Android/Java 创建助手 class 来创建图表

Question

目标：

为图形生成创建助手class

背景：

我有 3 个片段，每个片段收集一些传感器数据（加速度计、陀螺仪、旋转）并使用 GraphView 绘制图表。以下是其中一个片段的代码（此代码目前可以正常工作）：

public class GyroscopeFragment extends Fragment implements SensorEventListener {

    private final short TYPE_GYROSCOPE = Sensor.TYPE_GYROSCOPE;
    private final short POLL_FREQUENCY = 100; //in milliseconds
    private final short MAX_POINTS_DISPLAYED = 50;
    private SensorManager sensorManager;
    private Sensor sensor;
    private Sensor gyroscope;
    private long lastUpdate = -1;

    float curGyroX;
    float curGyroY;
    float curGyroZ;

    private LineGraphSeries<DataPoint> gyroXSeries;
    private LineGraphSeries<DataPoint> gyroYSeries;
    private LineGraphSeries<DataPoint> gyroZSeries;
    private double graphXTime = 1d;

    public GyroscopeFragment() {
        // Required empty public constructor
    }


    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {

        // Inflate the layout for this fragment
        View view = inflater.inflate(R.layout.fragment_gyroscope, container, false);

        //Set the nav drawer item highlight
        MainActivity mainActivity = (MainActivity) getActivity();
        mainActivity.navigationView.setCheckedItem(R.id.nav_gyroscope);

        //Set actionbar title
        mainActivity.setTitle("Gyroscope");

        //Sensor manager
        sensorManager = (SensorManager) getContext().getSystemService(Context.SENSOR_SERVICE);
        gyroscope = (Sensor) sensorManager.getDefaultSensor(TYPE_GYROSCOPE);

        return view;
    }


    @Override
    public void onResume() {
        super.onResume();
        sensorManager.registerListener(this, gyroscope, SensorManager.SENSOR_DELAY_FASTEST);

        //Create graph
        GraphView gyroGraph = (GraphView) getView().findViewById(R.id.gyroGraph);

        gyroGraph.getLegendRenderer().setVisible(true);
        gyroGraph.getLegendRenderer().setFixedPosition(0,0);

        gyroGraph.getGridLabelRenderer().setHighlightZeroLines(false);

        gyroXSeries = new LineGraphSeries<DataPoint>();
        gyroYSeries = new LineGraphSeries<DataPoint>();
        gyroZSeries = new LineGraphSeries<DataPoint>();

        gyroXSeries.setTitle("X");
        gyroYSeries.setTitle("Y");
        gyroZSeries.setTitle("Z");

        gyroXSeries.setColor(Color.RED);
        gyroYSeries.setColor(Color.GREEN);
        gyroZSeries.setColor(Color.BLUE);

        gyroGraph.addSeries(gyroXSeries);
        gyroGraph.addSeries(gyroYSeries);
        gyroGraph.addSeries(gyroZSeries);

        gyroGraph.getViewport().setYAxisBoundsManual(true);
        gyroGraph.getViewport().setMinY(-10);
        gyroGraph.getViewport().setMaxY(10);

        gyroGraph.getViewport().setXAxisBoundsManual(true);
        gyroGraph.getViewport().setMinX(0);
        gyroGraph.getViewport().setMaxX(MAX_POINTS_DISPLAYED);
    }

    @Override
    public void onPause() {
        super.onPause();
        sensorManager.unregisterListener(this);
    }

    @Override
    public void onDestroy() {
        super.onDestroy();
        sensorManager.unregisterListener(this);
    }

    @Override
    public void onLowMemory() {
        super.onLowMemory();
        sensorManager.unregisterListener(this);
    }

    @Override
    public void onSensorChanged(SensorEvent event) {
        sensor = event.sensor;

        curGyroX = event.values[0];
        curGyroY = event.values[1];
        curGyroZ = event.values[2];

        long curTime = System.currentTimeMillis();
        long diffTime = (curTime - lastUpdate);

        // only allow one update every POLL_FREQUENCY.
        if (diffTime > POLL_FREQUENCY) {
            lastUpdate = curTime;

            graphXTime += 1d;
            gyroXSeries.appendData(new DataPoint(graphXTime, curGyroX), true, MAX_POINTS_DISPLAYED);
            gyroYSeries.appendData(new DataPoint(graphXTime, curGyroY), true, MAX_POINTS_DISPLAYED);
            gyroZSeries.appendData(new DataPoint(graphXTime, curGyroZ), true, MAX_POINTS_DISPLAYED);
        }
    }

    @Override
    public void onAccuracyChanged(Sensor sensor, int accuracy) {
        //Safe not to implement
    }
}

我发现在 3 个片段中我重复了 onResume 中的大量图形生成代码，所以我想创建一个 GraphHelper class，我可以实例化它来创建图形，如果我想改变图表的外观，只需更改一个地方的代码。但是，我是 Java 的新手，所以在创建这个新的 class.

