block 简单使用

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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);}];

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