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How to use new class wiith media player in main activity?

I'm trying to create new class, becouse I will have there many of sound file, but I don't know how to use it in main ativity. Here is my example code of sound.java:
package app.damian.komunikat_v1;
import android.media.MediaPlayer;
import android.support.v7.app.AppCompatActivity;
public class sound extends MainActivity{
final MediaPlayer sound1 = MediaPlayer.create(this,R.raw.miau);
final MediaPlayer sound2 = MediaPlayer.create(this,R.raw.lol);
}
And now i'm trying to use sound1.start(); in main activity, but i don't know how. Any suggestions?
EDIT:
This is my MainActivity.java:
this is my MainActivity.java:
package app.damian.komunikat_v1;
import android.media.MediaPlayer;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
public class MainActivity extends AppCompatActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Button guzik = findViewById(R.id.button);
final MediaPlayer sound1 = MediaPlayer.create(this,R.raw.miau);
guzik.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
sound1.start();
};
});
}
}

I found a different solution. Instead of creating new class with list of sound file, I had created an array of sounds in main activity class.

OnSharedPreferenceChangeListener Won't Work?

I am trying to change the application background color, and the font type via theme when a preference is changed in the prefs area.
So far I have the preferences working but when I put the listener in, it just does not get called. I am testing using toasts to see if it appears.
My Code:
package alertssystem.lsa13tafeproj.lsa13.resistorcalculator;
import android.app.ActionBar;
import android.content.Intent;
import android.content.SharedPreferences;
import android.graphics.Color;
import android.os.Bundle;
import android.preference.PreferenceActivity;
import android.preference.PreferenceFragment;
import android.preference.PreferenceManager;
import android.widget.RelativeLayout;
import android.widget.Toast;
import java.util.prefs.PreferenceChangeEvent;
import java.util.prefs.PreferenceChangeListener;
public class Prefs extends PreferenceActivity
{
#Override
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
getFragmentManager().beginTransaction().replace(android.R.id.content, new PreferencesFragment()).commit();
}
#Override
public void onBackPressed()
{
Intent intent = new Intent(getApplicationContext(), MainActivity.class);
startActivity(intent);
}
public static class PreferencesFragment extends PreferenceFragment
{
#Override
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
addPreferencesFromResource(R.xml.prefs);
}
}
}
There is no changeListener in above code as none of the solutions I found worked, can someone please tell me how I can implement this into this.
The user clicks on the ListPreference and it has the 2 options I have inserted, but nothing happens when new option is selected.

This works for me:
public class MyPreferenceFragment extends PreferenceFragment implements
OnSharedPreferenceChangeListener {
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
addPreferencesFromResource(R.xml.prefs);
PreferenceManager.getDefaultSharedPreferences(getActivity()).registerOnSharedPreferenceChangeListener(this);
}
#Override
public void onDestroy() {
PreferenceManager.getDefaultSharedPreferences(getActivity()).unregisterOnSharedPreferenceChangeListener(this);
super.onDestroy();
}
#Override
public void onSharedPreferenceChanged(SharedPreferences sharedPreferences, String key) {
// Toast
}
}
Make sure you register your listener before changing the pref, and not unregistering it until you do.

main cannot be resolved or is not a field # helloworld

So I just started programming in eclipse, and I got the error ``main cannot be resolved or is not a field" with this code:
package com.example.wouter1;
import android.app.Activity;
import android.os.Bundle;
import android.widget.TextView;
import com.example.wouter1.R;
public class HelloWorldActivity extends Activity {
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main); // PROBLEM HERE <<<< # MAIN
TextView myText = new TextView(this);
myText.setText("hello world");
setContentView(myText);
}
}

My Junit test doesn't run

I'm new to Java, Android and JUnit. I want to learn how to write JUnit tests for an Android application. To that end, I have a very simple Android app (2 activities, 2 buttons, each button goes to the other activity). I want to test the button. This app runs fine on my phone when it's plugged in. I've been looking at the samples provided in the SDK, and I am trying to emulate them.
My problem is that when I right-click on my test project, and choose Run As -> Android JUnit test, nothing happens. I don't know why.
My test code.
package com.example.twoactivities.test;
import android.app.Instrumentation.ActivityMonitor;
import android.test.ActivityInstrumentationTestCase2;
import android.test.suitebuilder.annotation.SmallTest;
import android.widget.Button;
import com.example.twoactivities.MainActivity;
import com.example.twoactivities.MainActivity2;
public class ClickButton extends ActivityInstrumentationTestCase2<MainActivity> {
private Button mButton2;
private long TIMEOUT_IN_MS = 100000;
public ClickButton() {
super(MainActivity.class);
}
#Override
protected void setUp() throws Exception {
super.setUp();
final MainActivity a = getActivity();
// ensure a valid handle to the activity has been returned
assertNotNull(a);
}
#SmallTest
public void click(){
// Set up an ActivityMonitor
ActivityMonitor activityMonitor = getInstrumentation().addMonitor(MainActivity2.class.getName(), null, false);
//check if button is enabled
assertTrue("button is enabled", mButton2.isEnabled());
//click button
mButton2.performClick();
MainActivity2 MainActivity2 = (MainActivity2) activityMonitor.waitForActivityWithTimeout(TIMEOUT_IN_MS );
assertNotNull("MainActivity2 is null", MainActivity2);
// assertEquals("Monitor for MainActivity2 has not been called", 1, activityMonitor.getHits());
// assertEquals("Activity is of wrong type", MainActivity2.class, MainActivity2.getClass());
// Remove the ActivityMonitor
getInstrumentation().removeMonitor(activityMonitor);
}
// public void tearDown() {
// }
}
(I know it's really simple, but I'm just trying to get the basics down.)
My application.
package com.example.twoactivities;
import com.example.twoactivities.R;
import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
public class MainActivity extends Activity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}
public void activity2(View view){
Intent intent = new Intent(this,com.example.twoactivities.MainActivity2.class);
startActivity(intent);
}
}
Activity 2 of my application.
package com.example.twoactivities;
import com.example.twoactivities.R;
import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
public class MainActivity2 extends Activity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main2);
}
public void activity1(View view){
Intent intent = new Intent(this,com.example.twoactivities.MainActivity.class);
startActivity(intent);
}
}
Any ideas why my test class doesn't run?
Thanks,
Stephanie

You have to right click on the test itself, not the project.
According to documentation Android testing API supports JUnit 3 code style, but not JUnit 4. Try naming your test method testClick

imageView android not recognized error

I am wondering why image view in java class pots error
like ImageView smtin;
And there's error.
It dont recognize it like class...
My project code is:
package com.klemenjezakon.koceSLO;
import android.os.Bundle;
import android.app.Activity;
import android.content.Intent;
import android.view.Window;
import android.view.WindowManager;
import android.widget.ImageView;
ImageView slika;
public class MainActivity extends Activity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
requestWindowFeature(Window.FEATURE_NO_TITLE);
getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN,
WindowManager.LayoutParams.FLAG_FULLSCREEN);
Intent i = getIntent();
koca podatki=(koca)i.getSerializableExtra("koca");
setContentView(R.layout.koca);
}
}

You have to put inside your class. So instead of:
ImageView slika;
public class MainActivity extends Activity {
it have to be:
public class MainActivity extends Activity {
ImageView slika;