第二个，蓝牙的搜索模式差不多，但是连接操作和写入操作完全不一样了。搜索的话，都是先通过注册一个蓝牙广播BtReceiver，再通过startDiscovery进行搜索，添加设备都是通过跟系统建立intent来获取搜索到的设备。但在连接和写入方面，经典蓝牙是通过创建一个Scoket，再通过其输入流getInputStream、输出流getOutputStream完成。BLE是通过BluetoothGatt的connectGatt、disconnect完成连接和断连，而发送消息必须要通过UUID获取BluetoothGatt的服务再进行写入。

二、具体实现

1.查看系统app目录下的build.gradle配置

因为创建项目选的是API 28，所以需要修改下面红色的配置。大部分点击搜索按钮后，没有显示任何蓝牙设备的时候，可以看看这个地方配置是否跟API版本一致，手机安卓系统是否支持该版本。

compileSdkVersion 28
buildToolsVersion '28.0.3'

defaultConfig {
    applicationId "com.example.myapplication"
    minSdkVersion 21
    targetSdkVersion 28
    versionCode 1
    versionName "1.0"

    testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
}

2.获取系统权限

（1）AndroidManifest.xml文件


    <uses-permission android:name="android.permission.BLUETOOTH" />
    <uses-permission android:name="android.permission.BLUETOOTH_ADMIN" />
    <uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION"/>
    <uses-feature android:name="android.hardware.bluetooth_le"  android:required="true" />

完整的AndroidManifest.xml文件，并增加一个后面的文本框类的关联，android:name=".APP"


<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.myapplication">
 
    <uses-permission android:name="android.permission.BLUETOOTH" />
    <uses-permission android:name="android.permission.BLUETOOTH_ADMIN" />
    <uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION"/>
    <uses-feature android:name="android.hardware.bluetooth_le"  android:required="true" />
 
    <application
        android:name=".APP"
        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/Theme.MyApplication">
        <activity
            android:name=".MainActivity"
            android:label="@string/app_name"
            android:theme="@style/Theme.MyApplication.NoActionBar">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
 
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>
 
</manifest>

（2）创建一个文本弹出框的类APP


package com.example.myapplication;
 
import android.annotation.SuppressLint;
import android.app.Application;
import android.os.Handler;
import android.widget.Toast;
 
public class APP extends Application {
    private static final Handler sHandler = new Handler();
    private static Toast sToast; // 单例Toast,避免重复创建，显示时间过长
 
    @SuppressLint("ShowToast")
    @Override
    public void onCreate() {
        super.onCreate();
        sToast = Toast.makeText(this, "", Toast.LENGTH_SHORT);
    }
 
    public static void toast(String txt, int duration) {
        sToast.setText(txt);
        sToast.setDuration(duration);
        sToast.show();
    }
 
    public static void runUi(Runnable runnable) {
        sHandler.post(runnable);
    }
}

（3）MainActivity文件

增加静态常量，删除fab按钮，增加蓝牙硬件的检查，蓝牙是否开启，动态获取定位授权。


    private static final int PERMISSION_REQUEST_COARSE_LOCATION = 1;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
 
        // 检查蓝牙开关
        BluetoothAdapter adapter = BluetoothAdapter.getDefaultAdapter();
        if (adapter == null) {
            APP.toast("本机没有找到蓝牙硬件或驱动！", 0);
            finish();
            return;
        } else {
            if (!adapter.isEnabled()) {
                //直接开启蓝牙
                adapter.enable();
                //跳转到设置界面
                //startActivityForResult(new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE), 112);
            }
        }
 
        //检查是否支持BLE
        if (!getPackageManager().hasSystemFeature(PackageManager.FEATURE_BLUETOOTH_LE)) {
            APP.toast("系统不支持BLE", Toast.LENGTH_SHORT);
            finish();
        }
 
        // Make sure we have access coarse location enabled, if not, prompt the user to enable it
        if (ContextCompat.checkSelfPermission(this, Manifest.permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_GRANTED) {
            final android.app.AlertDialog.Builder builder = new AlertDialog.Builder(this);
            builder.setTitle("定位授权");
            builder.setMessage("请授予位置访问权限，以便此应用可以检测外围设备");
            builder.setPositiveButton(android.R.string.ok, null);
            builder.setOnDismissListener(dialog -> requestPermissions(new String[]{Manifest.permission.ACCESS_COARSE_LOCATION}, PERMISSION_REQUEST_COARSE_LOCATION));
            builder.show();
        }
 
