android - 创建 ArrayAdapter 时出现 NullPointerException

Question

我不知道为什么会出现 NullPointerException。我认为问题产生于 ArrayAdapter。需要帮忙。提前致谢。

LogCat:

android.widget.ArrayAdapter.createViewFromResource(ArrayAdapter.java:394)

Activity :

package com.map.map;



import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashMap;
import java.util.PriorityQueue;
import java.util.StringTokenizer;
import android.os.Bundle;
import android.app.Activity;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.view.Menu;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.ScrollView;
import android.widget.ListView;
import android.widget.TextView;

public class MainActivity extends Activity {
    Map map;
    String Source = "Blank";
    String Destination = "Blank";
    ListView list1;
    ListView list2;
    String [] listArray;
    BufferedReader a;
    BufferedReader b;

    public static Integer Number_Of_Airport = 1168; //Total number of Airport in the World
    public HashMap<Integer,Time> Clock;   //The Clock of each Airport
    public HashMap<String,Integer> Airport;  //airport mapped to representative integer
    public HashMap<String,Coordinate> Coordinate; // airport mapped to their co-ordinates
    public HashMap<String,ArrayList<IntegerFour>> AirportInfo;  // airport mapped to their information
    public ArrayList<String> shortestPath; // the list of coordinates indicates the way to shortest path 
    public HashMap<Integer,String> AirportName; //index mapped to the Airport
    String [] listAirport; // holds the Airports name 
    int [] Parent;  // For getting the ShortestPath way Parent keep track the Child



    @Override
    protected void onCreate(Bundle savedInstanceState){
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        try {
            a = new BufferedReader(
                                                 new InputStreamReader(getAssets().open("a.txt")));
        } catch (IOException e) {
            e.printStackTrace();
        }

        try {
            b = new BufferedReader(
                                                 new InputStreamReader(getAssets().open("b.txt")));
        } catch (IOException e) {
            e.printStackTrace();
        }

        listArray = new String[1168];
        AirportName = new HashMap<Integer,String>();
        Airport = new HashMap<String,Integer>();
        Coordinate = new HashMap<String,Coordinate>();
        AirportInfo = new HashMap<String,ArrayList<IntegerFour>>();
        shortestPath = new ArrayList<String>();
        Clock = new HashMap<Integer,Time>();
        listAirport = new String[Number_Of_Airport];
        Parent = new int[Number_Of_Airport];



        String line1;
        int c = 0;// location detector
        try{
            while((line1 = AirportLocation.readLine())!=null){
                StringTokenizer s = new StringTokenizer(line1);
                String airport = s.nextToken();
                //AirportNameByString.put(c, airport);
                listAirport[c] = airport;
                Airport.put(airport,c);
                XY a = new XY(s.nextToken()); // setting the coordinates in exact form
                int x = a.x;int y = a.y;
                AirportName.put(c,airport); 
                Coordinate.put(airport, new Coordinate(x,y));
                c++;// next Airport
            }
        }
        catch (IOException e) {
            e.printStackTrace();
        }



        String line2;
        try{
            while((line2 = AirportInformation.readLine())!=null){
                String airportName = line2;
                ArrayList<IntegerFour> list = new ArrayList<IntegerFour>();
                for(int t = 0;t<3;t++){
                    StringTokenizer info = new StringTokenizer(AirportInformation.readLine());
                    String destinationAirport = info.nextToken();
                    Time slotTime = new Time(info.nextToken());
                    Time duration = new Time(info.nextToken());
                    int expense = Integer.valueOf(info.nextToken().replace("$",""));
                    list.add(new IntegerFour(destinationAirport,slotTime,duration,expense));
                }
                AirportInfo.put(airportName,list);
            }
        }
        catch (IOException e) {
            e.printStackTrace();
        }




        list1 = (ListView) findViewById(R.id.list1);
        list2 = (ListView) findViewById(R.id.list2);
        ArrayAdapter<String> adapter1 = new ArrayAdapter<String>(this,android.R.layout.simple_list_item_1,listArray);
        ArrayAdapter<String> adapter2 = new ArrayAdapter<String>(this,android.R.layout.simple_list_item_1,listArray);
        list1.setAdapter(adapter1);
        list2.setAdapter(adapter2);
        list1.setOnItemClickListener(new SourceSelection());
        list2.setOnItemClickListener(new DestinationSelection());

    }

    public void shortestPath(){



        int [] shortestpath = new int[Number_Of_Airport];
        Arrays.fill(shortestpath,1000000000);
        PriorityQueue<Pair> q = new PriorityQueue<Pair>();
        q.add(new Pair(Source,0));
        shortestpath[Airport.get(Source)] = 0;

