应用广播接收器无法检测附近可用的蓝牙设备，但手机检测

Question

这里是我的代码

import android.bluetooth.BluetoothAdapter; 
import android.bluetooth.BluetoothDevice; 
import android.content.BroadcastReceiver; 
import android.content.Context; 
import android.content.Intent; 
import android.content.IntentFilter; 
import android.support.v7.app.AppCompatActivity; 
import android.os.Bundle; 
import android.widget.ArrayAdapter; 
import android.widget.ListView; 
import android.widget.Toast; 
import java.util.ArrayList; 

public class MainActivity extends AppCompatActivity { 

    private final BroadcastReceiver mReceiver = new BroadcastReceiver() { 
     @Override 
     public void onReceive(Context context, Intent intent) { 
      String action = intent.getAction(); 

      if (BluetoothDevice.ACTION_FOUND.equals(action)) {     
       BluetoothDevice device = intent.getParcelableExtra(BluetoothDevice.EXTRA_DEVICE); 
       devices.add(device.getName());     
      } else if (BluetoothAdapter.ACTION_DISCOVERY_FINISHED.equals(action)) { 
       mBtAdapter.startDiscovery(); 
       Toast.makeText(MainActivity.this,"Discovering "+devices.size(),Toast.LENGTH_SHORT).show(); 
       ArrayAdapter arrayAdapter=new ArrayAdapter(MainActivity.this,android.R.layout.simple_list_item_1,devices); 
       listView.setAdapter(arrayAdapter); 
       } 
      } 

    }; 

    ListView listView; 
    ArrayList<String> devices; 
    private BluetoothAdapter mBtAdapter; 

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

     listView=(ListView) findViewById(R.id.listView); 
     devices=new ArrayList<String>(); 

     IntentFilter filter = new IntentFilter(BluetoothDevice.ACTION_FOUND); 
     this.registerReceiver(mReceiver, filter); 

     filter = new IntentFilter(BluetoothAdapter.ACTION_DISCOVERY_FINISHED); 
     this.registerReceiver(mReceiver, filter); 

     mBtAdapter = BluetoothAdapter.getDefaultAdapter(); 

     if(!mBtAdapter.isEnabled()){ 
      mBtAdapter.enable(); 
     } 

     mBtAdapter.startDiscovery();   
    } 

    @Override 
    protected void onDestroy(){ 
     super.onDestroy(); 
     mBtAdapter.cancelDiscovery(); 
     unregisterReceiver(mReceiver); 
    } 
} 

问题是，它总是显示发现0作为设备的ArrayList的大小始终为0，但手机检测附近的可用设备如下图所示Screenshot of phone bluetooth settings。我认为我的应用广播接收器不检测蓝牙设备可用，因为我的代码中有错误。请帮助我

Answer 1

您不必注册您的接收器两次，意图过滤器可以容纳多个动作。

IntentFilter intentFilter = new IntentFilter(); 
intentFilter.addAction(BluetoothDevice.ACTION_FOUND); 
intentFilter.addAction(BluetoothAdapter.ACTION_DISCOVERY_FINISHED); 
registerReceiver(yourReceiver, intentFilter); 

检查是否有权限所必需的扫描：

<uses-permission android:name="android.permission.BLUETOOTH" /> 
<uses-permission android:name="android.permission.BLUETOOTH_ADMIN" /> 
<uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION" /> 

并非所有的蓝牙设备都在正常模式下可发现，请大家看看蓝牙适配器的BluetoothLeScanner和startLeScan方法：

BluetoothManager bluetoothManager = (BluetoothManager) getSystemService(Context.BLUETOOTH_SERVICE); 
BluetoothAdapter bluetoothAdapter = bluetoothManager.getAdapter(); 

bluetoothAdapter.getBluetoothLeScanner().startScan(yourCallback); // API 21+ 
bluetoothAdapter.startLeScan(yourCallback); // API 18+ 

同样需要一段时间才能打开设备上的蓝牙，您应该听取蓝牙状态更改并在发现蓝牙状态后开始发现打开并准备好使用，看看这个answer。