        Toolbar toolbar = findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);
    }

（4）增加一个蓝牙设备列表数据结构LeDeviceListAdapter


package com.example.myapplication;
 
import android.bluetooth.BluetoothAdapter;
import android.bluetooth.BluetoothDevice;
import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.TextView;
 
import java.util.ArrayList;
import java.util.List;
import java.util.Set;
 
/**
 * Created by xanadw on 10/24/2021.
 */
public class LeDeviceListAdapter extends BaseAdapter {
    private ArrayList<BluetoothDevice> deviceArrayList;
    private Context context;
    private LayoutInflater mInflater;
    private List<Integer> mRssis;
    private List<String> mBletype;
 
 
    public LeDeviceListAdapter(Context context, ArrayList<BluetoothDevice> devices, List<Integer> rssis, List<String> bletype) {
        this.context = context;
        this.deviceArrayList = devices;
        mInflater = LayoutInflater.from(this.context);
        mRssis = rssis;
        mBletype = bletype;
    }
 
    @Override
    public int getCount() {
        return deviceArrayList.size();
    }
 
    @Override
    public BluetoothDevice getItem(int position){
        return deviceArrayList.get(position);
    }
 
    @Override
    public long getItemId(int position) {
        return position;
    }
 
    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        MyViewHolder mViewHolder;
 
        if (convertView == null) {
            convertView = mInflater.inflate(R.layout.activity_listview, parent, false);
            mViewHolder = new MyViewHolder(convertView);
            convertView.setTag(mViewHolder);
        }else {
            mViewHolder = (MyViewHolder) convertView.getTag();
        }
 
        BluetoothDevice currentListData = getItem(position);
 
        if (currentListData.getName()==null) {
            mViewHolder.tvname.setText("No name");
        }
        else{
            mViewHolder.tvname.setText(currentListData.getName());
        }
        mViewHolder.tvmac.setText(currentListData.getAddress());
        mViewHolder.tvRssi.setText(String.format("%ddBm", mRssis.get(position)));
        mViewHolder.tvBletype.setText(mBletype.get(position));
 
        return convertView;
    }
 
    private class MyViewHolder {
        TextView tvname, tvmac, tvRssi, tvSate, tvBletype;
 
        public MyViewHolder(View item) {
            tvname = (TextView)item.findViewById(R.id.name);
            tvmac = (TextView)item.findViewById(R.id.mac);
            tvRssi = (TextView)item.findViewById(R.id.rssi);
            tvBletype = (TextView)item.findViewById(R.id.bluetoothtype);
        }
    }
 
    public void clear() {
        deviceArrayList.clear();
        mRssis.clear();
        mBletype.clear();
    }
 
    public boolean addDevice (BluetoothDevice device) {
        boolean returnValue;
        if (!deviceArrayList.contains(device)) {
            deviceArrayList.add(device);
            returnValue = true;
        } else {
            returnValue = false;
        }
 
        return returnValue;
    }
 
    public void addBound() {
        Set<BluetoothDevice> bondedDevices = BluetoothAdapter.getDefaultAdapter().getBondedDevices();
        if (bondedDevices != null)
            deviceArrayList.addAll(bondedDevices);
    }
}

（5）增加一个广播接收类BtReceiver

这个类放在util包里面，下面这个是目录结构。


package com.example.myapplication.util;
 
import android.bluetooth.BluetoothA2dp;
import android.bluetooth.BluetoothAdapter;
import android.bluetooth.BluetoothDevice;
import android.bluetooth.BluetoothHeadset;
import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.content.IntentFilter;
import android.util.Log;
 
