我正在尝试使用Firebase实时数据库中的数据在Android中制作折线图。
这是数据库的结构:
这是代码:
public class TemperaturaActivity extends AppCompatActivity {
private LineChart Temp_linechart;
ArrayList<Entry> yData;
ValueEventListener valueEventListener;
DatabaseReference mPostReference;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_temperatura);
Temp_linechart = (LineChart) findViewById(R.id.linechart1);
mPostReference = FirebaseDatabase.getInstance().getReference("dht");
mPostReference.addValueEventListener(valueEventListener = new ValueEventListener() {
@Override
public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
yData = new ArrayList<>();
float i = 0;
for (DataSnapshot ds : dataSnapshot.getChildren()) {
i = i + 1;
String SV = ds.child("temp").getValue().toString();
Float SensorValue = Float.parseFloat(SV);
yData.add(new Entry(i, SensorValue));
}
final LineDataSet lineDataSet = new LineDataSet(yData, "Temp");
lineDataSet.setLineWidth(4);
LineData lineData = new LineData(lineDataSet);
Temp_linechart.clear();
Temp_linechart.setData(lineData);
//Temp_linechart.notifyDataSetChanged();
Temp_linechart.invalidate();
}
@Override
public void onCancelled(@NonNull DatabaseError databaseError) {
}
});
}
}
我在折线图中没有收到任何数据,也不知道为什么。
To get the values of
temp
property, please use the following lines of code:The result in the logcat will be the values of
temp
property:我对折线图库不熟悉,但是现在有了这些值,您可以使用它们进行任何操作。
P.S. Always add calls to all nodes that are present in your reference, including the one to
.child("sensor")
.