ios并发会造成什么问题_iOS 多个网络请求并发执行的解决方案

在项目中往往会遇到这种需求:UI 的更新要在2~3个网络请求后才执行.这里提供两种执行方案.

一.利用 GCD

通过 gcd_group可以解决这个问题.具体做法如下

//

// ViewController.m

// tableview

//

// Created by myMac on 16/12/26.

// Copyright © 2016年 myMac. All rights reserved.

//

#import "ViewController.h"

typedef void(^FinishNetwork)();

@interface ViewController ()

@property (nonatomic, copy ) FinishNetwork block;

@property (nonatomic, copy ) NSString *string1;

@property (nonatomic, copy ) NSString *string2;

@property (nonatomic, copy ) NSString *string3;

@end

@implementation ViewController

- (void)viewDidLoad {

[super viewDidLoad];

// Do any additional setup after loading the view, typically from a nib.

[self initData];

}

- (void)initData {

// 创建信号量

dispatch_semaphore_t semaphore = dispatch_semaphore_create(0);

// 创建全局并行

dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);

dispatch_group_t group = dispatch_group_create();

dispatch_group_async(group, queue, ^{

// 请求一

//这里通过 block 表示请求结束,并标记一个信号量

[self getList1:^{

dispatch_semaphore_signal(semaphore);

}];

});

dispatch_group_async(group, queue, ^{

// 请求二

[self getList2:^{

dispatch_semaphore_signal(semaphore);

}];

});

dispatch_group_async(group, queue, ^{

// 请求三

[self getList3:^{

dispatch_semaphore_signal(semaphore);

}];

});

dispatch_group_notify(group, queue, ^{

//在这里 进行请求后的方法

NSLog(@"string1:___%@", _string1);

NSLog(@"string2:___%@", _string2);

NSLog(@"string3:___%@", _string3);

// 三个请求对应三次信号等待

dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);

dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);

dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);

});

}

- (void)getList1:(FinishNetwork)block {

NSLog(@"加载列表1");

self.string1 = @"加载列表1";

}

- (void)getList2:(FinishNetwork)block {

NSLog(@"加载列表2");

self.string2 = @"加载列表2";

}

- (void)getList3:(FinishNetwork)block {

NSLog(@"加载列表3");

self.string3 = @"加载列表3";

}

- (void)didReceiveMemoryWarning {

[super didReceiveMemoryWarning];

// Dispose of any resources that can be recreated.

}

@end

打印结果如下

二.通过 RAC

利用 RAC 的 merge 也可以解决这个问题,具体做法如下

ViewController

[[RACSignal merge:@[[TestViewModel fetchList1], [TestViewModel fetchList2]]] subscribeNext:^(id x) {

NSLog(@"%@", x);

if (!_string1.length) {

self.string1 = x;

} else {

self.string2 = x;

}

} completed:^{

NSLog(@"string1: %@nstring2: %@ n", _string1, _string2);

}];

ViewModel

#import "TestViewModel.h"

@implementation TestViewModel

+ (RACSignal *)fetchList1 {

return [RACSignal createSignal:^RACDisposable *(idsubscriber) {

[subscriber sendNext:@"请求1"];

[subscriber sendCompleted];

return nil;

}];

}

+ (RACSignal *)fetchList2 {

return [RACSignal createSignal:^RACDisposable *(idsubscriber) {

[subscriber sendNext:@"请求2"];

[subscriber sendCompleted];

return nil;

}];

}

@end

打印出的结果

另外,通过下面的方法也可以实现

/// Like -rac_liftSelector:withSignals:, but accepts an array instead of

/// a variadic list of arguments.

- (RACSignal *)rac_liftSelector:(SEL)selector withSignalsFromArray:(NSArray *)signals;

具体实现代码

[self rac_liftSelector:@selector(responseA:B:) withSignalsFromArray:@[[TestViewModel fetchList1], [TestViewModel fetchList2]]];

- (void)responseA:(id)a B:(id)b {

NSLog(@"%@, %@", a, b);

}

打印出的结果