public void ApkWrite(byte[] buff,int ii)
	    {
		    string dirPath = "/sdcard/updateVersion/version";
		    var filePath = Path.Combine(dirPath, "Game.apk");
		    if (!Directory.Exists(dirPath))
		    {
			    Directory.CreateDirectory(dirPath);
		    }
		    else
		    {
			    if (File.Exists(filePath))
			    {
				    File.Delete(filePath);
			    }
		    }
		    using (FileStream fos = new FileStream(filePath, FileMode.Create))
		    {
			    fos.Write(buff, 0, ii);
		    }
		}

DependencyService.Get<IToken>().ApkWrite(buffer, totaltotal);

//void ApkWrite(byte[] buff, int ii);