1、block的特点： block是C语言； block是一种数据类型、可以当做参数，也可以用做返回值；——总之，对比int的用法用即可（当然，定义的时候，最好跟函数对比）； block是预先准备好的代码块、在需要的时候调用，（需要好好理解“需要时”）；
2、定义block 有返回值、有参数：返回类型 ^(blockName)(参数) ＝ ^返回类型（参数列表）｛///代码 ｝； 无返回值、有参数：void ^(blockName)(参数) ＝ ^（参数列表）｛///代码 ｝； 无返回值、无参数： void (^blockName)() = ^ { /// 代码实现; }； 上面这么多，也记不住： 速记代码快：inlineBlock ，编译器会提示：（根据需要删减就好了）；
3、block引用外部变量 在定义block时，如果使用了外部变量，block内部会默认对外部变量做一次copy； 默认情况下，不允许在block内部修改外部变量的值； 在外部变量声明时，使用__block修饰符，则可以在block内部修改外部变量的值；
4、 数组的遍历&排序； 遍历：enumerateObjectsUsingBlock: 所有的参数都已经准备到位，可以直接使用 效率比for高，官方推荐使用； 举例：懒加载 enumerateObjectsUsingBlock遍历： [tempArray enumerateObjectsUsingBlock:^(id _Nonnullobj, NSUInteger idx, BOOL *_Nonnullstop) { NSDictionary*dict = (NSDictionary*)obj;
Heros *hero = [HerosherosWithDict:dict]; [ArrMaddObject:hero]; }]; for—IN遍历： for(NSDictionary*dictin tempArray) {
Heros *heros = [HerosherosWithDict:dict];
[ArrM addObject:heros]; }
排序：sortedArrayUsingComparator:5、block的数据的逆向传值 被调用方： 准备块代码； 调用方： 定义块代码属性，在适当的时候调用block； 举例：（以下三个举例实现了自定义NSOperation，异步下载一张图片，并在主线程中显示） 调用方： 定义块代码属性
#import <Foundation/Foundation.h>
#import <UIKit/UIKit.h>
@class YSCNSOperationOP;
typedef void(^setUpUIImage)(YSCNSOperationOP *);
@interface YSCNSOperationOP : NSOperation
@property (nonatomic, copy) NSString *urlString;
@property (nonatomic, strong) UIImage *image;
@property (nonatomic, copy) setUpUIImage myBlock;
- (void)setUpUIImage:(setUpUIImage )block;
@end
在适当的时候执行：
#import "YSCNSOperationOP.h"
@implementation YSCNSOperationOP
- (void)main {
@autoreleasepool {
UIImage *image = [self downLoadImage:self.urlString];
self.image = image;
dispatch_async(dispatch_get_main_queue(), ^{
self.myBlock(self);
});
}
}
- (UIImage *)downLoadImage:(NSString *)urlString{
NSURL *url = [NSURL URLWithString:urlString];
NSData *data = [NSData dataWithContentsOfURL:url];
UIImage *image = [UIImage imageWithData:data];
return image;
}
- (void)setUpUIImage:(setUpUIImage )block {
if (block) {
self.myBlock = block;
}
}
@end
被调用方： 准备代码块：
#import "ViewController.h"
#import "YSCNSOperationOP.h"
@interface ViewController ()
@property (weak, nonatomic) IBOutlet UIImageView *iamgeView;
@end
@implementation ViewController
- (void)viewDidLoad {
[super viewDidLoad];
// Do any additional setup after loading the view, typically from a nib.
