java - 从 getParcelableArrayListExtra 读取自定义对象的 ArrayList 返回 NullPointerException

Question

我正在尝试将我的车辆数组列表从主要 Activity 传递到我的 MapView 类，但是当我尝试读取 ArrayList 时它一直给我 NullPointerException。

车辆代码

public class Vehicle implements Parcelable
{
    private String name = "";
    private String GPSDateTime = "";
    private long latitude = 0;
    private long longtitude = 0;
    private String event = "";


    public Vehicle (String vName, String vGpsDateTime, long vLatitude, 
            long vLongtitude, String vEvent)
    {
        this.name = vName;
        this.GPSDateTime = vGpsDateTime;
        this.latitude = vLatitude;
        this.longtitude = vLongtitude;
        this.event = vEvent;
    }

    protected Vehicle(Parcel in) {
        this.name = in.readString();
        this.GPSDateTime = in.readString();
        this.latitude = in.readLong();
        this.longtitude = in.readLong();
        this.event = in.readString();
    }

    public String getName()
    {
        return name;
    }
    public void setName(String vName)
    {
        name = vName;
    }
    public String getGpsDateTime()
    {
        return GPSDateTime;
    }
    public void setGpsDateTime(String vGpsDateTime)
    {
        GPSDateTime = vGpsDateTime;
    }
    public long getLatitude()
    {
        return latitude;
    }
    public void setLatitude(Long vLatitude)
    {
        latitude = vLatitude;
    }
    public long getLongtitude()
    {
        return longtitude;
    }
    public void setLongtitude(Long vLongtitude)
    {
        longtitude = vLongtitude;
    }
    public String getEvent()
    {
        return event;
    }
    public void setEvent(String vEvent)
    {
        event = vEvent;
    }

    @Override
    public String toString() {
        return name;
    }

    @Override
    public int describeContents() {
        return 0;
    }

    @Override
    public void writeToParcel(Parcel dest, int flags) {
        dest.writeString(name);
        dest.writeString(GPSDateTime);
        dest.writeLong(latitude);
        dest.writeLong(longtitude);
        dest.writeString(event);
    }

    public static final Parcelable.Creator<Vehicle> CREATOR = new Parcelable.Creator<Vehicle>() {
        @Override
        public Vehicle createFromParcel(Parcel in) {
            return new Vehicle(in);
        }

        @Override
        public Vehicle[] newArray(int size) {
            return new Vehicle[size];
        }
    };
}

主要 Activity 类

public class MainActivity extends Activity {
    public static String rslt=""; 
    //VehicleList vehicleList = new VehicleList();
    public static ArrayList<Vehicle> vehicleList = new ArrayList<Vehicle>();
    @Override
    protected void onCreate(Bundle savedInstanceState) {


      parseReturnStringFromWebASMX(rslt);
      Intent intent = new Intent(MainActivity.this, MapView.class);
      intent.putParcelableArrayListExtra("vlist", vehicleList);
      startActivity(intent);
 }

 public boolean parseReturnStringFromWebASMX(String input){
        boolean ok = false;

        String vehicleDelims = "\\|#\\|";
        String [] vehicleData = input.split(vehicleDelims);
        for(int j=0; j<vehicleData.length; j++){
            String delims = "\\$\\#\\$";

            String[] tokens = vehicleData[j].split(delims);
            if(j!=0){
                Vehicle v = parseNewVehicleString(tokens, parse);
                ok = this.vehicleList.add(v);
            }

        }
    }

    public Vehicle parseNewVehicleString(String[] tokens, String parse)
    {
        String name = "", datetime = "", event = "";
        Long latitude = (long) 0, longtitude = (long) 0;
        for(int i=0; i<tokens.length; i++){
            //parse = parse + "in here \n";
            //parse = parse + tokens[i] + "\n";
            if(!tokens[i].equalsIgnoreCase("")){
                //parse = parse + "in here 2\n";
                if (i==0){
                    name = (String)tokens[0];
                    //parse = parse + "Add name " + name + "\n";
                }
                else if (i==1){
                    datetime = (String) tokens[1];
                    //parse = parse + "Add datetime " + datetime + "\n";
                }
                else if (i==2){
                    latitude = (Long.parseLong(tokens[2]));
                }
                else if (i==3){
                    longtitude = (Long.parseLong(tokens[3]));
                }
                else if (i==4){
                    event = tokens[4];
                }

