如何使用Firebase Realtime数据库检索数据

Question

I want to get data that I stored on my realtime database.

With breakpoint, I can see that my dataSnapshot contains the good values. Then I want to instantiate a line object from the dataSnapshot (Line class contains x1 , y1 , x2 and y2 fields).

databaseReference.addValueEventListener(new ValueEventListener() {
      @Override
      public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
        if (isDrawer()) {
          return;
        }
        Line line = dataSnapshot.getValue(Line.class);
        if (line != null) {
          Log.i("cc", "Values : " + line.getX1() + " " + line.getX2() + " " + line.getY1() + " " + line.getY2());
          addLine(line);
        }
}

My problem is that the line object I get contains x1 = 0, x2 = 0, y1 = 0, y2 = 0 instead of same coordinate as the snapshot.

Edit : My current implementation of line is quite basic :

public class Line {

private float x1;
private float y1;
private float x2;
private float y2;

public Line() {
}

public Line(float x1, float y1, float x2, float y2) {
    this.x1 = x1;
    this.y1 = y1;
    this.x2 = x2;
    this.y2 = y2;
}

public Line(Line line) {
    this.x1 = line.getX1();
    this.x2 = line.getX2();
    this.y1 = line.getY1();
    this.y2 = line.getY2();
}

public float getX1() {
    return x1;
}

public void setX1(float x1) {
    this.x1 = x1;
}

public float getY1() {
    return y1;
}

public void setY1(float y1) {
    this.y1 = y1;
}

public float getX2() {
    return x2;
}

public void setX2(float x2) {
    this.x2 = x2;
}

public float getY2() {
    return y2;
}

public void setY2(float y2) {
    this.y2 = y2;
}

I create my Database reference the following way :

        databaseReference = database.getReference("draws/unique_draw");

And I store my data like this :

databaseReference.push().setValue(line);

@Alex Mamo Here is a preview of my data (lines)

Why?

Answer 1

you need to access the individual items with .getChildren() :

@Override
public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
    for (DataSnapshot dataSnapshot: dataSnapshot.getChildren()) {
        Line line = dataSnapshot.getValue(Line.class);
        if (line != null) {
            Log.i("cc", "Values : " + line.getX1() + " " + line.getX2() + " " + line.getY1() + " " + line.getY2());
            addLine(line);
        }
    }
}