大家好我经过多次努力后真的很累我发布这个问题请帮助。应用程序崩溃不知道为什么。任何帮助将不胜感激。 请帮助我使用android studio。
DEVICELISTACTIVITY
package com.smarthomeASAD.echohome;
import java.util.Set;
import android.app.Activity;
import android.bluetooth.BluetoothAdapter;
import android.bluetooth.BluetoothDevice;
import android.content.Intent;
import android.media.MediaPlayer;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.ListView;
import android.widget.TextView;
import android.widget.Toast;
public class DeviceListActivity extends Activity {
// Debugging for LOGCAT
private static final String TAG = "DeviceListActivity";
// private static final boolean D = true;
// declare button for launching website and textview for connection status
Button tlbutton;
TextView textView1;
// EXTRA string to send on to mainactivity
public static String EXTRA_DEVICE_ADDRESS = "device_address";
// Member fields
private BluetoothAdapter mBtAdapter;
private ArrayAdapter<String> mPairedDevicesArrayAdapter;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.device_list);
super.onResume();
checkBTState();
textView1 = (TextView) findViewById(R.id.connecting);
textView1.setTextSize(40);
textView1.setText(" ");
// Initialize array adapter for paired devices
mPairedDevicesArrayAdapter = new ArrayAdapter<String>(this,
R.layout.device_name);
// Find and set up the ListView for paired devices
ListView pairedListView = (ListView) findViewById(R.id.paired_devices);
pairedListView.setAdapter(mPairedDevicesArrayAdapter);
pairedListView.setOnItemClickListener(mDeviceClickListener);
// Get the local Bluetooth adapter
mBtAdapter = BluetoothAdapter.getDefaultAdapter();
// Get a set of currently paired devices and append to 'pairedDevices'
Set<BluetoothDevice> pairedDevices = mBtAdapter.getBondedDevices();
// Add previosuly paired devices to the array
if (pairedDevices.size() > 0) {
findViewById(R.id.title_paired_devices).setVisibility(View.VISIBLE);// make
// title
// viewable
for (BluetoothDevice device : pairedDevices) {
mPairedDevicesArrayAdapter.add(device.getName() + "\n"
+ device.getAddress());
}
} else {
String noDevices = getResources().getText(R.string.none_paired)
.toString();
mPairedDevicesArrayAdapter.add(noDevices);
}
MediaPlayer welcome = MediaPlayer.create(getApplicationContext(),
R.raw.wlcom);
welcome.setOnCompletionListener(new MediaPlayer.OnCompletionListener() {
@Override
public void onCompletion(MediaPlayer mp) {
// Code to start the next audio in the sequence
final MediaPlayer selectroom = MediaPlayer.create(
getApplicationContext(), R.raw.selectroom);
selectroom.start();
}
});
welcome.start();
}
// Set up on-click listener for the list (nicked this - unsure)
private OnItemClickListener mDeviceClickListener = new OnItemClickListener() {
public void onItemClick(AdapterView<?> av, View v, int arg2, long arg3) {
textView1.setText("Connecting...");
// Get the device MAC address, which is the last 17 chars in the
// View
String info = ((TextView) v).getText().toString();
String address = info.substring(info.length() - 17);
// Make an intent to start next activity while taking an extra which
// is the MAC address.
Intent i = new Intent(DeviceListActivity.this, MainActivity.class);
i.putExtra(EXTRA_DEVICE_ADDRESS, address);
startActivity(i);
Toast.makeText(getBaseContext(), "main acitvity started...",
Toast.LENGTH_LONG).show();
}
};
private void checkBTState() {
// Check device has Bluetooth and that it is turned on
mBtAdapter = BluetoothAdapter.getDefaultAdapter(); // CHECK THIS OUT
// THAT IT WORKS!!!