            }
        }
        Vehicle v = new Vehicle(name, datetime, latitude, longtitude, event);
        return v;
        //return parse;
    }
}

map View

package com.example.myfirstapp;

import java.util.ArrayList;

import android.support.v7.app.ActionBarActivity;
import android.support.v7.app.ActionBar;
import android.support.v4.app.Fragment;
import android.app.AlertDialog;
import android.content.Intent;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.os.Build;

public class MapView extends ActionBarActivity {

    public static ArrayList<Vehicle> vehicleList = new ArrayList<Vehicle>();

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_map_view);
        if (savedInstanceState == null) {
            getSupportFragmentManager().beginTransaction()
                    .add(R.id.container, new PlaceholderFragment()).commit();
        }

        Intent i = this.getIntent();
        vehicleList = i.getParcelableArrayListExtra("vList");//*


        final  AlertDialog ad1=new AlertDialog.Builder(this).create();
        ad1.setMessage(test);
        ad1.show();
    }

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

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();
        if (id == R.id.action_settings) {
            return true;
        }
        return super.onOptionsItemSelected(item);
    }

    /**
     * A placeholder fragment containing a simple view.
     */
    public static class PlaceholderFragment extends Fragment {

        public PlaceholderFragment() {
        }

        @Override
        public View onCreateView(LayoutInflater inflater, ViewGroup container,
                Bundle savedInstanceState) {
            View rootView = inflater.inflate(R.layout.fragment_map_view,
                    container, false);
            return rootView;
        }
    }
}

我遇到的错误是每当我尝试访问 vehicleList 时

vehicleList = i.getParcelableArrayListExtra("vList");//*

过去几周我一直在拔头发。有人可以帮帮我吗~~

来自 LogCat 的错误日志

02-11 15:23:17.032: E/AndroidRuntime(24050): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.myfirstapp/com.example.myfirstapp.MapView}: java.lang.NullPointerException 02-11 15:23:17.032: E/AndroidRuntime(24050): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2396) 02-11 15:23:17.032: E/AndroidRuntime(24050): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2448) 02-11 15:23:17.032: E/AndroidRuntime(24050): at android.app.ActivityThread.access$600(ActivityThread.java:173) 02-11 15:23:17.032: E/AndroidRuntime(24050): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1392) 02-11 15:23:17.032: E/AndroidRuntime(24050): at android.os.Handler.dispatchMessage(Handler.java:107) 02-11 15:23:17.032: E/AndroidRuntime(24050): at android.os.Looper.loop(Looper.java:194) 02-11 15:23:17.032: E/AndroidRuntime(24050): at android.app.ActivityThread.main(ActivityThread.java:5469) 02-11 15:23:17.032: E/AndroidRuntime(24050): at java.lang.reflect.Method.invokeNative(Native Method) 02-11 15:23:17.032: E/AndroidRuntime(24050): at java.lang.reflect.Method.invoke(Method.java:525) 02-11 15:23:17.032: E/AndroidRuntime(24050): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:857) 02-11 15:23:17.032: E/AndroidRuntime(24050): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:624) 02-11 15:23:17.032: E/AndroidRuntime(24050): at dalvik.system.NativeStart.main(Native Method) 02-11 15:23:17.032: E/AndroidRuntime(24050): Caused by: java.lang.NullPointerException 02-11 15:23:17.032: E/AndroidRuntime(24050): at com.example.myfirstapp.MapView.onCreate(MapView.java:35) 02-11 15:23:17.032: E/AndroidRuntime(24050): at android.app.Activity.performCreate(Activity.java:5226) 02-11 15:23:17.032: E/AndroidRuntime(24050): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1151) 02-11 15:23:17.032: E/AndroidRuntime(24050): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2360)

Answer 1

你在放

intent.putParcelableArrayListExtra("vlist", vehicleList);

并试图得到

vehicleList = i.getParcelableArrayListExtra("vList");

您的 key 不匹配，因为您有错字。为避免将来出现这种情况，您应该使用常量。

public static VEHICLE_LIST_EXTRA = "vList";

并在两种情况下访问它。