/**
 * 监听蓝牙广播-各种状态
 */
public class BtReceiver extends BroadcastReceiver {
    private static final String TAG = BtReceiver.class.getSimpleName();
    private final Listener mListener;
 
    public BtReceiver(Context cxt, Listener listener) {
        mListener = listener;
        IntentFilter filter = new IntentFilter();
        filter.addAction(BluetoothAdapter.ACTION_STATE_CHANGED);//蓝牙开关状态
        filter.addAction(BluetoothAdapter.ACTION_DISCOVERY_STARTED);//蓝牙开始搜索
        filter.addAction(BluetoothAdapter.ACTION_DISCOVERY_FINISHED);//蓝牙搜索结束
 
        filter.addAction(BluetoothDevice.ACTION_FOUND);//蓝牙发现新设备(未配对的设备)
        filter.addAction(BluetoothDevice.ACTION_PAIRING_REQUEST);//在系统弹出配对框之前(确认/输入配对码)
        filter.addAction(BluetoothDevice.ACTION_BOND_STATE_CHANGED);//设备配对状态改变
        filter.addAction(BluetoothDevice.ACTION_ACL_CONNECTED);//最底层连接建立
        filter.addAction(BluetoothDevice.ACTION_ACL_DISCONNECTED);//最底层连接断开
 
        filter.addAction(BluetoothAdapter.ACTION_CONNECTION_STATE_CHANGED); //BluetoothAdapter连接状态
        filter.addAction(BluetoothHeadset.ACTION_CONNECTION_STATE_CHANGED); //BluetoothHeadset连接状态
        filter.addAction(BluetoothA2dp.ACTION_CONNECTION_STATE_CHANGED); //BluetoothA2dp连接状态
        cxt.registerReceiver(this, filter);
    }
 
    @Override
    public void onReceive(Context context, Intent intent) {
        String action = intent.getAction();
        if (action == null)
            return;
        Log.i(TAG, "===" + action);
        BluetoothDevice dev = intent.getParcelableExtra(BluetoothDevice.EXTRA_DEVICE);
        if (dev != null)
            Log.i(TAG, "BluetoothDevice: " + dev.getName() + ", " + dev.getAddress());
        switch (action) {
            case BluetoothAdapter.ACTION_STATE_CHANGED:
                int state = intent.getIntExtra(BluetoothAdapter.EXTRA_STATE, 0);
                Log.i(TAG, "STATE: " + state);
                break;
            case BluetoothAdapter.ACTION_DISCOVERY_STARTED:
                break;
            case BluetoothAdapter.ACTION_DISCOVERY_FINISHED:
                break;
 
            case BluetoothDevice.ACTION_FOUND:
                short rssi = intent.getShortExtra(BluetoothDevice.EXTRA_RSSI, Short.MAX_VALUE);
                Log.i(TAG, "EXTRA_RSSI:" + rssi);
                mListener.foundDev(dev, rssi);
                break;
            case BluetoothDevice.ACTION_PAIRING_REQUEST: //在系统弹出配对框之前，实现自动配对，取消系统配对框
                /*try {
                    abortBroadcast();//终止配对广播，取消系统配对框
                    boolean ret = dev.setPin("1234".getBytes()); //设置PIN配对码(必须是固定的)
                } catch (Exception e) {
                    e.printStackTrace();
                }*/
                break;
            case BluetoothDevice.ACTION_BOND_STATE_CHANGED:
                Log.i(TAG, "BOND_STATE: " + intent.getIntExtra(BluetoothDevice.EXTRA_BOND_STATE, 0));
                break;
            case BluetoothDevice.ACTION_ACL_CONNECTED:
                break;
            case BluetoothDevice.ACTION_ACL_DISCONNECTED:
                break;
 
            case BluetoothAdapter.ACTION_CONNECTION_STATE_CHANGED:
                Log.i(TAG, "CONN_STATE: " + intent.getIntExtra(BluetoothAdapter.EXTRA_CONNECTION_STATE, 0));
                break;
            case BluetoothHeadset.ACTION_CONNECTION_STATE_CHANGED:
                Log.i(TAG, "CONN_STATE: " + intent.getIntExtra(BluetoothHeadset.EXTRA_STATE, 0));
                break;
            case BluetoothA2dp.ACTION_CONNECTION_STATE_CHANGED:
                Log.i(TAG, "CONN_STATE: " + intent.getIntExtra(BluetoothA2dp.EXTRA_STATE, 0));
                break;
        }
    }
 
    public interface Listener {
        void foundDev(BluetoothDevice dev, short devrssi);
    }
}

（6）FirstFragment文件

（I）引入BtReceiver，修改主类

import com.example.myapplication.util.BtReceiver;

public class FirstFragment extends Fragment implements BtReceiver.Listener {

然后根据错误提示需要新增foundDev函数，这个函数是经典蓝牙搜索的结果


    @Override
    public void foundDev(BluetoothDevice dev, short devrssi) {
        mLeDeviceListAdapter.addDevice(dev);
        mRssis.add((int) devrssi);
        mfbletype.add("old");
        mLeDeviceListAdapter.notifyDataSetChanged();
    }

