36.Block页面间传值

1.基本概念

block是匿名函数, 能够实现函数回调功能, 用于页面之间通信和传值.

定义属性接收block必须使用copy修饰, retain和assign会造成野指针问题.

block在某个方法中定义是存储在栈区, 在另一个雷中使用需要进行copy, 存储在堆区.

当不使用block时需要用自己的有的方法销毁, Block_Release()

在block实现部分, 不能直接使用实例变量, self调用属性, 因为block会造成self引用计数加1, 最终导致循引用问题. 使用__block解决循环引用的问题.

2.简单举例

MainViewController.m文件

#import "MainViewController.h"
#import "SecondViewController.h"
@interface MainViewController ()
@end
@implementation MainViewController

- (void)viewDidLoad {
[super viewDidLoad];
self.view.backgroundColor = [UIColor cyanColor];
self.navigationController.navigationBar.translucent = NO;
UIButton *button = [UIButton buttonWithType:UIButtonTypeCustom];
button.frame = CGRectMake(100, 300, 200, 49);
button.layer.borderWidth = 1;
button.layer.cornerRadius = 10;
[button setTitle:@"下一页" forState:UIControlStateNormal];
[self.view addSubview:button];
[button addTarget:self action:@selector(click:) forControlEvents:UIControlEventTouchUpInside];
}
- (void)click:(UIButton *)button{
SecondViewController *secondVC = [[SecondViewController alloc] init];
//没有参数,没有返回值的block,通过block,改变self.view的背景颜色
void (^myBlock)() = ^(){
self.view.backgroundColor = [UIColor colorWithRed:arc4random()%256/255.0 green:arc4random()%256/255.0 blue:arc4random()%256/255.0 alpha:1];
};
//2.通过第二页的属性来接收block
secondVC.myBlock = myBlock;

//通过block实现从后向前传值,不需要返回值,因为调用更需要返回值,所以传值的时候只要参数
void (^myblock)(NSString *) = ^(NSString *str){
NSLog(@"%@",str);
};
secondVC.myblock = myblock;

void (^block)(NSArray *) = ^(NSArray *arr){
//传过来的arr的有效范围就这对大括号里,所以穿过来的数据处理都在block里面
NSLog(@"%@",arr);
};
secondVC.block = block;
[self.navigationController pushViewController:secondVC animated:YES];
[secondVC release];
}

SecondViewController.h和SecondViewController.m文件

#import <UIKit/UIKit.h>
typedef void(^Block)(NSArray *);
@interface SecondViewController : UIViewController

//1.写一条属性,负责接受第一页向第二页传递过来的block
@property(nonatomic,copy)void(^myBlock)();
@property(nonatomic,copy)void(^myblock)(NSString *);
@property(nonatomic,copy)Block block;
//block作为属性时为了防止block进入到栈区,栈区内存不需要我们进行管理,很可能出现block消失的情况,所以需要拷贝一份到堆区
@end

#import "SecondViewController.h"
@interface SecondViewController ()
@end
@implementation SecondViewController
- (void)dealloc
{
//这是block自己的release的方法
Block_release(_myBlock);
Block_release(_myblock);
Block_release(_block);
[super dealloc];
}
- (void)viewDidLoad {
[super viewDidLoad];
self.view.backgroundColor = [UIColor cyanColor];
self.navigationController.navigationBar.translucent = NO;
UIButton *button = [UIButton buttonWithType:UIButtonTypeCustom];
button.frame = CGRectMake(100, 300, 200, 49);
button.layer.borderWidth = 1;
button.layer.cornerRadius = 10;
[button setTitle:@"返回" forState:UIControlStateNormal];
[self.view addSubview:button];
[button addTarget:self action:@selector(click:) forControlEvents:UIControlEventTouchUpInside];
}
- (void)click:(UIButton *)button{
//3.调用传过来的block
self.myBlock();
self.myblock(@"网易新闻");
NSArray *arr = @[@"zhangsan",@"lishi"];
self.block(arr);
[self.navigationController popToRootViewControllerAnimated:YES];
}