"iOS Dev-98" File download: @ "HEAD" and [Request Setvalue:range forhttpheaderfield:@ "range"]

(1) file download, the general download can be downloaded directly. Download for video or download software needs to be downloaded in sections. The following is a staged download of the simulation, that is, using the request setting range, this range is a "bytes=1-1024" or the scope of the request or download.

(2) write with Nsfilehandle control file.

(3) Request header file head only, can obtain information without downloading the file.

#import "ViewController.h" #define Ksizepertime 50000@interface Viewcontroller () @property (weak, nonatomic) Iboutlet    Uiimageview *imgview; @end @implementation viewcontroller-(void) viewdidload {[Super viewdidload];    Nsurl *url=[[nsbundle mainbundle]urlforresource:@ "test.jpg" withextension:nil];    1. Get file size long long fizesize=[self filesizewithurl:url];    Compare local whether there are files long long localfile=[self localfilesize];        if (localfile==fizesize) {NSLog (@ "file already exists");    Return    }//2, determine packet size long long fromb=0;    Long Long tob=0;        while (fizesize>ksizepertime) {tob=fromb+ksizepertime-1;        3. Download the packet [self downloadwithurl:url fromb:fromb Tob:tob];        Fizesize-=ksizepertime;    Fromb+=ksizepertime;    } tob=fromb+fizesize-1;    [Self Downloadwithurl:url fromb:fromb Tob:tob]; NSString *path=[[nssearchpathfordirectoriesindomains (Nscachesdirectory, Nsuserdomainmask, YES) LastObject]    stringbyappendingpathcomponent:@ "1.jpg"]; Self.imGview.image=[uiimage Imagewithcontentsoffile:path];} -(Long Long) Filesizewithurl: (Nsurl *) url{nsmutableurlrequest *request=[nsmutableurlrequest Requestwithurl:url    Cachepolicy:nsurlrequestreloadignoringcachedata timeoutinterval:2.0f];    [email protected] "HEAD";    Nsurlresponse *response=nil;    [Nsurlconnection sendsynchronousrequest:request returningresponse:&response Error:NULL]; return response.expectedcontentlength;} -(Long Long) localfilesize{nsstring *path=[[nssearchpathfordirectoriesindomains (nscachesdirectory,    Nsuserdomainmask, YES) lastobject]stringbyappendingpathcomponent:@ "1.jpg"];    Nsdictionary *dict=[[nsfilemanager Defaultmanager]attributesofitematpath:path Error:NULL]; return [dict[nsfilesize] longlongvalue];} -(void) Downloadwithurl: (nsurl *) URL Fromb: (Long Long) Fromb ToB: (Long Long) tob{nsmutableurlrequest *request=[    Nsmutableurlrequest Requestwithurl:url Cachepolicy:nsurlrequestreloadignoringcachedata timeoutInterval:2.0f]; NSString *range=[nsString stringwithformat:@ "Bytes=%lld-%lld", Fromb,tob];    [Request Setvalue:range forhttpheaderfield:@ "range"];    Nsurlresponse *response=nil;        NSData *data=[nsurlconnection sendsynchronousrequest:request returningresponse:&response Error:NULL];    Write file [self appenddata:data]; NSLog (@ "%@", Response);} -(void) AppendData: (NSData *) data{nsstring *path=[[nssearchpathfordirectoriesindomains (nscachesdirectory,    Nsuserdomainmask, YES) lastobject]stringbyappendingpathcomponent:@ "1.jpg"];    Nsfilehandle *fh=[nsfilehandle Filehandleforwritingatpath:path];    if (!FH) {[Data writetofile:path atomically:yes];        }else{[FH Seektoendoffile];        [FH Writedata:data];    [FH CloseFile]; }} @end

"iOS Dev-98" File download: @ "HEAD" and [Request Setvalue:range forhttpheaderfield:@ "range"]