IOS development-How files are downloaded

• File Upload

1. Create File Upload class FileDownload.h

   // //   FileDownload.h//  01. File Download ////  Created by Wyh on 15-1-29.//  Copyright (c) 2015 Itcast. All rights reserved. // #import <Foundation/Foundation.h>@interface  filedownload:nsobject-(  void) Downloadfilewithurl: (nsurl *) URL completion: (void (^) (UIImage *image)) completion; @end

2. Create File Upload class FILEDOWNLOAD.M

   ////FILEDOWNLOAD.M//01. File Download////Created by Wyh on 15-1-29.//Copyright (c) 2015 Itcast. All rights reserved.//#import "FileDownload.h"#import "nsstring+password.h"#defineKtimeout 2.0f//number of bytes downloaded per download#defineKbytespertimes 20250@interfacefiledownload () @property (nonatomic, strong) NSString*Cachefile, @property (nonatomic, strong) UIImage*Cacheimage;@end@implementationFileDownload/** In order to ensure that the development of the simple, all methods do not use multi-threading, all the attention is maintained in the file download in the development if you encounter a comparison of computational problems, it is recommended that: 1> test data is not too large 2> test data changes, you can use written calculation to calculate the accurate value 3> Writing code-controlled tests*///-(NSString *) Cachefile//{//if (!_cachefile) {//nsstring *cachedir = Nssearchpathfordirectoriesindomains (Nscachesdirectory, Nsuserdomainmask, YES) [0];//_cachefile = [Cachedir stringbyappendingpathcomponent:@ "123.png"];//    }//return _cachefile;//}-(UIImage *) cacheimage{if(!_cacheimage) {_cacheimage=[UIImage ImageWithContentsOfFile:self.cacheFile]; }    return_cacheimage;}- (void) Setcachefile: (NSString *) urlstr{NSString*cachedir = Nssearchpathfordirectoriesindomains (Nscachesdirectory, Nsuserdomainmask, YES) [0]; Urlstr=[Urlstr MD5]; _cachefile=[Cachedir stringbyappendingpathcomponent:urlstr];}- (void) Downloadfilewithurl: (nsurl *) URL completion: (void(^) (UIImage *image)) completion{//a serial queue asynchronous method in GCDdispatch_queue_t q = dispatch_queue_create ("Cn.itcast.download", dispatch_queue_serial); Dispatch_async (q,^{NSLog (@"%@", [Nsthread CurrentThread]); //The result of MD5 encryption of the URL is treated as a file nameSelf.cachefile =[url absolutestring]; //1. Download files from the network, you need to know the size of this file        Long LongFileSize =[self filesizewithurl:url]; //calculate local cache file size        Long LongCachefilesize =[self localfilesize]; if(Cachefilesize = =fileSize) {Dispatch_async (Dispatch_get_main_queue (),^{completion (self.cacheimage);            }); NSLog (@"file already exists"); return; }                //2. Determine the size of each packet        Long LongFromb =0; Long LongToB =0; //computes the number of bytes starting and ending         while(FileSize >kbytespertimes) {            //20480 + 20480//ToB = Fromb + Kbytespertimes-1; //3. Segment Download File[self Downloaddatawithurl:url fromb:fromb Tob:tob]; FileSize-=Kbytespertimes; Fromb+=Kbytespertimes; } [self Downloaddatawithurl:url fromb:fromb tob:fromb+ FileSize-1]; Dispatch_async (Dispatch_get_main_queue (),^{completion (self.cacheimage);            }); });}#pragmaMark downloads packets with a specified byte range/** nsurlrequestuseprotocolcachepolicy = 0,//default cache policy, memory cache Nsurlrequestreloadignoringlocalcachedata = 1,//Ignore Local Memory Cache Nsurlrequestreloadignoringcachedata*/- (void) Downloaddatawithurl: (nsurl *) URL Fromb: (Long Long) Fromb ToB: (Long Long) tob{NSLog (@"data packet:%@", [Nsthread CurrentThread]); Nsmutableurlrequest*request =[nsmutableurlrequest requestwithurl:url cachepolicy:nsurlrequestreloadignoringcachedata TimeoutInterval:        Ktimeout]; //Specify the range of bytes to get in the requestNSString *range = [NSString stringWithFormat:@"Bytes=%lld-%lld", Fromb, ToB]; [Request Setvalue:range Forhttpheaderfield:@"Range"]; NSLog (@"%@", Range); Nsurlresponse*response =Nil; NSData*data = [Nsurlconnection sendsynchronousrequest:request returningresponse:&response Error:null]; //write file, overwrite file does not append//[Data writetofile:@ "/users/aplle/desktop/1.png" atomically:yes];[self appenddata:data]; NSLog (@"%@", response);}#pragmaMark-Reads the local cache file size-(Long Long) localfilesize{//read local file informationNsdictionary *dict =[[Nsfilemanager Defaultmanager] AttributesOfItemAtPath:self.cacheFile error:null]; NSLog (@"%lld", [dict[nsfilesize] longlongvalue]); return[dict[nsfilesize] longlongvalue];}#pragmaMark-Append data to File-(void) AppendData: (NSData *) data{//determine if a file existsNsfilehandle *FP =[Nsfilehandle FileHandleForWritingAtPath:self.cacheFile]; //Create file If file does not exist    if(!FP)    {[Data writeToFile:self.cacheFile atomically:yes]; } Else {        //If an append file already exists for the file//1> move to end of file[FP seektoendoffile]; //2> Append Data[FP Writedata:data]; //3> Writing Files[FP CloseFile]; }}#pragmaMark-Get Network File Size-(Long Long) Filesizewithurl: (Nsurl *) url{//The default is getNsmutableurlrequest *request = [Nsmutableurlrequest requestwithurl:url cachepolicy:0Timeoutinterval:ktimeout]; //head Header, just returns information about the file resource and does not return specific data//If you want to get the mimetype of a resource, you must also use head, otherwise the data will be downloaded two times repeatedlyRequest. HttpMethod =@"HEAD"; //To get the file size using the synchronous methodNsurlresponse *response =Nil; [Nsurlconnection sendsynchronousrequest:request Returningresponse:&response Error:null]; //size of the Expectedcontentlength file on the networkNSLog (@"%lld", response.expectedcontentlength); returnresponse.expectedcontentlength;}@end

3. Called in the Controller

   ////VIEWCONTROLLER.M//01. File Download////Created by Wyh on 15-1-29.//Copyright (c) 2015 Itcast. All rights reserved.//#import "ViewController.h"#warningInclude FileDownload.h file#import "FileDownload.h"@interfaceViewcontroller () @property (nonatomic, strong) FileDownload*Download, @property (weak, nonatomic) Iboutlet Uiimageview*ImageView;@end@implementationViewcontroller- (void) viewdidload{[Super Viewdidload];#warningCreate the FileDownload object and call method Downloadfilewithurl:Self.download=[[FileDownload alloc] init]; [Self.download downloadfilewithurl:[nsurl urlwithstring:@"Http://localhost/itcast/images/head4.png"] completion:^ (UIImage *image) {Self.imageView.image=image; }];}@end

IOS development-How files are downloaded