为什么来自不同布局文件的 textView 不能正确运行 setText 但来自 activity_main 的 textViews 会？

Question

The program is supposed to run getCurrentLocation and then set the textView "coordinates" to the value of the coordinates called. That text view is part of a pager view that draws from a separate .xml file than the main layout "activity_main".

 public class MainActivity extends AppCompatActivity { CardAdapter CardAdapter; String coordinatesFinal; FusedLocationProviderClient fusedLocationProviderClient; TextView coordinates; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); fusedLocationProviderClient = LocationServices.getFusedLocationProviderClient(MainActivity.this); if (ActivityCompat.checkSelfPermission(MainActivity.this, Manifest.permission.ACCESS_FINE_LOCATION) == PackageManager.PERMISSION_GRANTED && ActivityCompat.checkSelfPermission(MainActivity.this, Manifest.permission.ACCESS_COARSE_LOCATION) == PackageManager.PERMISSION_GRANTED) { getCurrentLocation(); }else { ActivityCompat.requestPermissions(MainActivity.this, new String[]{Manifest.permission.ACCESS_FINE_LOCATION, Manifest.permission.ACCESS_COARSE_LOCATION},100); } setupCardItems(); ViewPager2 CardViewPager = findViewById(R.id.cardViewPager); CardViewPager.setAdapter(CardAdapter); } @Override public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) { if (requestCode == 100 & grantResults.length > 0 && (grantResults[0] + grantResults[1]) == PackageManager.PERMISSION_GRANTED) { getCurrentLocation(); }else { Toast.makeText(getApplicationContext(), "Permission denied.",Toast.LENGTH_SHORT).show(); } } @SuppressLint("MissingPermission") public void getCurrentLocation() { coordinates = findViewById(R.id.coordinates); LocationManager locationManager = (LocationManager) getSystemService ( Context.LOCATION_SERVICE ); if (locationManager.isProviderEnabled(LocationManager.GPS_PROVIDER) || locationManager.isProviderEnabled(LocationManager.NETWORK_PROVIDER)) { fusedLocationProviderClient.getLastLocation().addOnCompleteListener(task -> { Location location = task.getResult(); if (location != null) { coordinates.setText(location.getLatitude()+", "+location.getLongitude()); }else { LocationRequest locationRequest = new LocationRequest().setPriority(LocationRequest.PRIORITY_HIGH_ACCURACY).setInterval(10000).setFastestInterval(1000).setNumUpdates(1); LocationCallback locationCallback = new LocationCallback() { @Override public void onLocationResult(LocationResult locationResult) { Location location1 = locationResult.getLastLocation(); coordinatesFinal = location1.getLatitude()+", "+location1.getLongitude(); } }; fusedLocationProviderClient.requestLocationUpdates(locationRequest,locationCallback, Looper.myLooper()); } }); }else { startActivity(new Intent(Settings.ACTION_LOCATION_SOURCE_SETTINGS).setFlags(Intent.FLAG_ACTIVITY_NEW_TASK)); } } //card view private void setupCardItems() { List<CardItem> CardItems = new ArrayList<>(); CardItem itemPageOne = new CardItem(); itemPageOne.setLocation("Home"); itemPageOne.setTemp("60°f"); itemPageOne.setWeatherDesc("Cloudy"); itemPageOne.setWeatherIcon(R.drawable.cloud); itemPageOne.setHum("75%"); itemPageOne.setVis("10"); itemPageOne.setPrecip("50%"); itemPageOne.setDew("40°f"); itemPageOne.setCloud("80%"); itemPageOne.setFog("75%"); CardItem itemPageTwo = new CardItem(); itemPageTwo.setLocation("Madison"); itemPageTwo.setTemp("60°f"); itemPageTwo.setWeatherDesc("Sunny"); itemPageTwo.setWeatherIcon(R.drawable.sun); itemPageTwo.setHum("75%"); itemPageTwo.setVis("10"); itemPageTwo.setPrecip("50%"); itemPageTwo.setDew("40°f"); itemPageTwo.setCloud("80%"); itemPageTwo.setFog("75%"); CardItem itemPageThree = new CardItem(); itemPageThree.setLocation("Milwaukee"); itemPageThree.setTemp("60°f"); itemPageThree.setWeatherDesc("Rainy"); itemPageThree.setWeatherIcon(R.drawable.rain); itemPageThree.setHum("75%"); itemPageThree.setVis("10"); itemPageThree.setPrecip("50%"); itemPageThree.setDew("40°f"); itemPageThree.setCloud("80%"); itemPageThree.setFog("75%"); CardItems.add(itemPageOne); CardItems.add(itemPageTwo); CardItems.add(itemPageThree); CardAdapter = new CardAdapter(CardItems); } }

