我是Android应用程序开发的新手，这是我第一次尝试使Android设备与BLE设备（将与微控制器通话）对话。目的是发送一个值，在这种情况下，将字符串“绿色”或“蓝色”转换为字节，以告诉微控制器打开LED。
由于我不熟悉蓝牙技术，因此我一直在网上寻找各种资源来帮助编写一些代码。现在，当我到达已连接到设备的位置并尝试发送信号时，出现以下错误代码：
java.lang.NullPointerException：尝试在com.example.andres.battle_bots.DeviceControlActivity.makeChange（DeviceControlActivity.java:366）上的空对象引用上调用虚拟方法'boolean android.bluetooth.BluetoothGattCharacteristic.setValue（byte []）'在com.example.andres.battle_bots.DeviceControlActivity.access $ 800（DeviceControlActivity.java:52）处com.example.andres.battle_bots.DeviceControlActivity $ 3.onClick（DeviceControlActivity.java:151）
我不太确定自己缺少什么，因为我在使用它们之前实例化了我正在使用的变量，并且仍然引发异常。我可能会误解我要修改的代码。到目前为止，我有2个活动，即DeviceScanActivity（用于扫描设备和连接）以及DeviceControlActivity（用于进行主要设备交互并发生错误）。这是代码：
import android.app.Activity;
import android.bluetooth.BluetoothGattCharacteristic;
import android.bluetooth.BluetoothGattService;
import android.content.BroadcastReceiver;
import android.content.ComponentName;
import android.content.Context;
import android.content.Intent;
import android.content.IntentFilter;
import android.content.ServiceConnection;
import android.os.Bundle;
import android.os.IBinder;
import android.util.Log;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.ExpandableListView;
import android.widget.ImageButton;
import android.widget.SeekBar;
import android.widget.SimpleExpandableListAdapter;
import android.widget.TextView;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.UUID;
public class DeviceControlActivity extends Activity {
private final static String TAG = DeviceControlActivity.class.getSimpleName();
public static final String EXTRAS_DEVICE_NAME = "DEVICE_NAME";
public static final String EXTRAS_DEVICE_ADDRESS = "DEVICE_ADDRESS";
private int[] RGBFrame = {0, 0, 0};
private TextView isSerial;
private TextView mConnectionState;
private TextView mDataField;
private String mDeviceName;
private String mDeviceAddress;
// private ExpandableListView mGattServicesList;
private BluetoothLeService mBluetoothLeService;
private boolean mConnected = false;
private BluetoothGattCharacteristic characteristicTX;
private BluetoothGattCharacteristic characteristicRX;
public final static UUID HM_RX_TX =
UUID.fromString(SampleGattAttributes.HM_RX_TX);
private final String LIST_NAME = "NAME";
private final String LIST_UUID = "UUID";
// Code to manage Service lifecycle.
private final ServiceConnection mServiceConnection = new ServiceConnection() {
@Override
public void onServiceConnected(ComponentName componentName, IBinder service) {
mBluetoothLeService = ((BluetoothLeService.LocalBinder) service).getService();
if (!mBluetoothLeService.initialize()) {
Log.e(TAG, "Unable to initialize Bluetooth");
finish();
}
// Automatically connects to the device upon successful start-up initialization.
mBluetoothLeService.connect(mDeviceAddress);
}
@Override
public void onServiceDisconnected(ComponentName componentName) {
mBluetoothLeService = null;
}
};
// Handles various events fired by the Service.
// ACTION_GATT_CONNECTED: connected to a GATT server.
// ACTION_GATT_DISCONNECTED: disconnected from a GATT server.
// ACTION_GATT_SERVICES_DISCOVERED: discovered GATT services.
