Android 从活动返回后，闪光灯功能崩溃
我有一个android应用程序，它连接到mqtt代理，并监听播放/暂停铃声或打开/关闭手电筒的指令 它按预期运行，直到我更改设置并在此之后调用函数flashOnOff。然后我得到一个空指针异常，但我不明白为什么 这是我的代码（我没有包括我的导入以节省空间）：Android 从活动返回后，闪光灯功能崩溃,android,nullpointerexception,Android,Nullpointerexception,我有一个android应用程序，它连接到mqtt代理，并监听播放/暂停铃声或打开/关闭手电筒的指令 它按预期运行，直到我更改设置并在此之后调用函数flashOnOff。然后我得到一个空指针异常，但我不明白为什么 这是我的代码（我没有包括我的导入以节省空间）： public类MainActivity扩展了AppCompatActivity{ //布局相关参数 工具栏我的工具栏； 纺纱机； 图像按钮闪光灯按钮； 按键铃声； 编辑短信； //相机/手电筒相关参数 摄像机； 摄像机参数； //MQTT相
public类MainActivity扩展了AppCompatActivity{
//布局相关参数
工具栏我的工具栏；
纺纱机；
图像按钮闪光灯按钮；
按键铃声；
编辑短信；
//相机/手电筒相关参数
摄像机；
摄像机参数；
//MQTT相关参数
私有字符串BrokerIp=”tcp://192.168.1.3:1883";
私有intqos=2；
静态字符串Username=“user1”；
静态字符串Password=“user1”；
字符串topicStr=“commands”；
字符串clientId=“AndroidClient”；
MqttConnectOptions选项；
MQTTandroid客户端；
振动器；
//铃声相关参数
手机铃声；
MediaPlayer ringtoneMP；
@凌驾
创建时受保护的void（Bundle savedInstanceState）{
super.onCreate（savedInstanceState）；
setContentView（R.layout.activity_main）；
可控震源=（可控震源）getSystemService（可控震源服务）；
Uri Uri=RingtoneManager.getDefaultUri（RingtoneManager.TYPE_通知）；
myRingtone=RingtoneManager.getRingtone（getApplicationContext（），uri）；
myToolbar=（Toolbar）findviewbyd（R.id.Toolbar）；
mySpinner=（微调器）findviewbyd（R.id.Spinner）；
flashlightButton=（ImageButton）findViewById（R.id.image）；
myToolbar.setLogo（R.drawable.twoogyswatchmrrobot）；
setTitle（getResources（）.getString（R.string.app_name））；
ArrayAdapter myAdapter=新的ArrayAdapter（MainActivity.this，
R.layout.custom_微调器_itam，
getResources（）.getStringArray（R.array.Toolbar_下拉菜单_条目））；
myAdapter.setDropDownViewResource（android.R.layout.simple\u微调器\u下拉菜单\u项）；
setAdapter（myAdapter）；
ringtoneMP=MediaPlayer.create（这个，R.raw.games\u of the_王座）；
ringtone=（按钮）this.findViewById（R.id.ringtone）；
message=（EditText）findViewById（R.id.messagePublish）；
mySpinner.setOnItemSelectedListener（新的AdapterView.OnItemSelectedListener（）{
@凌驾
已选择公共视图（AdapterView AdapterView、View视图、int i、long l）{
Toast.makeText（MainActivity.this，
mySpinner.getSelectedItem（）.toString（），
吐司，长度（短）
.show（）；
if（mySpinner.getSelectedItem（）.toString（）.equals（“退出应用程序”））{
退出（）；
}else if（mySpinner.getSelectedItem（）.toString（）.equals（“设置”））
{
意图；
intent=新intent（MainActivity.this、setingsActivity.class）；
intent.putExtra（“CURRENT_IP”，client.getServerURI（））；
intent.putExtra（“当前_QOS”，Integer.toString（QOS））；
intent.putExtra（“当前主题”，topicStr）；
startActivityForResult（intent，1）；//这样我们以后就可以将结果带回mainActivity
}否则{
系统输出打印（“ara3e，den exw diale3ei tipota”）；
}
}
@凌驾
未选择公共无效（AdapterView AdapterView）{
}
});
//开始创建时使用手电筒
if（isFlashAvailable（））//检查此设备上是否有闪光灯，是否打开摄像头（模块），并使按钮可单击
{
camera=camera.open（）；
parameters=camera.getParameters（）；
}否则
{//如果不支持手电筒，请不要让用户单击按钮
flashlightButton.setEnabled（错误）；
AlertDialog.Builder=新建AlertDialog.Builder（MainActivity.this）；
builder.setTitle（“错误”）；
builder.setMessage（“手电筒在此设备上不可用。\nExit？”）；//通知用户并让他选择如何继续
builder.setPositiveButton（“是”，新建DialogInterface.OnClickListener（）{
@凌驾
公共void onClick（DialogInterface，inti）{
dialogInterface.dismise（）；
退出（）；
}
});
setNegativeButton（“不用手电筒”，新建DialogInterface.OnClickListener（））{
@凌驾
公共void onClick（DialogInterface，inti）{
dialogInterface.dismise（）；
}
});
AlertDialog AlertDialog=builder.create（）；
alertDialog.show（）；
}
