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我正在處理一個應用程序，它將按下按鈕時通過藍牙發送一個字符串。從onCreate創建類方法的實例
藍牙連接正常工作，我可以發送數據正常，但是我在創建write（）方法的實例時遇到了一些麻煩，我在按鈕的單擊處理程序中，特別是我應該使用的上下文，這是我得到一個空指針異常。
這裏是我的代碼：
package sjtech.rompa.wifi;
public class Wifi extends Activity implements OnItemClickListener {
ArrayAdapter<String> listAdapter;
ListView listView;
BluetoothAdapter btAdapter;
Set<BluetoothDevice> devicesArray;
ArrayList<String> pairedDevices;
ArrayList<BluetoothDevice> devices;
public static final UUID MY_UUID = UUID.fromString("00001101-0000-1000-8000-00805F9B34FB");
protected static final int SUCCESS_CONNECT = 0;
protected static final int MESSAGE_READ = 1;
IntentFilter filter;
BroadcastReceiver receiver;
String tag = "debugging";
private Button currentcolour;
private Button redbtn;
private Button grnbtn;
private Button bluebtn;
private Button yellowbtn;
private Button orangebtn;
private Button purplebtn;
private Button pinkbtn;
private Button whitebtn;
private Button resetbtn;
private Button blueleftarrow;
public BluetoothDevice mBluetoothAdapter;
public String outputStream;
public InputStream inStream;
public ImageView btoff;
MediaPlayer sndred;
MediaPlayer sndgrn;
MediaPlayer sndblue;
MediaPlayer sndyel;
MediaPlayer sndwht;
MediaPlayer sndpnk;
MediaPlayer sndpple;
MediaPlayer sndorng;
MediaPlayer sndrst;
Handler mHandler = new Handler(){
@Override
public void handleMessage(Message msg) {
// TODO Auto-generated method stub
Log.i(tag, "in handler");
super.handleMessage(msg);
switch(msg.what){
case SUCCESS_CONNECT:
// DO something
ConnectedThread connectedThread = new ConnectedThread((BluetoothSocket)msg.obj);
Toast toast= Toast.makeText(getApplicationContext(),
"CONNECT", Toast.LENGTH_SHORT);
toast.setGravity(Gravity.CENTER, 0, 0);
toast.show();
String s = "successfully connected";
connectedThread.write(s.getBytes());
Log.i(tag, "connected");
break;
case MESSAGE_READ:
byte[] readBuf = (byte[])msg.obj;
String string = new String(readBuf);
Toast toast2= Toast.makeText(getApplicationContext(), string, Toast.LENGTH_SHORT);
toast2.setGravity(Gravity.CENTER, 0, 0);
toast2.show();
break;
}
}
};
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
currentcolour= (Button) findViewById(R.id.currentcolour);
init();
if(btAdapter==null){ //if no BT then show toast and close. Toast toast3= Toast.makeText(getApplicationContext(), "No bluetooth detected", Toast.LENGTH_SHORT);
toast3.setGravity(Gravity.CENTER, 0, 0);
toast3.show();
finish();
}
else{
if(!btAdapter.isEnabled()){ //if BT available but not enabled turn on BT.
turnOnBT();
}
getPairedDevices();
startDiscovery();
}
//**********************************************RED BUTTON*********** ***************************************
sndred = MediaPlayer.create(Wifi.this, R.raw.sndred); // create instance of mediaPlayer
redbtn = (Button) findViewById(R.id.redbtn); // Get a reference to the button
redbtn.setOnClickListener(new View.OnClickListener() { // Set the click listener to run the code.
@Override
public void onClick(View v) { // red button's click event
sndred.start(); // play red sound
currentcolour.setBackgroundColor(Color.RED); //set currentColour to red.
ConnectedThread con = new ConnectedThread(null);
con.write("".getBytes()); //Send string via bluetooth.
// con.write(new byte[] {0x30, 0x38,}); //Send byte via bluetooth.