时遇到了麻烦

尝试的解决方案：

为了解决问题，我想出了以下 class：

public class GraphHelper {

    private final GraphView graph;
    private final LineGraphSeries<DataPoint> xSeries;
    private final LineGraphSeries<DataPoint> ySeries;
    private final LineGraphSeries<DataPoint> zSeries;

    public GraphHelper(GraphView graph, LineGraphSeries<DataPoint> xSeries,
                            LineGraphSeries<DataPoint> ySeries, LineGraphSeries<DataPoint> zSeries, short maxDisplayed){
        this.graph = graph;
        this.xSeries = xSeries;
        this.ySeries = ySeries;
        this.zSeries = zSeries;

        graph.getLegendRenderer().setVisible(true);
        graph.getLegendRenderer().setFixedPosition(0, 0);

        graph.getGridLabelRenderer().setHighlightZeroLines(false);

        xSeries = new LineGraphSeries<DataPoint>();
        ySeries = new LineGraphSeries<DataPoint>();
        zSeries = new LineGraphSeries<DataPoint>();

        xSeries.setTitle("X");
        ySeries.setTitle("Y");
        zSeries.setTitle("Z");

        xSeries.setColor(Color.RED);
        ySeries.setColor(Color.GREEN);
        zSeries.setColor(Color.BLUE);

        graph.addSeries(xSeries);
        graph.addSeries(ySeries);
        graph.addSeries(zSeries);

        graph.getViewport().setYAxisBoundsManual(true);
        graph.getViewport().setMinY(-10);
        graph.getViewport().setMaxY(10);

        graph.getViewport().setXAxisBoundsManual(true);
        graph.getViewport().setMinX(0);
        graph.getViewport().setMaxX(maxDisplayed);
    }
}

并已将我的片段 onResume 更改为如下所示（其他一切都相同）：

@Override
public void onResume() {
    super.onResume();
    sensorManager.registerListener(this, gyroscope, SensorManager.SENSOR_DELAY_FASTEST);

    //Create graph
    GraphView gyroGraph = (GraphView) getView().findViewById(R.id.gyroGraph);

    new GraphHelper(gyroGraph, gyroXSeries, gyroYSeries, gyroZSeries, MAX_POINTS_DISPLAYED);
}

问题 #1：

每当我尝试查看图表片段时，我都会收到以下错误消息：

java.lang.NullPointerException: Attempt to invoke virtual method 'void com.jjoe64.graphview.series.LineGraphSeries.appendData(com.jjoe64.graphview.series.DataPointInterface, boolean, int)' on a null object reference

这是指 onSensorChanged 方法，我在该方法中尝试将数据附加到系列。它似乎不知道 gyroXSeries 是什么，因为我将它添加到帮助程序中的图表中。

问题#2：

目前我在主片段 class 以及助手 class 的顶部声明了 gyroXSeries，并且还创建了一个新的 LineGraphSeries 对象在助手构造函数中。有没有办法减少这段代码的重复？

编辑

为了回应下面的评论，我做了以下更改，新的 GraphHelper class 看起来像这样：

public class GraphHelper {

    private final GraphView graph;
    private final LineGraphSeries<DataPoint> xSeries;
    private final LineGraphSeries<DataPoint> ySeries;
    private final LineGraphSeries<DataPoint> zSeries;


    public GraphHelper(GraphView graph, LineGraphSeries<DataPoint> xSeries,
                            LineGraphSeries<DataPoint> ySeries, LineGraphSeries<DataPoint> zSeries, short maxDisplayed){
        this.graph = graph;
        this.xSeries = xSeries;
        this.ySeries = ySeries;
        this.zSeries = zSeries;

        graph.getLegendRenderer().setVisible(true);
        graph.getLegendRenderer().setFixedPosition(0, 0);

        graph.getGridLabelRenderer().setHighlightZeroLines(false);

        xSeries.setTitle("X");
        ySeries.setTitle("Y");
        zSeries.setTitle("Z");

        xSeries.setColor(Color.RED);
        ySeries.setColor(Color.GREEN);
        zSeries.setColor(Color.BLUE);

        graph.addSeries(xSeries);
        graph.addSeries(ySeries);
        graph.addSeries(zSeries);

        graph.getViewport().setYAxisBoundsManual(true);
        graph.getViewport().setMinY(-10);
        graph.getViewport().setMaxY(10);

        graph.getViewport().setXAxisBoundsManual(true);
        graph.getViewport().setMinX(0);
        graph.getViewport().setMaxX(maxDisplayed);
    }
}