flashlightButton.setOnClickListener（新视图.OnClickListener（）{//侦听flash按钮的单击
@凌驾
公共void onClick（视图）{
flashOnOff（）；
}
});
ringtone.setOnClickListener（新视图.OnClickListener（）{//ringtone listener
@凌驾
公共void onClick（视图）{
ringtoneOnOff（ringtoneMP）；
}
});
client=新的MqttAndroidClient（MainActivity.this、brokerrip、clientId）；
//client=pahoMqttClient.getMqttClient（MainActivity.this、BrokerIp、clientId）；
选项=新的MqttConnectOptions（）；
options.setUserName（用户名）；
options.setPassword（Password.toCharArray（））；
试一试{
imqttoken令牌=client.connect（选项）；
token.setActionCallback（新的IMqttActionListener（）{
@凌驾
成功时公共无效（IMqttToken asyncActionToken）{
//我们是有联系的
Toast.makeText（MainActivity.this，“connected”，Toast.LENGTH_SHORT.show（）；
setSubscription（客户端、topicStr、qos）；
}
@凌驾
public void onFailure（IMqttToken asyncActionToken，可丢弃异常）{
//出现问题，例如连接超时或火灾
public class MainActivity extends AppCompatActivity {
// Layout related parameters
Toolbar myToolbar;
Spinner mySpinner;
ImageButton flashlightButton;
Button ringtone;
EditText message;
// Camera/flashlight related parameters
Camera camera;
Camera.Parameters parameters;
// MQTT related parameters
private String BrokerIp = "tcp://192.168.1.3:1883";
private int qos = 2;
static String Username = "user1";
static String Password = "user1";
String topicStr = "commands";
String clientId = "AndroidClient";
MqttConnectOptions options;
MqttAndroidClient client;
Vibrator vibrator;
// Ringtone related parameters
Ringtone myRingtone;
MediaPlayer ringtoneMP ;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
vibrator = (Vibrator)getSystemService(VIBRATOR_SERVICE);
Uri uri = RingtoneManager.getDefaultUri(RingtoneManager.TYPE_NOTIFICATION);
myRingtone = RingtoneManager.getRingtone(getApplicationContext(),uri);
myToolbar = (Toolbar) findViewById(R.id.toolbar);
mySpinner = (Spinner) findViewById(R.id.spinner);
flashlightButton = (ImageButton) findViewById(R.id.image);
myToolbar.setLogo(R.drawable.twoguyswatchmrrobot);
myToolbar.setTitle(getResources().getString(R.string.app_name));
ArrayAdapter<String> myAdapter = new ArrayAdapter<String>(MainActivity.this,
R.layout.custom_spinner_itam,
getResources().getStringArray(R.array.Toolbar_dropdown_entries));
myAdapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
mySpinner.setAdapter(myAdapter);
ringtoneMP = MediaPlayer.create(this,R.raw.games_of_thrones);
ringtone = (Button) this.findViewById(R.id.ringtone);
message = (EditText)findViewById(R.id.messagePublish);
mySpinner.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {
@Override
public void onItemSelected(AdapterView<?> adapterView, View view, int i, long l) {
Toast.makeText(MainActivity.this,
mySpinner.getSelectedItem().toString(),
Toast.LENGTH_SHORT)
.show();
if (mySpinner.getSelectedItem().toString().equals("Exit App")){
exit();
}else if(mySpinner.getSelectedItem().toString().equals("Settings"))
{
Intent intent;
intent = new Intent(MainActivity.this, SettingsActivity.class);
intent.putExtra("CURRENT_IP",client.getServerURI());
intent.putExtra("CURRENT_QOS", Integer.toString(qos));
intent.putExtra("CURRENT_TOPIC",topicStr);
startActivityForResult(intent,1); // this is so we can take the results back to mainActivity later
}else{
System.out.println("ara3e, den exw diale3ei tipota");