}
});
}
});
}
private void startDiscovery() {
// TODO Auto-generated method stub
btAdapter.cancelDiscovery();
btAdapter.startDiscovery();
}
private void turnOnBT() {
// TODO Auto-generated method stub
Intent intent =new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE);
startActivityForResult(intent, 1);
}
private void getPairedDevices() {
// TODO Auto-generated method stub
devicesArray = btAdapter.getBondedDevices();
if(devicesArray.size()>0){
for(BluetoothDevice device:devicesArray){
pairedDevices.add(device.getName());
}
}
}
private void init() {
// TODO Auto-generated method stub
listView=(ListView)findViewById(R.id.listView);
listView.setOnItemClickListener(this);
listAdapter= new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1,0);
listView.setAdapter(listAdapter);
btAdapter = BluetoothAdapter.getDefaultAdapter();
pairedDevices = new ArrayList<String>();
filter = new IntentFilter(BluetoothDevice.ACTION_FOUND);
devices = new ArrayList<BluetoothDevice>();
receiver = new BroadcastReceiver(){
@Override
public void onReceive(Context context, Intent intent) {
// TODO Auto-generated method stub
String action = intent.getAction();
if(BluetoothDevice.ACTION_FOUND.equals(action)){
BluetoothDevice device = intent.getParcelableExtra(BluetoothDevice.EXTRA_DEVICE);
devices.add(device);
String s = "";
for(int a = 0; a < pairedDevices.size(); a++){
if(device.getName().equals(pairedDevices.get(a))){
//append
s = "(Paired)";
break;
}
}
listAdapter.add(device.getName()+" "+s+" "+"\n"+device.getAddress());
}
else if(BluetoothAdapter.ACTION_DISCOVERY_STARTED.equals(action)){
Toast toast= Toast.makeText(getApplicationContext(), //Show toast that bluetooth is already disabled.
"STARTED DEVICE DISCOVERY", Toast.LENGTH_SHORT);
toast.setGravity(Gravity.CENTER, 0, 0);
toast.show();
}
else if(BluetoothAdapter.ACTION_DISCOVERY_FINISHED.equals(action)){
Toast toast= Toast.makeText(getApplicationContext(), //Show toast that bluetooth is already disabled.
"FINISHED DEVICE DISCOVERY!", Toast.LENGTH_SHORT);
toast.setGravity(Gravity.CENTER, 0, 0);
toast.show();
}
else if(BluetoothAdapter.ACTION_STATE_CHANGED.equals(action)){
if(btAdapter.getState() == btAdapter.STATE_OFF){
turnOnBT();
}
}
}
};
registerReceiver(receiver, filter);
filter = new IntentFilter(BluetoothAdapter.ACTION_DISCOVERY_STARTED);
registerReceiver(receiver, filter);
filter = new IntentFilter(BluetoothAdapter.ACTION_DISCOVERY_FINISHED);
registerReceiver(receiver, filter);
filter = new IntentFilter(BluetoothAdapter.ACTION_STATE_CHANGED);
registerReceiver(receiver, filter);
}
@Override
protected void onPause() {
// TODO Auto-generated method stub
super.onPause();
unregisterReceiver(receiver);
}
@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
// TODO Auto-generated method stub
super.onActivityResult(requestCode, resultCode, data);
if(resultCode == RESULT_CANCELED){
Toast.makeText(getApplicationContext(), "Bluetooth must be enabled to continue", Toast.LENGTH_SHORT).show();
finish();
}
}
public void onItemClick(AdapterView<?> arg0, View arg1, int arg2, //when discovered item in listview is selected then: cancel discovery, start connection
long arg3) {
// TODO Auto-generated method stub
if(btAdapter.isDiscovering()){
btAdapter.cancelDiscovery();
}
if(listAdapter.getItem(arg2).contains("Paired")){
BluetoothDevice selectedDevice = devices.get(arg2);
ConnectThread connect = new ConnectThread(selectedDevice);
connect.start();
Log.i(tag, "in click listener");
}
else{
Toast.makeText(getApplicationContext(), "device is not paired", 0).show();
}
}
private class ConnectThread extends Thread {
private final BluetoothSocket mmSocket;
private final BluetoothDevice mmDevice;
public ConnectThread(BluetoothDevice device) {
// Use a temporary object that is later assigned to mmSocket,
// because mmSocket is final
BluetoothSocket tmp = null;
mmDevice = device;
Log.i(tag, "construct");
// Get a BluetoothSocket to connect with the given BluetoothDevice
try {
// MY_UUID is the app's UUID string, also used by the server code
tmp = device.createRfcommSocketToServiceRecord(MY_UUID);
} catch (IOException e) {
Log.i(tag, "get socket failed");
