OC-16. large File Download

Big File Download Considerations

• If you do not dump the downloaded files, it will cause a sharp increase in memory consumption, or even run out of memory resources, causing the program to terminate.
• In the file download process usually occurs midway stop situation, if not to do processing, it is necessary to restart the download, waste traffic.

Solutions for large file downloads

• Process the downloaded files, write the data to disk (usually in a sandbox), and avoid accumulating data in memory (nsurlconnection download), with every bit of data downloaded

  • Implementing write Data using the Nsfilehandle class
  • Implementing write Data using the Nsoutputstream class

• When the download task terminates, log the location information at the end of the task so that the next time you start the download

Large file Download (nsurlconnection)

• Breakpoint Download not supported
• Download files using the Nsurlconnection proxy method
• The task of transferring the downloaded file and recording the end location in the proxy method of the callback at different stages of the download task

• To use the Nsfilehandle class to implement the download procedure for writing data ( 完整核心代码 )

  • Set related member properties

     /** the total length of the file to download */  @property (nonatomic, assign) Nsinteger contentlength; /** total length of downloaded files */ @property (nonatomic, assign) Nsinteger Currentlength/** file handle, used to implement file storage */ @property (Nonatomic, Strong) Nsfilehandle *handle;        

  • Create, send requests

    // 1. 创建请求路径NSURL *url = [NSURL URLWithString:@"此处为URL字符串"];// 2. 将URL封装成请求NSURLRequest *request = [NSURLRequest requestWithURL:url];// 3. 通过NSURLConnection，并设置代理[NSURLConnection connectionWithRequest:request delegate:self];

  • Comply with Agent protocol Nsurlconnectiondatadelegate, implement proxy method

    /*** the method that is called when the server response is received */-(void) Connection: (Nsurlconnection *) connection didreceiveresponse: (Nshttpurlresponse *) response{Get the total length of the file you want to downloadSelf. contentlength = [Response. allheaderfields[@ "Content-length"] integervalue];Stitching a file path in a sandboxNSString *filepath = [[Nssearchpathfordirectoriesindomains (Nscachesdirectory,Nsuserdomainmask,YES) Lastobject] stringByAppendingPathComponent:@ "Minion_15.mp4"];Creates a file of the specified path [[Nsfilemanager Defaultmanager] Createfileatpath:filepath contents:Nil attributes:NIL];To create a file handleSelf. Handle = [Nsfilehandle Filehandleforwritingatpath:filepath];}/*** the method that is called when receiving data from the server */-(void) Connection: (Nsurlconnection *) connection Didreceivedata: (NSData *) data{Navigates to the end of the file, stitching the file data returned by the server every time to the end of the file [Self. Handle Seektoendoffile];Writes a file to the sandbox through a file handle [Self. Handle Writedata:data];The total length of the downloaded file is splicedSelf. currentlength + = Data .length; //calculate download Progress cgfloat progress = 1.0 * Span class= "Hljs-keyword" >self.currentlength/self.contentlength;} /*** file is downloaded when the method */-(void) connectiondidfinishloading: ( Span class= "hljs-built_in" >nsurlconnection *) Connection{//close file handle and clear [self.handle CloseFile]; self.handle = nil;//empty downloaded file length self.currentlength = 0;}               

• To use the Nsoutputstream class to implement the download procedure for writing data ( 部分代码，其他部分代码同上 )

  • Set Nsoutputstream member properties

    @property (nonatomic, strong) NSOutputStream *stream;

  • Initialize the Nsoutputstream object to open the output stream

    /** call */-When the server response is received (void) Connection: (Nsurlconnection *) connection didreceiveresponse: (nsurlresponse *) Response{//get the path to save the download data nsstring *cache = [nssearchpathfordirectoriesindomains ( Span class= "hljs-built_in" >nscachesdirectory, nsuserdomainmask, yes) Lastobject]; nsstring *filepath = [Cache Stringbyappendingpathcomponent:response.suggestedfilename"; //use Nsoutputstream to write data to the FilePath file, if the append parameter is yes, it will be written to the end of the file .stream = [[nsoutputstream alloc] InitToFileAtPath: FilePath append:yes]; //Open Data stream [self.stream Open];}  

  • Write file data

    /**接收到数据的时候调用*/- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data{[self.stream write:[data bytes] maxLength:data.length];}

  • Turn off the output stream

    /**数据下载完毕的时候调用*/- (void)connectionDidFinishLoading:(NSURLConnection *)connection{[self.stream close];}

Large file Download (nsurlsession)

• Support breakpoint download, automatically record the location of breakpoints when stopping download
• Compliance with Nsurlsessiondownloaddelegate Protocol
• Using nsurlsession to download large files, the downloaded files will be automatically written to the sandbox Temp folder tmp
• After downloading, it is usually necessary to move the downloaded files elsewhere (the data in the TMP folder is deleted periodically), usually in the cache folder

• Detailed download steps

  • Set Download task task as member variable

    @property (nonatomic, strong) NSURLSessionDownloadTask *task;

  • Get Nsurlsession Object

    NSURLSession *session = [NSURLSession sessionWithConfiguration:[NSURLSessionConfiguration defaultSessionConfiguration] delegate:self delegateQueue:[[NSOperationQueue alloc] init]];

  • Initializing the Download Task task

    self.task = [session downloadTaskWithURL:（此处为下载文件路径URL）];

  • Implementing Proxy methods

    /** each time the data is written to a temporary file, the method is called once, usually in this method to get the download Progress */-(void) Urlsession: (Nsurlsession *) session Downloadtask: (Nsurlsessiondownloadtask *) Downloadtask didwritedata: (int64_t) Byteswritten Totalbyteswritten: (int64_t) Totalbyteswritten totalbytesexpectedtowrite: (int64_t) totalbytesexpectedtowrite{Calculate Download ProgressCGFloat progress =1.0 * TOTALBYTESWRITTEN/TOTALBYTESEXPECTEDTOWRITE;}/** the method that is called when the task terminates, typically used for breakpoint download */-(void) Urlsession: (Nsurlsession *) session Downloadtask: (Nsurlsessiondownloadtask *) Downloadtask Didresumeatoffset: (int64_t) Fileoffset expectedtotalbytes: (int64_t) expectedtotalbytes{Fileoffset: The offset when the download task is aborted}/** is called when an error is encountered, the error parameter can only pass the client's errors */-(void) Urlsession: (Nsurlsession *) Session task: (Nsurlsessiontask *) Task Didcompletewitherror: (Nserror *) error{}/** when the download is complete, you need to cut the file to a folder that can be saved for a long time */-(void) Urlsession: (Nsurlsession *) session Downloadtask: (Nsurlsessiondownloadtask *) Downloadtask Didfinishdownloadingtourl: (nsurl *) Location{//generate file long-term saved path nsstring *file = [nssearchpathfordirectoriesindomains ( Span class= "hljs-built_in" >nscachesdirectory, nsuserdomainmask, yes) Lastobject] Stringbyappendingpathcomponent:downloadtask .response.suggestedfilename]; //get file handle nsfilemanager *filemanager = [ nsfilemanager Defaultmanager]; //through the file handle, cut the file to the long-term saved path of the file [FileManager moveitematurl:location Tourl:[nsurl Fileurlwithpath:file] error:nil];}      

  • Operation Task Status

    /**开始/继续下载任务*/[self.task resume];/**暂停下载任务*/[self.task suspend];

OC-16. large File Download