I have narrowed it down to the line that doesn't work properly:

 coordinates.setText(location.getLatitude()+", "+location.getLongitude());

I have tested the exact same line as above, only using a textView from inside activity main, which works just fine. Any help is greatly appreciated.

Edit: The file actually does crash, I mistakenly said it didn't, and I added both .xml Files:

activity_main.xml:

<?xml version="1.0" encoding="utf-8"?>
<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"
    android:background="#566D8F"
    tools:context=".MainActivity">

    <LinearLayout
        android:id="@+id/topBar"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        app:layout_constraintTop_toTopOf="parent"
        android:gravity="center_horizontal"
        android:orientation="horizontal"
        android:paddingTop="15dp"
        android:paddingBottom="15dp">

        <ImageButton
            android:id="@+id/settingsBar2"
            android:layout_width="27sp"
            android:layout_height="27sp"
            android:layout_gravity="left"
            android:layout_marginStart="20sp"
            android:layout_marginEnd="70sp"
            android:background="@color/background"
            android:cropToPadding="true"
            android:scaleType="fitCenter" />

        <TextView
            android:id="@+id/homeName"
            android:layout_width="wrap_content"
            android:layout_height="match_parent"
            android:fontFamily="sans-serif-condensed-light"
            android:gravity="center_horizontal"
            android:maxLines="1"
            android:text="@string/app_name"
            android:textAlignment="center"
            android:textAllCaps="false"
            android:textColor="#FFFFFF"
            android:textSize="20sp"
            android:typeface="normal" />

        <ImageButton
            android:id="@+id/settingsBar"
            android:layout_width="27sp"
            android:layout_height="27sp"
            android:layout_gravity="right"
            android:layout_marginStart="70sp"
            android:layout_marginEnd="20sp"
            android:background="@drawable/settings_handle"
            android:cropToPadding="true"
            android:scaleType="fitCenter" />

    </LinearLayout>

    <androidx.viewpager2.widget.ViewPager2
        android:id="@+id/cardViewPager"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:layout_constraintTop_toBottomOf="@+id/topBar" />

</androidx.constraintlayout.widget.ConstraintLayout>

item_container_card.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"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:gravity="center"
    android:orientation="vertical"
    android:padding="20dp">

    <androidx.cardview.widget.CardView
        android:id="@+id/pagerCard"
        android:layout_width="match_parent"
        android:layout_height="440dp"
        android:layout_margin="20dp"
        app:cardBackgroundColor="#EAC0A0"
        app:cardCornerRadius="30dp"
        app:cardElevation="20dp">

        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:gravity="center"
            android:orientation="vertical">

            <TextView
                android:id="@+id/locationName"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:fontFamily="sans-serif-condensed-medium"
                android:gravity="center"
                android:textColor="@color/white"
                android:textSize="18sp" />

            <TextView
                android:id="@+id/coordinates"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:fontFamily="sans-serif-condensed-light"
                android:gravity="center"
                android:textColor="@color/white"
                android:textSize="12sp" />

            <TextView
                android:id="@+id/temperature"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:fontFamily="sans-serif-black"
                android:gravity="center"
                android:textColor="@color/white"
                android:textSize="50sp" />

            <TextView
                android:id="@+id/weatherDesc"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:fontFamily="sans-serif-condensed-light"
                android:gravity="center"
                android:textColor="@color/white"
                android:textSize="12sp" />

