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ASIHTTPRequest實現斷點續傳

編輯:關於IOS

ASIHTTPRequest可以實現斷點續傳。網上有一些介紹類似使用:

  [request setAllowResumeForFileDownloads:YES];   方法的。但是它不是真正意義的斷點續傳。它只能讓應用在下載過程中,暫停和繼續。如果退出應用再進入是無效的。   不過,通過ASIHTTPRequest的異步請求以及delegate還是可以實現斷點續傳的。   本文還是以Grails編寫斷點續傳服務器端為例。   異步請求的代碼:       -(void) doSimpleGetBinary{      NSURL *url = [NSURL URLWithString:@"http://localhost:8080/BookProto/book/image"];      ASIHTTPRequest *request = [ASIHTTPRequest requestWithURL:url];      [request setRequestMethod:@"GET"];      //[request addRequestHeader:@"Range" value:@"bytes=3-"];      [request setDelegate:self];           [request startAsynchronous];  }   這裡設置了Delegate, 要在頭文件中實現相應的protocol:   @interface CFHttpDemoViewController : UIViewController<ASIProgressDelegate> {   本例中使用到了delegate的如下方法。   requestFinished:   - (void)requestFinished:(ASIHTTPRequest *)request{      NSLog(@"response status code: %i",[request responseStatusCode]);      NSLog(@"response content length: %@",[[request responseHeaders] objectForKey:@"Content-Length" ]);      NSLog(@"request finished.");      label.text=@"request finished.";  }       這個方法在異步請求結束後調用。   下面的方法,是當緩沖區接收到部分數據後調用,看起來是每間隔一定的毫秒,就調用一下,並傳入緩沖區的NSData對象。   -(void)request:(ASIHTTPRequest *)request  didReceiveData:(NSData *)data{      NSLog(@"did receive data, data length: %i",[data length]);           //復制到字節數組中      Byte *byteData=(Byte *)malloc([data length]);      memcpy(byteData,[data bytes],[data length]);           for (int i=0; i<=10; i++) {          NSLog(@"%i: %i",i+1,byteData[i]);      }           free(byteData);           [request cancel];      label.text=@"canceled.";  }       運行代碼,屏蔽:   [request addRequestHeader:@"Range" value:@"bytes=3-"];   和取消屏蔽,數據分別如下:   2011-07-12 14:17:13.497 CFHttpDemo[2647:207] did receive data, data length: 10172  2011-07-12 14:17:13.514 CFHttpDemo[2647:207] 1: 137  2011-07-12 14:17:13.515 CFHttpDemo[2647:207] 2: 80  2011-07-12 14:17:13.516 CFHttpDemo[2647:207] 3: 78  2011-07-12 14:17:13.516 CFHttpDemo[2647:207] 4: 71  2011-07-12 14:17:13.517 CFHttpDemo[2647:207] 5: 13  2011-07-12 14:17:13.518 CFHttpDemo[2647:207] 6: 10  2011-07-12 14:17:13.518 CFHttpDemo[2647:207] 7: 26  2011-07-12 14:17:13.519 CFHttpDemo[2647:207] 8: 10  2011-07-12 14:17:13.520 CFHttpDemo[2647:207] 9: 0  2011-07-12 14:17:13.520 CFHttpDemo[2647:207] 10: 0  2011-07-12 14:17:13.521 CFHttpDemo[2647:207] 11: 0  2011-07-12 14:17:13.522 CFHttpDemo[2647:207] response status code: 200  2011-07-12 14:17:13.523 CFHttpDemo[2647:207] response content length: 10172  2011-07-12 14:17:13.523 CFHttpDemo[2647:207] request finished.   2011-07-12 14:02:24.551 CFHttpDemo[2578:207] did receive data, data length: 10169  2011-07-12 14:02:24.553 CFHttpDemo[2578:207] byteData ok.  2011-07-12 14:02:24.554 CFHttpDemo[2578:207] 1: 71  2011-07-12 14:02:24.554 CFHttpDemo[2578:207] 2: 13  2011-07-12 14:02:24.555 CFHttpDemo[2578:207] 3: 10  2011-07-12 14:02:24.555 CFHttpDemo[2578:207] 4: 26  2011-07-12 14:02:24.556 CFHttpDemo[2578:207] 5: 10  2011-07-12 14:02:24.556 CFHttpDemo[2578:207] 6: 0  2011-07-12 14:02:24.557 CFHttpDemo[2578:207] 7: 0  2011-07-12 14:02:24.557 CFHttpDemo[2578:207] 8: 0  2011-07-12 14:02:24.558 CFHttpDemo[2578:207] 9: 13  2011-07-12 14:02:24.558 CFHttpDemo[2578:207] 10: 73  2011-07-12 14:02:24.560 CFHttpDemo[2578:207] 11: 72  2011-07-12 14:02:24.561 CFHttpDemo[2578:207] response status code: 206  2011-07-12 14:02:24.561 CFHttpDemo[2578:207] response content length: 10169  2011-07-12 14:02:24.562 CFHttpDemo[2578:207] request finished.   2.   NSUrlConnection實現斷點續傳的關鍵是自定義http request的頭部的range域屬性。    Range頭域   Range頭域可以請求實體的一個或者多個子范圍。例如,   表示頭500個字節:bytes=0-499   表示第二個500字節:bytes=500-999   表示最後500個字節:bytes=-500   表示500字節以後的范圍:bytes=500-   第一個和最後一個字節:bytes=0-0,-1   同時指定幾個范圍:bytes=500-600,601-999   但是服務器可以忽略此請求頭,如果無條件GET包含Range請求頭,響應會以狀態碼206(PartialContent)返回而不是以200(OK)。   在ios中使用NSMutableURLRequest來定義頭部域 NSURL *url1=[NSURL URLWithString:@"下載地址";   NSMutableURLRequest* request1=[NSMutableURLRequest requestWithURL:url1];   [request1 setValue:@"bytes=20000-" forHTTPHeaderField:@"Range"];    [request1 setCachePolicy:NSURLRequestReloadIgnoringLocalCacheData];   NSData *returnData1 = [NSURLConnection sendSynchronousRequest:request1 returningResponse:nil error:nil];    [self writeToFile:returnData1 fileName:@"SOMEPATH"];               -(void)writeToFile:(NSData *)data fileName:(NSString *) fileName   {       NSString *filePath=[NSString stringWithFormat:@"%@",fileName];       if([[NSFileManager defaultManager] fileExistsAtPath:filePath] == NO){           NSLog(@"file not exist,create it...");           [[NSFileManager defaultManager] createFileAtPath:filePath contents:nil attributes:nil];       }else {       NSLog(@"file exist!!!");       }          FILE *file = fopen([fileName UTF8String], [@"ab+" UTF8String]);          if(file != NULL){           fseek(file, 0, SEEK_END);       }       int readSize = [data length];       fwrite((const void *)[data bytes], readSize, 1, file);       fclose(file);   }    
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