Android 6.0 Bluetooth LE can't scan

開心的將Nexus 7 二代升級到6.0，
悲劇隨即發生，為什麼我的藍牙都scan不到其他裝置，
拿其他的設備（5.0）藍牙scan 都是正常的，
上網搜尋了一下，這才發現Android 6.0 有在這部分做一些變更，
以下為解決方法：

Quick Start

Enable access coarse location permission

if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {

            if (this.checkSelfPermission(Manifest.permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_GRANTED) {

                final AlertDialog.Builder builder = new AlertDialog.Builder(this);
                builder.setTitle("This app needs location access");
                builder.setMessage("Please grant location access to this app can detect beacons.");
                builder.setPositiveButton(android.R.string.ok, null);
                builder.setOnDismissListener(new DialogInterface.OnDismissListener() {
                    @Override
                    public void onDismiss(DialogInterface dialog) {
                        requestPermissions(new String[]{Manifest.permission.ACCESS_COARSE_LOCATION}, PERMISSION_REQUEST_COARSE_LOCATION);
                    }
                });
                builder.show();
            }
        }

@Override
    public void onRequestPermissionsResult(int requestCode, String[] permissions, int[] grantResults) {

        switch (requestCode) {
            case PERMISSION_REQUEST_COARSE_LOCATION: {

                if (grantResults[0] == PackageManager.PERMISSION_GRANTED) {
                    Log.d(TAG, "coarse location permission granted");
                }else {

                    final AlertDialog.Builder builder = new AlertDialog.Builder(this);
                    builder.setTitle("Functionality limited");
                    builder.setMessage("Since location access has not been granted, this app will not be able to discover beacons when in the background.");
                    builder.setPositiveButton(android.R.string.ok, null);
                    builder.setOnDismissListener(new DialogInterface.OnDismissListener() {
                        @Override
                        public void onDismiss(DialogInterface dialog) {

                        }
                    });
                    builder.show();
                }
                return;
            }
        }
    }

AndroidManifest.xml

Add permission:

• access coarse location
• access fine location

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

Android 6.0 changes

Access to Hardware Identifier

To access the hardware identifiers of nearby external devices via Bluetooth and Wi-Fi scans, your app must now have the ACCESS_FINE_LOCATION or ACCESS_COARSE_LOCATION permissions:

• WifiManager.getScanResults()
• BluetoothDevice.ACTION_FOUND
• BluetoothLeScanner.startScan()

Reference: http://developer.android.com/intl/ko/about/versions/marshmallow/android-6.0-changes.html#behavior-hardware-id