        Time starting = new Time("12Hour13Minute19Second");
        Clock.put(Airport.get(Source),starting);
        while(!q.isEmpty()){
            String u = q.poll().airport;
            if(!u.equals(Destination)){
                ArrayList<IntegerFour> listOfInfo = AirportInfo.get(u);
                for(int i = 0;i<listOfInfo.size();i++){
                    String airport = listOfInfo.get(i).destinationAirport;
                    int expense = listOfInfo.get(i).expense;
                    Time slotTime = listOfInfo.get(i).slotTime;
                    Time duration = listOfInfo.get(i).duration;
                    if(shortestpath[Airport.get(airport)]>shortestpath[Airport.get(u)]+expense){
                        Parent[Airport.get(airport)] = Airport.get(u);
                        Clock.put(Airport.get(airport),slotTime);
                        shortestpath[Airport.get(airport)] = shortestpath[Airport.get(u)]+expense;
                        q.add(new Pair(airport,shortestpath[Airport.get(airport)]));
                    }
                }
            }
            else{
                break;
            }
        }       
    }

    public void getTheShortestPath(){
        int start = Airport.get(Destination);
        while(start!=Airport.get(Source)){
            shortestPath.add(AirportName.get(start));
            start = Parent[start];
       }
        shortestPath.add(AirportName.get(start));
    }




    public void Draw(){
        map = new Map(this);
        ScrollView scrollView = new ScrollView(this);
        scrollView.addView(map);
        setContentView(scrollView); 
        //setContentView(map);
    } 

    class SourceSelection implements AdapterView.OnItemClickListener{

        @Override
        public void onItemClick(AdapterView<?> arg0, View arg1, int arg2, long arg3) {
            TextView temp = (TextView) arg1;
            Source = temp.getText()+"";
            if(!Source.equals("Blank") && !Destination.equals("Blank")){
                //shortestPath();
                Draw();
            }
        }
    }

    class DestinationSelection implements AdapterView.OnItemClickListener{

        @Override
        public void onItemClick(AdapterView<?> arg0, View arg1, int arg2, long arg3) {
            TextView temp = (TextView) arg1;
            Destination = temp.getText()+"";
            if(!Source.equals("Blank") && !Destination.equals("Blank")){
                //shortestPath();
                Draw();
            }
        }
    }
    @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;
    }
    public class Map extends View {
        Paint paint = new Paint();
        public Map(Context context) {
            super(context);
        }
        @Override
        public void onDraw(Canvas canvas) {
            paint.setColor(Color.RED);
            canvas.drawCircle(100, 100, 20, paint);
            canvas.drawLine(2000, 2000, 5000, 5000, paint);
        }
        @Override
        protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
            // Compute the height required to render the view
            // Assume Width will always be MATCH_PARENT.
            int width = MeasureSpec.getSize(widthMeasureSpec);
            int height = 3000 + 50; // Since 3000 is bottom of last Rect to be drawn added and 50 for padding.
            setMeasuredDimension(width, height);
        }
    }
}


class Coordinate{
    int x,y;
    public Coordinate(int x,int y){
        this.x = x;
        this.y = y;
    }
    public int hashCode() {
        final int prime = 31;
        int result = 1;
        result = prime * result + x;
        result = prime * result + y;
        return result;
    }
    public boolean equals(Object obj) {
        if (this == obj)
            return true;
        if (obj == null)
            return false;
        if (getClass() != obj.getClass())
            return false;
        Coordinate other = (Coordinate) obj;
        if (x != other.x)
            return false;
        if (y != other.y)
            return false;
        return true;
    }
}


class Time{
    int hour,minute,second;
    int totalSecond;
    public Time(String s){
        s = s.replace("Hour"," ");s = s.replace("Minute"," ");s = s.replace("Second"," ");
        StringTokenizer ss = new StringTokenizer(s);
        this.hour = Integer.valueOf(ss.nextToken());
        this.minute = Integer.valueOf(ss.nextToken());
        this.second = Integer.valueOf(ss.nextToken());
        this.totalSecond = (this.second) + ((this.minute)*60) + ((this.hour)*3600); 
    }
}


class IntegerFour{
    String destinationAirport;
    Time slotTime;// in hour,minute,second 3 of them
    Time duration;
    int expense;
    public IntegerFour(String destinationAirport,Time slotTime,Time duration,int expense){
        this.destinationAirport = destinationAirport;
        this.duration = duration;
        this.slotTime = slotTime;
        this.expense = expense;
    }
}



class Pair implements Comparable{
    String airport;
    int dollar;
    public Pair(String airport,int dollar){
        this.airport =  airport;
        this.dollar = dollar;
    }

    public int compareTo(Object o) {
        return (this.dollar - ((Pair)o).dollar);
    }

}



class XY{
    int x,y;
    public XY(String s){
        s = s.replace("(","");s = s.replace(")","");s = s.replace(","," ");
        StringTokenizer ss  =  new StringTokenizer(s);
        x = Integer.valueOf(ss.nextToken()); y = Integer.valueOf(ss.nextToken());
    }
}

布局:

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
   android:layout_width="fill_parent"
   android:layout_height="fill_parent"
   android:paddingLeft="16dp"
   android:paddingRight="16dp" >

   <ListView
       android:id="@+id/list1"
       android:layout_width="60dp"
       android:layout_height="fill_parent"
       android:layout_alignParentLeft="true" />

   <ListView
       android:id="@+id/list2"
       android:layout_width="60dp"
       android:layout_height="fill_parent"
       android:layout_alignParentRight="true" />

   <View
        android:id="@+id/mapview1"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"/>  

</RelativeLayout>

Answer 1

您收到此错误是因为 listArray 的元素为空。在 Java 中，当你初始化一个数组时，它只是可以存储一些对象的东西。但是它的元素是null!您必须一个一个地设置数组元素。