我正在尝试使用android studio创建一个应用程序，它应该连接到我的adruino板并在按下某些按钮时发送一些数字。
现在我无法解决一个错误，说我的BluetoothAdapter变量每次使用时都会返回NULL。我在手机上尝试了该应用程序，但它不会运行（不幸的是，您的应用已关闭）。
MainActivity.java：
public class MainActivity extends AppCompatActivity {
//variables-not using all of them but some are required in many examples for finding the MAC address
Handler bluetoothIn;
final int handlerState = 0;
private BluetoothAdapter BA;
private BluetoothSocket btSocket = null;
private ConnectedThread mConnectedThread;
private static final UUID BTMODULEUUID = UUID.fromString("00001101-0000-1000-8000-00805F9B34FB");
//list for addresses
private static final String TAG = "DeviceListActivity";
public static String EXTRA_DEVICE_ADDRESS = "device_address";
private ArrayAdapter<String> mNewDevicesArrayAdapter;
@Override
protected void onCreate(Bundle savedInstanceState) { //here I define my buttons
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
setResult(Activity.RESULT_CANCELED);
final Button Up = (Button) findViewById(R.id.up);
Up.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
mConnectedThread.write("1");
}
});
final Button Down = (Button) findViewById(R.id.down);
Down.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
mConnectedThread.write("2");
}
});
final Button Right = (Button) findViewById(R.id.right);
Right.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
mConnectedThread.write("3");
}
});
final Button Left = (Button) findViewById(R.id.left);
Left.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
mConnectedThread.write("4");
}
});
final Button Connect = (Button) findViewById(R.id.connect);
Connect.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
checkBTState();
doDiscovery();
v.setVisibility(View.GONE);
}
});
ArrayAdapter<String> pairedDevicesArrayAdapter =
new ArrayAdapter<String>(this, R.layout.activity_main);
mNewDevicesArrayAdapter = new ArrayAdapter<String>(this, R.layout.activity_main);
ListView pairedListView = (ListView) findViewById(R.id.paired_devices);
pairedListView.setAdapter(pairedDevicesArrayAdapter);
pairedListView.setOnItemClickListener(mDeviceClickListener);
ListView newDevicesListView = (ListView) findViewById(R.id.new_devices);
newDevicesListView.setAdapter(mNewDevicesArrayAdapter);
newDevicesListView.setOnItemClickListener(mDeviceClickListener);
// Register for broadcasts when a device is discovered
IntentFilter filter = new IntentFilter(BluetoothDevice.ACTION_FOUND);
this.registerReceiver(mReceiver, filter);
// Register for broadcasts when discovery has finished
filter = new IntentFilter(BluetoothAdapter.ACTION_DISCOVERY_FINISHED);
this.registerReceiver(mReceiver, filter);
// Get the local Bluetooth adapter
BA = BluetoothAdapter.getDefaultAdapter();
checkBTState();
if(BA.isEnabled()) {
// Get a set of currently paired devices
Set<BluetoothDevice> pairedDevices = BA.getBondedDevices();
// If there are paired devices, add each one to the ArrayAdapter
if (pairedDevices.size() > 0) {
findViewById(R.id.title_paired_devices).setVisibility(View.VISIBLE);
for (BluetoothDevice device : pairedDevices) {
pairedDevicesArrayAdapter.add(device.getName() + "\n" + device.getAddress());
}
} else {
String noDevices = getResources().getText(R.string.none_paired).toString();
pairedDevicesArrayAdapter.add(noDevices);
}
}
}
private BluetoothSocket createBluetoothSocket(BluetoothDevice device) throws IOException { //something I have seen in one example I tried to copy
return device.createRfcommSocketToServiceRecord(BTMODULEUUID);
//creates secure outgoing connecetion with BT device using UUID
}
@Override
protected void onDestroy() {
super.onDestroy();
// Make sure we're not doing discovery anymore
if (BA != null) {
BA.cancelDiscovery();
}
// Unregister broadcast listeners
this.unregisterReceiver(mReceiver);
}
@Override
public void onResume() {
super.onResume();
/***************************************************/ // code here
BluetoothDevice device = BA.getRemoteDevice(EXTRA_DEVICE_ADDRESS);
try {
btSocket = createBluetoothSocket(device);
} catch (IOException e) {
Toast.makeText(getBaseContext(), "Socket creation failed", Toast.LENGTH_LONG).show();
}
// Establish the Bluetooth socket connection.
