深入研究block语法
我举一个简单的例子来定义和使用block
void (^block1)(void) = ^void (void){
NSLog(@"hello");
};
block1();
是不是很简单啊！么得什么难度嘛！
block的存在样式
.h
typedef returnType(^name)(arguments);
typedef void(^block2)(void);
typedef void(^block3)(NSInteger index);
-(void)doSomethingWithBlock:(block2)block;
@property (nonatomic, strong) block3 block3;
@property (nonatomic, strong) dispatch_block_t block4;
.m
self.block4 = ^{
NSLog(@"hello");
};
self.block4();
self.block3 = ^(NSInteger index){
NSLog(@"%ld",index);
};
self.block3(1);
[self doSomethingWithBlock:^{
NSLog(@"hello");
}];
-(void)doSomethingWithBlock:(block2)block{
block();
}
block的用处
首先我们可以回想下ASI网络访问处理异步回调的方法，首先得设置当前使用类的代理，然后写两个回调方法
-(void)requestFinished:(ASIHTTPRequest *)req{
}
-(void)requestFailed:(ASIHTTPRequest *)req{
}
如果当前类处理请求多的话，那么可能需要设置不同的回调方法以区分
[request setDidFinishSelector:@selector(topSecretFetchComplete:)];
[request setDidFailSelector:@selector(topSecretFetchFailed:)];
好烦啊，好多个方法👀都看不清了。我们来改一改吧。建一个ASIHTTPRequest的分类 ASIHTTPRequest+blockAddtion.h
#import "ASIHTTPRequest.h"
typedef void (^requestSuccessHandler)(ASIHTTPRequest *request);
typedef void (^requestFailedHandler)(ASIHTTPRequest *request);
@interface ASIHTTPRequest (blockAddtion)<ASIHTTPRequestDelegate>
-(void)startAsynchronousWithSuccess:(requestSuccessHandler)success failed:(requestFailedHandler)failed;
@end
ASIHTTPRequest+blockAddtion.m
#import "ASIHTTPRequest+blockAddtion.h"
#import <objc/runtime.h>
static NSString * const handlerRunTimeAccosiationKey1 = @"requestSuccessHandler";
static NSString * const handlerRunTimeAccosiationKey2 = @"requestFailedHandler";
@implementation ASIHTTPRequest (blockAddtion)
-(void)startAsynchronousWithSuccess:(requestSuccessHandler)success failed:(requestFailedHandler)failed{
objc_setAssociatedObject(self, (__bridge const void *)(handlerRunTimeAccosiationKey1), success, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
objc_setAssociatedObject(self, (__bridge const void *)(handlerRunTimeAccosiationKey2), failed, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
[self setDelegate:self];
}
-(void)dealloc{
objc_removeAssociatedObjects(handlerRunTimeAccosiationKey1);
objc_removeAssociatedObjects(handlerRunTimeAccosiationKey2);
[super dealloc];
}
-(void)requestFinished:(ASIHTTPRequest *)req{
requestSuccessHandler completionHandler = objc_getAssociatedObject(self, (__bridge const void *)(handlerRunTimeAccosiationKey1));
if(completionHandler){
completionHandler(req);
}
}
-(void)requestFailed:(ASIHTTPRequest *)req{
requestFailedHandler completionHandler = objc_getAssociatedObject(self, (__bridge const void *)(handlerRunTimeAccosiationKey2));
if(completionHandler){
completionHandler(req);
}
}
@end
那么现在我们在数据请求的时候就可以这样写
[request startAsynchronousWithSuccess:^(ASIHTTPRequest *request) {
} failed:^(ASIHTTPRequest *request) {
}];
请求成功或者失败都在里面写就好啦！不过好的是现在主流的网络访问比如AFNetWorking,MKNetWorkKit都支持block了。
block的风格特点
block块是c语言的拓展，它以(^)作为标记，省略了函数名，因此也被称作匿名函数。现在Apple官方的API也使用block风格，因此使用的人越来越多。例:NSArray遍历实现
-(void)enumerateObjectsUsingBlock2:(void (^)(id, NSUInteger, BOOL *))block{
NSEnumerator *enumerator = [self objectEnumerator];
id thing;
NSUInteger idx = 0;
BOOL *stop = malloc(1);
while (thing = [enumerator nextObject]) {
if(*stop)
break;
block(thing,idx,stop);
idx ++;
}
}
例:链式语法实现
@interface DemoModule (){
float tip;
}
@end
@implementation DemoModule
-(instancetype)init{
if(self = [super init]){
self.mult(20);
NSLog(@"%f",tip);
}
return self;
}
-(DemoModule *(^)(float))mult{
return ^id(float multip){
tip = multip;
return self;
};
}