block 在开发中的用途多种多样，一下是我遇到的block的常见用法
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block 保存代码
#import <Foundation/Foundation.h>
@interface CellItem : NSObject
@property (nonatomic, strong) NSString *title;
// 保存每个cell做的事情
@property (nonatomic, strong) void(^block)();
+ (instancetype)itemWithTitle:(NSString *)title;
@end
/************************/
#import "CellItem.h"
@implementation CellItem
+ (instancetype)itemWithTitle:(NSString *)title
{
CellItem *item = [[self alloc] init];
item.title = title;
return item;
}
@end
/************************/
#import "TableViewController.h"
#import "CellItem.h"
@interface TableViewController ()
@property (nonatomic, strong) NSArray *items;
@end
@implementation TableViewController
- (void)viewDidLoad {
[super viewDidLoad];
// 创建模型
CellItem *item1 = [CellItem itemWithTitle:@"打电话"];
item1.block = ^{
NSLog(@"打电话");
};
CellItem *item2 = [CellItem itemWithTitle:@"发短信"];
item2.block = ^{
NSLog(@"发短信");
};
CellItem *item3 = [CellItem itemWithTitle:@"发邮件"];
item3.block = ^{
NSLog(@"发邮件");
};
_items = @[item1,item2,item3];
}
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
return _items.count;
}
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
static NSString *ID = @"cell";
// 1.从缓存池取
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:ID];
if (cell == nil) {
cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:ID];
}
CellItem *item = self.items[indexPath.row];
cell.textLabel.text = item.title;
return cell;
}
// 点击cell就会调用
- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath
{
// 把要做的事情(代码)保存到模型
CellItem *item = self.items[indexPath.row];
if (item.block) {
item.block();
}
}
@end
-
block传值
#import <UIKit/UIKit.h>
@interface ModalViewController : UIViewController
@property(nonatomic,strong)void(^block)(NSString *);
@end
/**********************/
#import "ModalViewController.h"
@interface ModalViewController ()
@end
@implementation ModalViewController
- (void)viewDidLoad {
[super viewDidLoad];
}
-(void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event
{
if (_block) {
_block(@"123");
}
[self dismissViewControllerAnimated:YES completion:nil];
}
@end
/**********************/
#import "ViewController.h"
#import "ModalViewController.h"
@interface ViewController ()
@end
@implementation ViewController
- (void)viewDidLoad {
[super viewDidLoad];
}
-(void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event
{
ModalViewController *modal = [[ModalViewController alloc]init];
modal.view.backgroundColor = [UIColor blueColor];
modal.block = ^(NSString *value){
NSLog(@"value = %@",value);
};
[self presentViewController:modal animated:YES completion:nil];
}
@end
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block内存管理
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MRC:管理block
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只要Block引用外部局部变量,block放在栈里面.
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-
block只能使用copy,不能使用retain,使用retain,block还是在栈里面
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ARC:管理block
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只要block引用外部局部变量,block放在堆里面
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block使用strong.最好不要使用copy
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只要block没有引用外部局部变量,block放在全局区
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block造成的循环引用
block中到底什么时候用weakSelf和strongSelf
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在看AFNetworking框架时我发现一种特别的block循环引用问题
#import "ModalViewController.h"
@interface ModalViewController ()
@property (nonatomic, strong) void(^block)();
@end
@implementation ModalViewController
- (void)dealloc
{
NSLog(@"ModalViewController销毁");
}
- (void)viewDidLoad {
[super viewDidLoad];
__weak typeof(self) weakSelf = self;
_block = ^{
__strong typeof(weakSelf) strongSelf = weakSelf;
/**
这种block两次引用第一次是把self修饰改成__weak,第二次的修饰改成了__strong又变成了强引用，而dispatch_after的block是由系统帮我们管理生命周期，所以两秒之后页面才会销毁
*/
dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(2 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
NSLog(@"%@",strongSelf);
});
};
_block();
}
- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event
{
[self dismissViewControllerAnimated:YES completion:nil];
}
@end
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block变量传递
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如果block是局部变量，block是值传递
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如果是静态比那两，全局变量__block修饰的变量,block都是指针传递
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block作为参数传递
#import <Foundation/Foundation.h>
@interface Manager : NSObject
@property(nonatomic,assign)NSInteger result ;
-(void)cacultor:(NSInteger(^)(NSInteger value))cacultorBlock;
@end
/*****************/
#import "Manager.h"
@implementation Manager
-(void)cacultor:(NSInteger (^)(NSInteger))cacultorBlock
{
if (cacultorBlock) {
_result = cacultorBlock(_result);
}
}
@end
/*****************/
#import "ViewController.h"
#import "Manager.h"
@interface ViewController ()
@end
@implementation ViewController
- (void)viewDidLoad {
[super viewDidLoad];
// 把block当做参数,并不是马上就调用Block,什么时候调用,由方法内部决定
// 什么时候需要把block当做参数去使用:做的事情由外界决定,但是什么时候做由内部决定.
Manager *mgr = [[Manager alloc]init];
[mgr cacultor:^NSInteger(NSInteger value) {
value +=2;
value *=2;
NSLog(@"value = %ld",(long)value);
return value;
}];
}
@end
-
在看masonry框架时发现一种block更加神奇的用法。
#import <Foundation/Foundation.h>
@interface Manager : NSObject
@property(nonatomic,assign)NSInteger result ;
-(Manager *(^)(NSInteger value))add;
@end
/***************/
#import "Manager.h"
@implementation Manager
-(Manager *(^)(NSInteger))add
{
return ^(NSInteger value){
_result += value;
return self;
};
}
@end
/***************/
#import "ViewController.h"
#import "Manager.h"
@interface ViewController ()
@end
@implementation ViewController
- (void)viewDidLoad {
[super viewDidLoad];
Manager *mgr = [[Manager alloc]init];
mgr.add(5).add(5).add(3);
NSLog(@"result = %ld",(long)mgr.result);
self.test();
}
-(void(^)())test
{
return ^(){
NSLog(@"block");
};
// void(^block)() = ^{
// 写法等同于上面
// };
}
@end
