Java 蓝牙发现期间应用程序崩溃

我想做的事

我正在尝试创建一个应用程序，搜索附近的所有蓝牙设备，并连接到用户希望连接的设备

我正在尝试在一个活动中创建一个连接按钮，以启动另一个活动中的查找功能

我是如何做到这一点的

因此，我有一个MainActivity.java类/活动，它有连接按钮。单击此按钮后，它应执行三项操作：

检查我的智能手机上的蓝牙是否已打开&如果未打开，请将其打开

显示TOAST消息以显示BT是否已成功打开

启动名为SearchBTDevice.java的新活动，查找附近的BT设备并在

列表视图中列出它们

前两个按钮在MainActivity.java上运行良好&我的按钮就是在这里创建的

当它创建新活动并尝试执行第三个活动时，问题就出现了。应用程序崩溃了

这就是我的MainActivity.java的样子

package vertex2016.mvjce.edu.bluealert;

import android.bluetooth.BluetoothAdapter;
import android.content.Intent;
import android.os.Bundle;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.Snackbar;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.Gravity;
import android.view.View;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.Toast;

import static java.lang.Thread.sleep;

public class MainActivity extends AppCompatActivity {

    public BluetoothAdapter BA = BluetoothAdapter.getDefaultAdapter();
    private int REQ_CODE = 1;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);

    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.menu_main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }

    public void connect(View v)
    {
        if(BA == null)
            Toast.makeText(MainActivity.this, "System Doesn't Support Bluetooth", Toast.LENGTH_SHORT).show();

        else if(!BA.isEnabled())
        {
            Intent enableBT = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE);
            startActivityForResult(enableBT, REQ_CODE);
        }
        else {
            Toast.makeText(MainActivity.this, "ALREADY ON!!", Toast.LENGTH_SHORT).show();
            searchBTDevices();
        }
    }


    @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data) {
        super.onActivityResult(requestCode, resultCode, data);
        if(resultCode!=RESULT_CANCELED) {
            Toast.makeText(MainActivity.this, "TURNED ON!", Toast.LENGTH_SHORT).show();
            searchBTDevices();
        }
        else
            Toast.makeText(MainActivity.this,"FAILED TO ENABLE BLUETOOTH", Toast.LENGTH_LONG).show();
    }




    public void searchBTDevices()
    {
        Thread searchThread = new Thread() {
            @Override
            public void run() {
                Intent searchBT = new Intent(getApplicationContext(), SearchBTDevice.class);
                startActivity(searchBT);
            }
        };
        searchThread.start();
    }
}

这就是我的SearchBTDevice.java的样子

package vertex2016.mvjce.edu.bluealert;

import android.bluetooth.BluetoothDevice;
import android.bluetooth.BluetoothGattDescriptor;
import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.content.IntentFilter;
import android.os.Bundle;
import android.bluetooth.BluetoothAdapter;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.Snackbar;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.util.AttributeSet;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.ListView;

import java.util.Set;

public class SearchBTDevice extends AppCompatActivity {

    public BluetoothAdapter BlueAdapter = BluetoothAdapter.getDefaultAdapter();
    public ArrayAdapter PairedArrayAdapter, BTArrayAdapter;
    public IntentFilter filter = new IntentFilter();
    public ListView devicesFound;
    public Set<BluetoothDevice> pairedDevices;


    private final BroadcastReceiver BTReceiver = new BroadcastReceiver() {
        @Override
        public void onReceive(Context context, Intent intent) {
            String action = intent.getAction();
            if(BluetoothDevice.ACTION_FOUND.equals(action)) {
                BluetoothDevice btd = intent.getParcelableExtra(BluetoothDevice.EXTRA_DEVICE);
                BTArrayAdapter.add(btd.getName() + "\t\t" + btd.getAddress() + "\n");
                PairedArrayAdapter.add(btd.getName() + "\t\t" + btd.getAddress() + "\n");
            }
        }
    };





    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_search_btdevice);
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);
        getSupportActionBar().setDisplayHomeAsUpEnabled(true);

        if(!BTArrayAdapter.isEmpty())
            BTArrayAdapter.clear();

        searchBTDevices();

