Android：蓝牙应用在启动时崩溃

Question

I'm new to Android app development. I'm trying to program an app that can discover bluetooth devices and shows them in a list. I'm using a BroadcastReceiver to add the discovered devices to the list, but since I added the BroadcastReceiver the app keeps crashing on startup.

I tested the app on a Oneplus 3 (Android 7.1.1) and a Huawei P8 Lite (Android 6).

My code: MainActivity.java

package com.example.jeroen.testbluetooth;

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.view.View;
import android.widget.ArrayAdapter;
import android.widget.ListView;

import java.util.ArrayList;
import java.util.Set;

public class MainActivity extends AppCompatActivity {

    private final static int REQUEST_ENABLE_BT = 1; // static variable for intent to start BT, must be locally declared
    private final ArrayAdapter<String> btArrayAdapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1);
    private ListView listView = (ListView) findViewById(R.id.ListView); // findViewById(int id), id must match with id of view in layout file

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


    // callback function must have view parameter
    public void BtnConnectToDevice(View view) {

        // check if BT is supported
        BluetoothAdapter mBluetoothAdapter = BluetoothAdapter.getDefaultAdapter(); // get bluetooth adapter of this device
        if (mBluetoothAdapter == null) {
            // Device does not support Bluetooth
            // app shuts down
            // TODO show message for user
            finishAndRemoveTask();
        }

        // check if BT is enabled, if not turn on
        // startActivityForResult returns result of request (successful or cancelled)
        if (!mBluetoothAdapter.isEnabled()) {
            Intent enableBtIntent = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE); // create Intent to enable bluetooth
            startActivityForResult(enableBtIntent, REQUEST_ENABLE_BT); // TODO no result in the moment
        }

        // get all paired devices as set (set = unsorted array/list)
        Set<BluetoothDevice> pairedDevices = mBluetoothAdapter.getBondedDevices();

        // add names and addresses of paired devices to array
        if (pairedDevices.size() > 0) {
            // There are paired devices. Get the name and address of each paired device.
            // for loop every element of pairedDevices is passed and temporary copied into "device"
            for (BluetoothDevice device : pairedDevices) {
                String deviceName = device.getName();
                String deviceHardwareAddress = device.getAddress(); // MAC address

                // add items to adapter
                btArrayAdapter.add(deviceName + "\n"
                        + deviceHardwareAddress);
            }
        }

        // if scanning already running, stop
        if (mBluetoothAdapter.isDiscovering()) {
            mBluetoothAdapter.cancelDiscovery();
        }

        // search for devices
        mBluetoothAdapter.startDiscovery();

        // Register the broadcast receiver
        IntentFilter filter = new IntentFilter(BluetoothDevice.ACTION_FOUND);
        registerReceiver(mReceiver, filter);

        // TODO do something with the list

        // show array in listView
        // connect btArrayAdapter to ListView
        // ListView listView = (ListView) findViewById(R.id.ListView); // findViewById(int id), id must match with id of view in layout file
//        listView.setAdapter(btArrayAdapter);

    }


    @Override
    protected void onDestroy() {
        // Don't forget to unregister the ACTION_FOUND receiver.
        unregisterReceiver(mReceiver);

        // super.onDestroy();
    }



    private final BroadcastReceiver mReceiver = new BroadcastReceiver() {
        public void onReceive(Context context, Intent intent) {
            String action = intent.getAction();
            if (BluetoothDevice.ACTION_FOUND.equals(action)) {
                // A Bluetooth device was found
                // Getting device information from the intent
                BluetoothDevice device = intent.getParcelableExtra(BluetoothDevice.EXTRA_DEVICE);

                // add newly discovered devices to list
                String deviceName = device.getName();
                String deviceHardwareAddress = device.getAddress(); // MAC address

                // add items to adapter
                btArrayAdapter.add(deviceName + "\n"
                        + deviceHardwareAddress);
            }
        }
    };

}

activity_main.xml:

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:app="http://schemas.android.com/apk/res-auto"
        xmlns:tools="http://schemas.android.com/tools"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        tools:context="com.example.jeroen.testbluetooth.MainActivity">

        <Button
            android:id="@+id/BtnConnectToDevice"
            android:layout_width="144dp"
            android:layout_height="48dp"
            android:layout_marginLeft="120dp"
            android:layout_marginStart="120dp"
            android:layout_marginTop="16dp"
            android:elevation="0dp"
            android:onClick="BtnConnectToDevice"
            android:text="Connect"
            app:layout_constraintLeft_toLeftOf="parent"
            app:layout_constraintTop_toTopOf="parent" />

        <ListView
            android:id="@+id/ListView"
            android:layout_width="368dp"
            android:layout_height="437dp"
            android:layout_marginBottom="10dp"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintLeft_toLeftOf="parent"
            app:layout_constraintRight_toRightOf="parent" />

</android.support.constraint.ConstraintLayout>

AndroidManifest.xml:

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.jeroen.testbluetooth">

    // permissions
    <uses-permission android:name="android.permission.BLUETOOTH" /> // Allows applications to connect to paired bluetooth devices
    <uses-permission android:name="android.permission.BLUETOOTH_ADMIN" /> // Allows applications to discover and pair bluetooth devices
    <uses-permission android:name="android.permission.RECEIVE_BOOT_COMPLETED"/>
    <uses-permission android:name="android.permission.ACCESS_FINE_LOCATION"/>
    <uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION"/>

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">

        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>

When I delete the BroadcastReceiver the app starts just fine, but without it I cannot scan for devices.