try {
btSocket.connect();
} catch (IOException e) {
try {
btSocket.close();
} catch (IOException e2) {
//insert code to deal with this
}
}
mConnectedThread = new ConnectedThread(btSocket);
mConnectedThread.start();
//I send a character when resuming.beginning transmission to check device is connected
//If it is not an exception will be thrown in the write method and finish() will be called
// mConnectedThread.write("x");
}
@Override
public void onPause() {
super.onPause();
try {
//Don't leave Bluetooth sockets open when leaving activity
btSocket.close();
} catch (IOException e2) {
//insert code to deal with this
}
}
private class ConnectedThread extends Thread {
private final InputStream mmInStream;
private final OutputStream mmOutStream;
//creation of the connect thread
public ConnectedThread(BluetoothSocket socket) {
InputStream tmpIn = null;
OutputStream tmpOut = null;
try {
//Create I/O streams for connection
tmpIn = socket.getInputStream();
tmpOut = socket.getOutputStream();
} catch (IOException e) {
}
mmInStream = tmpIn;
mmOutStream = tmpOut;
}
public void run() {
byte[] buffer = new byte[256];
int bytes;
// Keep looping to listen for received messages
while (true) {
try {
bytes = mmInStream.read(buffer); //read bytes from input buffer
String readMessage = new String(buffer, 0, bytes);
// Send the obtained bytes to the UI Activity via handler
bluetoothIn.obtainMessage(handlerState, bytes, -1, readMessage).sendToTarget();
} catch (IOException e) {
break;
}
}
}
//write method
public void write(String input) {
byte[] msgBuffer = input.getBytes(); //converts entered String into bytes
try {
mmOutStream.write(msgBuffer); //write bytes over BT connection via outstream
} catch (IOException e) {
//if you cannot write, close the application
Toast.makeText(getBaseContext(), "Connection Failure", Toast.LENGTH_LONG).show();
finish();
}
}
}
private void doDiscovery() {
Log.d(TAG, "doDiscovery()");
// Indicate scanning in the title
setProgressBarIndeterminateVisibility(true);
// If we're already discovering, stop it
if (BA.isDiscovering()) {
BA.cancelDiscovery();
}
// Request discover from BluetoothAdapter
BA.startDiscovery();
}
/**
* The on-click listener for all devices in the ListViews
*/
private AdapterView.OnItemClickListener mDeviceClickListener
= new AdapterView.OnItemClickListener() {
public void onItemClick(AdapterView<?> av, View v, int arg2, long arg3) {
// Cancel discovery because it's costly and we're about to connect
BA.cancelDiscovery();
// Get the device MAC address, which is the last 17 chars in the View
String info = ((TextView) v).getText().toString();
String address = info.substring(info.length() - 17);
// Create the result Intent and include the MAC address
Intent intent = new Intent();
intent.putExtra(EXTRA_DEVICE_ADDRESS, address);
// Set result and finish this Activity
setResult(Activity.RESULT_OK, intent);
finish();
}
};
private final BroadcastReceiver mReceiver = new BroadcastReceiver() {
@Override
public void onReceive(Context context, Intent intent) {
String action = intent.getAction();
// When discovery finds a device
if (BluetoothDevice.ACTION_FOUND.equals(action)) {
// Get the BluetoothDevice object from the Intent
BluetoothDevice device = intent.getParcelableExtra(BluetoothDevice.EXTRA_DEVICE);
// If it's already paired, skip it, because it's been listed already
if (device.getBondState() != BluetoothDevice.BOND_BONDED) {
mNewDevicesArrayAdapter.add(device.getName() + "\n" + device.getAddress());
}
// When discovery is finished, change the Activity title
} else if (BluetoothAdapter.ACTION_DISCOVERY_FINISHED.equals(action)) {
setProgressBarIndeterminateVisibility(false);
setTitle(R.string.select_device);
if (mNewDevicesArrayAdapter.getCount() == 0) {
String noDevices = getResources().getText(R.string.none_found).toString();
mNewDevicesArrayAdapter.add(noDevices);
}
}
}
};
private void checkBTState() {
// Check device has Bluetooth and that it is turned on
BA=BluetoothAdapter.getDefaultAdapter();
if(BA==null) {
Toast.makeText(getBaseContext(), "Device does not support Bluetooth", Toast.LENGTH_SHORT).show();
} else {
if (BA.isEnabled()) {
Log.d(TAG, "...Bluetooth ON...");
} else {
//Prompt user to turn on Bluetooth
Intent enableBtIntent = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE);
startActivityForResult(enableBtIntent, 1);
}
}
}
}
Logcat：
com.example.mihaianca.helloword, PID: 13051
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.mihaianca.helloword/com.example.mihaianca.helloword.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'boolean android.bluetooth.BluetoothAdapter.isEnabled()' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2416)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
at android.app.ActivityThread.-wrap11(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'boolean android.bluetooth.BluetoothAdapter.isEnabled()' on a null object reference
at com.example.mihaianca.helloword.MainActivity.onCreate(MainActivity.java:113)
at android.app.Activity.performCreate(Activity.java:6237)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1107)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2369)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
at android.app.ActivityThread.-wrap11(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
I/Process: Sending signal. PID: 13051 SIG: 9
谢谢！
答案 0 :(得分：0)
您可以尝试使用这样的蓝牙适配器：
BluetoothManager bluetoothManager = (BluetoothManager) context.getSystemService(Context.BLUETOOTH_SERVICE);
BluetoothAdapter bluetoothAdapter = bluetoothManager.getAdapter();
我正在以这种方式使用它并且它工作正常。