}
mmSocket = tmp;
}
public void run() {
// Cancel discovery because it will slow down the connection
btAdapter.cancelDiscovery();
Log.i(tag, "connect - run");
try {
// Connect the device through the socket. This will block
// until it succeeds or throws an exception
mmSocket.connect();
Log.i(tag, "connect - succeeded");
} catch (IOException connectException) { Log.i(tag, "connect failed");
// Unable to connect; close the socket and get out
try {
mmSocket.close();
} catch (IOException closeException) { }
return;
}
// Do work to manage the connection (in a separate thread)
mHandler.obtainMessage(SUCCESS_CONNECT, mmSocket).sendToTarget();
}
/** Will cancel an in-progress connection, and close the socket */
public void cancel() {
try {
mmSocket.close();
} catch (IOException e) { }
}
}
private class ConnectedThread extends Thread {
private final BluetoothSocket mmSocket;
private final InputStream mmInStream;
private final OutputStream mmOutStream;
public ConnectedThread(BluetoothSocket socket) {
mmSocket = socket;
InputStream tmpIn = null;
OutputStream tmpOut = null;
// Get the input and output streams, using temp objects because
// member streams are final
try {
Null pointer points here>>>> tmpIn = socket.getInputStream(); <<<<*******************
tmpOut = socket.getOutputStream();
} catch (IOException e) { }
mmInStream = tmpIn;
mmOutStream = tmpOut;
}
public void run() {
byte[] buffer; // buffer store for the stream
int bytes; // bytes returned from read()
// Keep listening to the InputStream until an exception occurs
while (true) {
try {
// Read from the InputStream
buffer = new byte[1024];
bytes = mmInStream.read(buffer);
// Send the obtained bytes to the UI activity
mHandler.obtainMessage(MESSAGE_READ, bytes, -1, buffer)
.sendToTarget();
} catch (IOException e) {
break;
}
}
}
/* Call this from the main activity to send data to the remote device */
public void write(byte[] bytes) {
try {
mmOutStream.write(bytes);
} catch (IOException e) {
e.printStackTrace();
}
}
/* Call this from the main activity to shutdown the connection */
public void cancel() {
try {
mmSocket.close();
} catch (IOException e) { }
}
}
我調用write（）這樣的：
ConnectedThread con = new ConnectedThread(what context to use??); //Create an instance of ConnectedThread
con.write("ABC".getBytes()); //Send string via bluetooth.
// con.write(new byte[] {0x30, 0x38,}); //Send byte via bluetooth.
這裏有來自logcat中的臺詞：
10-02 08:02:44.539: E/AndroidRuntime(23489): FATAL EXCEPTION: main
10-02 08:02:44.539: E/AndroidRuntime(23489): java.lang.NullPointerException
10-02 08:02:44.539: E/AndroidRuntime(23489): at sjtech.rompa.wifi.Wifi$ConnectedThread.<init>(Wifi.java:491)
10-02 08:02:44.539: E/AndroidRuntime(23489): at sjtech.rompa.wifi.Wifi$2.onClick(Wifi.java:158)
10-02 08:02:44.539: E/AndroidRuntime(23489): at android.view.View.performClick(View.java:4452)
10-02 08:02:44.539: E/AndroidRuntime(23489): at android.widget.Button.performClick(Button.java:148)
10-02 08:02:44.539: E/AndroidRuntime(23489): at android.view.View$PerformClick.run(View.java:18428)
10-02 08:02:44.539: E/AndroidRuntime(23489): at android.os.Handler.handleCallback(Handler.java:725)
10-02 08:02:44.539: E/AndroidRuntime(23489): at android.os.Handler.dispatchMessage(Handler.java:92)
10-02 08:02:44.539: E/AndroidRuntime(23489): at android.os.Looper.loop(Looper.java:176)
10-02 08:02:44.539: E/AndroidRuntime(23489): at android.app.ActivityThread.main(ActivityThread.java:5365)
10-02 08:02:44.539: E/AndroidRuntime(23489): at java.lang.reflect.Method.invokeNative(Native Method)
10-02 08:02:44.539: E/AndroidRuntime(23489): at java.lang.reflect.Method.invoke(Method.java:511)
10-02 08:02:44.539: E/AndroidRuntime(23489): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1102)
10-02 08:02:44.539: E/AndroidRuntime(23489): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:869)
10-02 08:02:44.539: E/AndroidRuntime(23489): at dalvik.system.NativeStart.main(Native Method)
ID真的在這裏得到一些幫助，我是新在這個和不能理解上下文，不幸的是我沒有選擇，只能得到這個工作！
在此先感謝，併爲任何能幫助我的人提供一個大金星。
感謝您的答案，雖然我不知道如何使用您的建議，我想訪問我的onCreate中的ConnectedThread類的write（）方法 – user3812950 2014-10-02 14:07:53