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mqttブローカーに接続し、着信音を一時停止または懐中電灯を開閉する手順を聴くこのアンドロイドアプリがあります。アクティビティから復帰した後に懐中電灯機能がクラッシュする
設定を変更してからこの後に関数flashOnOffを呼び出すまでは、次のように動作します。それから私はnullポインタの例外を得るが、私はなぜ理解できない。
これは、（私はいくつかのスペースを節約するために私の輸入が含まれていませんでした）私のコードです：
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));
}
私も設定アクティビティコードを提供することができますが
なぜこのポストや私をより良くすることはできません...何かが間違っている場合は何を教えて、それを修正することができます –
あなたはNullpointer例外がメソッド "flashOnOff"おそらく変数 "camera"と "parameters"が初期化されていないからでしょうか？また、より多くの情報と少ないコードは良いと思います。 – Tyrmos
[NullPointerExceptionとは何ですか？それを修正するにはどうすればいいですか？]（https://stackoverflow.com/questions/218384/what-is-a-nullpointerexception- and-how-do-i-fix-it） – csmckelvey