// ACTION_DATA_AVAILABLE: received data from the device. This can be a result of read
// or notification operations.
private final BroadcastReceiver mGattUpdateReceiver = new BroadcastReceiver() {
@Override
public void onReceive(Context context, Intent intent) {
final String action = intent.getAction();
if (BluetoothLeService.ACTION_GATT_CONNECTED.equals(action)) {
mConnected = true;
updateConnectionState(R.string.connected);
invalidateOptionsMenu();
} else if (BluetoothLeService.ACTION_GATT_DISCONNECTED.equals(action)) {
mConnected = false;
updateConnectionState(R.string.disconnected);
invalidateOptionsMenu();
clearUI();
} else if (BluetoothLeService.ACTION_GATT_SERVICES_DISCOVERED.equals(action)) {
// Show all the supported services and characteristics on the user interface.
displayGattServices(mBluetoothLeService.getSupportedGattServices());
} else if (BluetoothLeService.ACTION_DATA_AVAILABLE.equals(action)) {
displayData(intent.getStringExtra(mBluetoothLeService.EXTRA_DATA));
}
}
};
private void clearUI() {
// mDataField.setText(R.string.no_data);
}
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
final Intent intent = getIntent();
mDeviceName = intent.getStringExtra(EXTRAS_DEVICE_NAME);
mDeviceAddress = intent.getStringExtra(EXTRAS_DEVICE_ADDRESS);
getActionBar().setTitle(mDeviceName);
getActionBar().setDisplayHomeAsUpEnabled(true);
Intent gattServiceIntent = new Intent(this, BluetoothLeService.class);
bindService(gattServiceIntent, mServiceConnection, BIND_AUTO_CREATE);
ImageButton U1 = (ImageButton) findViewById(R.id.up_btn1);
U1.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
//Do something with Bluetooth
if(mBluetoothLeService != null) {
String codeGreen = "green";
makeChange(codeGreen);
}
}
});
ImageButton R1 = (ImageButton) findViewById(R.id.right_btn1);
R1.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
//Do something with Bluetooth
}
});
ImageButton D1 = (ImageButton) findViewById(R.id.down_btn1);
D1.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
//Do something with Bluetooth
}
});
ImageButton L1 = (ImageButton) findViewById(R.id.left_btn1);
L1.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
//Do something with Bluetooth
}
});
ImageButton U2 = (ImageButton) findViewById(R.id.up_btn2);
U2.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
if(mBluetoothLeService != null) {
String codeBlue = "blue";
makeChange(codeBlue);
}
}
});
ImageButton R2 = (ImageButton) findViewById(R.id.right_btn2);
R2.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
//Do something with Bluetooth
}
});
ImageButton D2 = (ImageButton) findViewById(R.id.down_btn2);
D2.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
//Do something with Bluetooth
}
});
ImageButton L2 = (ImageButton) findViewById(R.id.left_btn2);
L2.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
//Do something with Bluetooth
}
});
ImageButton BLE = (ImageButton) findViewById(R.id.ble_btn);
BLE.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
//Do something with Bluetooth
Intent intent = new Intent(DeviceControlActivity.this, com.example.andres.battle_bots.DeviceScanActivity.class);
startActivity(intent);
}
});
ImageButton Options = (ImageButton) findViewById(R.id.options_btn);
Options.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
//Do something with Bluetooth
}
});
// Sets up UI references.
// ((TextView) findViewById(R.id.device_address)).setText(mDeviceAddress);
// mConnectionState = (TextView) findViewById(R.id.connection_state);
// is serial present?
