Is there a way to include TextViews in custom views in Android?

so I am trying to make a ListItem in an App that I am making, and I want it to look something like this:

When I hop into my layout.xml file, without the ListItem, the preview renders properly and so does the app.

However with the ListItem, the preview and app do not render.

The error was

Error inflating class ListItem

which was caused by

Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference

So it had to be something with the TextView.

Here is my code (I just removed all imports and constructors):

public class ListItem extends View {

    private String subjectName;
    private int backgroundColor;
    TextView subjectNameTextView;

    public void setSubjectName() {
        if (this.subjectName != null) {
            subjectNameTextView.setText(this.subjectName);
        }
    }

    public void setColor() {
        if (this.backgroundColor != 0) {
            this.setBackgroundColor(this.backgroundColor);
        }
    }
}

Here is activity_maths.xml if needed.

<?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"
    tools:context=".MathsActivity">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Hello!"
        android:textSize="50sp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <com.atharvnadkarni.funlurn.ListItem
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" app:title="Text" />

</androidx.constraintlayout.widget.ConstraintLayout>

Alright everyone, I found another post that said to do addView on a ViewGroup, so I changed my setSubjectName function to this:

public class ListItem extends RelativeLayout {

    public void setSubjectName() {
        if (this.subjectName != null) {
            addView(subjectNameTextView);
            subjectNameTextView.setText(this.subjectName);
        }
}
}

But this does not work, and shows that you
Cannot add a null child view to a ViewGroup

The problem is you do not initialize subjectNameTextView, so it is null. And after that, you are trying to call the textView's method on a null object reference.
Try doing this:

public class ListItem extends RelativeLayout {

    public void setSubjectName() {
        if (this.subjectName != null) {
            if (this.subjectNameTextView == null){
                this.subjectNameTextView = new TextView(context);
            }
            subjectNameTextView = new TextView(context);
            addView(subjectNameTextView);
            subjectNameTextView.setText(this.subjectName);
        }
    }
}

Also, you can put text view initialization into your constructor, but be sure you call it if you have multiple constructors.
The context instance can be acquired from any view class instances, so you got it covered, because your ListItem extends View.

You are getting the nullPointerException because you did not initialized you textview "subjectNameTextView". please change

public class ListItem extends View {

private String subjectName;
private int backgroundColor;
TextView subjectNameTextView;

public void setSubjectName() {
    if (this.subjectName != null) {
        subjectNameTextView.setText(this.subjectName);
    }
}

public void setColor() {
    if (this.backgroundColor != 0) {
        this.setBackgroundColor(this.backgroundColor);
    }
}
}

to

public class ListItem extends View {

private String subjectName;
private int backgroundColor;
TextView subjectNameTextView;

public void setSubjectName() {
 subjectNameTextView = new TextView(this); // this code you have to add
    if (this.subjectName != null) {
        subjectNameTextView.setText(this.subjectName);
    }
}

public void setColor() {
    if (this.backgroundColor != 0) {
        this.setBackgroundColor(this.backgroundColor);
    }
}
}