Question

我正在尝试创建一个激活和停用蓝牙的应用程序，找到配对的蓝牙设备并扫描发现的蓝牙设备。我将权限添加到AndroidManifest.xml。一切似乎都没问题。但是，当我在设备上调试应用程序（Samsung Galaxy tab 3 Lite）时，我得到NullPointerException并且应用程序崩溃了。你知道可能导致问题的原因吗？请在下面找到我的代码和异常堆栈跟踪。

package dyankov.mylibraryrecommender.MainActivities.GUI;

import android.app.Activity;
import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import dyankov.mylibraryrecommender.R;
import android.os.Bundle;
import android.app.Activity;
import android.bluetooth.BluetoothAdapter;
import android.bluetooth.BluetoothDevice;
import android.content.BroadcastReceiver;
import android.content.Context;
import java.util.Set;
import android.content.Intent;
import android.content.IntentFilter;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.ListView;
import android.widget.TextView;
import android.widget.Toast;

public class AroundMeActivity extends Activity {

private static final int REQUEST_ENABLE_BT = 1;
private Button turnOn;
private Button offBtn;
private Button listBtn;
private Button findBtn;
private TextView text;
private BluetoothAdapter myBluetoothAdapter;
private Set<BluetoothDevice> pairedDevices;
private ListView myListView;
private ArrayAdapter<String> BTArrayAdapter;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    // take an instance of BluetoothAdapter - Bluetooth radio
    myBluetoothAdapter = BluetoothAdapter.getDefaultAdapter();
    if(myBluetoothAdapter == null) {
        turnOn.setEnabled(false);
        offBtn.setEnabled(false);
        listBtn.setEnabled(false);
        findBtn.setEnabled(false);
        text.setText("Status: not supported");

        Toast.makeText(getApplicationContext(),"Your device does not support Bluetooth",

                Toast.LENGTH_LONG).show();

    } else {
        text = (TextView) findViewById(R.id.text);
        turnOn = (Button)findViewById(R.id.turnOn);
        turnOn.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View v) {
                // TODO Auto-generated method stub
                on(v);
            }
        });

        offBtn = (Button)findViewById(R.id.turnOff);
        offBtn.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View v) {
                // TODO Auto-generated method stub
                off(v);
            }
        });
        listBtn = (Button)findViewById(R.id.paired);
        listBtn.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View v) {
                // TODO Auto-generated method stub
                list(v);

            }
        });

        findBtn = (Button)findViewById(R.id.search);
        findBtn.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View v) {
                // TODO Auto-generated method stub
                find(v);
            }
        });

        myListView = (ListView)findViewById(R.id.listView1);

        // create the arrayAdapter that contains the BTDevices, and set it to the ListView
        BTArrayAdapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1);
        myListView.setAdapter(BTArrayAdapter);
    }
}

public void on(View view){
    if (!myBluetoothAdapter.isEnabled()) {
        Intent turnOnIntent = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE);
        startActivityForResult(turnOnIntent, REQUEST_ENABLE_BT);

        Toast.makeText(getApplicationContext(),"Bluetooth turned on" ,
                Toast.LENGTH_LONG).show();
    }
    else{
        Toast.makeText(getApplicationContext(),"Bluetooth is already on",
                Toast.LENGTH_LONG).show();
    }
}

@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
    // TODO Auto-generated method stub
    if(requestCode == REQUEST_ENABLE_BT){
        if(myBluetoothAdapter.isEnabled()) {
            text.setText("Status: Enabled");
        } else {
            text.setText("Status: Disabled");
        }
    }
}

public void list(View view){
    // get paired devices
    pairedDevices = myBluetoothAdapter.getBondedDevices();

    // put it's one to the adapter
    for(BluetoothDevice device : pairedDevices)
        BTArrayAdapter.add(device.getName()+ "\n" + device.getAddress());

    Toast.makeText(getApplicationContext(),"Show Paired Devices",
            Toast.LENGTH_SHORT).show();
}

final BroadcastReceiver bReceiver = new BroadcastReceiver() {
    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);
            // add the name and the MAC address of the object to the arrayAdapter
            BTArrayAdapter.add(device.getName() + "\n" + device.getAddress());
            BTArrayAdapter.notifyDataSetChanged();
        }
    }
};

public void find(View view) {
    if (myBluetoothAdapter.isDiscovering()) {
        // the button is pressed when it discovers, so cancel the discovery
        myBluetoothAdapter.cancelDiscovery();
    }
    else {
        BTArrayAdapter.clear();
        myBluetoothAdapter.startDiscovery();

        registerReceiver(bReceiver, new IntentFilter(BluetoothDevice.ACTION_FOUND));
    }
}

public void off(View view){
    myBluetoothAdapter.disable();
    text.setText("Status: Disconnected");

    Toast.makeText(getApplicationContext(),"Bluetooth turned off",
            Toast.LENGTH_LONG).show();
}

@Override
protected void onDestroy() {
    // TODO Auto-generated method stub
    super.onDestroy();
    unregisterReceiver(bReceiver);
}
}

这是我的Logcat文件：

Caused by: java.lang.NullPointerException
        at dyankov.mylibraryrecommender.MainActivities.GUI.AroundMeActivity.onCreate(AroundMeActivity.java:60)
        at android.app.Activity.performCreate(Activity.java:5326)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1097)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2225)

第60行的代码是：

turnOn.setOnClickListener(new OnClickListener() { ... }

Answer 1

在为其设置值之前尝试使用按钮。

试试这段代码：

text = (TextView) findViewById(R.id.text);
turnOn = (Button)findViewById(R.id.turnOn);
if(myBluetoothAdapter == null) {
turnOn.setEnabled(false);
offBtn.setEnabled(false);
listBtn.setEnabled(false);
findBtn.setEnabled(false);
text.setText("Status: not supported");
Toast.makeText(getApplicationContext(),"Your device does not support Bluetooth",
Toast.LENGTH_LONG).show();
} else {

turnOn.setOnClickListener(new OnClickListener() {

当我尝试测试实现的蓝牙功能时NullPointerException

1 个答案: