数组总是返回空

Question

我正在制作一个Android应用程序，用于从文件夹中读取文件，从中生成数组，然后在地图上绘制数组的纬度+经度点。我起初在一个单独的程序中开发了数组返回方法作为void方法（它的功能正确）。我对它做的唯一更改是我使它返回数组，以便Android应用程序可以使用它。不过，我总是收到武力。经过一些调试后，我发现我的方法每次都返回'null'（我设置了一个if语句，如果数组为空，则显示一个屏幕显示“FAIL！” - 并且该应用程序始终显示“FAIL！”） 。

我检查以确保文件位于正确的位置 - 它的确是。不过，我不确定程序为什么返回null。下面是我的一些代码：

package net.learn2develop.GoogleMaps; 

import java.io.BufferedReader; 
import java.io.File; 
import java.io.FileNotFoundException; 
import java.io.FileReader; 
import java.util.List; 
import java.util.StringTokenizer; 

import com.google.android.maps.GeoPoint; 
import com.google.android.maps.MapActivity; 
import com.google.android.maps.MapController; 
import com.google.android.maps.MapView; 
import com.google.android.maps.Overlay; 
import com.google.android.maps.MapView.LayoutParams; 

import android.graphics.Bitmap; 
import android.graphics.BitmapFactory; 
import android.graphics.Canvas; 
import android.graphics.Point; 
import android.os.Bundle; 
import android.view.View; 
import android.widget.LinearLayout; 


public class MapsActivity extends MapActivity 
{  
    MapView mapView; 
    MapController mc; 
    GeoPoint p; 
    GeoPoint p2; 
    GeoPoint p99; 

/** Called when the activity is first created. */ 
@Override 
public void onCreate(Bundle savedInstanceState) 
{ 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.main); 

    // Map code goes here..... 


    // Add points from ReadCsv.java 
    File fileToUse = new File("/Users/csrobot/Desktop/TrainingData/Training4.csv"); 
    String[][] bump = getArray(fileToUse); 
    if(bump == null){ 
     setContentView(R.layout.deleteme); 
    } 
//  for(int i = 0; i < bump.length; i++) { 
//   String coordinates99[] = {bump[i][0], bump[i][1]}; 
//   double lat99 = Double.parseDouble(coordinates99[0]); 
//   double lng99 = Double.parseDouble(coordinates99[1]); 
//   p99 = new GeoPoint(
//     (int) (lat99 * 1E6), 
//     (int) (lng99 * 1E6)); 
//   MapOverlay mapOverlay99 = new MapOverlay(); 
//   List<Overlay> listOfOverlays99 = mapView.getOverlays(); 
//   listOfOverlays99.add(mapOverlay99); 
//  } 

    mapView.invalidate(); 
} 

@Override 
protected boolean isRouteDisplayed() { 
    return false; 
} 

public String[][] getArray(File file) { 

    try { 
     int row = 0; 
     int col = 0; 
     String[][] numbers=new String[5258][16]; 

     BufferedReader bufRdr; 
     bufRdr = new BufferedReader(new FileReader(file)); 
     String line = null; 

     //read each line of text file 
     while((line = bufRdr.readLine()) != null) { 
      StringTokenizer st = new StringTokenizer(line,","); 
      col=0; 

      while (st.hasMoreTokens()) { 
       //get next token and store it in the array 
       numbers[row][col] = st.nextToken(); 
       col++; 
      } 
      row++; 
     } 

     // ... Here is the code that will make the array 
        // ... 

     //close the file 
     bufRdr.close(); 

     return arrayOfBumps; 

    } catch (FileNotFoundException e) { 
     e.printStackTrace(); 
    } catch(Exception e) { 
       // System.out.println("The following error occurred "+e); 
    } 
    return null; 

} 

所以这是我的活动样子。

07-28 09:11:10.962: ERROR/AndroidRuntime(13014): FATAL EXCEPTION: main 
07-28 09:11:10.962: ERROR/AndroidRuntime(13014): java.lang.RuntimeException: Unable to start activity ComponentInfo{net.learn2develop.GoogleMaps/net.learn2develop.GoogleMaps.MapsActivity}: java.lang.NullPointerException 
07-28 09:11:10.962: ERROR/AndroidRuntime(13014):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2663) 
07-28 09:11:10.962: ERROR/AndroidRuntime(13014):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2679) 
07-28 09:11:10.962: ERROR/AndroidRuntime(13014):  at android.app.ActivityThread.access$2300(ActivityThread.java:125) 
07-28 09:11:10.962: ERROR/AndroidRuntime(13014):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2033) 
07-28 09:11:10.962: ERROR/AndroidRuntime(13014):  at android.os.Handler.dispatchMessage(Handler.java:99) 
07-28 09:11:10.962: ERROR/AndroidRuntime(13014):  at android.os.Looper.loop(Looper.java:123) 
07-28 09:11:10.962: ERROR/AndroidRuntime(13014):  at android.app.ActivityThread.main(ActivityThread.java:4627) 
07-28 09:11:10.962: ERROR/AndroidRuntime(13014):  at java.lang.reflect.Method.invokeNative(Native Method) 
07-28 09:11:10.962: ERROR/AndroidRuntime(13014):  at java.lang.reflect.Method.invoke(Method.java:521) 
07-28 09:11:10.962: ERROR/AndroidRuntime(13014):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:858) 
07-28 09:11:10.962: ERROR/AndroidRuntime(13014):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616) 
07-28 09:11:10.962: ERROR/AndroidRuntime(13014):  at dalvik.system.NativeStart.main(Native Method) 
07-28 09:11:10.962: ERROR/AndroidRuntime(13014): Caused by: java.lang.NullPointerException 
07-28 09:11:10.962: ERROR/AndroidRuntime(13014):  at net.learn2develop.GoogleMaps.MapsActivity.onCreate(MapsActivity.java:89) 
07-28 09:11:10.962: ERROR/AndroidRuntime(13014):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047) 
07-28 09:11:10.962: ERROR/AndroidRuntime(13014):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2627) 
07-28 09:11:10.962: ERROR/AndroidRuntime(13014):  ... 11 more 

因此，谁能帮助我在这里：添加“如果（凹凸== NULL）”语句，并取消注释的“for”循环跟随它以前我logcat的？我已经在这里呆了几天，但仍然无法弄清楚。

Answer 1

File fileToUse = new File("/Users/csrobot/Desktop/TrainingData/Training4.csv");

这是NullPointerException的来源。

文件的路径必须以这种形式/data/data/yourpackagename/somefolder/yourfile

你不能做到这一点是这样的。该文件必须存储在模拟器/电话数据存储器内。您必须将文件推送到仿真器数据，例如将您的csv文件移动到assets/raw resource，然后将其加载到InputStreamReader对象中并执行您计划要执行的操作。从assets文件夹或res/raw文件夹中搜索更多开放文件的示例