Develop Reference

New layout doesn't pop up

I am making an app in android Studio and if you open the app on your phone you see the Launcer activity. I have a button that sends you to a new activity where te game is located. Once i click the Start button, The app closes and doesn't goes to the other activity. Why is that?
This is my code of the Launcher activity:
package joenio.sirname;
import android.content.Intent;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;
public class SirName_launcher extends AppCompatActivity {
public static Button button_start;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_sir_name_launcher);
StartButton();
}
public void StartButton(){
button_start = (Button) findViewById(R.id.button_start);
button_start.setOnClickListener(
new View.OnClickListener() {
#Override
public void onClick(View v) {
Intent intent1 = new Intent("joenio.sirname.Game");
startActivity(intent1);
}
}
);
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
getMenuInflater().inflate(R.menu.menu_sir_name_launcher, menu);
return true;
}
#Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
//noinspection SimplifiableIfStatement
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
}
And this is the code of the second activity:
package joenio.sirname;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import java.util.ArrayList;
import android.widget.Toast;
public class Game extends AppCompatActivity {
public static EditText editText_surname;
public static TextView textView_name;
public static Button button_check;
int x =0; //to keep track of qustions
//Context editText_this = this;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_game);
Displayquestions();
}
public void Displayquestions(){
final ArrayList<String> mQuestionList = new ArrayList<>();
mQuestionList.add("1+2");
mQuestionList.add("6+8");
mQuestionList.add("5 * 6");
mQuestionList.add("8*5");
mQuestionList.add("6+16");
mQuestionList.add("18-5");
textView_displayquestion.setText((mQuestionList.get(x)));//displayquestion is textview
final ArrayList<String> mAnswerList=new ArrayList<>();
mAnswerList.add("3");
mAnswerList.add("14");
mAnswerList.add("30");
mAnswerList.add("40");
mAnswerList.add("22");
mAnswerList.add("13");
//button_check is the button when user click it will first check answer and than move to next question if answer is correct
button_check.setOnClickListener(new View.OnClickListener(){
#Override
public void onClick(View v) {
//editText_this;
String answer = editText_ans.getText().toString();
if (answer.equals(mAnswerList.get(x))) {
x = x + 1;
textView_displayquestion.setText(mQuestionList.get(x)); //answer is correct display next quesion
Toast.makeText(getApplication().getBaseContext(),
(R.string.Nice), Toast.LENGTH_SHORT).show();
} else {
Toast.makeText(getApplication().getBaseContext(),
(R.string.tryagain), Toast.LENGTH_SHORT).show();
}
}
});
}
}

You are no where initializing your TextView and Button which must be causing NullPointerException.
Change your Game activity like this
TextView textView_displayquestion;
Button button_check;
EditText editText_ans;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_game);
textView_displayquestion = (TextView)findViewById(R.id.displayquestion); //change as per your id
button_check = (Button)findViewById(R.id.buttoncheck); //change as per your id
editText_ans = (EditText)findViewById(R.id.answer); //change as per your id
Displayquestions();
}

In your button click , change the code as below.
Intent intent1 = new Intent(SirName_launcher.this, Game.class);
startActivity(intent1);
And also add the new Game Activity in your Manifest file too.

Sequential display of images automatically

I am using the code below to display images sequentially via button click. Now I want to display these images automatically after a particular time period. They should be displayed and change after a particular time and where the addition will be needed in the same code.
import android.os.Bundle;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.Snackbar;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.View;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.Button;
import android.widget.ImageView;
public class MainActivity extends AppCompatActivity {
private static ImageView imgView;
private static Button ButtonSbm;
private int current_image_index;
int [] images={R.mipmap.ic_launcher,R.mipmap.ic_launcher1};
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
FloatingActionButton fab=(FloatingActionButton)findViewById(R.id.fab);
fab.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
Snackbar.make(view, "Replace with your own action",Snackbar.LENGTH_LONG)
.setAction("Action", null).show();
}
});
buttonClick();
}
public void buttonClick(){
imgView =(ImageView)findViewById(R.id.imageView);
ButtonSbm=(Button)findViewById(R.id.button);
ButtonSbm.setOnClickListener(
new View.OnClickListener(){
public void onClick(View v){
current_image_index++;
current_image_index=current_image_index %images.length;
imgView.setImageResource(images[current_image_index]);
}
}
);
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_main, menu);
return true;
}
#Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
//noinspection SimplifiableIfStatement
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
}

