Android - Get push key based on a child Firebase

Question

This is how my data looks like:

{
  "courses":{
    "Business":{
        "PushKey_1":{
                "courseC":"B1111",
                "name":"Business Year 1"
        },
        "PushKey_2":{
                "courseC":"B2222",
                "name":"Business Year 2"
        },
    }
  }
}

I'm trying to retrieve the push key based on a child. Code I'm trying now:

String testCourseC = "B2222";
String showCourseKey;

        DatabaseReference mRef = FirebaseDatabase.getInstance().getReference().child("courses").child("Business");
        mRef.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {
                for (DataSnapshot ds : dataSnapshot.getChildren()){
                    CourseDetails data = ds.getValue(CourseDetails.class);
                    String compareC = data.getCourseC();
                    if (compareC.equals(testCourseC)){
                        showCourseKey = dataSnapshot.getKey();
                    }
                }
            }

            @Override
            public void onCancelled(DatabaseError databaseError) {

            }
        });

        textview1.setText(showCourseKey);

My CourseDetails class:

public class CourseDetails {
    private String courseC;
    private String name;

    public CourseDetails() {
    }

    public CourseDetails(String courseC, String name) {
        this.courseC = courseC;
        this.name = name;
    }

    public String getCourseC() {
        return courseC;
    }

    public void setCourseC(String courseC) {
        this.courseC = courseC;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}

textview1 should display PushKey_2. If the code was wrong, shouldn't textview1 display "courses"?

I got NullPointerException from the code above. I have read the documentation and gone through similar questions, but still got this wrong. Please don't mind my silly question

Answer 1

I run your code and do not get a NullPointerException. Please post the stack trace.

I will point out what looks like an error.

This:

showCourseKey = dataSnapshot.getKey();

should be:

showCourseKey = ds.getKey();