我正在尝试创建自己的Android应用，但我遇到了错误
logcat的：
02-20 05:51:45.955: I/DB(2527): Database opened
02-20 05:51:46.555: I/DB(2527): Returned 3 rows
02-20 05:51:46.595: D/AndroidRuntime(2527): Shutting down VM
02-20 05:51:46.647: W/dalvikvm(2527): threadid=1: thread exiting with uncaught exception (group=0x40a71930)
02-20 05:51:46.666: E/AndroidRuntime(2527): FATAL EXCEPTION: main
02-20 05:51:46.666: E/AndroidRuntime(2527): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.namecardlistview/com.example.namecardlistview.MainActivity}: java.lang.NullPointerException
02-20 05:51:46.666: E/AndroidRuntime(2527): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2180)
02-20 05:51:46.666: E/AndroidRuntime(2527): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
02-20 05:51:46.666: E/AndroidRuntime(2527): at android.app.ActivityThread.access$600(ActivityThread.java:141)
02-20 05:51:46.666: E/AndroidRuntime(2527): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
02-20 05:51:46.666: E/AndroidRuntime(2527): at android.os.Handler.dispatchMessage(Handler.java:99)
02-20 05:51:46.666: E/AndroidRuntime(2527): at android.os.Looper.loop(Looper.java:137)
02-20 05:51:46.666: E/AndroidRuntime(2527): at android.app.ActivityThread.main(ActivityThread.java:5041)
02-20 05:51:46.666: E/AndroidRuntime(2527): at java.lang.reflect.Method.invokeNative(Native Method)
02-20 05:51:46.666: E/AndroidRuntime(2527): at java.lang.reflect.Method.invoke(Method.java:511)
02-20 05:51:46.666: E/AndroidRuntime(2527): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
02-20 05:51:46.666: E/AndroidRuntime(2527): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
02-20 05:51:46.666: E/AndroidRuntime(2527): at dalvik.system.NativeStart.main(Native Method)
02-20 05:51:46.666: E/AndroidRuntime(2527): Caused by: java.lang.NullPointerException
02-20 05:51:46.666: E/AndroidRuntime(2527): at com.example.namecardlistview.MainActivity.refreshDisplay(MainActivity.java:65)
02-20 05:51:46.666: E/AndroidRuntime(2527): at com.example.namecardlistview.MainActivity.onCreate(MainActivity.java:46)
02-20 05:51:46.666: E/AndroidRuntime(2527): at android.app.Activity.performCreate(Activity.java:5104)
02-20 05:51:46.666: E/AndroidRuntime(2527): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080)
02-20 05:51:46.666: E/AndroidRuntime(2527): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2144)
02-20 05:51:46.666: E/AndroidRuntime(2527): ... 11 more
02-20 05:56:46.835: I/Process(2527): Sending signal. PID: 2527 SIG: 9
MainActivity：
package com.example.namecardlistview;
import java.util.List;
import com.example.namecardlistview.NewActivity;
import com.example.namecardlistview.DetailActivity;
import com.example.namecardlistview.CardDataSource;
import com.example.namecardlistview.R;
import com.example.namecardlistview.NameCard;
import android.widget.ListView;
import android.app.ListActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.TextView;
import android.widget.Toast;
import android.widget.AdapterView.OnItemClickListener;
import android.app.Activity;
import android.content.Intent;
public class MainActivity extends ListActivity {
CardDataSource datasource;
List<NameCard> cards;
Long cardID;
String cardName;
ListView listView;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
datasource = new CardDataSource(this);
datasource.open();
listView = (ListView) findViewById(R.id.listview); //getListView();
//ViewGroup header = (ViewGroup) getLayoutInflater().inflate(R.layout.header, listView, false);
//listView.addHeaderView(header, null, false);
refreshDisplay();
//setListAdapter(new ArrayAdapter<String>(this, R.layout.list_fruit,FRUITS));
listView.setTextFilterEnabled(true);
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
getMenuInflater().inflate(R.menu.main, menu);
return super.onCreateOptionsMenu(menu);
}
private void refreshDisplay() {
cards = datasource.findAll();
String[] cardArray= new String[cards.size()];
for (int i=0; i<cards.size();i++)