            <ImageView
                android:id="@+id/imageOnboarding"
                android:layout_width="150dp"
                android:layout_height="150dp"
                android:layout_margin="15dp"
                android:adjustViewBounds="true"
                android:contentDescription="@string/app_name" />

            <TableLayout
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:stretchColumns="1">

                <TableRow
                    android:layout_width="match_parent"
                    android:layout_height="match_parent"
                    android:gravity="center_horizontal">

                    <TextView
                        android:id="@+id/humidity"
                        android:layout_width="wrap_content"
                        android:layout_height="wrap_content"
                        android:layout_gravity="fill_horizontal"
                        android:fontFamily="sans-serif-condensed-light"
                        android:paddingLeft="30sp"
                        android:paddingBottom="5sp"
                        android:text="Humidity"
                        android:textColor="#FFFFFF"
                        android:textSize="18sp" />

                    <TextView
                        android:id="@+id/humVal"
                        android:layout_width="wrap_content"
                        android:layout_height="wrap_content"
                        android:layout_gravity="fill_horizontal"
                        android:fontFamily="sans-serif-condensed-medium"
                        android:paddingStart="10sp"
                        android:paddingEnd="15sp"
                        android:paddingBottom="5sp"
                        android:textColor="#FFFFFF"
                        android:textSize="18sp" />

                    <TextView
                        android:id="@+id/visibility"
                        android:layout_width="wrap_content"
                        android:layout_height="wrap_content"
                        android:fontFamily="sans-serif-condensed-light"
                        android:paddingStart="15sp"
                        android:paddingEnd="10sp"
                        android:paddingBottom="5sp"
                        android:text="Visibility"
                        android:textColor="#FFFFFF"
                        android:textSize="18sp" />

                    <TextView
                        android:id="@+id/visVal"
                        android:layout_width="wrap_content"
                        android:layout_height="wrap_content"
                        android:layout_gravity="fill_horizontal"
                        android:fontFamily="sans-serif-condensed-medium"
                        android:paddingStart="10sp"
                        android:paddingRight="30sp"
                        android:paddingBottom="5sp"
                        android:textColor="#FFFFFF"
                        android:textSize="18sp" />

                </TableRow>

                <TableRow
                    android:layout_width="match_parent"
                    android:layout_height="match_parent"
                    android:gravity="center_horizontal">

                    <TextView
                        android:id="@+id/precipitation"
                        android:layout_width="wrap_content"
                        android:layout_height="wrap_content"
                        android:layout_gravity="fill_horizontal"
                        android:fontFamily="sans-serif-condensed-light"
                        android:paddingLeft="30sp"
                        android:paddingTop="5sp"
                        android:paddingBottom="5sp"
                        android:text="Precip. "
                        android:textColor="#FFFFFF"
                        android:textSize="18sp" />

                    <TextView
                        android:id="@+id/precipVal"
                        android:layout_width="wrap_content"
                        android:layout_height="wrap_content"
                        android:layout_gravity="fill_horizontal"
                        android:fontFamily="sans-serif-condensed-medium"
                        android:paddingStart="10sp"
                        android:paddingTop="5sp"
                        android:paddingEnd="15sp"
                        android:paddingBottom="5sp"
                        android:textColor="#FFFFFF"
                        android:textSize="18sp" />

                    <TextView
                        android:id="@+id/dewPoint"
                        android:layout_width="wrap_content"
                        android:layout_height="wrap_content"
                        android:fontFamily="sans-serif-condensed-light"
                        android:paddingStart="15sp"
                        android:paddingTop="5sp"
                        android:paddingBottom="5sp"
                        android:text="Dew Point"
                        android:textColor="#FFFFFF"
                        android:textSize="18sp" />

                    <TextView
                        android:id="@+id/dewVal"
                        android:layout_width="wrap_content"
                        android:layout_height="wrap_content"
                        android:layout_gravity="fill_horizontal"
                        android:fontFamily="sans-serif-condensed-medium"
                        android:paddingStart="10sp"
                        android:paddingTop="5sp"
                        android:paddingRight="30sp"
                        android:paddingBottom="5sp"
                        android:textColor="#FFFFFF"
                        android:textSize="18sp" />