if (mBtAdapter == null) {
Toast.makeText(getBaseContext(),
"Device does not support Bluetooth", Toast.LENGTH_SHORT)
.show();
} else {
if (mBtAdapter.isEnabled()) {
Log.d(TAG, "...Bluetooth ON...");
} else {
// Prompt user to turn on Bluetooth
Intent enableBtIntent = new Intent(
BluetoothAdapter.ACTION_REQUEST_ENABLE);
startActivityForResult(enableBtIntent, 1);
}
}
}
}
ACTIVITY_MAIN
package com.smarthomeASAD.echohome;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.util.UUID;
import android.annotation.SuppressLint;
import android.app.Activity;
import android.bluetooth.BluetoothAdapter;
import android.bluetooth.BluetoothDevice;
import android.bluetooth.BluetoothSocket;
import android.content.Intent;
import android.media.MediaPlayer;
import android.os.Bundle;
import android.os.Handler;
import android.util.Log;
import android.view.WindowManager;
import android.widget.Button;
import android.widget.CompoundButton;
import android.widget.TextView;
import android.widget.Toast;
import android.widget.ToggleButton;
import com.smarthomeASAD.echohome.R;
public class MainActivity extends Activity {
public InputStream mmInStream = null;
public OutputStream mmOutStream = null;
public boolean connectionfailureb = false;
Button btnOn, btnOff;
TextView txtArduino, txtString, txtStringLength, sensorView0, sensorView1,
sensorView2, sensorView3;
static Handler bluetoothIn;
final int handlerState = 0; // used to identify handler message
private BluetoothAdapter btAdapter = null;
private BluetoothSocket btSocket = null;
private StringBuilder recDataString = new StringBuilder();
private ConnectedThread mConnectedThread;
// SPP UUID service - this should work for most devices
private static final UUID BTMODULEUUID = UUID
.fromString("00001101-0000-1000-8000-00805F9B34FB");
// String for MAC address
private static String address;
@SuppressLint("HandlerLeak")
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
getWindow().addFlags(WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON);
// ==========================TOGGLE BUTTONS=============
ToggleButton t1 = (ToggleButton) findViewById(R.id.tb1);
ToggleButton t2 = (ToggleButton) findViewById(R.id.tb2);
ToggleButton t3 = (ToggleButton) findViewById(R.id.tb3);
ToggleButton t4 = (ToggleButton) findViewById(R.id.tb4);
ToggleButton t5 = (ToggleButton) findViewById(R.id.tb5);
// =========================TOGGLE BUTTONS==============
// >>>>>>>>>>>>>>>>>>>MEDIA--------------------------
final MediaPlayer sciencedanger = MediaPlayer.create(
getApplicationContext(), R.raw.science_fiction_danger_alarm);
final MediaPlayer motiondetected = MediaPlayer.create(
getApplicationContext(), R.raw.motion_detected);
// <<<<<<<<<<<<<<<<<<<MEDIA-<<<<<<<<<<<<<<<<<<<<<<<<
// Link the buttons and textViews to respective views
txtString = (TextView) findViewById(R.id.txtString);
txtStringLength = (TextView) findViewById(R.id.testView1);
sensorView0 = (TextView) findViewById(R.id.sensorView0);
sensorView1 = (TextView) findViewById(R.id.sensorView1);
sensorView2 = (TextView) findViewById(R.id.sensorView2);
sensorView3 = (TextView) findViewById(R.id.sensorView3);
bluetoothIn = new Handler() {
public void handleMessage(android.os.Message msg) {
if (msg.what == handlerState) { // if message is what we want
Log.i("handler", null);
String readMessage = (String) msg.obj;
recDataString.append(readMessage);
int endOfLineIndex = recDataString.indexOf("~");
if (endOfLineIndex > 0) { // make sure there data before ~
String dataInPrint = recDataString.substring(0,
endOfLineIndex); // extract string
txtString.setText("Data Received = " + dataInPrint);
int dataLength = dataInPrint.length();
txtStringLength.setText("String Length = "
+ String.valueOf(dataLength));
if (recDataString.charAt(0) == '#') {
String sensor0 = recDataString.substring(1, 5);
// =================================================MOD--------------------
Log.i("IN RecData", readMessage);
if (sensor0.equals("1.00")) {
sciencedanger.start();
motiondetected.start();
