Question

我想获取存储在实时数据库中的数据。

有了断点，我可以看到我的dataSnapshot包含好的值。然后，我想从dataSnapshot实例化一个线对象（线类包含x1，y1，x2和y2字段）。

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);
        }
}

我的问题是我得到的线对象包含x1 = 0, x2 = 0, y1 = 0, y2 = 0，而不是与快照相同的坐标。

编辑：我当前对line的实现是非常基本的：

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;
}

我通过以下方式创建数据库引用：

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

我这样存储我的数据：

databaseReference.push().setValue(line);

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

为什么？

Answer 1

您需要使用.getChildren()访问单个项目：

@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);
        }
    }
}

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