搜索不到蓝牙设备

使用两台真机测试，从系统设置中可以扫描到另一台手机，但是用app扫描不出来。

package com.fanxin.android.bluetoothchatdemo;

import android.bluetooth.BluetoothDevice;
import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.content.IntentFilter;
import android.support.annotation.Nullable;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.bluetooth.BluetoothAdapter;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.Toast;

import java.util.Set;

public class MainActivity extends AppCompatActivity {

   private static final int REQUEST_ENABLE_BT = 10;

   private static final String TAG = "MainActivity-app";

   private Button pairedButton,scanButton;

   private BluetoothAdapter bluetoothAdapater;

   private BroadcastReceiver broadcastReceiver = new BroadcastReceiver() {
       @Override
       public void onReceive(Context context, Intent intent) {
           String action = intent.getAction();
           Log.d(TAG,"ACTION: "+action);
           if (action.equals(BluetoothDevice.ACTION_FOUND)){
               BluetoothDevice device = intent.getParcelableExtra(BluetoothDevice.EXTRA_DEVICE);
               Log.d(TAG,"New Device name: "+device.getName());
               Log.d(TAG,"New Device addr: "+device.getAddress());


           }else if (action.equals(BluetoothAdapter.ACTION_DISCOVERY_FINISHED)){
               Log.d(TAG,"Discovery Done! ");

           }
       }
   };

   @Override
   protected void onCreate(Bundle savedInstanceState) {
       super.onCreate(savedInstanceState);
       setContentView(R.layout.activity_main);

       bluetoothAdapater = BluetoothAdapter.getDefaultAdapter();
       if (bluetoothAdapater == null){
           Log.e(TAG,"Device not support bluetooth");

       }else {
           Log.e(TAG,"Device support bluetooth");
       }


       pairedButton = (Button)findViewById(R.id.id_button_paired_devices);
       scanButton = (Button)findViewById(R.id.id_button_scan_devices);

       pairedButton.setOnClickListener(new View.OnClickListener() {
           @Override
           public void onClick(View v) {
               Set<BluetoothDevice> pairedDevices =  bluetoothAdapater.getBondedDevices();
               for (BluetoothDevice device: pairedDevices){
                   Log.d(TAG,"Device name: "+device.getName());
                   Log.d(TAG,"Device addr: "+device.getAddress());

               }

           }
       });

       scanButton.setOnClickListener(new View.OnClickListener() {
           @Override
           public void onClick(View v) {
               //如果正在扫描，则停止扫描
               if(bluetoothAdapater.isDiscovering()){
                   bluetoothAdapater.cancelDiscovery();
               }
               bluetoothAdapater.startDiscovery();



           }
       });

       IntentFilter filter = new IntentFilter();
       filter.addAction(BluetoothDevice.ACTION_FOUND);
       filter.addAction(BluetoothAdapter.ACTION_DISCOVERY_FINISHED);
       registerReceiver(broadcastReceiver,filter);



   }

   @Override
   protected void onDestroy() {
       super.onDestroy();
       unregisterReceiver(broadcastReceiver);
   }

   @Override
   protected void onStart() {
       super.onStart();
       if (!bluetoothAdapater.isEnabled()){
           //向系统请求开启蓝牙
           Intent enableIntent = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE);
           startActivityForResult(enableIntent,REQUEST_ENABLE_BT);

       }else {
           //已经开启了蓝牙
           Toast.makeText(this, "蓝牙已经开启",Toast.LENGTH_SHORT).show();
       }

   }

   @Override
   protected void onActivityResult(int requestCode, int resultCode, @Nullable Intent data) {
       super.onActivityResult(requestCode, resultCode, data);
       if (requestCode == REQUEST_ENABLE_BT){
           Toast.makeText(this,"蓝牙已经开启kkkkk",Toast.LENGTH_SHORT).show();
       }

   }
}

权限在manifest中已经注册过了