} else {
}
// =================================================MOD--------------------
sensorView0.setText(" Sensor 0 Voltage = "
+ sensor0);
}
recDataString.delete(0, recDataString.length());
dataInPrint = " ";
}
}
}
};
btAdapter = BluetoothAdapter.getDefaultAdapter(); // get Bluetooth
// adapter
checkBTState();
// Set up onClick listeners for buttons to send 1 or 0 to turn on/off
// LED
// ========================================================
// ========================================================
t1.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
public void onCheckedChanged(CompoundButton buttonView,
boolean isChecked) {
if (isChecked) {
try {
mConnectedThread.write("1");
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
Toast.makeText(getBaseContext(), "ON", Toast.LENGTH_SHORT)
.show();
} else {
// The toggle is disabled
try {
mConnectedThread.write("0");
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
Toast.makeText(getBaseContext(), "OFF", Toast.LENGTH_SHORT)
.show();
}
}
});
t2.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
public void onCheckedChanged(CompoundButton buttonView,
boolean isChecked) {
if (isChecked) {
try {
mConnectedThread.write("2");
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
Toast.makeText(getBaseContext(), "ON", Toast.LENGTH_SHORT)
.show();
} else {
// The toggle is disabled
try {
mConnectedThread.write("3");
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
Toast.makeText(getBaseContext(), "OFF", Toast.LENGTH_SHORT)
.show();
}
}
});
t3.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
public void onCheckedChanged(CompoundButton buttonView,
boolean isChecked) {
if (isChecked) {
try {
mConnectedThread.write("4");
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
Toast.makeText(getBaseContext(), "ON", Toast.LENGTH_SHORT)
.show();
} else {
// The toggle is disabled
try {
mConnectedThread.write("5");
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
Toast.makeText(getBaseContext(), "OFF", Toast.LENGTH_SHORT)
.show();
}
}
});
t4.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
public void onCheckedChanged(CompoundButton buttonView,
boolean isChecked) {
if (isChecked) {
try {
mConnectedThread.write("6");
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
Toast.makeText(getBaseContext(), "ON", Toast.LENGTH_SHORT)
.show();
} else {
// The toggle is disabled
try {
mConnectedThread.write("7");
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
Toast.makeText(getBaseContext(), "OFF", Toast.LENGTH_SHORT)
.show();
}
}
});
t5.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
public void onCheckedChanged(CompoundButton buttonView,
boolean isChecked) {
if (isChecked) {
try {
mConnectedThread.write("8");
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
Toast.makeText(getBaseContext(), "ON", Toast.LENGTH_SHORT)
.show();
} else {
// The toggle is disabled
try {
mConnectedThread.write("9");
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
Toast.makeText(getBaseContext(), "OFF", Toast.LENGTH_SHORT)
.show();
}
}
});
// =========================================================
// ==========================================================
}
private BluetoothSocket createBluetoothSocket(BluetoothDevice device)
throws IOException {
return device.createRfcommSocketToServiceRecord(BTMODULEUUID);
// creates secure outgoing connecetion with BT device using UUID
}
@Override
public void onResume() {
super.onResume();
// Get MAC address from DeviceListActivity via intent
Intent intent = getIntent();
// Get the MAC address from the DeviceListActivty via EXTRA
address = intent
.getStringExtra(DeviceListActivity.EXTRA_DEVICE_ADDRESS);
// create device and set the MAC address
BluetoothDevice device = btAdapter.getRemoteDevice(address);
try {
btSocket = createBluetoothSocket(device);
} catch (IOException e) {
Toast.makeText(getBaseContext(), "Socket creation failed",
Toast.LENGTH_LONG).show();
}
// Establish the Bluetooth socket connection.
