aChartEngine XYSeries.add（x，y）方法上的NullPointerExeption方法

嗨，我试图实现aChartEngine库，当我在代码中添加值时（如本教程by JavaCodeGeeks），它完美地工作，但如果我使用函数应用程序崩溃并在mCurrentSeries.add（x，y）上给出NullPointerExepction。当我调试，看看问题mCurrentSeries.add（x，y）重复两次（在同一周期），然后崩溃。aChartEngine XYSeries.add（x，y）方法上的NullPointerExeption方法

这是类

package com.example.achartengine; 

import org.achartengine.ChartFactory; 
import org.achartengine.GraphicalView; 
import org.achartengine.model.XYMultipleSeriesDataset; 
import org.achartengine.model.XYSeries; 
import org.achartengine.renderer.XYMultipleSeriesRenderer; 
import org.achartengine.renderer.XYSeriesRenderer; 

import com.towel.math.Expression; 

import android.os.Bundle; 
import android.app.Activity; 
import android.view.Menu; 
import android.view.View; 
import android.widget.Button; 
import android.widget.EditText; 
import android.widget.LinearLayout; 

public class MainActivity extends Activity { 

    private GraphicalView mChart; 
    private XYMultipleSeriesDataset mDataset = new XYMultipleSeriesDataset(); 
    private XYMultipleSeriesRenderer mRenderer = new XYMultipleSeriesRenderer(); 
    private XYSeries mCurrentSeries; 
    private XYSeriesRenderer mCurrentRenderer; 

    private Expression function; 
    private EditText textFunction; 

    public void initChart() { 
     mCurrentSeries = new XYSeries("Sample Data"); 
     mDataset.addSeries(mCurrentSeries); 
     mCurrentRenderer = new XYSeriesRenderer(); 
     mRenderer.addSeriesRenderer(mCurrentRenderer); 
    } 

    View.OnClickListener handler = new View.OnClickListener() { 

     @Override 
     public void onClick(View v) { 
      addGraphData();   
     } 
    }; 

    private void addGraphData(){ 
     String f = textFunction.getText().toString(); 
     function = new Expression(f); 

     Double y; 
     for (int x = 0; x < 15; x++){ 
      function.setVariable("x", x); 
      y = function.resolve(); 
      mCurrentSeries.add(x, y); 
     } 

     LinearLayout layout = (LinearLayout) findViewById(R.id.chart); 
     if(mChart==null){ 
      initChart(); 
      mChart = ChartFactory.getCubeLineChartView(this, mDataset, mRenderer, 0.3f); 
      layout.addView(mChart); 
     } else { 
      mChart.repaint(); 
     } 


    } 

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

     Button draw = (Button) findViewById(R.id.buttonDraw); 
     draw.setOnClickListener(handler); 

     textFunction = (EditText) findViewById(R.id.textFunction); 
    } 

    @Override 
    public boolean onCreateOptionsMenu(Menu menu) { 
     // Inflate the menu; this adds items to the action bar if it is present. 
     getMenuInflater().inflate(R.menu.main, menu); 
     return true; 
    } 


}

，这是logcat的

03-10 08:11:24.609: D/AndroidRuntime(2450): Shutting down VM 
03-10 08:11:24.609: W/dalvikvm(2450): threadid=1: thread exiting with uncaught exception (group=0x40a71930) 
03-10 08:11:24.619: E/AndroidRuntime(2450): FATAL EXCEPTION: main 
03-10 08:11:24.619: E/AndroidRuntime(2450): java.lang.NullPointerException 
03-10 08:11:24.619: E/AndroidRuntime(2450):  at com.example.achartengine.MainActivity.addGraphData(MainActivity.java:54) 
03-10 08:11:24.619: E/AndroidRuntime(2450):  at com.example.achartengine.MainActivity.access$0(MainActivity.java:46) 
03-10 08:11:24.619: E/AndroidRuntime(2450):  at com.example.achartengine.MainActivity$1.onClick(MainActivity.java:42) 
03-10 08:11:24.619: E/AndroidRuntime(2450):  at android.view.View.performClick(View.java:4204) 
03-10 08:11:24.619: E/AndroidRuntime(2450):  at android.view.View$PerformClick.run(View.java:17355) 
03-10 08:11:24.619: E/AndroidRuntime(2450):  at android.os.Handler.handleCallback(Handler.java:725) 
03-10 08:11:24.619: E/AndroidRuntime(2450):  at android.os.Handler.dispatchMessage(Handler.java:92) 
03-10 08:11:24.619: E/AndroidRuntime(2450):  at android.os.Looper.loop(Looper.java:137) 
03-10 08:11:24.619: E/AndroidRuntime(2450):  at android.app.ActivityThread.main(ActivityThread.java:5041) 
03-10 08:11:24.619: E/AndroidRuntime(2450):  at java.lang.reflect.Method.invokeNative(Native Method) 
03-10 08:11:24.619: E/AndroidRuntime(2450):  at java.lang.reflect.Method.invoke(Method.java:511) 
03-10 08:11:24.619: E/AndroidRuntime(2450):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793) 
03-10 08:11:24.619: E/AndroidRuntime(2450):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560) 
03-10 08:11:24.619: E/AndroidRuntime(2450):  at dalvik.system.NativeStart.main(Native Method)

来源

2013-03-10 Cezar Sas

什么是在线否MainActivity.java:54。 – 2013-03-10 08:24:35

你确定initChart在'onClick'之前被调用吗？也许'mCurrentSeries'在访问它时为空？ – BobTheBuilder 2013-03-10 08:26:02

@TGMCians mCurrentSeries.add（x，y）; – 2013-03-10 08:26:03

您需要先拨打initChart才能初始化mCurrentSeries，然后在onClick中使用它。

来源

2013-03-10 08:30:16 BobTheBuilder

mCurrentSeries = new XYSeries("Sample Data");

你在哪里得到的错误并没有前行调用。

来源

2013-03-10 08:28:57 eski

aChartEngine XYSeries.add（x，y）方法上的NullPointerExeption方法

回答

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