我正在搜索Google，并在stackoverflow中找到了一个代码。我开始使用它，但行list.setAdapter(aa);正在生成NullPointerException。我该如何解决？这是我的MainActivity.java：
public class MainActivity extends Activity {
private static int DISCOVERY_REQUEST = 1;
private Handler handler = new Handler();
private ArrayList<BluetoothDevice> foundDevices;
private ArrayAdapter<BluetoothDevice> aa;
private ListView list;
private BluetoothAdapter bluetooth;
private BluetoothSocket socket;
private UUID uuid = UUID.fromString("a60f35f0-b93a-11de-8a39-08002009c666");
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
configureBluetooth();
setupListView();
setupSearchButton();
setupListenButton();
}
private void configureBluetooth() {
bluetooth = BluetoothAdapter.getDefaultAdapter();
}
private void setupListenButton() {
Button listenButton = (Button) findViewById(R.id.button_listen);
listenButton.setOnClickListener(new OnClickListener() {
public void onClick(View view) {
Intent disc = new Intent(
BluetoothAdapter.ACTION_REQUEST_DISCOVERABLE);
startActivityForResult(disc, DISCOVERY_REQUEST);
}
});
}
@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
if (requestCode == DISCOVERY_REQUEST) {
boolean isDiscoverable = resultCode > 0;
if (isDiscoverable) {
String name = "bluetoothserver";
try {
final BluetoothServerSocket btserver = bluetooth
.listenUsingRfcommWithServiceRecord(name, uuid);
AsyncTask<Integer, Void, BluetoothSocket> acceptThread = new AsyncTask<Integer, Void, BluetoothSocket>() {
@Override
protected BluetoothSocket doInBackground(
Integer... params) {
try {
socket = btserver.accept(params[0] * 1000);
return socket;
} catch (IOException e) {
Log.d("BLUETOOTH", e.getMessage());
}
return null;
}
@Override
protected void onPostExecute(BluetoothSocket result) {
if (result != null)
switchUI();
}
};
acceptThread.execute(resultCode);
} catch (IOException e) {
Log.d("BLUETOOTH", e.getMessage());
}
}
}
}
private void setupListView() {
aa = new ArrayAdapter<BluetoothDevice>(this,
android.R.layout.simple_list_item_1, foundDevices);
list = (ListView) findViewById(R.id.list_discovered);
list.setAdapter(aa); //the error comes from this line
list.setOnItemClickListener(new OnItemClickListener() {
public void onItemClick(AdapterView<?> arg0, View view, int index,
long arg3) {
AsyncTask<Integer, Void, Void> connectTask = new AsyncTask<Integer, Void, Void>() {
@Override
protected Void doInBackground(Integer... params) {
try {
BluetoothDevice device = foundDevices
.get(params[0]);
socket = device
.createRfcommSocketToServiceRecord(uuid);
socket.connect();
} catch (IOException e) {
Log.d("BLUETOOTH_CLIENT", e.getMessage());
}
return null;
}
@Override
protected void onPostExecute(Void result) {
switchUI();
}
};
connectTask.execute(index);
}
});
}
private void setupSearchButton() {
Button searchButton = (Button) findViewById(R.id.button_search);
searchButton.setOnClickListener(new OnClickListener() {
public void onClick(View view) {
registerReceiver(discoveryResult, new IntentFilter(
BluetoothDevice.ACTION_FOUND));
if (!bluetooth.isDiscovering()) {
foundDevices.clear();
bluetooth.startDiscovery();
}
}
});
}
private void switchUI() {
final TextView messageText = (TextView) findViewById(R.id.text_messages);
final EditText textEntry = (EditText) findViewById(R.id.text_message);
messageText.setVisibility(View.VISIBLE);
list.setVisibility(View.GONE);
textEntry.setEnabled(true);
textEntry.setOnKeyListener(new OnKeyListener() {
public boolean onKey(View view, int keyCode, KeyEvent keyEvent) {
if ((keyEvent.getAction() == KeyEvent.ACTION_DOWN)
&& (keyCode == KeyEvent.KEYCODE_DPAD_CENTER)) {