陀螺仪片段和原来的一样，只是我在上面做了onResume的改动

这会导致以下错误：

致命异常：主要进程：net.binarysea.sensorload，PID：25997 java.lang.NullPointerException：尝试在空对象引用上调用虚方法 'void com.jjoe64.graphview.series.LineGraphSeries.setTitle(java.lang.String)' 在 net.binarysea.sensorload.GraphHelper.(GraphHelper.java:30) 在 net.binarysea.sensorload.GyroscopeFragment.onResume(GyroscopeFragment.java:73) 在 android.support.v4.app.Fragment.performResume(Fragment.java:2005) 在 android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1108) 在 android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1248) 在 android.support.v4.app.BackStackRecord.run(BackStackRecord.java:738) 在 android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1613) 在 android.support.v4.app.FragmentManagerImpl$1.run(FragmentManager.java:517) 在 android.os.Handler.handleCallback(Handler.java:739) 在 android.os.Handler.dispatchMessage(Handler.java:95) 在 android.os.Looper.loop(Looper.java:148) 在 android.app.ActivityThread.main(ActivityThread.java:5417) 在 java.lang.reflect.Method.invoke（本机方法）在 com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726) 在 com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)

Answer 1

将您的图表助手 class 更改为此。

public class GraphHelper {
    public GraphHelper(GraphView graph, LineGraphSeries<DataPoint> xSeries,
                   LineGraphSeries<DataPoint> ySeries, LineGraphSeries<DataPoint> zSeries, short maxDisplayed){

    graph.getLegendRenderer().setVisible(true);
    graph.getLegendRenderer().setFixedPosition(0, 0);

    graph.getGridLabelRenderer().setHighlightZeroLines(false);

    xSeries.setTitle("X");
    ySeries.setTitle("Y");
    zSeries.setTitle("Z");

    xSeries.setColor(Color.RED);
    ySeries.setColor(Color.GREEN);
    zSeries.setColor(Color.BLUE);

    graph.addSeries(xSeries);
    graph.addSeries(ySeries);
    graph.addSeries(zSeries);

    graph.getViewport().setYAxisBoundsManual(true);
    graph.getViewport().setMinY(-10);
    graph.getViewport().setMaxY(10);

    graph.getViewport().setXAxisBoundsManual(true);
    graph.getViewport().setMinX(0);
    graph.getViewport().setMaxX(maxDisplayed);
    }
}

这样称呼它：

@Override
public void onResume() {
    super.onResume();
    sensorManager.registerListener(this, gyroscope, SensorManager.SENSOR_DELAY_FASTEST);

    //Create graph
    GraphView gyroGraph = (GraphView) getView().findViewById(R.id.gyroGraph);

    gyroXSeries = new LineGraphSeries<DataPoint>();
    gyroYSeries = new LineGraphSeries<DataPoint>();
    gyroZSeries = new LineGraphSeries<DataPoint>();

    new GraphHelper(gyroGraph, gyroXSeries, gyroYSeries, gyroZSeries, MAX_POINTS_DISPLAYED);
}

此外，这是在 java 中做助手的更合适的方法：

public class GraphHelper {

public GraphHelper() { }

public static void initializeGraph(GraphView graph, LineGraphSeries<DataPoint> xSeries,
                                   LineGraphSeries<DataPoint> ySeries, LineGraphSeries<DataPoint> zSeries, short maxDisplayed){
    graph.getLegendRenderer().setVisible(true);
    graph.getLegendRenderer().setFixedPosition(0, 0);

    graph.getGridLabelRenderer().setHighlightZeroLines(false);

    xSeries.setTitle("X");
    ySeries.setTitle("Y");
    zSeries.setTitle("Z");

    xSeries.setColor(Color.RED);
    ySeries.setColor(Color.GREEN);
    zSeries.setColor(Color.BLUE);

    graph.addSeries(xSeries);
    graph.addSeries(ySeries);
    graph.addSeries(zSeries);

    graph.getViewport().setYAxisBoundsManual(true);
    graph.getViewport().setMinY(-10);
    graph.getViewport().setMaxY(10);

    graph.getViewport().setXAxisBoundsManual(true);
    graph.getViewport().setMinX(0);
    graph.getViewport().setMaxX(maxDisplayed);
}
}

这样您就没有等待被垃圾回收的随机对象。要调用它，请使用：

GraphHelper.initializeGraph(...)

Android/Java 创建助手 class 来创建图表

Android/Java creating a helper class to create graphs

java

android

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android-fragments

android-graphview