BluetoothAdapter在Android6.0/7.0+以上startDiscovery不能发现蓝牙设备问题

BluetoothAdapter在Android6.0+以上startDiscovery不能发现蓝牙设备问题

问题的重要原因之一是Android 6.0+，Android 7.0+的权限问题引起的。在Android 4.0+上运行良好的蓝牙代码，在高版本运行异常。比如BluetoothAdapter的startDiscovery虽然启动了发现蓝牙任务，但是不能发现蓝牙设备。解决问题是针对最新高版本的Android系统增加权限申请。现在给出一个完整例子。

activity_main.xml：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context="zhangphil.bluetooth.MainActivity">

    <Button
        android:id="@+id/init"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="初始化蓝牙设备" />

    <Button
        android:id="@+id/discovery"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="发现设备" />

    <Button
        android:id="@+id/enable_discovery"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="使自身可被其他蓝牙设备发现" />

    <ListView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:id="@+id/listView">
    </ListView>
</LinearLayout>

测试的MainActivity.java：

package zhangphil.bluetooth;

import android.Manifest;
import android.app.Activity;
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.content.pm.PackageManager;
import android.os.Build;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.ArrayAdapter;
import android.widget.ListView;

public class MainActivity extends Activity implements View.OnClickListener {
    private final int REQUEST_ENABLE_BT = 0xa01;
    private final int PERMISSION_REQUEST_COARSE_LOCATION = 0xb01;

    private String TAG = "zhangphil";

    private ArrayAdapter<String> mAdapter;
    private BluetoothAdapter mBluetoothAdapter;

    // 广播接收发现蓝牙设备
    private BroadcastReceiver mReceiver = new BroadcastReceiver() {

        @Override
        public void onReceive(Context context, Intent intent) {
            String action = intent.getAction();

            if (BluetoothAdapter.ACTION_DISCOVERY_STARTED.equals(action)) {
                Log.d(TAG, "开始扫描...");
            }

            if (BluetoothDevice.ACTION_FOUND.equals(action)) {
                BluetoothDevice device = intent.getParcelableExtra(BluetoothDevice.EXTRA_DEVICE);
                if (device != null) {
                    // 添加到ListView的Adapter。
                    mAdapter.add("设备名:" + device.getName() + "\n设备地址:" + device.getAddress());
                    mAdapter.notifyDataSetChanged();
                }
            }

            if (BluetoothAdapter.ACTION_DISCOVERY_FINISHED.equals(action)) {
                Log.d(TAG, "扫描结束.");
            }
        }
    };

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

        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
            if (this.checkSelfPermission(Manifest.permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_GRANTED) {
                requestPermissions(new String[]{Manifest.permission.ACCESS_COARSE_LOCATION}, PERMISSION_REQUEST_COARSE_LOCATION);
            }
        }


        // 注册广播接收器。
        // 接收蓝牙发现
        IntentFilter filterFound = new IntentFilter(BluetoothDevice.ACTION_FOUND);
        registerReceiver(mReceiver, filterFound);

        IntentFilter filterStart = new IntentFilter(BluetoothAdapter.ACTION_DISCOVERY_STARTED);
        registerReceiver(mReceiver, filterStart);

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

        mAdapter = new ArrayAdapter<>(this, android.R.layout.simple_list_item_1, android.R.id.text1);
        ((ListView) findViewById(R.id.listView)).setAdapter(mAdapter);

        findViewById(R.id.init).setOnClickListener(this);
        findViewById(R.id.discovery).setOnClickListener(this);
        findViewById(R.id.enable_discovery).setOnClickListener(this);
    }

    @Override
    public void onClick(View view) {
        switch (view.getId()) {
            case R.id.init:
                init();

            case R.id.discovery:
                discovery();

            case R.id.enable_discovery:
                enable_discovery();
        }
    }

    // 初始化蓝牙设备
    private void init() {
        mBluetoothAdapter = BluetoothAdapter.getDefaultAdapter();

        // 检查设备是否支持蓝牙设备
        if (mBluetoothAdapter == null) {
            Log.d(TAG, "设备不支持蓝牙");

            // 不支持蓝牙，退出。
            return;
        }

        // 如果用户的设备没有开启蓝牙，则弹出开启蓝牙设备的对话框，让用户开启蓝牙
        if (!mBluetoothAdapter.isEnabled()) {
            Log.d(TAG, "请求用户打开蓝牙");

            Intent enableBtIntent = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE);
            startActivityForResult(enableBtIntent, REQUEST_ENABLE_BT);
            // 接下去，在onActivityResult回调判断
        }
    }

    // 启动蓝牙发现...
    private void discovery() {
        if (mBluetoothAdapter == null) {
            init();
        }

        mBluetoothAdapter.startDiscovery();
    }

    // 可选方法，非必需
    // 此方法使自身的蓝牙设备可以被其他蓝牙设备扫描到，
    // 注意时间阈值。0 - 3600 秒。
    // 通常设置时间为120秒。
    private void enable_discovery() {
        Intent discoverableIntent = new Intent(BluetoothAdapter.ACTION_REQUEST_DISCOVERABLE);

        // 第二个参数可设置的范围是0~3600秒，在此时间区间（窗口期）内可被发现
        // 任何不在此区间的值都将被自动设置成120秒。
        discoverableIntent.putExtra(BluetoothAdapter.EXTRA_DISCOVERABLE_DURATION, 3600);

        startActivity(discoverableIntent);
    }

    @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data) {
        super.onActivityResult(requestCode, resultCode, data);

        if (requestCode == REQUEST_ENABLE_BT) {
            if (resultCode == RESULT_OK) {
                Log.d(TAG, "打开蓝牙成功！");
            }

            if (resultCode == RESULT_CANCELED) {
                Log.d(TAG, "放弃打开蓝牙！");
            }

        } else {
            Log.d(TAG, "蓝牙异常！");
        }
    }

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


    @Override
    public void onRequestPermissionsResult(int requestCode, String permissions[], int[] grantResults) {
        switch (requestCode) {
            case PERMISSION_REQUEST_COARSE_LOCATION:
                if (grantResults[0] == PackageManager.PERMISSION_GRANTED) {

                }

                break;
        }
    }
}

不要忘记增加权限：

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

代码运行结果：

以上代码运行测试环境：硬件设备是三星S7Edge，Android版本：7.0