iOS网络开发之NSURLSession学习<2>

这篇文章主要介绍了

NSURLSession

以及

NSURLSessionTask

这个抽象类，和

NSURLSessionDataTask

的使用和代理方法。

一.

NSURLSessionTask

的介绍

Task是由Session创建的，Session会保持对Task的一个强引用，直到Task完成或者出错才会释放。通过NSURLSessionTask可以获得Task的各种状态，以及对Task进行取消，挂起，继续等操作。一共包括三种Task，三种Task的结构如图。本文主要讲解的是DataTask。



1.管理task的状态的方法

-(void)cancel

//取消一个task

-(void)resume

//如果task在挂起状态，则继续执行task

(void)suspend

//挂起task

2.获得task的执行情况的属性

countOfBytesExpectedToReceive

countOfBytesReceivedcountOfBytesExpectedToSendcountOfBytesSent

3.task的综合信息

currentRequest // 当前活跃的request

originalRequest // 在task创建的时候传入的request（有可能会重定向）

response // 服务器对当前活跃请求的响应

taskDescription // 描述当前task

taskIdentifier// 用来区分Task的描述符

error //Task失败的错误信息

4.task状态的枚举

typedef NS_ENUM (NSInteger, NSURLSessionTaskState ) { NSURLSessionTaskStateRunning = 0, NSURLSessionTaskStateSuspended = 1, NSURLSessionTaskStateCanceling = 2, NSURLSessionTaskStateCompleted = 3,};

二.

NSURLSessionDataTask

代理

DataTask是用来干嘛的呢？ 用来下载数据到内存里，数据的格式是

NSData

。

dataTask使用的过程中，有两种方式来处理结果

通过block的方式（不关注过程，只关注结果，使用简单）

下载一幅图片，完成后显示到ImageView。代码：

NSURLSessionDataTask * task = [self.session dataTaskWithURL:[NSURL URLWithString:imageURL] completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) {
if (!error) {
UIImage * image = [UIImage imageWithData:data];
self.imageview.image = image;
}
}];
[task resume];

通过代理方法来管理session和task。( 可以获得全部过程，但是较为复杂)

1.

NSURLSessionDelegate

用来处理Session层次的事件

2.

NSURLSessionTaskDelegate

是使用代理的时候，任何种类task都要实现的代理

3.

NSURLSessionDataDelegate

特别用来处理dataTask的事件

代码示例：

#import "ViewController.h"

@interface ViewController ()<NSURLSessionDelegate,NSURLSessionTaskDelegate,NSURLSessionDataDelegate>

@property (strong,nonatomic)UIImageView * imageview;
@property (strong,nonatomic)NSURLSession * session;
@property (strong,nonatomic)NSURLSessionDataTask * dataTask;
@property (weak, nonatomic) IBOutlet UIProgressView *progressview;
@property (nonatomic)NSUInteger expectlength;
@property (strong,nonatomic) NSMutableData * buffer;
@end

static NSString * imageURL = @"http://f12.topit.me/o129/10129120625790e866.jpg";

@implementation ViewController//属性全部采用惰性初始化
#pragma mark - lazy property

-(UIImageView *)imageview{
if (!_imageview) {
_imageview = [[UIImageView alloc] initWithFrame:CGRectMake(40,40,300,200)];        _imageview.backgroundColor = [UIColor lightGrayColor];        _imageview.contentMode = UIViewContentModeScaleToFill;    }
return _imageview;}

-(NSMutableData *)buffer{
if (!_buffer) {
_buffer = [[NSMutableData alloc] init];
}
return _buffer;}

-(NSURLSession*)session{
if (!_session) {
NSURLSessionConfiguration * configuration = [NSURLSessionConfiguration ephemeralSessionConfiguration];
_session = [NSURLSession sessionWithConfiguration:configuration                                                 delegate:self                                            delegateQueue:[NSOperationQueue mainQueue]];    }    return _session;}

-(NSURLSessionDataTask *)dataTask{
if (!_dataTask) {
_dataTask = [self.session dataTaskWithURL:[NSURL URLWithString:imageURL]];    }
return _dataTask;}

#pragma mark - life circle of viewcontroller

- (void)viewDidLoad {
[self.view addSubview:self.imageview];

[self.dataTask resume];//Task要resume彩绘进行实际的数据传输

[self.session finishTasksAndInvalidate];//完成task就invalidate
}

#pragma mark - target-action//注意判断当前Task的状态

- (IBAction)pause:(UIButton *)sender {
if (self.dataTask.state == NSURLSessionTaskStateRunning) {
[self.dataTask pause];
}
}

- (IBAction)cancel:(id)sender {

if (self.dataTask.state == NSURLSessionTaskStateRunning||self.dataTask.state ==NSURLSessionTaskStateSuspended) {
[self.dataTask cancel];
}
}

- (IBAction)resume:(id)sender {

if (self.dataTask.state == NSURLSessionTaskStateSuspended) {        [self.dataTask resume];
}}

-(void)URLSession:(NSURLSession *)session dataTask:(NSURLSessionDataTask *)dataTask didReceiveResponse:(NSURLResponse *)response completionHandler:(void (^)(NSURLSessionResponseDisposition))completionHandler{

NSUInteger length = [response expectedContentLength];

if (length != -1) {
self.expectlength = [response expectedContentLength];//存储一共要传输的数据长度

completionHandler(NSURLSessionResponseAllow);//继续数据传输
}else{        completionHandler(NSURLSessionResponseCancel);//如果Response里不包括数据长度的信息，就取消数据传输        UIAlertView * alert = [[UIAlertView alloc] initWithTitle:@"error"                                                         message:@"Do not contain property of expectedlength"                                                        delegate:nil                                               cancelButtonTitle:@"OK"                                               otherButtonTitles:nil];

[alert show];    }}

-(void)URLSession:(NSURLSession *)session dataTask:(NSURLSessionDataTask *)dataTask didReceiveData:(NSData *)data{

[self.buffer appendData:data];//数据放到缓冲区里

self.progressview.progress = [self.buffer length]/((float) self.expectlength);//更改progressview的progress}

-(void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task didCompleteWithError:(NSError *)error{

if (!error) {        dispatch_async(dispatch_get_main_queue(), ^{//用GCD的方式，保证在主线程上更新UI

UIImage * image = [UIImage imageWithData:self.buffer];            self.imageview.image = image;            self.progressview.hidden = YES;            self.session = nil;
self.dataTask = nil;
});
}else{
NSDictionary * userinfo = [error userInfo];        NSString * failurl = [userinfo objectForKey:NSURLErrorFailingURLStringErrorKey];        NSString * localDescription = [userinfo objectForKey:NSLocalizedDescriptionKey];

if ([failurl isEqualToString:imageURL] && [localDescription isEqualToString:@"cancelled"]) {
//如果是task被取消了，就弹出提示框

UIAlertView * alert = [[UIAlertView alloc] initWithTitle:@"Message"                                                             message:@"The task is canceled"                                                            delegate:nil                                                   cancelButtonTitle:@"OK"                                                   otherButtonTitles:nil];
[alert show];
}else{
UIAlertView * alert = [[UIAlertView alloc] initWithTitle:@"Unknown type error"//其他错误，则弹出错误描述                                                             message:error.localizedDescription                                                            delegate:nil                                                   cancelButtonTitle:@"OK"                                                   otherButtonTitles:nil];
[alert show];
}

self.progressview.hidden = YES;
self.session = nil;
self.dataTask = nil;
}}

@end