    }


    public void searchBTDevices()
    {
        pairedDevices = BlueAdapter.getBondedDevices();

        if(pairedDevices.size()>0)
            for(BluetoothDevice device: pairedDevices)
                PairedArrayAdapter.add(device.getName() + "\t\t" + device.getAddress() + "\n");


        filter.addAction(BluetoothDevice.ACTION_FOUND);
        filter.addAction(BluetoothAdapter.ACTION_DISCOVERY_STARTED);
        filter.addAction(BluetoothAdapter.ACTION_DISCOVERY_FINISHED);

        final BroadcastReceiver BTReceiver = new BroadcastReceiver() {
            @Override
            public void onReceive(Context context, Intent intent) {
                String action = intent.getAction();
                if(BluetoothDevice.ACTION_FOUND.equals(action)) {
                    BluetoothDevice btd = intent.getParcelableExtra(BluetoothDevice.EXTRA_DEVICE);
                    BTArrayAdapter.add(btd.getName() + "\t\t" + btd.getAddress() + "\n");
                    PairedArrayAdapter.add(btd.getName() + "\t\t" + btd.getAddress() + "\n");
                }
            }
        };

        BlueAdapter.startDiscovery();

        devicesFound = (ListView)findViewById(R.id.searchpagelistView);
        devicesFound.setAdapter(BTArrayAdapter);

    }


}

以下是我的问题：

• 我哪里做错了&我该怎么办
• 是否有任何方法可以检索

  BluetoothAdapter

  ，该适配器是在名为

  SearchBTDevice.java

  的新活动中在我的

  MainActivity.java

  中创建的
• 我是否可以从另一个活动中设置一个活动中定义的按钮的onClick操作

---

谢谢你抽出时间

在SearchBTDevice类中定义BTArrayAdapter对象。在onCreate（）中调用BTArrayAdapter.isEmpty（）时，该值为null

03-17 11:51:40.120 19178-19178/vertex2016.mvjce.edu.bluealert E/AndroidRuntime: FATAL EXCEPTION: main
                                                                                Process: vertex2016.mvjce.edu.bluealert, PID: 19178
                                                                                java.lang.RuntimeException: Unable to start activity ComponentInfo{vertex2016.mvjce.edu.bluealert/vertex2016.mvjce.edu.bluealert.SearchBTDevice}: java.lang.NullPointerException: Attempt to invoke virtual method 'boolean android.widget.ArrayAdapter.isEmpty()' on a null object reference
                                                                                    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2358)
                                                                                    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2420)
                                                                                    at android.app.ActivityThread.access$900(ActivityThread.java:154)
                                                                                    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1321)
                                                                                    at android.os.Handler.dispatchMessage(Handler.java:102)
                                                                                    at android.os.Looper.loop(Looper.java:135)
                                                                                    at android.app.ActivityThread.main(ActivityThread.java:5292)
                                                                                    at java.lang.reflect.Method.invoke(Native Method)
                                                                                    at java.lang.reflect.Method.invoke(Method.java:372)
                                                                                    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:904)
                                                                                    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:699)
                                                                                 Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'boolean android.widget.ArrayAdapter.isEmpty()' on a null object reference
                                                                                    at vertex2016.mvjce.edu.bluealert.SearchBTDevice.onCreate(SearchBTDevice.java:57)
                                                                                    at android.app.Activity.performCreate(Activity.java:5990)
                                                                                    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1106)
                                                                                    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2311)
                                                                                    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2420) 
                                                                                    at android.app.ActivityThread.access$900(ActivityThread.java:154) 
                                                                                    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1321) 
                                                                                    at android.os.Handler.dispatchMessage(Handler.java:102) 
                                                                                    at android.os.Looper.loop(Looper.java:135) 
                                                                                    at android.app.ActivityThread.main(ActivityThread.java:5292) 
                                                                                    at java.lang.reflect.Method.invoke(Native Method) 
                                                                                    at java.lang.reflect.Method.invoke(Method.java:372) 
                                                                                    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:904) 
                                                                                    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:699)