sendMessage(socket, textEntry.getText().toString());
textEntry.setText("");
return true;
}
return false;
}
});
BluetoothSocketListener bsl = new BluetoothSocketListener(socket,
handler, messageText);
Thread messageListener = new Thread(bsl);
messageListener.start();
}
private void sendMessage(BluetoothSocket socket, String msg) {
OutputStream outStream;
try {
outStream = socket.getOutputStream();
byte[] byteString = (msg + " ").getBytes();
byteString[byteString.length - 1] = 0;
outStream.write(byteString);
} catch (IOException e) {
Log.d("BLUETOOTH_COMMS", e.getMessage());
}
}
BroadcastReceiver discoveryResult = new BroadcastReceiver() {
@Override
public void onReceive(Context context, Intent intent) {
BluetoothDevice remoteDevice;
remoteDevice = intent
.getParcelableExtra(BluetoothDevice.EXTRA_DEVICE);
if (bluetooth.getBondedDevices().contains(remoteDevice)) {
foundDevices.add(remoteDevice);
aa.notifyDataSetChanged();
}
}
};
private class MessagePoster implements Runnable {
private TextView textView;
private String message;
public MessagePoster(TextView textView, String message) {
this.textView = textView;
this.message = message;
}
public void run() {
textView.setText(message);
}
}
private class BluetoothSocketListener implements Runnable {
private BluetoothSocket socket;
private TextView textView;
private Handler handler;
public BluetoothSocketListener(BluetoothSocket socket, Handler handler,
TextView textView) {
this.socket = socket;
this.textView = textView;
this.handler = handler;
}
public void run() {
int bufferSize = 1024;
byte[] buffer = new byte[bufferSize];
try {
InputStream instream = socket.getInputStream();
int bytesRead = -1;
String message = "";
while (true) {
message = "";
bytesRead = instream.read(buffer);
if (bytesRead != -1) {
while ((bytesRead == bufferSize)
&& (buffer[bufferSize - 1] != 0)) {
message = message
+ new String(buffer, 0, bytesRead);
bytesRead = instream.read(buffer);
}
message = message
+ new String(buffer, 0, bytesRead - 1);
handler.post(new MessagePoster(textView, message));
socket.getInputStream();
}
}
} catch (IOException e) {
Log.d("BLUETOOTH_COMMS", e.getMessage());
}
}
}
}
错误是：
Caused by: java.lang.NullPointerException
at android.widget.ArrayAdapter.getCount(ArrayAdapter.java:330)
at android.widget.ListView.setAdapter(ListView.java:464)
at com.example.testbluetooth.MainActivity.setupListView(MainActivity.java:113)
这是我的activity_main.xml：
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical" >
<EditText
android:id="@+id/text_message"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_alignParentBottom="true"
android:enabled="false" />
<Button
android:id="@+id/button_search"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_above="@id/text_message"
android:text="Search for listener" />
<Button
android:id="@+id/button_listen"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_above="@id/button_search"
android:text="Listen for connection" />
<ListView
android:id="@+id/list_discovered"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:layout_above="@id/button_listen"
android:layout_alignParentTop="true" />
<TextView
android:id="@+id/text_messages"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:layout_above="@id/button_listen"
android:layout_alignParentTop="true"
android:visibility="gone" />
</RelativeLayout>
答案 0 :(得分：0)
您有空列表，在设置列表之前设置数组列表。
尝试删除
来自setupListView() 的 onCreate()
并在创建设备列表后将其放置到位。
你可以尝试这样做：
private ArrayList<BluetoothDevice> foundDevices = new ArrayList<BluetoothDevice>(); foundDevices.add(remoteDevice); aa.addAll(foundDevices)然后致电aa.notifyDataSetChanged(); 参考文献： ArrayAdapter.AddAll()