新建蓝牙相关的变量以及一些常量


    private static final String TAG = "FirstFragment";
    private final static int REQUEST_ENABLE_BT = 1; 
   
    //获取主页面
    MainActivity mActivity;
 
    BluetoothManager btManager;
    BluetoothAdapter btAdapter;
    BluetoothLeScanner btScanner;
    private BtReceiver mBtReceiver;

（II）获取主页面的Activity，因为我们的first页面是fragment页面，只能用主页面Activity去获取系统设备，第一个OnAttach是从Activity创建Fragment时调用的，第二个是OnDetach是从Fragment销毁返回到Activity时调用的。


    @Override
    public void onAttach(@NonNull Activity  activity) {
        super.onAttach(activity);
        mActivity = (MainActivity) activity;
    }
 
    @Override
    public void onDetach() {
        super.onDetach();
        mActivity = null;
    }

（III）修改onCreateView函数页面创建方式


        // Inflate the layout for this fragment
        View view=inflater.inflate(R.layout.fragment_first, container, false);
 
        return view;

（IV）判断系统是否支持蓝牙，并获取，并跟蓝牙建立一个Intent数据链接，放在onCreateView函数return前面。


        btManager = (BluetoothManager)mActivity.getSystemService(Context.BLUETOOTH_SERVICE);
        btAdapter = btManager.getAdapter();
        if (btAdapter == null || !btAdapter.isEnabled()) {
            Intent enableBtIntent = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE);
            startActivityForResult(enableBtIntent, REQUEST_ENABLE_BT);
        }
        btScanner = btAdapter.getBluetoothLeScanner();

（V）FirstFragment继续增加变量


    final ArrayList<BluetoothDevice> availableBT = new ArrayList<>();
    private static List<String> mfbletype;
    private static List<Integer> mRssis;
    private static LeDeviceListAdapter mLeDeviceListAdapter;
    private static BluetoothGatt firstGatt = null;
    private static String conbletype = "";
    private static BluetoothDevice condev = null;

（VI）增加界面显示搜索到的设备，同样放置在onCreateView函数的return之前。


        mLeDeviceListAdapter = new LeDeviceListAdapter(mActivity.getApplicationContext(), availableBT, mRssis, mfbletype);
        final ListView listView_available = view.findViewById(R.id.listview2);
        listView_available.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
                firstGatt = null;
                conbletype = mfbletype.get(position);
                condev = mLeDeviceListAdapter.getItem(position);
 
                if (btAdapter.isDiscovering()) {
                    btAdapter.cancelDiscovery();
                }
 
                NavHostFragment.findNavController(FirstFragment.this)
                        .navigate(R.id.action_FirstFragment_to_SecondFragment);
            }
        });

（VII）增加一个蓝牙扫描设备的按钮，蓝牙扫描是最消耗能量的动作了，不符合BLE的思想所以一般手机都设置了30秒内扫描5次的限制，所以改成手动触发扫描，一次扫描时间挺长的，靠近一点等一等就会扫描到你要连接的蓝牙设备。

增加一个变量和常量


private Handler mHandler;
private static final long SCAN_PERIOD = 15000;


        mHandler = new Handler();
        mfbletype = new ArrayList<>();
        mRssis = new ArrayList<>();
        
        Button scan = view.findViewById(R.id.scan);
        scan.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                APP.toast("Scanning...", Toast.LENGTH_SHORT);
                mLeDeviceListAdapter.clear();
                mfbletype.clear();
                mRssis.clear();
 
                conbletype = "";
                condev = null;
 
 
                if (!btAdapter.isDiscovering()) {
                    btAdapter.startDiscovery();
                }
 
                mHandler.postDelayed(new Runnable() {
                    @Override
                    public void run() {
                        stopScanning();
 
                    }
                },SCAN_PERIOD);
 
                scanLeDevice(true);
 
                mLeDeviceListAdapter.notifyDataSetChanged();
                listView_available.setAdapter(mLeDeviceListAdapter);
            }
        });

（VIII）onViewCreated这个原来用来控制页面一(蓝牙搜索页面)跳转到页面二(按钮控制页面)函数删除，之后采用点击对应的蓝牙设备直接跳转到页面二，然后增加缺少的一些函数，