I would appreciate if someone could help me. If you need additional information don't hesitate to ask.

Best regard,

Jeroen

Answer 1

Here is my working code to scan for devices

 mBluetoothAdapter = BluetoothAdapter.getDefaultAdapter();
  mBluetoothAdapter.startDiscovery();
  mReceiver = new BroadcastReceiver() {
   public void onReceive(Context context, Intent intent) {
    String action = intent.getAction();

    //Finding devices
    if (BluetoothDevice.ACTION_FOUND.equals(action))
    {
     // Get the BluetoothDevice object from the Intent
     BluetoothDevice device = intent.getParcelableExtra(BluetoothDevice.EXTRA_DEVICE);


//Here you get scan device info
String DeviveName=device.getName();


    }
    else {

     if (mainActivity!=null)mainActivity.status.setText("Status:No device found");
    }
   }
  };

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

Answer 2

MainActivity.java

public class MainActivity extends AppCompatActivity {
       private final static int REQUEST_ENABLE_BT = 1; // static variable for intent to start BT, must be locally declared
       private ArrayAdapter<String> btArrayAdapter ;
       private ListView listView ; // findViewById(int id), id must match with id of view in layout file

       @Override
       protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activimain);
            if(ContextCompat.checkSelfPermission(this, android.Manifest.permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_GRANTED)
            ActivityCompat.requestPermissions(this, new String[]{android.Manifest.permission.ACCESS_COARSE_LOCATION}, 1);

            listView = (ListView) findViewById(R.id.ListView);
            btArrayAdapter = new ArrayAdapter<>(this, android.R.layout.simple_list_item_1);

      }


// callback function must have view parameter
       public void BtnConnectToDevice(View view) {

    // check if BT is supported
    BluetoothAdapter mBluetoothAdapter = BluetoothAdapter.getDefaultAdapter(); // get bluetooth adapter of this device
    if (mBluetoothAdapter == null) {
        // Device does not support Bluetooth
        // app shuts down
        // TODO show message for user
        finishAndRemoveTask();
    }

    // check if BT is enabled, if not turn on
    // startActivityForResult returns result of request (successful or cancelled)
    if (!mBluetoothAdapter.isEnabled()) {
        Intent enableBtIntent = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE); // create Intent to enable bluetooth
        startActivityForResult(enableBtIntent, REQUEST_ENABLE_BT); // TODO no result in the moment
    }

    // get all paired devices as set (set = unsorted array/list)
    Set<BluetoothDevice> pairedDevices = mBluetoothAdapter.getBondedDevices();

    // add names and addresses of paired devices to array
    if (pairedDevices.size() > 0) {
        // There are paired devices. Get the name and address of each paired device.
        // for loop every element of pairedDevices is passed and temporary copied into "device"
        for (BluetoothDevice device : pairedDevices) {
            String deviceName = device.getName();
            String deviceHardwareAddress = device.getAddress(); // MAC address

            // add items to adapter
            btArrayAdapter.add(deviceName + "\n"
                    + deviceHardwareAddress);
        }
    }

    // if scanning already running, stop
    if (mBluetoothAdapter.isDiscovering()) {
        mBluetoothAdapter.cancelDiscovery();
    }

    // search for devices
    mBluetoothAdapter.startDiscovery();

    // Register the broadcast receiver
    IntentFilter filter = new IntentFilter(BluetoothDevice.ACTION_FOUND);
    registerReceiver(mReceiver, filter);

    // TODO do something with the list

    // show array in listView
    // connect btArrayAdapter to ListView
    //ListView listView = (ListView) findViewById(R.id.ListView); // findViewById(int id), id must match with id of view in layout file
    listView.setAdapter(btArrayAdapter);

}

@Override
protected void onResume() {
    registerReceiver(mReceiver, new IntentFilter(BluetoothDevice.ACTION_FOUND));
    super.onResume();
}

@Override
protected void onDestroy() {
    // Don't forget to unregister the ACTION_FOUND receiver.
    unregisterReceiver(mReceiver);

     super.onDestroy();
}



public BroadcastReceiver mReceiver = new BroadcastReceiver() {
    public void onReceive(Context context, Intent intent) {
        String action = intent.getAction();
        if (BluetoothDevice.ACTION_FOUND.equals(action)) {
            // A Bluetooth device was found
            // Getting device information from the intent
            BluetoothDevice device = intent.getParcelableExtra(BluetoothDevice.EXTRA_DEVICE);

            // add newly discovered devices to list
            String deviceName = device.getName();
            String deviceHardwareAddress = device.getAddress(); // MAC address

            // add items to adapter
            btArrayAdapter.add(deviceName + "\n"
                    + deviceHardwareAddress);
        }
    }
};

}

manifest.xml

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

      <permission android:name="android.permission.BLUETOOTH" android:label="BLUETOOTH" />
      <permission android:name="android.permission.BLUETOOTH_ADMIN" />
      <permission android:name="android.permission.ACCESS_FINE_LOCATION" />
      <permission android:name="android.permission.ACCESS_COARSE_LOCATION" />