当我的主要活动开始时，它会给出一个空指针异常。 我认为它的wehen我给列表视图一个costom适配器。
LogCat日志：
10-10 10:07:46.312: D/AbsListView(8971): Get MotionRecognitionManager
10-10 10:07:46.492: D/AndroidRuntime(8971): Shutting down VM
10-10 10:07:46.492: W/dalvikvm(8971): threadid=1: thread exiting with uncaught exception (group=0x41fd6ac8)
10-10 10:07:46.502: E/AndroidRuntime(8971): FATAL EXCEPTION: main
10-10 10:07:46.502: E/AndroidRuntime(8971): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.csi_week1/com.example.csi_week1.CriminalListActivitie}: java.lang.NullPointerException
10-10 10:07:46.502: E/AndroidRuntime(8971): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2249)
10-10 10:07:46.502: E/AndroidRuntime(8971): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2299)
10-10 10:07:46.502: E/AndroidRuntime(8971): at android.app.ActivityThread.access$700(ActivityThread.java:154)
10-10 10:07:46.502: E/AndroidRuntime(8971): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1284)
10-10 10:07:46.502: E/AndroidRuntime(8971): at android.os.Handler.dispatchMessage(Handler.java:99)
10-10 10:07:46.502: E/AndroidRuntime(8971): at android.os.Looper.loop(Looper.java:137)
10-10 10:07:46.502: E/AndroidRuntime(8971): at android.app.ActivityThread.main(ActivityThread.java:5306)
10-10 10:07:46.502: E/AndroidRuntime(8971): at java.lang.reflect.Method.invokeNative(Native Method)
10-10 10:07:46.502: E/AndroidRuntime(8971): at java.lang.reflect.Method.invoke(Method.java:511)
10-10 10:07:46.502: E/AndroidRuntime(8971): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1102)
10-10 10:07:46.502: E/AndroidRuntime(8971): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:869)
10-10 10:07:46.502: E/AndroidRuntime(8971): at dalvik.system.NativeStart.main(Native Method)
10-10 10:07:46.502: E/AndroidRuntime(8971): Caused by: java.lang.NullPointerException
10-10 10:07:46.502: E/AndroidRuntime(8971): at android.widget.ArrayAdapter.getCount(ArrayAdapter.java:330)
10-10 10:07:46.502: E/AndroidRuntime(8971): at android.widget.ListView.setAdapter(ListView.java:469)
10-10 10:07:46.502: E/AndroidRuntime(8971): at com.example.csi_week1.CriminalListActivitie.onCreate(CriminalListActivitie.java:22)
10-10 10:07:46.502: E/AndroidRuntime(8971): at android.app.Activity.performCreate(Activity.java:5255)
10-10 10:07:46.502: E/AndroidRuntime(8971): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1097)
10-10 10:07:46.502: E/AndroidRuntime(8971): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2213)
10-10 10:07:46.502: E/AndroidRuntime(8971): ... 11 more
CriminalListActivitie：
package com.example.csi_week1;
import android.support.v7.app.ActionBarActivity;
import android.content.Intent;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.ListView;
public class CriminalListActivitie extends ActionBarActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activitie_activity_criminal_list);
ListView listview = (ListView) findViewById(R.id.listViewCriminals);
listview.setAdapter(new CriminalProvider(this.getApplicationContext()));
listview.setOnItemClickListener(new OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
CriminalProvider provider = (CriminalProvider)parent.getAdapter();
Criminal criminal = provider.GetCriminal(position);
Intent i = new Intent();
i.setClass(getBaseContext(), MainActivity.class);
i.putExtra("criminal", criminal);
startActivity(i);
}});
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.criminal_list_activitie, 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);
}
}
CriminalAdapter：
package com.example.csi_week1;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Random;
import android.annotation.SuppressLint;
import android.content.Context;
import android.location.Location;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.ImageView;
import android.widget.TextView;
/**
* This class can be used to generate random criminals, and retrieve them based on their index.
* @author Michael
*
*/
@SuppressLint("UseSparseArrays")
public class CriminalProvider extends ArrayAdapter<Criminal>{
/**
* This list contains the generated criminals.
* Notice the static. This means that all CriminalProvider classes share the same list.
*/
private static List<Criminal> criminalList;
/**
* This context can be used to acquire the resources.
*/
private Context context;
/**
* Constructor of the CriminalProvider.
