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app crashes when getting a reference on android studio

I'm a newbie in programming and stuff.. I'm using the android-youtube-player package from Pierfrancesco Soffritti.. and when I try to Get a reference to YouTubePlayer and run the app it crashes..
`
package com.example.youtuuuuuuuuuuuuuuube;
import androidx.annotation.LayoutRes;
import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;
import android.content.Context;
import android.os.Bundle;
import android.view.View;
import com.pierfrancescosoffritti.androidyoutubeplayer.core.player.YouTubePlayer;
import com.pierfrancescosoffritti.androidyoutubeplayer.core.player.listeners.AbstractYouTubePlayerListener;
import com.pierfrancescosoffritti.androidyoutubeplayer.core.player.listeners.YouTubePlayerListener;
import com.pierfrancescosoffritti.androidyoutubeplayer.core.player.options.IFramePlayerOptions;
import com.pierfrancescosoffritti.androidyoutubeplayer.core.player.views.YouTubePlayerView;
import com.pierfrancescosoffritti.androidyoutubeplayer.core.ui.DefaultPlayerUiController;
import com.pierfrancescosoffritti.androidyoutubeplayer.core.ui.PlayerUiController;
import com.pierfrancescosoffritti.androidyoutubeplayer.core.ui.menu.YouTubePlayerMenu;
public class MainActivity extends AppCompatActivity {
private YouTubePlayer youTubePlayer;
private YouTubePlayerView youTubePlayerView;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}
public void playvideo(View v){
youTubePlayer.loadVideo("S0Q4gqBUs7c", 1f);
}
}
`
my XML code
<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" >
<com.pierfrancescosoffritti.androidyoutubeplayer.core.player.views.YouTubePlayerView
android:id="#+id/youtube_player_view"
android:layout_width="match_parent"
android:layout_height="wrap_content"
app:videoId="S0Q4gqBUs7c"
app:autoPlay="true"
/>
<Button
android:id="#+id/button2"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:onClick="playvideo"
android:text="Button" />
I tried to get the reference using OnStart() method, added a button but all of that don't work :(

How to change multiple fragments by clicking on a single button in android?

Greeting!
I’m practicing on fragments topic. My main issue is how to change multiple fragments by clicking a single button “NEXT” or “PREVIOUS” as you may know some apps or books change pages by clicking on the next or previous buttons. If there are only two are four fragments then no issue to add buttons but what if there are multiple fragments like 50 or 100? First I try to find solutions from Google and YouTube but I find that we can change pictures through this method. Is it possible that we can change fragments through this method or not if possible so please some articles with the same solutions to share your experience? Or I should need to use images to do this. My main activity java code and XML code are below and the first fragment and code other three fragments are also the same.
// Main_Activity.java
package com.test.fragment_practice;
import androidx.appcompat.app.ActionBar;
import androidx.appcompat.app.AppCompatActivity;
import androidx.fragment.app.Fragment;
import androidx.fragment.app.FragmentManager;
import androidx.fragment.app.FragmentTransaction;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.LinearLayout;
import com.test.fragment_practice.Fragments.FirstFragment;
import com.test.fragment_practice.Fragments.ForthFragment;
import com.test.fragment_practice.Fragments.SecondFragment;
import com.test.fragment_practice.Fragments.ThirdFragment;
import java.util.ArrayList;
import java.util.List;
public class MainActivity extends AppCompatActivity {
LinearLayout layout;
Button btn1,btn2;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
layout = (LinearLayout) findViewById(R.id.linearLayout2);
btn1 = (Button) findViewById(R.id.btnpre);
btn2 = (Button) findViewById(R.id.btnnxt);
btn1.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
FirstFragment fragment = new FirstFragment();
FragmentTransaction fragmentTransaction = getSupportFragmentManager().beginTransaction();
fragmentTransaction.replace(R.id.linearLayout2, fragment);
fragmentTransaction.commit();
}
});
btn2.setOnClickListener((view) ->{
SecondFragment fragment2 = new SecondFragment();
FragmentTransaction fragmentTransaction = getSupportFragmentManager().beginTransaction();
fragmentTransaction.replace(R.id.linearLayout2, fragment2);
fragmentTransaction.commit();
});
}
}
//activity_main.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
tools:context=".MainActivity">
<LinearLayout
android:id="#+id/linearLayout"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:background="#FF3700B3"
android:orientation="horizontal">
<Button
android:id="#+id/btnpre"
android:layout_width="wrap_content"
android:layout_height="match_parent"
android:layout_margin="5dp"
android:layout_weight="1"
android:backgroundTint="#FF0000"
android:text="Previous"
android:textColor="#6900FF"
android:textSize="24sp" />
<Button
android:id="#+id/btnnxt"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_margin="5dp"
android:layout_weight="1"
android:backgroundTint="#FFFF00"
android:text="Next"
android:textColor="#6900FF"
android:textSize="24sp" />
</LinearLayout>
<LinearLayout
android:id="#+id/linearLayout2"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"/>
</LinearLayout>
// First_Fragment.java
package com.test.fragment_practice.Fragments;
import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import androidx.fragment.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;
import com.test.fragment_practice.R;
import com.test.fragment_practice.SecondActivity;
public class FirstFragment extends Fragment {
public FirstFragment() {
// Required empty public constructor
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
super.onCreateView(inflater, container, savedInstanceState);
return inflater.inflate(R.layout.fragment_first, container, false);
}
}