try {
btSocket.connect();
} catch (IOException e) {
try {
mmInStream.close();
mmOutStream.close();
btSocket.close();
} catch (IOException e2) {
Toast.makeText(getBaseContext(),
"closing exception btSocket sonnection problem",
Toast.LENGTH_LONG).show();
// insert code to deal with this
}
}
mConnectedThread = new ConnectedThread(btSocket);
mConnectedThread.start();
// I send a character when resuming.beginning transmission to check
// device is connected
// If it is not an exception will be thrown in the write method and
// finish() will be called
try {
mConnectedThread.write("x");
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
Toast.makeText(getBaseContext(), "Thread can't write",
Toast.LENGTH_LONG).show();
}
}
@Override
public void onPause() {
super.onPause();
try {
// Don't leave Bluetooth sockets open when leaving activity
btSocket.close();
} catch (IOException e2) {
// insert code to deal with this
}
}
// Checks that the Android device Bluetooth is available and prompts to be
// turned on if off
private void checkBTState() {
if (btAdapter == null) {
Toast.makeText(getBaseContext(),
"Device does not support bluetooth", Toast.LENGTH_LONG)
.show();
} else {
if (btAdapter.isEnabled()) {
} else {
Intent enableBtIntent = new Intent(
BluetoothAdapter.ACTION_REQUEST_ENABLE);
startActivityForResult(enableBtIntent, 1);
}
}
}
// create new class for connect thread
private class ConnectedThread extends Thread {
// creation of the connect thread
public ConnectedThread(BluetoothSocket socket) {
InputStream tmpIn = null;
OutputStream tmpOut = null;
try {
// Create I/O streams for connection
tmpIn = socket.getInputStream();
tmpOut = socket.getOutputStream();
} catch (IOException e) {
}
mmInStream = tmpIn;
mmOutStream = tmpOut;
}
// =================================================MOD--------------------
public void run() {
byte[] buffer = new byte[256];
int bytes;
// Keep looping to listen for received messages
while (true) {
try {
bytes = mmInStream.read(buffer); // read bytes from input
// buffer
String readMessage = new String(buffer, 0, bytes); // Send
// the
// obtained
// bytes
// to
// the
// UI
// Activity
// via
// handler
bluetoothIn.obtainMessage(handlerState, bytes, -1,
readMessage).sendToTarget();
} catch (IOException e) {
Toast.makeText(getBaseContext(), "listner eror",
Toast.LENGTH_LONG).show();
break;
}
}
}
// =================================================MOD--------------------
// write method
public void write(String input) throws InterruptedException {
byte[] msgBuffer = input.getBytes(); // converts entered String into
// bytes
try {
mmOutStream.write(msgBuffer); // write bytes over BT connection
// via outstream
MediaPlayer connected = MediaPlayer.create(
getApplicationContext(), R.raw.connected);
connected.start();
} catch (IOException e) {
// if you cannot write, close the application
final MediaPlayer connectionfailure = MediaPlayer.create(
getApplicationContext(), R.raw.connectionfailure);
connectionfailure
.setOnCompletionListener(new MediaPlayer.OnCompletionListener() {
@Override
public void onCompletion(MediaPlayer mp) {
// Code to start the next audio in the sequence
Toast.makeText(getBaseContext(),
"Connection Failure", Toast.LENGTH_LONG)
.show();
finish();
}
});
connectionfailure.start();
}
Thread.sleep(1000);
}
}
}
logcat的
10-22 17:43:19.712 32054-32054/com.smarthomeASAD.echohome E/AndroidRuntime: FATAL EXCEPTION: main
10-22 17:43:19.712 32054-32054/com.smarthomeASAD.echohome E/AndroidRuntime: java.lang.RuntimeException: Unable to resume activity {com.smarthomeASAD.echohome/com.smarthomeASAD.echohome.MainActivity}: java.lang.NullPointerException
10-22 17:43:19.712 32054-32054/com.smarthomeASAD.echohome E/AndroidRuntime: at android.app.ActivityThread.performResumeActivity(ActivityThread.java:2918)
10-22 17:43:19.712 32054-32054/com.smarthomeASAD.echohome E/AndroidRuntime: at android.app.ActivityThread.handleResumeActivity(ActivityThread.java:2947)
10-22 17:43:19.712 32054-32054/com.smarthomeASAD.echohome E/AndroidRuntime: at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2382)
10-22 17:43:19.712 32054-32054/com.smarthomeASAD.echohome E/AndroidRuntime: at android.app.ActivityThread.access$600(ActivityThread.java:167)
10-22 17:43:19.712 32054-32054/com.smarthomeASAD.echohome E/AndroidRuntime: at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1356)