// isSerial = (TextView) findViewById(R.id.isSerial);
/*
mDataField = (TextView) findViewById(R.id.data_value);
mRed = (SeekBar) findViewById(R.id.seekRed);
mGreen = (SeekBar) findViewById(R.id.seekGreen);
mBlue = (SeekBar) findViewById(R.id.seekBlue);
readSeek(mRed, 0);
readSeek(mGreen, 1);
readSeek(mBlue, 2);
*/
}
@Override
protected void onResume() {
super.onResume();
registerReceiver(mGattUpdateReceiver, makeGattUpdateIntentFilter());
if (mBluetoothLeService != null) {
final boolean result = mBluetoothLeService.connect(mDeviceAddress);
Log.d(TAG, "Connect request result=" + result);
}
}
@Override
protected void onPause() {
super.onPause();
unregisterReceiver(mGattUpdateReceiver);
}
@Override
protected void onDestroy() {
super.onDestroy();
unbindService(mServiceConnection);
mBluetoothLeService = null;
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
getMenuInflater().inflate(R.menu.gatt_services, menu);
if (mConnected) {
menu.findItem(R.id.menu_connect).setVisible(false);
menu.findItem(R.id.menu_disconnect).setVisible(true);
} else {
menu.findItem(R.id.menu_connect).setVisible(true);
menu.findItem(R.id.menu_disconnect).setVisible(false);
}
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
switch (item.getItemId()) {
case R.id.menu_connect:
mBluetoothLeService.connect(mDeviceAddress);
return true;
case R.id.menu_disconnect:
mBluetoothLeService.disconnect();
return true;
case android.R.id.home:
onBackPressed();
return true;
}
return super.onOptionsItemSelected(item);
}
private void updateConnectionState(final int resourceId) {
runOnUiThread(new Runnable() {
@Override
public void run() {
// mConnectionState.setText(resourceId);
}
});
}
private void displayData(String data) {
if (data != null) {
mDataField.setText(data);
}
}
// Demonstrates how to iterate through the supported GATT Services/Characteristics.
// In this sample, we populate the data structure that is bound to the ExpandableListView
// on the UI.
private void displayGattServices(List<BluetoothGattService> gattServices) {
if (gattServices == null) return;
String uuid = null;
String unknownServiceString = getResources().getString(R.string.unknown_service);
ArrayList<HashMap<String, String>> gattServiceData = new ArrayList<HashMap<String, String>>();
// Loops through available GATT Services.
for (BluetoothGattService gattService : gattServices) {
HashMap<String, String> currentServiceData = new HashMap<String, String>();
uuid = gattService.getUuid().toString();
currentServiceData.put(
LIST_NAME, SampleGattAttributes.lookup(uuid, unknownServiceString));
// If the service exists for HM 10 Serial, say so.
if (SampleGattAttributes.lookup(uuid, unknownServiceString) == "HM 10 Serial") {
// isSerial.setText("Yes, serial :-)");
} else {
// isSerial.setText("No, serial :-(");
}
currentServiceData.put(LIST_UUID, uuid);
gattServiceData.add(currentServiceData);
// get characteristic when UUID matches RX/TX UUID
characteristicTX = gattService.getCharacteristic(BluetoothLeService.UUID_HM_RX_TX);
characteristicRX = gattService.getCharacteristic(BluetoothLeService.UUID_HM_RX_TX);
}
}
private static IntentFilter makeGattUpdateIntentFilter() {
final IntentFilter intentFilter = new IntentFilter();
intentFilter.addAction(BluetoothLeService.ACTION_GATT_CONNECTED);
intentFilter.addAction(BluetoothLeService.ACTION_GATT_DISCONNECTED);
intentFilter.addAction(BluetoothLeService.ACTION_GATT_SERVICES_DISCOVERED);
intentFilter.addAction(BluetoothLeService.ACTION_DATA_AVAILABLE);
return intentFilter;
}
// on change of bars write char
private void makeChange(String str) {
Log.d(TAG, "Sending result=" + str);
final byte[] tx = str.getBytes();
if (mConnected) {
characteristicTX.setValue(tx);
mBluetoothLeService.writeCharacteristic(characteristicTX);
mBluetoothLeService.setCharacteristicNotification(characteristicRX, true);
Log.d(TAG,"Success");
}
else
{
Log.d(TAG,"Failed");
}
}
}
任何帮助是极大的赞赏。您肯定会让我的生活更轻松，并且可能会帮助其他开始使用Android / Bluetooth开发的人。
谢谢！
最佳答案
事实证明我的特征为空，因为我从该服务收到的UUID不等于我的期望。一旦我编辑了示例代码以期望与我所使用的蓝牙模块相关联的UUID，该代码就可以正常工作。