}
}
@Override
public void onNothingSelected(AdapterView<?> adapterView) {
}
});
//Flashlight on Create start
if(isFlashAvailable()) // check if flash is available on this device, if it is open camera (module) and make button clickable
{
camera = Camera.open();
parameters = camera.getParameters();
}else
{ // if flashlight is not supported dont let the user click the button
flashlightButton.setEnabled(false);
AlertDialog.Builder builder = new AlertDialog.Builder(MainActivity.this);
builder.setTitle("Error.");
builder.setMessage("Flashlight not available on this device. \nExit?"); // inform the user and let him choose how to continue
builder.setPositiveButton("Yes", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialogInterface, int i) {
dialogInterface.dismiss();
exit();
}
});
builder.setNegativeButton("Stay without flashlight", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialogInterface, int i) {
dialogInterface.dismiss();
}
});
AlertDialog alertDialog = builder.create();
alertDialog.show();
}
flashlightButton.setOnClickListener(new View.OnClickListener() { // listen for flash button clicks
@Override
public void onClick(View view) {
flashOnOff();
}
});
ringtone.setOnClickListener(new View.OnClickListener() { // Ringtone listener
@Override
public void onClick(View view) {
ringtoneOnOff(ringtoneMP);
}
});
client = new MqttAndroidClient(MainActivity.this, BrokerIp, clientId);
// client = pahoMqttClient.getMqttClient(MainActivity.this,BrokerIp,clientId);
options = new MqttConnectOptions();
options.setUserName(Username);
options.setPassword(Password.toCharArray());
try {
IMqttToken token = client.connect(options);
token.setActionCallback(new IMqttActionListener() {
@Override
public void onSuccess(IMqttToken asyncActionToken) {
// We are connected
Toast.makeText(MainActivity.this, "connected", Toast.LENGTH_SHORT).show();
setSubscription(client,topicStr,qos);
}
@Override
public void onFailure(IMqttToken asyncActionToken, Throwable exception) {
// Something went wrong e.g. connection timeout or firewall problems
Log.w("Mqtt","Failed to connect to:"+ BrokerIp + exception.toString());
Toast.makeText(MainActivity.this, "Failed to connect to:" +exception.toString(), Toast.LENGTH_SHORT).show();
}
});
} catch (MqttException e) {
e.printStackTrace();
}
client.setCallback(new MqttCallback() {
@Override
public void connectionLost(Throwable throwable) {
Log.d("Connection:"," Lost");
}
@Override
public void messageArrived(String s, MqttMessage mqttMessage) throws Exception {
myMessageArrived(s,mqttMessage);
}
@Override
public void deliveryComplete(IMqttDeliveryToken iMqttDeliveryToken) {
Log.d("Delivery"," completed with iMqttDeliveryToken: " + iMqttDeliveryToken);
}
});
}
//Flashlight start
@Override
protected void onStop() {
super.onStop();
if(camera!=null)
{
camera.release();
camera = null;
}
}
//Flashlight end
//Backkey exit confirmation
public boolean onKeyDown(int keyCode, KeyEvent event) {
if (keyCode == KeyEvent.KEYCODE_BACK) {
exitByBackKey();
return true;
}
return super.onKeyDown(keyCode, event);
}
protected void exitByBackKey() {
AlertDialog alertbox = new AlertDialog.Builder(this)
.setMessage("Do you want to exit application?")