Hi you can use he following code
public class TestService extends IntentService {
Context ctx;
private CountDownTimer countDownTimer;
public static final String Tag="TestService";
private long startTime= 2 * 1000;
int index = 0;
private final long interval = 1 * 1000;
public TestService() {
super("TestService");
// TODO Auto-generated constructor stub
}
#Override
protected void onHandleIntent(Intent intent) {
countDownTimer = new MyCountDownTimer(startTime, interval);
countDownTimer.start();
Looper.loop();
}
public class MyCountDownTimer extends CountDownTimer {
public MyCountDownTimer(long startTime, long interval) {
super(startTime, interval);
}
#Override
public void onFinish() {
// do as per you required
}
#Override
public void onTick(long millisUntilFinished) {
Log.v(Tag,"Inside OnTick()");
// do as per you required
}
}
}

Class won't execute properly inside main activity? [duplicate]

This question already has answers here:
How to use java classes within one activity?
(4 answers)
Closed 7 years ago.
How can you use a java class within one activity, by that I mean is having different components of that activity spread out in a bunch of java classes. I'm a little new to android and this is what I have tried so far:
MainActivity.java
package com.example.alex.myapplication;
import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
public class MainActivity extends ActionBarActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
new Something(this);
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_main, menu);
return true;
}
#Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
//noinspection SimplifiableIfStatement
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
}
Something.java
import android.view.View;
import android.widget.EditText;
import android.widget.Button;
import android.app.Activity;
public class Something {
private Activity activity;
private Button add,subtract,multiply,devide;
private EditText editA, editB, editC;
private double doubleA,doubleB,doubleC;
public Something(Activity a){
activity=a;
click();
}
public void click(){
editA = (EditText) activity.findViewById(R.id.editText);
editB = (EditText) activity.findViewById(R.id.editText2);
editC = (EditText) activity.findViewById(R.id.editText3);
doubleA =Double.parseDouble(editA.getText().toString());
doubleB =Double.parseDouble(editB.getText().toString());
add = (Button) activity.findViewById(R.id.add);
subtract = (Button) activity.findViewById(R.id.subtract);
multiply = (Button) activity.findViewById(R.id.multiply);
devide = (Button) activity.findViewById(R.id.devide);
add.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
doubleC = doubleA+doubleB;
String s = "" + doubleC;
editC.setText(s);
}
});
subtract.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
doubleC = doubleA-doubleB;
String s = "" + doubleC;
editC.setText(s);
}
});
multiply.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
doubleC = doubleA*doubleB;
String s = "" + doubleC;
editC.setText(s);
}
});
devide.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
doubleC = doubleA/doubleB;
String s = "" + doubleC;
editC.setText(s);
}
});
}
}
So I wasn't sure why my listeners weren't working on my buttons so I tried passing the activity to the class that has the listeners added to the buttons but that didn't work in fact now my application won't even start in the emulator. All I wanted to do was have "MainActivity" handle the "Gui" and have the "Something" class handle the listeners but no matter what I do I can't seem to make them communicate with one another to form one Activity.
Someone suggested to do a pass in main activity Something s = new Something(MainActivity.this); and call it from within main activity like this s.click(); but that didn't work.

in android every class that extends activity just have a one xml Layout to view and handle this XML file just in it's Activities,and you can make a lot of java classes that send alot of parameter but when you want to handle XML behavioral you should do in own class that Extends Activity,so you can do this:
public class MainActivity extends ActionBarActivity {
Button myBtn;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
new Something(this);
myBtn=(Button)findViewById(R.id.Btn);
myBtn.setOnClickListener(new OnClickListener() {
#Override
public void onClick(View v) {
// TODO Auto-generated method stub
}
});
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_main, menu);
return true;
}
#Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
//noinspection SimplifiableIfStatement
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}

