BLE：全称为Bluetooth Low Energy。蓝牙规范4.0最重要的一个特性就是低功耗。BLE使得蓝牙设备可通过一粒纽扣电池供电以维持续工作数年之久。很明显，BLE使得蓝牙设备在钟表、远程控制、医疗保健及运动感应器等市场具有极光明的应用场景。
Google从Android 4.3开始添加了对蓝牙4.0的支持。本文一个demo为入口分析 BLE 搜索的流程。
package com.dy.ble;import android.annotation.SuppressLint;import android.app.Activity;import android.bluetooth.BluetoothAdapter;import android.bluetooth.BluetoothDevice;import android.os.Bundle;import android.util.Log;import android.view.View;import android.view.View.OnClickListener;import android.widget.Button;public class MainActivity extends Activity { private static final String TAG = "BLE"; private Button scanBtn; private BluetoothAdapter bluetoothAdapter; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); bluetoothAdapter = BluetoothAdapter.getDefaultAdapter(); if(!bluetoothAdapter.isEnabled()){ bluetoothAdapter.enable(); } scanBtn = (Button) this.findViewById(R.id.btn_scan); scanBtn.setOnClickListener(new OnClickListener(){ @SuppressLint("NewApi") @Override public void onClick(View arg0) { if(bluetoothAdapter.isEnabled()){ bluetoothAdapter.startLeScan(callback); } } }); } @SuppressLint("NewApi") private BluetoothAdapter.LeScanCallback callback = new BluetoothAdapter.LeScanCallback(){ @Override public void onLeScan(BluetoothDevice device, int rssi, byte[] scanRecord) { Log.d(TAG, "onLeScan device = " + device + ",rssi = " + rssi + "scanRecord = " + scanRecord); } };}点击按钮就会开始扫描，扫描到设备时，就会触发onLeScan这个回调方法，并且可以从参数中获取扫描到的蓝牙设备信息。下面分析BluetoothAdapter中的startLeScan方法。
public boolean startLeScan(LeScanCallback callback) { return startLeScan(null, callback); }这里调用了一个同名的方法，
public boolean startLeScan(UUID[] serviceUuids, LeScanCallback callback) { if (DBG) Log.d(TAG, "startLeScan(): " + serviceUuids); if (callback == null) { if (DBG) Log.e(TAG, "startLeScan: null callback"); return false; } synchronized(mLeScanClients) { if (mLeScanClients.containsKey(callback)) { if (DBG) Log.e(TAG, "LE Scan has already started"); return false; } try { IBluetoothGatt iGatt = mManagerService.getBluetoothGatt(); if (iGatt == null) { if (DBG) Log.e("BluetoothAdapterReceiver", "iGatt == null"); // BLE is not supported return false; } UUID uuid = UUID.randomUUID(); GattCallbackWrapper wrapper = new GattCallbackWrapper(this, callback, serviceUuids); iGatt.registerClient(new ParcelUuid(uuid), wrapper); if (wrapper.scanStarted()) { if (DBG) Log.e("BluetoothAdapterReceiver", "wrapper.scanStarted()==true"); mLeScanClients.put(callback, wrapper); return true; } } catch (RemoteException e) { Log.e(TAG,"",e); } } return false; }这个方法需要BLUETOOTH_ADMIN权限，第一个参数是各种蓝牙服务的UUID数组，UUID是“Universally Unique Identifier”的简称，通用唯一识别码的意思。对于蓝牙设备，每个服务都有通用、独立、唯一的UUID与之对应。也就是说，在同一时间、同一地点，不可能有两个相同的UUID标识的不同服务。第二个参数是前面传进来的LeScanCallback对象。