                </TableRow>

                <TableRow
                    android:layout_width="match_parent"
                    android:layout_height="match_parent"
                    android:gravity="center_horizontal">

                    <TextView
                        android:id="@+id/cloud"
                        android:layout_width="wrap_content"
                        android:layout_height="wrap_content"
                        android:layout_gravity="fill_horizontal"
                        android:fontFamily="sans-serif-condensed-light"
                        android:paddingLeft="30sp"
                        android:paddingTop="5sp"
                        android:paddingBottom="5sp"
                        android:text="Cloud"
                        android:textColor="#FFFFFF"
                        android:textSize="18sp" />

                    <TextView
                        android:id="@+id/cloudVal"
                        android:layout_width="wrap_content"
                        android:layout_height="wrap_content"
                        android:layout_gravity="fill_horizontal"
                        android:fontFamily="sans-serif-condensed-medium"
                        android:paddingStart="10sp"
                        android:paddingTop="5sp"
                        android:paddingEnd="15sp"
                        android:paddingBottom="5sp"
                        android:textColor="#FFFFFF"
                        android:textSize="18sp" />

                    <TextView
                        android:id="@+id/fog"
                        android:layout_width="wrap_content"
                        android:layout_height="wrap_content"
                        android:fontFamily="sans-serif-condensed-light"
                        android:paddingStart="15sp"
                        android:paddingTop="5sp"
                        android:paddingBottom="5sp"
                        android:text="Fog"
                        android:textColor="#FFFFFF"
                        android:textSize="18sp" />

                    <TextView
                        android:id="@+id/fogVal"
                        android:layout_width="wrap_content"
                        android:layout_height="wrap_content"
                        android:layout_gravity="fill_horizontal"
                        android:fontFamily="sans-serif-condensed-medium"
                        android:paddingStart="10sp"
                        android:paddingTop="5sp"
                        android:paddingEnd="30sp"
                        android:paddingBottom="5sp"
                        android:textColor="#FFFFFF"
                        android:textSize="18sp" />

                </TableRow>

            </TableLayout>

        </LinearLayout>

    </androidx.cardview.widget.CardView>


</LinearLayout>

Edit 2: CardAdapter.java and CardItem.java

CardAdapter.java:

public class CardAdapter extends RecyclerView.Adapter<CardAdapter.cardViewHolder>
{
    private List<CardItem> CardItems;

    public CardAdapter(List<CardItem> CardItems) {
        this.CardItems = CardItems;
    }

    @NonNull
    @Override
    public cardViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        return new cardViewHolder(
                LayoutInflater.from(parent.getContext()).inflate(
                        R.layout.item_container_card, parent, false
                )
        );
    }

    @Override
    public void onBindViewHolder(@NonNull cardViewHolder holder, int position) {
        holder.setCardData(CardItems.get(position));
    }

    @Override
    public int getItemCount() {
        return CardItems.size();
    }

    class cardViewHolder extends RecyclerView.ViewHolder
    {
        private TextView locationText;
        private TextView weatherDesc;
        private ImageView weatherIcon;
        private TextView tempVal;
        private TextView humVal;
        private TextView visVal;
        private TextView precipVal;
        private TextView dewVal;
        private TextView cloudVal;
        private TextView fogVal;

        public cardViewHolder(@NonNull View itemView)
        {
            super(itemView);
            locationText = itemView.findViewById(R.id.locationName);
            weatherDesc = itemView.findViewById(R.id.weatherDesc);
            weatherIcon = itemView.findViewById(R.id.imageOnboarding);
            tempVal = itemView.findViewById(R.id.temperature);
            humVal = itemView.findViewById(R.id.humVal);
            visVal = itemView.findViewById(R.id.visVal);
            precipVal = itemView.findViewById(R.id.precipVal);
            dewVal = itemView.findViewById(R.id.dewVal);
            cloudVal = itemView.findViewById(R.id.cloudVal);
            fogVal = itemView.findViewById(R.id.fogVal);

