IOS的同步下载及异步下载

川长思鸟来 2021-11-01 14:54 441阅读 0赞

下载就是把云端的信息，传输到本地。换句话说，只要是获得本地没有的信息操作，都可以成为下载。

先介绍IOS自带的两种下载方式：同步下载和异步下载。

同步下载的时候，该线程进入挂起、假死状态，等到全部下载完成，才能进行其他操作。在这期间，用户对界面的操作都是无效的，界面也不会响应任何事件。

另外一种是异步下载，异步下载的时候，用户还可以对界面进行操作，界面也可以响应事件。

从用户友好度的角度来说，异步下载的用户友好度远高于同步下载。我们平时操作的下载基本也都是异步下载。

IOS的异步下载需要实现NSURLConnectionDelegate里的4个代理方法（开始下载，下载中，完成下载，出错）

下面是代码：

创建一个带xib的ViewController，在上面创建2个按钮，分别是同步下载和异步下载

ViewController.h文件：

\#import <UIKit/UIKit.h>

@interface ViewController : UIViewController<NSURLConnectionDelegate>

@property (assign,nonatomic) longlong allLength;

@property (assign,nonatomic) longlong lastAllLength;

@property (assign,nonatomic) longlong downLoadingSpeed;

@property (retain,nonatomic) NSMutableData \* allData;

//用于显示进度条

@property (retain,nonatomic) UIProgressView \* progressView;

//用于显示进度

@property (retain,nonatomic) UILabel \* labelProgress;

//用于显示下载速度

@property (retain,nonatomic) UILabel \* labelDownLoadingSpeed;

@end

ViewController.m实现文件部分：

\#import "ViewController.h"

@interface ViewController ()

@end

@implementation ViewController

\#pragma mark - 同步下载按钮方法

\- (IBAction)DownLoad:(id)sender \{

//创建一个NSURL对象

NSURL \* url = \[NSURLURLWithString:@"http://bg.265g.com/1305/115432.html"\];

//创建一个NSrequest对象

NSURLRequest \* request = \[NSURLRequestrequestWithURL:url cachePolicy:NSURLRequestUseProtocolCachePolicytimeoutInterval:7\];

//发送request

NSError \* err = \[NSError alloc\];

NSData \* data = \[NSURLConnectionsendSynchronousRequest:request returningResponse:nilerror:&err\];

//保存接受到的数据

\[data writeToFile:@"/Users/ibokan/Desktop/bbb.html"atomically:YES\];

\#pragma mark - 异步下载按钮方法

\- (IBAction)yibu:(id)sender \{

//创建NSURL对象

NSURL \* url = \[NSURLURLWithString:@"http://yinyueshiting.baidu.com/data2/music/49919223/978262252000320.mp3?xcode=2d7d268ae3c96e23d98123b24900397e263f5c6ee17ec294"\];

//创建REQUEST对象

NSURLRequest \* request = \[NSURLRequestrequestWithURL:url cachePolicy:0timeoutInterval:10\];

//创建NSURLCONNECTION对象，并设置代理

\[NSURLConnectionconnectionWithRequest:request delegate:self\];

\#pragma mark - NSURLConnectionDelegate

\-(void) connection:(NSURLConnection \*)connection didReceiveResponse:(NSURLResponse \*)response \{

self.allData = \[\[NSMutableData alloc\]init\];

self.allLength = response.expectedContentLength;

NSLog(@"服务器已响应，开始接受数据");

\-(void) connection:(NSURLConnection \*)connection didReceiveData:(NSData \*)data \{

\[self.allData appendData:data\];

long long x = self.allData.length \* 100/self.allLength;

NSLog(@"正在接受数据,%lld%@",x,@"%");

//计算进度条位置

\_progressView.progress = self.allData.length \* 1.0 /  self.allLength;

/\*

//计算下载速度

\_downLoadingSpeed = \_allData.length - \_lastAllLength;

\_labelDownLoadingSpeed.text = \[NSString stringWithFormat:@"%lldKB/s",\_downLoadingSpeed/1000\];

\_lastAllLength = \_allData.length;

\*/

//计算进度

\_labelProgress.text = \[NSStringstringWithFormat:@"%dKB/%lldKB",self.allData.length/1000,self.allLength/1000\];

\-(void) connectionDidFinishLoading:(NSURLConnection \*)connection \{

\[self.allDatawriteToFile:@"/users/ibokan/desktop/a.mp3"atomically:YES\];

NSLog(@"数据接受完成");

\-(void) connection:(NSURLConnection \*)connection didFailWithError:(NSError \*)error \{

NSLog(@"数据连接失败,错误为:%@",error);

\#pragma end mark

\- (void)viewDidLoad \{

\[superviewDidLoad\];

\_progressView = \[\[UIProgressViewalloc\]initWithFrame:CGRectMake(20, 20,  200, 20)\];

\_progressView.progress = 0;

\[self.viewaddSubview:\_progressView\];

\_labelProgress = \[\[UILabelalloc\]initWithFrame:CGRectMake(20, 50,  200, 20)\];

\_labelProgress.text = @"0 KB/0 KB";

\[self.viewaddSubview:\_labelProgress\];

/\*

\_labelDownLoadingSpeed = \[\[UILabel alloc\]initWithFrame:CGRectMake(230, 20, 70, 20)\];

\_labelDownLoadingSpeed.text = @" 0 KB/s";

\[self.view addSubview:\_labelDownLoadingSpeed\];

\*/

\- (void)didReceiveMemoryWarning \{

\[superdidReceiveMemoryWarning\];

// Dispose of any resources that can be recreated.

@end

IOS的同步下载及异步下载

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