在android studio中扫描ble模块（蓝牙4.0）

Question

I'm trying to develop an app to scan for a BLE device. However, it only scans one time. I tried to use a while loop to loop it but it hangs there. The scanning part is at the proceed function:

package com.example.user.myfriend;

import android.bluetooth.BluetoothAdapter;
import android.bluetooth.BluetoothDevice;
import android.bluetooth.BluetoothManager;
import android.content.Context;
import android.content.Intent;
import android.graphics.Color;
import android.os.Handler;
import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.RelativeLayout;
import android.widget.TextView;
import android.widget.Toast;

import org.w3c.dom.Text;


public class MainActivity extends ActionBarActivity {
BluetoothAdapter mBluetoothAdapter;

@Override
protected void onCreate(Bundle savedInstanceState) {


    BluetoothManager bluetoothManager = (BluetoothManager) getSystemService(Context.BLUETOOTH_SERVICE);
    mBluetoothAdapter = bluetoothManager.getAdapter();

    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    hello();

}

public void hello() {

    if (mBluetoothAdapter == null || !mBluetoothAdapter.isEnabled()) {
        Intent enableBluetooth = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE);

        startActivityForResult(enableBluetooth, 1);


    }
    proceed();
}


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

    if (requestCode == 1) {
        if (resultCode == RESULT_OK) {
            proceed();


        }

    }
    super.onActivityResult(requestCode, resultCode, data);
}

private BluetoothAdapter.LeScanCallback mLeScanCallback = new BluetoothAdapter.LeScanCallback() {


    public void onLeScan(final BluetoothDevice device, final int rssi, final byte[] scanRecord) {

        int startByte = 2;
        boolean patternFound = false;
        while (startByte <= 5) {

            if (((int) scanRecord[startByte + 2] & 0xff) == 0x02 && //Identifies an iBeacon
                    ((int) scanRecord[startByte + 3] & 0xff) == 0x15) { //Identifies correct data length
                patternFound = true;
                break;
            }
            startByte++;
        }

        if (patternFound) {

            //Convert to hex String
            byte[] uuidBytes = new byte[16];
            System.arraycopy(scanRecord, startByte + 4, uuidBytes, 0, 16);
            String hexString = bytesToHex(uuidBytes);

            //Here is your UUID
            String uuid = hexString.substring(0, 8) + "-" +
                    hexString.substring(8, 12) + "-" +
                    hexString.substring(12, 16) + "-" +
                    hexString.substring(16, 20) + "-" +
                    hexString.substring(20, 32);

            //Here is your Major value
            int major = (scanRecord[startByte + 20] & 0xff) * 0x100 + (scanRecord[startByte + 21] & 0xff);

            //Here is your Minor value
            int minor = (scanRecord[startByte + 22] & 0xff) * 0x100 + (scanRecord[startByte + 23] & 0xff);

            if (major == 1) {
                RelativeLayout hai = (RelativeLayout) findViewById(R.id.hai);
                hai.setBackgroundColor(Color.YELLOW);

            }
            if (major == 2) {
                RelativeLayout hai = (RelativeLayout) findViewById(R.id.hai);
                hai.setBackgroundColor(Color.RED);

            }


        }


    }


};


private static String bytesToHex(byte[] bytes) {
    final char[] hexArray = "0123456789ABCDEF".toCharArray();
    char[] hexChars = new char[bytes.length * 2];
    for (int j = 0; j < bytes.length; j++) {
        int v = bytes[j] & 0xFF;
        hexChars[j * 2] = hexArray[v >>> 4];
        hexChars[j * 2 + 1] = hexArray[v & 0x0F];
    }
    return new String(hexChars);
}

public void proceed() {
    boolean scanning = true;

    mBluetoothAdapter.startLeScan(mLeScanCallback);


    Handler handler = new Handler();
    handler.postDelayed(new Runnable() {
        //  @Override
        public void run() {
            mBluetoothAdapter.stopLeScan(mLeScanCallback);


        }
    }, 50000000);

}

}

How can I make the app scan in a loop?

Answer 1

If "by scan in a loop?" you mean detect all nearby broadcasting devices, you have done it. The line of code:

mBluetoothAdapter.startLeScan(mLeScanCallback) 

causes scanning to begin. During scanning, the callback "mLeScanCallback" will be called as each broadcasting device is discovered. The scan will remain in effect until

mBluetoothAdapter.stopScan(mLeScanCallback) 

is called. In your case, this will get called after a very long time: 50000000 milliseconds.

Perhaps you only have 1 broadcasting device in the area so you only get 1 callback when you test.

Answer 2

Unfortunately it is highly probable that the model of the device that you're testing your app on behaves badly in terms of scan performance. It is because of this bug:

https://code.google.com/p/android/issues/detail?id=65863

The exact nature of the problem is unknown but according to most of the participants of the issue aforementioned it is up to the Bluetooth Chipset mounted into Android device.

The funny thing is that some devices handle the bluetooth performing it in loop instantly and some perform scan only once or several times.

I deal with BLE in Android on daily basis and the way I approached the problem was creation of the Object encapsulating periodic forcing Bluetooth scan. My scheduler encapsulates single thread in which the instance of the LeScanCallback is started and stopped every n hundred milliseconds. While it is a hack, it resolves the problem but starting from Android KitKat (BLE was introduced in API 18).

Of course using periodic force scan scheduler is optional in my library because of the fact that some Android devices don't need it to be working.

Btw., sooner or later you will experience the system crash on Android JELLY_BEAN_MR2 resulting in displaying dialog that something went wrong.

I suggest trying out the kontakt.io iBeacon library: documentation and howto can be found here: http://devdocs.kontakt.io .