.setPositiveButton("Yes", new
DialogInterface.OnClickListener() {
// when yes is clicked exit the application
public void onClick(DialogInterface arg0, int arg1) {
exit();
}
})
.setNegativeButton("No", new
DialogInterface.OnClickListener() {
// when no is clicked do nothing
public void onClick(DialogInterface arg0, int arg1) {
}
})
.show();
}
//Backkey end
// PUBLISH MESSAGE
private void setSubscription(MqttAndroidClient client, String topic, int qos){
try{
client.subscribe(topic, qos);
}
catch (MqttException e){
e.printStackTrace();
}
}
private void unsetSubscription(MqttAndroidClient client,String topic){
try{
client.unsubscribe(topic);
}catch (MqttException e){
e.printStackTrace();
}
}
public void conn(View v){
try {
IMqttToken token = client.connect(options);
token.setActionCallback(new IMqttActionListener() {
@Override
public void onSuccess(IMqttToken asyncActionToken) {
// We are connected
Toast.makeText(MainActivity.this, "connected", Toast.LENGTH_SHORT).show();
setSubscription(client,topicStr,qos);
// pub();
}
@Override
public void onFailure(IMqttToken asyncActionToken, Throwable exception) {
// Something went wrong e.g. connection timeout or firewall problems
Toast.makeText(MainActivity.this, "not connected", Toast.LENGTH_SHORT).show();
}
});
} catch (MqttException e) {
e.printStackTrace();
}
}
public void disconn(View v){
if (client.isConnected()) {
try {
IMqttToken token = client.disconnect();
token.setActionCallback(new IMqttActionListener() {
@Override
public void onSuccess(IMqttToken asyncActionToken) {
// We are connected
Toast.makeText(MainActivity.this, "disconnected", Toast.LENGTH_SHORT).show();
}
@Override
public void onFailure(IMqttToken asyncActionToken, Throwable exception) {
// Something went wrong e.g. connection timeout or firewall problems
Toast.makeText(MainActivity.this, "could not disconnect", Toast.LENGTH_SHORT).show();
}
});
} catch (MqttException e) {
e.printStackTrace();
}
}else {
Toast.makeText(MainActivity.this, "Client is already disconnected", Toast.LENGTH_LONG).show();
}
}
/////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
public void pub(View v) {
String topic = topicStr;
try {
client.publish(topic, String.valueOf(message.getText()).getBytes(),qos,false);
} catch (MqttException e) {
e.printStackTrace();
}
}
private void ringtoneOnOff(MediaPlayer ringtoneMP){
if (ringtoneMP.isPlaying()){
ringtoneMP.pause();
}else{
ringtoneMP.start();
}
}
private void myMessageArrived(String s,MqttMessage mqttMessage){
if ((mqttMessage.toString()).equals("Flash on")) {
if (isFlashOn()) {
Toast.makeText(MainActivity.this, "Flashlight already on", Toast.LENGTH_SHORT).show();
} else {
Toast.makeText(MainActivity.this, "Turning flashlight on", Toast.LENGTH_SHORT).show();
flashOnOff();
}
} else if ((mqttMessage.toString()).equals("Flash off")) {
if (isFlashOn()) {
Toast.makeText(MainActivity.this, "Turning flashlight off", Toast.LENGTH_SHORT).show();
flashOnOff();
} else {
Toast.makeText(MainActivity.this, "Flashlight already off", Toast.LENGTH_SHORT).show();
}
} else if ((mqttMessage.toString()).equals("Ringtone on")) {
if (ringtoneMP.isPlaying()) {
Toast.makeText(MainActivity.this, "Ringtone already playing", Toast.LENGTH_SHORT).show();
} else {
Toast.makeText(MainActivity.this, "Playing ringtone", Toast.LENGTH_SHORT).show();
ringtoneMP.start();
}
} else if ((mqttMessage.toString()).equals("Ringtone off")) {
if (ringtoneMP.isPlaying()) {
ringtoneMP.pause();
} else {
Toast.makeText(MainActivity.this, "Ringtone already not being played", Toast.LENGTH_SHORT).show();
}
} else {
Log.d("INFO:", "This Command does not exist");
}
vibrator.vibrate(500);
myRingtone.play();
}
public void exit(){
finish();
System.exit(0);
}
public boolean isFlashAvailable(){ // boolean function that returns true if flash is supported on this device
return getApplicationContext().getPackageManager().hasSystemFeature(PackageManager.FEATURE_CAMERA_FLASH);
}
public void flashOnOff(){ // self explanatory