Android Studio Display Long in Button Text

How would I go about displaying a Long or Int inside of a button element's text field (or a TextView)? Would the same method work for displaying a String inside the text field? Thanks.
Here is my code for MainActivity
import android.content.Intent;
import android.os.Bundle;
import android.os.Environment;
import android.os.StatFs;
import android.view.MenuInflater;
import android.view.View;
import android.view.Menu;
import android.widget.Button;
import android.widget.Toast;
import com.google.android.material.navigation.NavigationView;
import androidx.appcompat.widget.PopupMenu;
import androidx.navigation.NavController;
import androidx.navigation.Navigation;
import androidx.navigation.ui.AppBarConfiguration;
import androidx.navigation.ui.NavigationUI;
import androidx.drawerlayout.widget.DrawerLayout;
import androidx.appcompat.app.AppCompatActivity;
import androidx.appcompat.widget.Toolbar;
import java.io.File;
public class MainActivity extends AppCompatActivity {
Button mainstorage;
private AppBarConfiguration mAppBarConfiguration;
private static final int REQUEST_WRITE_STORAGE = 112;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Toolbar toolbar = findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
DrawerLayout drawer = findViewById(R.id.drawer_layout);
NavigationView navigationView = findViewById(R.id.nav_view);
StatFs statFs = new
StatFs(Environment.getRootDirectory().getAbsolutePath());
long blockSize = statFs.getBlockSize();
long totalSize = statFs.getBlockCount()*blockSize;
long availableSize = statFs.getAvailableBlocks()*blockSize;
long freeSize = statFs.getFreeBlocks()*blockSize;
String internalSize = Long.toString(blockSize);
myBtn.setText(internalSize);
}
}
And my XML for the Fragment.
<androidx.constraintlayout.widget.ConstraintLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".ui.home.HomeFragment">
<LinearLayout
android:background="#android:color/transparent"
android:id="#+id/firstrow"
android:layout_height="0dp"
android:layout_width="match_parent"
android:orientation="horizontal"
android:gravity="start"
app:layout_constraintHeight_percent="0.22"
tools:ignore="MissingConstraints">
<Button
android:contentDescription="#string/goInternalDesc"
android:id="#+id/main"
android:layout_width="0dp"
android:layout_height="match_parent"
android:layout_weight="1"
android:background="#android:color/transparent"
android:drawableTop="#drawable/storage"
android:minWidth="20dp"
android:text="Main Storage"
android:minHeight="20dp" />
</LinearLayout>
I am wondering why I am getting a build error when trying to set the text of the button to the String in my code. I thought it might be because I had set the text of the button in the XML but removing that had no effect- I am still getting a "Cannot resolve symbol" error on my MainActivity.

You can either use
btn.setText(String.valueOf(myLong));
btn.setText(String.valueOf(myInt));
Or
btn.setText(Long.toString(myLong));
btn.setText(Integer.toString(myInt));

I normally do this way
btn.setText(number+"");

For example:
If you have a button called jButton1, you just need to use this code:
String test = String.valueOf(your_int_or_long);
jButton1.setText(test);
And yes, for the text field is the same method.

Cannot find symbol id in button

Hello i am making a simple push button in android and this is my mainactivity file
package dk.troll.android;
import android.app.Activity;
import android.content.Intent;
import android.net.Uri;
import android.os.Bundle;
import android.widget.Button;
import android.view.View;
import android.view.View.OnClickListener;
public class MainActivity extends Activity {
Button button;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
addListenerOnButton();
}
public void addListenerOnButton() {
button = (Button) findViewById(R.id.button1);
button.setOnClickListener(new OnClickListener() {
#Override
public void onClick(View arg0) {
Intent browserIntent =
new Intent(Intent.ACTION_VIEW, Uri.parse("http://www.troll.dk"));
startActivity(browserIntent);
}
});
}
}
and this is my xml file
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
>
<TextView
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="Lorem Ipsum and so much other stuff"
/>
<Button
android:id="#+id/button1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Button - Go To Troll" />
</LinearLayout>
On this line button = (Button) findViewById(R.id.button1); i get the error
cannot find symbol:variable id location:class R
Since the contents of class
r
are auto-generated,how can i fix the error?

fist restart eclipse
then doing this :
1.import R class to your activity, Import dk.troll.android.R;
2.be sure the all recurse file have not any error then try to clean project from Project then Clean.
3.build your project