        }

        void setCardData(CardItem CardItem)
        {
            locationText.setText(CardItem.getLocation());
            weatherDesc.setText(CardItem.getWeatherDesc());
            weatherIcon.setImageResource(CardItem.getWeatherIcon());
            tempVal.setText(CardItem.getTemp());
            humVal.setText(CardItem.getHum());
            visVal.setText(CardItem.getVis());
            precipVal.setText(CardItem.getPrecip());
            dewVal.setText(CardItem.getDew());
            cloudVal.setText(CardItem.getCloud());
            fogVal.setText(CardItem.getFog());
        }

    }
}

CardItem.java:

package com.example.viewpagertest;

public class CardItem
{
    private int weatherIcon;
    private String location;
    private String temp;
    private String weatherDesc;
    private String hum;
    private String vis;
    private String precip;
    private String dew;
    private String cloud;
    private String fog;


    //weather icon
    public int getWeatherIcon() {
        return weatherIcon;
    }

    public void setWeatherIcon(int weatherIcon) {
        this.weatherIcon = weatherIcon;
    }

    //location title
    public String getLocation() {
        return location;
    }

    public void setLocation(String location) {
        this.location = location;
    }
    
    //temperature value
    public String getTemp() {
        return temp;
    }

    public void setTemp(String temp) {
        this.temp = temp;
    }

    //weather description
    public String getWeatherDesc() {
        return weatherDesc;
    }

    public void setWeatherDesc(String weatherDesc) {
        this.weatherDesc = weatherDesc;
    }

    //humidity value
    public String getHum() {
        return hum;
    }

    public void setHum(String hum) {
        this.hum = hum;
    }

    //visibility value
    public String getVis() {
        return vis;
    }

    public void setVis(String vis) {
        this.vis = vis;
    }

    //precipitation value
    public String getPrecip() {
        return precip;
    }

    public void setPrecip(String precip) {
        this.precip = precip;
    }

    //dew point value
    public String getDew() {
        return dew;
    }

    public void setDew(String dew) {
        this.dew = dew;
    }

    //cloud value
    public String getCloud() {
        return cloud;
    }

    public void setCloud(String cloud) {
        this.cloud = cloud;
    }

    //fog value
    public String getFog() {
        return fog;
    }

    public void setFog(String fog) {
        this.fog = fog;
    }
}

Here's the Console when running a debugger with the breakpoint at

coordinates.setText(location.getLatitude()+", "+location.getLongitude());

The whole console breaks the character limit so here's a document with the console text.

Console Text

Answer 1

                if (location != null)
                {
                    // coordinates.setText(location.getLatitude()+", "+location.getLongitude());
                    cardAdapter.setCoordinates(0 /*the cardItem number you want to update*/, location.getLatitude()+", "+location.getLongitude());
                }    

Since the coordinates TextView is in your item xml, you will not be able to address it from the root of your MainActivity, but from your item.

---

Update
Thanks for adding the Adapter code:

Easiest would be to create a method in your adapter like the following:

setCoordinates(int position, String coords) {
    holders.get(position).itemView.findViewById(R.id.coordinates).setText(coords);
}

To be able to access the holders on runtime, add the following:

public class CardAdapter extends RecyclerView.Adapter<CardAdapter.cardViewHolder>
{
    private List<CardItem> cardItems;
    private List<CardViewHolder> holders;
    ....

    @Override
    public cardViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        CardViewHolder holder = new cardViewHolder(
            LayoutInflater.from(parent.getContext()).inflate(
                    R.layout.item_container_card, parent, false
            )
        );
        holders.add(holder);
        return holder;
    }

Another option would be to add the field coordinates to your CardItem and write the setCoordinates method like so:

setCoordinates(int position, String coords) {
    cardItems.get(position).setCoordinates(coords);
    notifyDataSetChanged();  // to reload the holders, only notifying the specific position will be faster to reload only the changed holder
}

Answer 2

You need to update the adapter items by creating a method in CardAdapter and calling it from main activity as below -

Create this method in your adapter class

public void updateAdapter(List<CardItem> CardItems) {
    this.CardItems = CardItems;
    notifyDataSetChanged();
}

Replace below line

CardAdapter = new CardAdapter(CardItems);

With this one

CardAdapter.updateAdapter(CardItems);