尝试写入特征时出现Android BLE NullPointerException

我是Android应用程序开发的新手，这是我第一次尝试让Android设备与BLE设备（将与微控制器通信）通信。目标是发送一个值，在本例中，字符串“绿色”或“蓝色”转换为字节，以通知微控制器打开LED

由于我对蓝牙不太精通，我一直在网上寻找各种来源，以帮助整合一些代码。现在，当我连接到设备并试图发送信号时，我得到以下错误代码：

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（字节[]）”在com.example.andres.battle_bots.DeviceControlActivity.access$800（DeviceControlActivity.java:52）在com.example.andres.battle_bots.DeviceControlActivity$3.onClick（DeviceControlActivity.java:151）

我不太确定我遗漏了什么，因为我在使用之前实例化了我正在使用的变量，并且仍然抛出异常。有可能我误解了我正在修改的代码。到目前为止，我有两个活动，DeviceScanActivity，它扫描设备和连接，DeviceControlActivity，它是发生设备内交互并发生错误。以下是代码：

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");
    }
}
}

导入android.app.Activity；
导入android.bluetooth.BluetoothGattCharacteristic；
导入android.bluetooth.BluetoothGattService；
导入android.content.BroadcastReceiver；
导入android.content.ComponentName；
导入android.content.Context；
导入android.content.Intent；
导入android.content.IntentFilter；
导入android.content.ServiceConnection；
导入android.os.Bundle；
导入android.os.IBinder；
导入android.util.Log；
导入android.view.Menu；
导入android.view.MenuItem；
导入android.view.view；
导入android.widget.ExpandableListView；
导入android.widget.ImageButton；
导入android.widget.SeekBar；
导入android.widget.SimpleExpandableListAdapter；
导入android.widget.TextView；
导入java.util.ArrayList；
导入java.util.HashMap；
导入java.util.List；
导入java.util.UUID；
公共类设备ControlActivity扩展活动{
私有最终静态字符串标记=DeviceControlActivity.class.getSimpleName（）；
公共静态最终字符串EXTRAS\u DEVICE\u NAME=“DEVICE\u NAME”；
公共静态最终字符串EXTRAS\u DEVICE\u ADDRESS=“DEVICE\u ADDRESS”；
私有int[]RGBFrame={0,0,0}；
私有文本视图是串行的；
私有文本视图mConnectionState；
私有文本视图mDataField；
私有字符串mDeviceName；
私有字符串mDeviceAddress；
//私有可扩展列表视图mGattServicesList；
私人蓝牙服务mBluetoothLeService；
私有布尔值mConnected=false；
私人蓝牙GATT特征特征TX；
私人蓝牙GATT特征特征Rx；
公共最终静态UUID HM_RX_TX=
UUID.fromString（samplegattatattributes.HM_RX_TX）；
私有最终字符串列表\u NAME=“NAME”；
私有最终字符串列表\u UUID=“UUID”；
//用于管理服务生命周期的代码。
专用最终ServiceConnection mServiceConnection=新ServiceConnection（）{
@凌驾
服务连接上的公共无效（组件名称组件名称，IBinder服务）{
mBluetoothLeService=（（BluetoothLeService.LocalBinder）服务）.getService（）；
如果（！mBluetoothLeService.initialize（））{
Log.e（标记“无法初始化蓝牙”）；
完成（）；
}
//成功启动初始化后自动连接到设备。
mBluetoothLeService.connect（mDeviceAddress）；
}
@凌驾
ServiceDisconnected上的公共无效（ComponentName ComponentName）{
mBluetoothLeService=null；
}
};
//处理服务触发的各种事件。
//操作\u GATT\u已连接：连接到GATT服务器。
//操作\u GATT\u断开连接：从GATT服务器断开连接。
//行动\u GATT\u服务\u发现：发现的GATT服务。
//操作\u数据\u可用：从设备接收数据。这可能是读取的结果
//或通知操作。
private final BroadcastReceiver mGattUpdateReceiver=新的BroadcastReceiver（）{
@凌驾
公共void onReceive（上下文、意图）{
最后一个字符串action=intent.getAction（）；
if（蓝牙服务动作\关贸总协定\连接的相等动作）{
mConnected=true；
updateConnectionState（R.string.connected）；
无效操作菜单（）；
}else if（蓝牙服务操作\u GATT\u断开连接。等于（操作））{
mConnected=false；
updateConnectionState（R.string.disconnected）；
无效操作菜单（）；
clearUI（）；
}else if（BluetoothLeService.ACTION\u GATT\u SERVICES\u DISCOVERED.equals（ACTION））{
//在用户界面上显示所有支持的服务和特性。
displayGattServices（mBluetoothLeService.getSupportedGattServices（））；
}else if（BluetoothLeService.ACTION\u DATA\u AVAILABLE.equals（ACTION））{
显示数据（intent.getStringExtra（mBluetoothLeService.EXTRA_数据））；
}
}
};
私有void clearUI（）{
//mDataField.setText（R.string.no_数据）；
}
@凌驾
创建时的公共void（Bundle savedInstanceState）{
super.onCreate（savedInstanceState）；
setContentView（R.layout.activity_main）；
最终意图=getIntent（）；
mDeviceName=intent.getStringExtra（附加设备名称）；
mDeviceAddress=intent.getStringExtra（附加设备地址）；
getActionBar（）.setTitle(