The third link is not working

I created a button to take me to another page and in that other page, there is another button that takes to another page, so page1, page2 and page3 that it's not working with me, check http://oi62.tinypic.com/2m7g4et.jpg when I click on "Fish guide" it takes me to the other one which has another button "Fish", when I click on "Fish" it doesn't take me to the 3rd page!
activity_main.xml
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:background="#1d72c3" >
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_centerHorizontal="true"
android:gravity="center"
android:orientation="vertical"
android:textStyle="italic" >
<Button
android:id="#+id/fishguide"
android:layout_width="fill_parent"
android:layout_height="55dp"
android:layout_alignParentRight="true"
android:layout_alignParentTop="true"
android:text="Fish guide"
android:textSize="20sp"
android:textStyle="italic" />
</LinearLayout>
</RelativeLayout>
fishguide.xml
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:background="#1d72c3"
android:textStyle="italic" >
<LinearLayout
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_centerHorizontal="true"
android:orientation="vertical"
android:textStyle="italic" >
<Button
android:id="#+id/fish"
android:layout_width="fill_parent"
android:layout_height="60dp"
android:layout_alignParentRight="true"
android:layout_alignParentTop="true"
android:text="Fish"
android:textSize="22sp"
android:textStyle="italic" />
</LinearLayout>
</RelativeLayout>
fish.xml
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="#1d72c3" >
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_centerHorizontal="true"
android:orientation="vertical"
android:textStyle="italic" >
<ImageView
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:gravity="center"
android:src="#drawable/bala" />
<TextView
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:gravity="center"
android:text="Balabanka"
android:textSize="18sp"
android:textStyle="italic" />
</LinearLayout>
</RelativeLayout>
MainActivity.java
package com.d.di;
import android.app.Activity;
import android.content.Context;
import android.content.Intent;
import android.os.Bundle;
import android.widget.Button;
import android.view.View;
import android.view.View.OnClickListener;
public class MainActivity extends Activity {
Button button3;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
addListenerOnButton();
}
public void addListenerOnButton() {
final Context context = this;
button3 = (Button) findViewById(R.id.fishguide);
button3.setOnClickListener(new OnClickListener() {
#Override
public void onClick(View arg0) {
Intent intent = new Intent(context, PageThree.class);
startActivity(intent);
}
});
}
}
PageThree.java
package com.d.di;
import android.app.Activity;
import android.os.Bundle;
import android.widget.Button;
public class PageThree extends Activity {
Button button3;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.fishguide);
}
}
I did the third page, it runs but it was .. wrong
MainActivity2.java
package com.d.di;
import android.app.Activity;
import android.content.Context;
import android.content.Intent;
import android.os.Bundle;
import android.widget.Button;
import android.view.View;
import android.view.View.OnClickListener;
public class MainActivity2 extends Activity {
Button fishlink;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.fishguide);
addListenerOnButton();
}
public void addListenerOnButton() {
final Context context = this;
fishlink = (Button) findViewById(R.id.fish);
fishlink.setOnClickListener(new OnClickListener() {
#Override
public void onClick(View arg0) {
Intent intent = new Intent(context, PageFish.class);
startActivity(intent);
}
});
}
}
PageFish.java
package com.d.di;
import android.app.Activity;
import android.os.Bundle;
import android.widget.Button;
public class PageFish extends Activity {
Button fishlink;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.fish);
}
}
Help :)
Edit / it goes "Fish guide" to "Fish" when I click on "Fish" it takes me again to "Fish" and so on, it doesn't go to the third page!
PageThree.java
package com.d.di;
import android.app.Activity;
import android.content.Context;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
public class PageThree extends Activity {
Button button3;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.fishguide);
addListenerOnButton();
}
public void addListenerOnButton() {
final Context context = this;
button3 = (Button) findViewById(R.id.fish);
button3.setOnClickListener(new OnClickListener() {
#Override
public void onClick(View arg0) {
Intent intent = new Intent(context, PageThree.class);
startActivity(intent);
}
});
}
}

You have used
setContentView(R.layout.fishguide);
in PageThree.java
Change it to the xml you want to show with that third image in image. say, third.xml
setContentView(R.layout.third);
And you are done.

NOTE: You are getting the same Layout again and again because in PageThree.java you are starting the activity with intent PageThree.java. Instead just change that to PageFish.java.
So when you are at second layout (PageThree.java), just start activity for third layout (PageFish.java) on button click as follows -
PageThree.java
package com.d.di;
import android.app.Activity;
import android.os.Bundle;
import android.widget.Button;
public class PageThree extends Activity {
Button button3;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.fishguide);
button3 = (Button) findViewById(R.id.fish);
button3.setOnClickListener(new OnClickListener() {
#Override
public void onClick(View arg0) {
Intent intent = new Intent(PageThree.this, PageFish.class);
startActivity(intent);
}
});
}
}