if (this.parameters.getFlashMode().equals(android.hardware.Camera.Parameters.FLASH_MODE_ON) || this.parameters.getFlashMode().equals(android.hardware.Camera.Parameters.FLASH_MODE_TORCH)){ // if the flash is on torch mode
Log.d("BHKE","408");
this.flashlightButton.setImageResource(R.drawable.off);
this.parameters.setFlashMode(Camera.Parameters.FLASH_MODE_OFF); // turn it off
}else{
Log.d("BHKE","412");
this.flashlightButton.setImageResource(R.drawable.on);
this.parameters.setFlashMode(Camera.Parameters.FLASH_MODE_TORCH); // else turn it on
}
this.camera.setParameters(this.parameters);
this.camera.startPreview();
}
@Override
public void onActivityResult(int requestCode, int resultCode, Intent data) {
String tempBrokerIp;
String temptopic="";
Integer tempqos;
Boolean BrokerIpChanged = true;
Boolean qosChanged = true;
Boolean topicChanged = true;
super.onActivityResult(requestCode, resultCode, data);
switch(requestCode) {
case (1) : {
if (resultCode == Activity.RESULT_OK) {
tempBrokerIp = data.getStringExtra("CURRENT_IP");
tempqos = Integer.parseInt(data.getStringExtra("CURRENT_QOS"));
temptopic = data.getStringExtra("CURRENT_TOPIC");
Log.d("Info BROKER, TOPIC, QOS", ":"+ tempBrokerIp+ " " + temptopic+ " " + tempqos);
if (tempBrokerIp.equals(BrokerIp)) {
BrokerIpChanged=false;
Log.i("BrokerIpChanged =", BrokerIpChanged.toString());
}
if (tempqos.equals(qos)) {
qosChanged=false;
Log.i("qosChanged =", qosChanged.toString());
}else {
qos = tempqos;
}
if (temptopic.equals(topicStr)){
topicChanged=false;
Log.i("topicChanged =", topicChanged.toString());
}else{
topicStr = temptopic;
}
if (!BrokerIpChanged && !qosChanged && !topicChanged) return;
if (BrokerIpChanged){
try {
client.disconnect();
BrokerIp = tempBrokerIp;
topicStr = temptopic;
qos = tempqos;
// final String clientId = MqttClient.generateClientId();
client = new MqttAndroidClient(MainActivity.this, BrokerIp, clientId);
options = new MqttConnectOptions();
options.setUserName(Username);
options.setPassword(Password.toCharArray());
// options.setMqttVersion(MqttConnectOptions.MQTT_VERSION_3_1); // to user the latest mqtt version
try {
IMqttToken token = client.connect(options);
token.setActionCallback(new IMqttActionListener() {
@Override
public void onSuccess(IMqttToken asyncActionToken) {
// We are connected
Toast.makeText(MainActivity.this, "connected", Toast.LENGTH_SHORT).show();
Log.w("Mqtt","Connected to:"+ BrokerIp);
try{
Log.v("INFO 11111:", "about to subscribe with: "+ topicStr + qos);
client.subscribe(topicStr,qos);
}catch (MqttException e){
e.printStackTrace();
}
}
@Override
public void onFailure(IMqttToken asyncActionToken, Throwable exception) {
// Something went wrong e.g. connection timeout or firewall problems
Log.w("Mqtt","Failed to connect to:"+ BrokerIp + exception.toString());
Toast.makeText(MainActivity.this, "Failed to connect to:" +exception.toString(), Toast.LENGTH_SHORT).show();
}
});
System.out.println(client.isConnected());
// if (client.isConnected()){
// Log.v("INFO 22222:", "about to subscribe with: "+ temptopic + tempqos);
// client.subscribe(temptopic,tempqos);
// }
} catch (MqttException e) {
e.printStackTrace();
}
client.setCallback(new MqttCallback() {
@Override
public void connectionLost(Throwable throwable) {
}
@Override
public void messageArrived(String s, MqttMessage mqttMessage) throws Exception {
myMessageArrived(s,mqttMessage);
}
@Override
public void deliveryComplete(IMqttDeliveryToken iMqttDeliveryToken) {
}
});
}catch (MqttException e){
e.printStackTrace();
}
}else
{
try {
client.unsubscribe(topicStr);
client.subscribe(temptopic,tempqos);
topicStr = temptopic;
qos = tempqos;
} catch (MqttException e) {
e.printStackTrace();
}
}
}
break;
}
}
}
public boolean isFlashOn(){
return (this.parameters.getFlashMode().equals(android.hardware.Camera.Parameters.FLASH_MODE_ON) || this.parameters.getFlashMode().equals(android.hardware.Camera.Parameters.FLASH_MODE_TORCH));
}
if (isFlashAvailable()){
camera = Camera.open();
parameters = camera.getParameters();
}