/** 设置rssi采样周期,即,计算该时间段内的平均RSSI(首末各去掉10%),缺省是20秒(20000毫秒) */
 public void onSamplePeriod(View view) {
   String period_str = SamplePeriod_edit.getText().toString();
   SamplePeroid = (int) (Double.parseDouble(period_str) * 1000.0D);
   FindBeacons.setSampleExpirationMilliseconds(SamplePeroid);
 }