i’m a new android programmer, i have this project that i created an android app which shows my data from firebase in a line chart. But i don’t know why the chart is not working like this:
enter image description here
This is my MainActivity.kt:

package com.example.sktt

import android.os.Bundle
import androidx.appcompat.app.AppCompatActivity
import com.google.firebase.database.*
import com.github.mikephil.charting.charts.LineChart
import com.github.mikephil.charting.data.Entry
import com.github.mikephil.charting.data.LineData
import com.github.mikephil.charting.data.LineDataSet
import kotlin.collections.ArrayList

class MainActivity : AppCompatActivity() {

    private lateinit var lineChart: LineChart
    private val entries = ArrayList<Entry>()

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        // Initialize Firebase Database
        val database = FirebaseDatabase.getInstance()
        val myRef = database.getReference("SKTT/EEG")

        lineChart = findViewById(R.id.lineChart)

        // Read from the database in real-time
        myRef.addValueEventListener(object : ValueEventListener {
            override fun onDataChange(dataSnapshot: DataSnapshot) {
                entries.clear() // Clear previous entries
                var index = 0

                for (data in dataSnapshot.children) {
                    val value = data.getValue(Double::class.java) ?: continue
                    entries.add(Entry(index++.toFloat(), value.toFloat()))
                }

                setupChart()
            }

            override fun onCancelled(error: DatabaseError) {
                // Handle possible errors.
            }
        })
    }

    private fun setupChart() {
        val dataSet = LineDataSet(entries, "EEG Data")
        dataSet.color = resources.getColor(R.color.teal_200)
        dataSet.valueTextColor = resources.getColor(R.color.black)

        val lineData = LineData(dataSet)
        lineChart.data = lineData
        lineChart.invalidate() // Refresh the chart
    }
}

This is my AndroidManifest.xml:

<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.sktt">

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/Theme.AppCompat.Light.NoActionBar">
        <activity
            android:name=".MainActivity"
            android:exported="true">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>

This is my activity_main.xml:

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <com.github.mikephil.charting.charts.LineChart
        android:id="@+id/lineChart"
        android:layout_width="match_parent"
        android:layout_height="match_parent"/>
</RelativeLayout>

Please help me solve this problem, thank you very much!!!