* @param context The context (i.e. the activity) that is using this provider.
*/
public CriminalProvider(Context context)
{
super(context, R.layout.activitie_activity_criminal_list, criminalList);
this.context = context;
if(criminalList == null)
{
criminalList = new ArrayList<Criminal>();
fillCriminalList();
}
}
/**
* Get the list with all stored criminals
* @return the list with criminals
*/
public List<Criminal> GetCriminals()
{
return criminalList;
}
/**
* Get a specific criminal
* @param the index of the criminal in the list
* @return the criminal
*/
public Criminal GetCriminal(int index) {
if(index >= criminalList.size() ) return null;
return criminalList.get(index);
}
/**
* Creates a criminals.
*/
private void fillCriminalList()
{
//Load criminal and crime information from resource xml files (see res/values folder):
String[] criminalNames = context.getResources().getStringArray(R.array.criminalNames);
String[] criminalDetails = context.getResources().getStringArray(R.array.criminalDetails);
int[] drawableIds = new int[] { R.drawable.mugshot1, R.drawable.mugshot2,
R.drawable.mugshot3, R.drawable.mugshot4, R.drawable.mugshot5 };
String[] crimeNames = context.getResources().getStringArray(R.array.crimeNames);
String[] crimeDetails = context.getResources().getStringArray(R.array.crimeDetails);
for(int criminalIndex = 0; criminalIndex < criminalNames.length; criminalIndex++)
{
Criminal someCriminal = new Criminal();
someCriminal.name = criminalNames[criminalIndex];
someCriminal.description = criminalDetails[criminalIndex];
int drawableId = drawableIds[criminalIndex];
someCriminal.mugshot = context.getResources().getDrawable(drawableId);
Random r = new Random();
someCriminal.gender = r.nextBoolean() ? "Male":"Female";
someCriminal.age = 10 + r.nextInt(100);
someCriminal.lastKnownLocation = new Location("");
someCriminal.lastKnownLocation.setLatitude(-180.0 + r.nextDouble() * 180.0);
someCriminal.lastKnownLocation.setLongitude(-180.0 + r.nextDouble() * 180.0);
someCriminal.crimes = new ArrayList<Crime>();
int maxNumberOfCrimes = context.getResources().getStringArray(R.array.crimeNames).length;
int numCrimes = 1 + r.nextInt(maxNumberOfCrimes);
for (int c = 0 ; c < numCrimes; c++)
{
Crime crime = createRandomCrime(crimeNames, crimeDetails);
someCriminal.crimes.add(crime);
}
criminalList.add(someCriminal);
}
Collections.shuffle(criminalList);
}
/**
* Creates a random crime. The name and description are picked from the resource files.
* @return The random crime.
*/
private Crime createRandomCrime(String [] crimeNames, String[] crimeDetails)
{
Crime randomCrime = new Crime();
Random r = new Random();
int randomInt = r.nextInt(crimeNames.length);
randomCrime.name = crimeNames[randomInt];
randomInt = r.nextInt(crimeDetails.length);
randomCrime.description = crimeDetails[randomInt];
randomCrime.bountyInDollars = r.nextInt(100000);
return randomCrime;
}
@Override
public View getView(int position, View convertView, ViewGroup parent)
{
LayoutInflater inflater = (LayoutInflater)context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
View criminalView = inflater.inflate(R.layout.item_criminal_list, null);
ImageView mug = (ImageView)criminalView.findViewById(R.id.imageView1);
mug.setImageDrawable(criminalList.get(position).mugshot);
TextView name = (TextView)criminalView.findViewById(R.id.textView1);
name.setText(criminalList.get(position).name);
TextView bountyTotal = (TextView)criminalView.findViewById(R.id.textView2);
bountyTotal.setText(criminalList.get(position).getBountyInDollars());
return criminalView;
}
}
答案 0 :(得分：0)
在您的CriminalProvider构造函数中，您将未初始化的criminalList（null）提供给超类ArrayAdapter构造函数。您只是在将空引用传递给超级构造函数后才初始化列表。
移动
criminalList = new ArrayList<Criminal>()
到成员变量初始化部分：
private static List<Criminal> criminalList = new ArrayList<Criminal>();
static这里有代码味道但是如果你坚持使用它，你可以例如检查列表＆＃39; size()以查看是否需要在适配器构造函数中填充它。