Java 图形视图不显示点

这是我使用GraphView网站编写的代码：

package com.example.sander.app;

import android.app.Fragment;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.LinearLayout;

import com.jjoe64.graphview.GraphView;
import com.jjoe64.graphview.series.DataPoint;
import com.jjoe64.graphview.series.LineGraphSeries;

/**
 * Created by Sander on 8-4-2017.
 */

public class GraphFrame extends Fragment {
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.fragment_graph,
                container, false);

        GraphView graph = (GraphView) view.findViewById(R.id.graph);
        LineGraphSeries<DataPoint> series = new LineGraphSeries<>(new DataPoint[] {
                new DataPoint(0, 1),
                new DataPoint(1, 5),
                new DataPoint(2, 3),
                new DataPoint(3, 2),
                new DataPoint(4, 6)
        });
        graph.addSeries(series);
        return view;
    }
}

这是匹配的XML

    <?xml version="1.0" encoding="utf-8"?>

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical" android:layout_width="match_parent"
    android:layout_height="match_parent">

    <com.jjoe64.graphview.GraphView
        android:layout_width="match_parent"
        android:layout_height="200dip"
        android:id="@+id/graph" />
</RelativeLayout>

我在LineGraphSeries中定义的点不会显示在图形上。我使用了与上几乎相同的示例。有人能帮我解决这个问题吗

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate( savedInstanceState );
        setContentView( R.layout.fragment_graph);

        GraphView graph = (GraphView) findViewById(R.id.graph);
        LineGraphSeries<DataPoint> series = new LineGraphSeries<>(new DataPoint[] {
                new DataPoint(0, 1),
                new DataPoint(1, 5),
                new DataPoint(2, 3),
                new DataPoint(3, 2),
                new DataPoint(4, 6)
        });
        graph.addSeries(series);

    }
}