10-22 17:43:19.712 32054-32054/com.smarthomeASAD.echohome E/AndroidRuntime: at android.os.Handler.dispatchMessage(Handler.java:99)
10-22 17:43:19.712 32054-32054/com.smarthomeASAD.echohome E/AndroidRuntime: at android.os.Looper.loop(Looper.java:153)
10-22 17:43:19.712 32054-32054/com.smarthomeASAD.echohome E/AndroidRuntime: at android.app.ActivityThread.main(ActivityThread.java:5341)
10-22 17:43:19.712 32054-32054/com.smarthomeASAD.echohome E/AndroidRuntime: at java.lang.reflect.Method.invokeNative(Native Method)
10-22 17:43:19.712 32054-32054/com.smarthomeASAD.echohome E/AndroidRuntime: at java.lang.reflect.Method.invoke(Method.java:511)
10-22 17:43:19.712 32054-32054/com.smarthomeASAD.echohome E/AndroidRuntime: at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:929)
10-22 17:43:19.712 32054-32054/com.smarthomeASAD.echohome E/AndroidRuntime: at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:696)
10-22 17:43:19.712 32054-32054/com.smarthomeASAD.echohome E/AndroidRuntime: at dalvik.system.NativeStart.main(Native Method)
10-22 17:43:19.712 32054-32054/com.smarthomeASAD.echohome E/AndroidRuntime: Caused by: java.lang.NullPointerException
10-22 17:43:19.712 32054-32054/com.smarthomeASAD.echohome E/AndroidRuntime: at com.smarthomeASAD.echohome.MainActivity.onResume(MainActivity.java:288)
10-22 17:43:19.712 32054-32054/com.smarthomeASAD.echohome E/AndroidRuntime: at android.app.Instrumentation.callActivityOnResume(Instrumentation.java:1190)
10-22 17:43:19.712 32054-32054/com.smarthomeASAD.echohome E/AndroidRuntime: at android.app.Activity.performResume(Activity.java:5203)
10-22 17:43:19.712 32054-32054/com.smarthomeASAD.echohome E/AndroidRuntime: at android.app.ActivityThread.performResumeActivity(ActivityThread.java:2905)
10-22 17:43:19.712 32054-32054/com.smarthomeASAD.echohome E/AndroidRuntime: at android.app.ActivityThread.handleResumeActivity(ActivityThread.java:2947)
10-22 17:43:19.712 32054-32054/com.smarthomeASAD.echohome E/AndroidRuntime: at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2382)
10-22 17:43:19.712 32054-32054/com.smarthomeASAD.echohome E/AndroidRuntime: at android.app.ActivityThread.access$600(ActivityThread.java:167)
10-22 17:43:19.712 32054-32054/com.smarthomeASAD.echohome E/AndroidRuntime: at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1356)
10-22 17:43:19.712 32054-32054/com.smarthomeASAD.echohome E/AndroidRuntime: at android.os.Handler.dispatchMessage(Handler.java:99)
10-22 17:43:19.712 32054-32054/com.smarthomeASAD.echohome E/AndroidRuntime: at android.os.Looper.loop(Looper.java:153)
10-22 17:43:19.712 32054-32054/com.smarthomeASAD.echohome E/AndroidRuntime: at android.app.ActivityThread.main(ActivityThread.java:5341)
10-22 17:43:19.712 32054-32054/com.smarthomeASAD.echohome E/AndroidRuntime: at java.lang.reflect.Method.invokeNative(Native Method)
10-22 17:43:19.712 32054-32054/com.smarthomeASAD.echohome E/AndroidRuntime: at java.lang.reflect.Method.invoke(Method.java:511)
10-22 17:43:19.712 32054-32054/com.smarthomeASAD.echohome E/AndroidRuntime: at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:929)
10-22 17:43:19.712 32054-32054/com.smarthomeASAD.echohome E/AndroidRuntime: at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:696)
10-22 17:43:19.712 32054-32054/com.smarthomeASAD.echohome E/AndroidRuntime: at dalvik.system.NativeStart.main(Native Method)
答案 0 :(得分：1)
在public class ClassB
{
public event MyEventHandler MyEvent;
public delegate void MyEventHandler(object sender, MyEventArgs e);
public class MyEventArgs : EventArgs
{
public MyEventArgs()
{ }
}
private virtual void OnMyEvent(MyEventArgs e)
{
MyEventHandler handler = MyEvent;
if (handler != null)
{
handler(this, e);
}
}
public ClassB()
{
/// do stuff
}
public void Method()
{
OnMyEvent(new MyEventArgs());
}
}
public class ClassA
{
private ClassB member = new ClassB();
public ClassA()
{
/// do stuff
}
public void Method()
{
member.Method();
}
}
static class Program
{
static List<ClassA> aList = new List<ClassA>();
static void Main()
{
aList.Add(new ClassA());
/// I would like to be able to do this...
aList[0].MyEvent += MyEvent_handler;
aList[0].Method();
}
void MyEvent_handler(object sender, ClassB.MyEventArgs e)
{
/// ... such that sender is the ClassA instance i.e. aList[0]
/// and e is the MyEventArgs passed to OnMyEvent in ClassB
}
}
中，无论何时使用意图，都必须添加空检查。执行onResume()时，它实际上可能会返回空意图