Question

I am trying to find nearby Bluetooth devices so I’m using BroadcastReceiver. Most of the time it works fine but sometimes I get this error.

04-30 09:50:15.277: E/AndroidRuntime(847): FATAL EXCEPTION: main
04-30 09:50:15.277: E/AndroidRuntime(847): java.lang.RuntimeException: Error receiving broadcast Intent { act=android.bluetooth.device.action.FOUND (has extras) } in com.waratah.app.SetMachineActivity$2@40582d20
04-30 09:50:15.277: E/AndroidRuntime(847):  at android.app.LoadedApk$ReceiverDispatcher$Args.run(LoadedApk.java:722)
04-30 09:50:15.277: E/AndroidRuntime(847):  at android.os.Handler.handleCallback(Handler.java:587)
04-30 09:50:15.277: E/AndroidRuntime(847):  at android.os.Handler.dispatchMessage(Handler.java:92)
04-30 09:50:15.277: E/AndroidRuntime(847):  at android.os.Looper.loop(Looper.java:130)
04-30 09:50:15.277: E/AndroidRuntime(847):  at android.app.ActivityThread.main(ActivityThread.java:3683)
04-30 09:50:15.277: E/AndroidRuntime(847):  at java.lang.reflect.Method.invokeNative(Native Method)
04-30 09:50:15.277: E/AndroidRuntime(847):  at java.lang.reflect.Method.invoke(Method.java:507)
04-30 09:50:15.277: E/AndroidRuntime(847):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
04-30 09:50:15.277: E/AndroidRuntime(847):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
04-30 09:50:15.277: E/AndroidRuntime(847):  at dalvik.system.NativeStart.main(Native Method)
04-30 09:50:15.277: E/AndroidRuntime(847): Caused by: java.lang.NullPointerException
04-30 09:50:15.277: E/AndroidRuntime(847):  at com.waratah.app.SetMachineActivity$2.onReceive(SetMachineActivity.java:532)
04-30 09:50:15.277: E/AndroidRuntime(847):  at android.app.LoadedApk$ReceiverDispatcher$Args.run(LoadedApk.java:709)
04-30 09:50:15.277: E/AndroidRuntime(847):  ... 9 more

It shows NullPointerException but I don’t see how this error can occur because I’m checking the variables to avoid the exception.

// The BroadcastReceiver that listens for discovered devices and
// changes the title when discovery is finished
private final BroadcastReceiver mReceiver = new BroadcastReceiver() {
    @Override
    public void onReceive(Context context, Intent intent) {
        if (intent == null) {
            return;
        }
        String action = intent.getAction();
        int i;
        Machine d;

        if (BluetoothAdapter.ACTION_STATE_CHANGED.equals(action)) {
            if (mBtAdapter.isEnabled()) {
                if(D) Log.d(BroadcastReceiver.class.getName(), "Bluetooth is enabled");
                pd.dismiss();                   
            }
            doDiscovery();

        // when bluetooth device is found 
        } else if (BluetoothDevice.ACTION_FOUND.equals(action)) { 
            if(D) Log.d(BroadcastReceiver.class.getName(), "found");
            // Get the BluetoothDevice object from the Intent
            BluetoothDevice device = intent.getParcelableExtra(BluetoothDevice.EXTRA_DEVICE);
            if (device != null) {

                // Check if the device has name
                if ((device.getName() != null)||(device.getName().length() > 0)) { //LINE 532 HERE 
                    d = new Machine(device);
                    if (d.getPairingState() != BluetoothDevice.BOND_BONDED) {
                        d.setBluetoothState(true);
                        addDevice(d);
                    } else {
                        for (i = 0; i < adapter.getCount(); i++) {
                            if (adapter.getItem(i).getAddress().equals(device.getAddress())) {
                                    adapter.getItem(i).setBluetoothState(true);
                            }
                        }
                    }
                }
            }
        // When discovery is finished, change the Activity title
        } else if (BluetoothAdapter.ACTION_DISCOVERY_FINISHED.equals(action)) {
            scanButton.setVisibility(View.VISIBLE);

            pb.setVisibility(View.GONE);
            scanning.setVisibility(View.GONE);
        }
    }
};

I have registered all my actions and registered my receiver correctly. This error occurs only occasionally. Is it possible for the onReceive() function to be triggered when there is nothing to receive?

Thanks for your help.

EDIT:
Line 532 is

 if ((device.getName() != null)||(device.getName().length() > 0)) { 

so this means device must be null, but the previous line checks for this.

if (device != null) {

By the way could two broadcast receivers running at the same time cause this kind of error? Does the BroadcastReceiver null the intent after it is received?

Answer 1

I suspect you mistakenly used || instead of &&.

if ((device.getName() != null)||(device.getName().length() > 0)) {

vs.

if ((device.getName() != null) && (device.getName().length() > 0)) {

As originally written, if device.getName() is null, then it attempts to evaluate the second part, which is calling length() on the null value, thus resulting in the NPE you are seeing.