Android SDK public void gets an error

I have a problem by following a tutorial for making an app. But now I get an error by adding an respond
for a button. It gives an error at public void sendMessage, but I cant see what is wrong.
package com.example.myfirstapp;
import android.os.Bundle;
import android.support.v7.app.ActionBarActivity;
import android.view.Menu;
import android.view.MenuItem;
import android.content.Intent;
/** Called when the user clicks the Send button */
public void sendMessage(View view){
Intent intent = new Intent(this, DisplayMessageActivity.class);
}
public class MainActivity extends ActionBarActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
#Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
}

those lines
/** Called when the user clicks the Send button */
public void sendMessage(View view){
Intent intent = new Intent(this, DisplayMessageActivity.class);
}
go into your class, after
public class MainActivity extends ActionBarActivity {

Your function is outside the activity.
Move
public void sendMessage(View view){
Intent intent = new Intent(this, DisplayMessageActivity.class);
}
inside Activity like this:
public class MainActivity extends ActionBarActivity {
//other code i.e. onCreate etc
public void sendMessage(View view){
Intent intent = new Intent(this, DisplayMessageActivity.class);
}
}

Android - How to re-start MainActivity after clicking a button in another class?

so I'm fairly new to Android. Lemme just explain first:
I'm trying to make a small portable music app, just for my phone and to test my skills/review what I've learned. I have the mainactivity setup to pick a song with 1 of 4 buttons, and it'll start another activity with buttons to pause, resume, and go back to the song selection screen (MainActivity). I'm trying to get the back button to both release the player and finish the activity, and I've tried many different things but nothing seems to work; the app closes due to some exception (a common one being NullPointerException).
So here's MainActivity:
package me.lemmy.portablemusic.app;
import android.media.MediaPlayer;
import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.content.Intent;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;
public class MainActivity extends ActionBarActivity {
Button wreckingBall, happy, lig, ligMulti;
Intent songPickedActivity = new Intent("me.lemmy.portablemusic.app.SONGPICKED");
public static MediaPlayer player;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
//set buttons
wreckingBall = (Button) findViewById(R.id.song_wreck);
happy = (Button) findViewById(R.id.song_happy);
lig = (Button) findViewById(R.id.song_lig);
ligMulti = (Button) findViewById(R.id.song_lig_multi);
//listeners
wreckingBall.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
startActivity(songPickedActivity);
player = MediaPlayer.create(MainActivity.this, R.raw.wrecking_ball);
player.start();
}
});
happy.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
startActivity(songPickedActivity);
player = MediaPlayer.create(MainActivity.this, R.raw.happy);
player.start();
}
});
lig.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
startActivity(songPickedActivity);
player = MediaPlayer.create(MainActivity.this, R.raw.let_it_go);
player.start();
}
});
ligMulti.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
startActivity(songPickedActivity);
player = MediaPlayer.create(MainActivity.this, R.raw.let_it_go_multi);
player.start();
}
});
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
#Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
public static MediaPlayer getPlayer(){
return player;
}
}
and here's my SongPicked activity:
package me.lemmy.portablemusic.app;
import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.media.MediaPlayer;
import android.widget.TextView;
/**
* Created by Lemuel on 6/20/14.
*/
public class SongPicked extends Activity {
TextView text;
Button pause, resume, back;
MediaPlayer player;
#Override
protected void onCreate(Bundle savedInstanceState){
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_songpicked);
text = (TextView) findViewById(R.id.tvPlaying);
pause = (Button) findViewById(R.id.buttonPause);
resume = (Button) findViewById(R.id.buttonResume);
back = (Button) findViewById(R.id.buttonBack);
player = MainActivity.getPlayer();
pause.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
player.pause();
}
});
resume.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
player.start();
}
});
back.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view){
player.release();
}
});
}
#Override
protected void onPause(){
super.onPause();
finish();
}
}
Any help is appreciated, thanks!
P.S. I know I can't use copyrighted music in my apps, this is just a test.

I suggest to first make sure the activity is in the AndroidManifest file. Second is to change your intent from this:
Intent songPickedActivity = new Intent("me.lemmy.portablemusic.app.SONGPICKED");
into:
Intent songPickedActivity = new Intent(this, SongPicked.class);
Do it as well on the songPickedActivity when going back to MainActivity. You can use putExtra to send data to next intent. For more information click this link.