block 简单使用

1.block进行声明定义以变量的形式使用在代码中

->声明一个Block

//声明一个square的Block Pointer，其所指向的Block有一个int输入和int输出
int (^square)(int);
//将Block实体指定给square
square = ^(int a){ return a*a ; };
//调用方法，感觉是是不是很像function的用法？
int result = square(5);

-》定义一个block

int (^mySquare)(int) = ^(int a){return a*a;};   //定义一个mySquare的Block pointer变量

->block作为函数的参数，在oc编程中block的名可以去掉。

-(void)objcMethod:(int(^)(int))square;  //square参数的类型是int(^)(int)

非oc中，block名保留。

void myFunction(int (^mySquare)(int));     //function的定义，将Block作为参数
int (^mySquare)(int) = ^(int a){return a*a;};   //定义一个mySquare的Block pointer变量
myFunction(mySquare);    //把mySquare作为myFunction的参数

》》》》》通过 类型重定义 函数书写更加简洁。block的名可以等效于block数据类型。

#if NS_BLOCKS_AVAILABLE
typedefNSComparisonResult (^NSComparator)(id obj1,id
obj2);

#endif
- (NSArray *)sortedArrayUsingComparator:(NSComparator)cmptr

等价于：

- (NSArray *)sortedArrayUsingComparator:(NSComparisonResult(^)(id
obj1,id obj2))cmptr

2.iOS中使用block进行网络请求回调

原文：http://www.tuicool.com/articles/JFRfmq

PS：简单的使用block进行网络请求回调，非常的方便，避免了delegate的繁琐

HttpRequest.h

#import <Foundation/Foundation.h>

typedef void (^FinishBlock)(NSString *dataString);

@interface HttpRequest : NSObject<NSURLConnectionDataDelegate>

@property (strong, nonatomic) NSMutableData *resultData;
@property (strong, nonatomic) FinishBlock finishBlock;

+ (void)postRequestWithURL:(NSString *)urlStr
paramters:(NSString *)paramters
finshedBlock:(FinishBlock)block;

@end

#import "HttpRequest.h"

@implementation HttpRequest

+ (void)postRequestWithURL:(NSString *)urlStr
paramters:(NSString *)paramters
finshedBlock:(FinishBlock)block
{
HttpRequest *httpRequest = [[HttpRequest alloc]init];
httpRequest.finishBlock = block;

NSURL *url = [NSURL URLWithString:urlStr];
NSMutableURLRequest *requset = [[NSMutableURLRequest alloc]initWithURL:url cachePolicy:NSURLRequestUseProtocolCachePolicy timeoutInterval:30];
[requset setHTTPBody:[paramters dataUsingEncoding:NSUTF8StringEncoding]];

NSURLConnection *connection = [[NSURLConnection alloc]initWithRequest:requset delegate:httpRequest];
NSLog(connection ? @"连接创建成功" : @"连接创建失败");
}
/**
*  接收到服务器回应的时回调
*/
- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response
{
NSHTTPURLResponse *httpResponse = (NSHTTPURLResponse *)response;
if (!self.resultData) {
self.resultData = [[NSMutableData alloc]init];
} else {
[self.resultData setLength:0];
}

if ([response respondsToSelector:@selector(allHeaderFields)]) {
NSDictionary *dic = [httpResponse allHeaderFields];
NSLog(@"[network]allHeaderFields:%@",[dic description]);
}
}
/**
*  接收到服务器传输数据的时候调用，此方法根据数据大小执行若干次
*/
- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data
{
[self.resultData appendData:data];
}
/**
*  数据传完之后调用此方法
*/
- (void)connectionDidFinishLoading:(NSURLConnection *)connection
{
NSString *resultStr = [[NSString alloc]initWithData:self.resultData
encoding:NSUTF8StringEncoding];
if (self.finishBlock) {
self.finishBlock(resultStr);
}
}
/**
*  网络请求过程中，出现任何错误（断网，连接超时等）会进入此方法
*/
- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error
{
NSLog(@"network error : %@", [error localizedDescription]);

if (self.finishBlock) {
self.finishBlock(nil);
}
}

@end

在ViewController中调用：

[HttpRequest postRequestWithURL:@"http://www.baidu.com"
paramters:@""
finshedBlock:^(NSString *dataString) {
NSLog(@"finish callback block, result: %@", dataString);
}];