使用ASIHttpRequest下载pdf

Question

我想使用ASIHttpRequest下载pdf文件。 使用的代码是

 NSURL *requestUrl = [NSURL URLWithString:[urlPath objectForKey:@"url"]];

        //Downloading Image
        ASIHTTPRequest *request = [ASIHTTPRequest requestWithURL:requestUrl];
        NSLog(@"request.url %@", request.url);

        //get the root directory:
        BOOL directoryExists = [Global checkWhetherLibraryDirExists];
        if(!directoryExists)
        {
            [[NSFileManager defaultManager] createDirectoryAtPath:[Global getLibraryDirRootPath]
                                      withIntermediateDirectories:NO
                                                       attributes:NO
                                                            error:nil];
        }
        [Global DirectoryInCacheWithName:[urlPath objectForKey:@"directory"]];

        NSArray *imgname = [[urlPath objectForKey:@"url"] componentsSeparatedByString:@"/"];

        NSString *downLoadPath = [[Global getLibraryDirRootPath] stringByAppendingPathComponent:[NSString stringWithFormat:@"%@",[imgname objectAtIndex:[imgname count]-1]]];


        [request setDownloadDestinationPath:downLoadPath];

        // This file has part of the download in it already
        [request setTemporaryFileDownloadPath:[NSString stringWithFormat:@"%@.download", downLoadPath]];
        [request setDelegate:self];

        [request setTimeOutSeconds:60.0];
        if([urlPath objectForKey:@"progressView"])
            [request setDownloadProgressDelegate:[urlPath objectForKey:@"progressView"]];
        [request setShowAccurateProgress:YES];
        [request setRequestMethod:@"GET"];
        [request setShouldContinueWhenAppEntersBackground:YES];

        [request startSynchronous];

我的问题是pdf文件已下载，但在webview中打开时，会出现pdf标记丢失的错误。

“找不到PDF标题：找不到'％PDF'。”