}
- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event {
YSCNSOperationOP *yscOp = [[YSCNSOperationOP alloc] init];
yscOp.urlString = @"http://h.hiphotos.baidu.com/image/pic/item/9825bc315c6034a8094ace24c9134954082376ee.jpg";
[yscOp setUpUIImage:^(YSCNSOperationOP *op) {
self.iamgeView.image = op.image ;
}];
NSOperationQueue *queue = [[NSOperationQueue alloc] init];
[queue addOperation:yscOp];
}
@end
其它方式的逆向传值：
一、代理： 代理方： 1）遵守协议； 2）设置代理； 3）实现代理方法； 委托方： 1）定义协议； 2）代理属性； 3）在需要的时候通知代理；‘ 举例 委托方：定义协议； 代理属性；
#import <Foundation/Foundation.h>
#import <UIKit/UIKit.h>
@class YSCNSOperation;
@protocol YSCNSOperationDelegate <NSObject>
- (void)yscNSOperation:(YSCNSOperation *)operation withImage:(UIImage *)image;
@end
@interface YSCNSOperation : NSOperation
@property (nonatomic, copy) NSString *urlString;
@property (nonatomic, strong) UIImage *image;
@property (nonatomic, weak) id<YSCNSOperationDelegate> delegate;
@end
在需要的时候通知代理：
#import "YSCNSOperation.h"
@implementation YSCNSOperation
- (void)main {
@autoreleasepool {
UIImage *image = [self downLoadImage:self.urlString];
self.image = image;
dispatch_async(dispatch_get_main_queue(), ^{
if ([self.delegate respondsToSelector:@selector(yscNSOperation:withImage:)]) {
[self.delegate yscNSOperation:self withImage:image];
}
});
}
}
- (UIImage *)downLoadImage:(NSString *)urlString{
NSURL *url = [NSURL URLWithString:urlString];
NSData *data = [NSData dataWithContentsOfURL:url];
UIImage *image = [UIImage imageWithData:data];
return image;
}
@end
代理方：
#import "ViewController.h"
#import "YSCNSOperation.h"
@interface ViewController () <YSCNSOperationDelegate>
@property (weak, nonatomic) IBOutlet UIImageView *iamgeView;
@end
@implementation ViewController
- (void)viewDidLoad {
[super viewDidLoad];
}
- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event {
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
YSCNSOperation *yscOp = [[YSCNSOperation alloc] init];
yscOp.delegate = self;
yscOp.urlString = @"http://h.hiphotos.baidu.com/image/pic/item/9825bc315c6034a8094ace24c9134954082376ee.jpg";
NSOperationQueue *queue = [[NSOperationQueue alloc] init];
[queue addOperation:yscOp];
});
}
- (void)yscNSOperation:(YSCNSOperation *)operation withImage:(UIImage *)image {
self.iamgeView.image = operation.image;
}
@end
二、通知： 通知方：注册通知； 观察者：注册观察者； 移除观察者对象； 举例： 通知方注册通知、并在恰当的时候发出通知：
#import "YSCNSOperation.h"
@implementation YSCNSOperation
- (void)main {
@autoreleasepool {
UIImage *image = [self downLoadImage:self.urlString];
self.image = image;
dispatch_async(dispatch_get_main_queue(), ^{
[[NSNotificationCenter defaultCenter] postNotificationName:@"setUpUI" object:self];
});
}
}
- (UIImage *)downLoadImage:(NSString *)urlString{
NSURL *url = [NSURL URLWithString:urlString];
NSData *data = [NSData dataWithContentsOfURL:url];
UIImage *image = [UIImage imageWithData:data];
return image;
}
@end
观察者：注册观察者、移除观察者
#import "ViewController.h"
#import "YSCNSOperation.h"
@interface ViewController ()
@property (weak, nonatomic) IBOutlet UIImageView *iamgeView;
@end
@implementation ViewController
- (void)viewDidLoad {
[super viewDidLoad];
// Do any additional setup after loading the view, typically from a nib.
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(lookNotifi:) name:@"setUpUI" object: nil];
}
- (void)lookNotifi:(NSNotification *)notifi{
YSCNSOperation *op= (YSCNSOperation *)notifi.object;
self.iamgeView.image = op.image;
//self.iamgeView.image = (UIImage *)notifi.object;
}
- (void)dealloc {
[[NSNotificationCenter defaultCenter] removeObserver:self];
}
- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event {
YSCNSOperation *yscOp = [[YSCNSOperation alloc] init];
yscOp.urlString = @"http://h.hiphotos.baidu.com/image/pic/item/9825bc315c6034a8094ace24c9134954082376ee.jpg";
NSOperationQueue *queue = [[NSOperationQueue alloc] init];
[queue addOperation:yscOp];
}
@end