添加已搜索到的设备到列表的回调函数leScanCallback，这个是BLE蓝牙搜索的结果。


 
    private final ScanCallback leScanCallback = new ScanCallback() {
        @RequiresApi(api = Build.VERSION_CODES.LOLLIPOP)
        @Override
        public void onScanResult(int callbackType, ScanResult result) {
            if (!(mActivity == null || mActivity.isFinishing())) {
                mActivity.runOnUiThread(() -> {
                    if (mLeDeviceListAdapter.addDevice(result.getDevice())) {
                        mRssis.add(result.getRssi());
                        mfbletype.add("ble");
                    }
                    mLeDeviceListAdapter.notifyDataSetChanged();
                });
            }
        }
    };

添加停止扫描函数stopScanning


    public void stopScanning() {
        Log.d(TAG, "stopping scanning" );
 
        AsyncTask.execute(new Runnable() {
            @RequiresApi(api = Build.VERSION_CODES.LOLLIPOP)
            @Override
            public void run() {
                btScanner.stopScan(leScanCallback);
            }
        });
    }

添加扫描函数scanLeDevice


    private void scanLeDevice(final boolean enable) {
        if (enable) {
            mHandler.postDelayed(new Runnable() {
                @Override
                public void run() {
                    stopScanning();
 
                }
            },SCAN_PERIOD);
 
            startScanning();
        } else {
            try {
                stopScanning();
            } catch (Exception e) {
            }
        }
    }

添加开始扫描函数startScanning


    public void startScanning() {
        //scan.setVisibility(View.INVISIBLE);
        //dc.setVisibility(View.VISIBLE);
        AsyncTask.execute(() -> btScanner.startScan(leScanCallback));
    }

（IX）onCreateView函数添加广播接收


        mBtReceiver = new BtReceiver(mActivity.getApplicationContext(), this);//注册蓝牙广播
        BluetoothAdapter.getDefaultAdapter().startDiscovery();

（X）onCreateView函数添加按钮的可见性


        Button button_first = view.findViewById(R.id.button_first);
        button_first.setVisibility(View.INVISIBLE);

3.页面设计

上面的代码添加完毕后，还是存在一些报错，那是因为我们还缺少一些页面的组件元素。

(1) fragment_first.xml 文件

删除textview_first，包含activity_listview页面

<include layout="@layout/activity_listview" />

增加available、listview2、scan元素


    <TextView
        android:text="Available Devices"
        android:id="@+id/available"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintTop_toTopOf="parent"/>
 
    <ListView
        android:id="@+id/listview2"
        android:layout_width="match_parent"
        android:layout_height="500dp"
        android:layout_alignParentStart="true"
        android:layout_below="@+id/available"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        android:layout_marginTop="30dp"/>
 
    <Button
        android:id="@+id/scan"
        android:text="Scan Devices"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentBottom="true"
        android:layout_alignParentLeft="true"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        android:layout_marginBottom="30dp"/>

修改button_first元素


    <Button
        android:id="@+id/button_first"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/next"
        android:layout_toStartOf="@+id/scan"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toRightOf="@+id/scan"
        android:layout_marginBottom="30dp"/>

(2) 增加activity_listview.xml 文件


<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:background="#ffffff"
    android:gravity="center_vertical"
    android:orientation="vertical">
 
    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="horizontal"
        android:paddingBottom="8dp"
        android:paddingLeft="12dp"
        android:paddingRight="12dp"
        android:paddingTop="8dp">
 
        <LinearLayout
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:orientation="vertical">
 
            <TextView
                android:id="@+id/name"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:ellipsize="end"
                android:singleLine="true"
                android:textSize="17sp" />
 
            <TextView
                android:id="@+id/mac"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_below="@+id/name"
                android:ellipsize="end"
                android:singleLine="true"
                android:textColor="#999999"
                android:textSize="12sp" />
 
            <TextView
                android:id="@+id/rssi"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_below="@+id/mac"
                android:text=""
                android:textColor="#303030"
                android:textSize="12sp" />
 
            <TextView
                android:id="@+id/bluetoothtype"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_below="@+id/rssi"
                android:ellipsize="end"
                android:singleLine="true"
                android:textSize="12sp" />
        </LinearLayout>
    </LinearLayout>
 
</LinearLayout>