenText:(ReturnTextStr)block;

2、在需要回调B界面: .m

//4、
-(void)returenText:(ReturnTextStr)block{
    _returnStrBlock = block;
}

//5、
- (IBAction)back:(id)sender {
    [self dismissViewControllerAnimated:YES completion:^{

    if (_returnStrBlock != nil ) {
        _returnStrBlock(self.blockTEXT.text);
    }

    }];

}

3、接收返回值得A界面

@interface ViewController (){
    BVCViewController*bvc;
}

- (IBAction)gotoVC:(id)sender {

    bvc = [[CViewController alloc]initWithNibName:@"CViewController" bundle:nil];

    // 5
    [bvc returenText:^(NSString *str) {
        self.A.text = str;
    }];

    [self presentViewController:bvc animated:YES completion:nil];

}