{
cardArray[i]= cards.get(i).getName();
}
listView.setAdapter(new ArrayAdapter<String>(this, R.layout.list_card,cardArray));
}
@Override
protected void onListItemClick(ListView l, View v, int position, long id) {
// TODO Auto-generated method stub
super.onListItemClick(l, v, position, id);
position-=1;
cardID=cards.get(position).getId();
cardName=cards.get(position).getName();
Intent intent = new Intent(this,DetailActivity.class);
intent.putExtra("name", cards.get(position).getName());
intent.putExtra("id", cards.get(position).getId());
startActivityForResult(intent, 2);
}
public void addCard (MenuItem item){
// Toast.makeText(this, "ok", Toast.LENGTH_SHORT).show();
/* Fruit myFruit = new Fruit();
myFruit.setTitle("Apple");
myFruit.setDescription("apple is good");
datasource.create(myFruit);*/
Intent intent = new Intent(this,NewActivity.class);
startActivityForResult(intent, 1);
}
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
// TODO Auto-generated method stub
// Toast.makeText(this, "listenered activated", Toast.LENGTH_SHORT).show();
super.onActivityResult(requestCode, resultCode, data);
if (resultCode==RESULT_OK)
{
//String mybenefit = data.getStringExtra("benefit");
//fruit.setDescription(mybenefit);
refreshDisplay();
Toast.makeText(this, cardName + " is added", Toast.LENGTH_SHORT).show();
}else if (resultCode==10)
{
datasource.removeCard(cardID);
refreshDisplay();
Toast.makeText(this, cardName +" is deleted", Toast.LENGTH_SHORT).show();
}else if (resultCode==11)
{
refreshDisplay();
Toast.makeText(this, cardName +" is updated", Toast.LENGTH_SHORT).show();
}
}
}
我刚开始使用stackoverflow，所以我不知道我应该做什么。 所以只需告诉我你需要的任何代码。
此外，除了为所有行添加4个空格之外，是否有更简单的方法来创建代码块？编辑：没关系fount快捷方式-.-我是一个白痴
编辑：
CardDataSource：
package com.example.namecardlistview;
import java.util.ArrayList;
import java.util.List;
import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.util.Log;
import com.example.namecardlistview.NameCard;
import com.example.namecardlistview.CardDBOpenHelper;
public class CardDataSource {
public static final String LOGTAG="DB";
private static final String[] allColumns = {
CardDBOpenHelper.COLUMN_ID,
CardDBOpenHelper.COLUMN_NAME,
CardDBOpenHelper.COLUMN_OCCUPATION,
CardDBOpenHelper.COLUMN_COMPANY,
CardDBOpenHelper.COLUMN_EMAIL,
CardDBOpenHelper.COLUMN_NUMBER,
CardDBOpenHelper.COLUMN_URL,
CardDBOpenHelper.COLUMN_SUMMARY,
CardDBOpenHelper.COLUMN_FAVOURITE};
SQLiteOpenHelper dbhelper;
SQLiteDatabase database;
public CardDataSource(Context context) {
dbhelper = new CardDBOpenHelper(context);
}
public void open() {
Log.i(LOGTAG, "Database opened");
database = dbhelper.getWritableDatabase();
}
public void close() {
Log.i(LOGTAG, "Database closed");
dbhelper.close();
}
public NameCard create(NameCard card) {
ContentValues values = new ContentValues();
values.put(CardDBOpenHelper.COLUMN_NAME, card.getName());
values.put(CardDBOpenHelper.COLUMN_COMPANY, card.getCompany());
values.put(CardDBOpenHelper.COLUMN_EMAIL, card.getEmail());
values.put(CardDBOpenHelper.COLUMN_FAVOURITE, card.isFavourite());
values.put(CardDBOpenHelper.COLUMN_NUMBER, card.getPhone());
values.put(CardDBOpenHelper.COLUMN_OCCUPATION, card.getOccupation());
values.put(CardDBOpenHelper.COLUMN_SUMMARY, card.getSummary());
values.put(CardDBOpenHelper.COLUMN_URL, card.getUrl());
long insertid = database.insert(CardDBOpenHelper.TABLE_CARDS, null, values);
card.setId(insertid);
return card;
}
public NameCard update(NameCard card) {
ContentValues values = new ContentValues();
values.put(CardDBOpenHelper.COLUMN_NAME, card.getName());
database.update(CardDBOpenHelper.TABLE_CARDS, values, CardDBOpenHelper.COLUMN_ID+'=' + card.getId(), null);
return card;
}
public List<NameCard> findAll() {
List<NameCard> cards = new ArrayList<NameCard>();
Cursor cursor = database.query(CardDBOpenHelper.TABLE_CARDS, allColumns,
null, null, null, null, null);
Log.i(LOGTAG, "Returned " + cursor.getCount() + " rows");
if (cursor.getCount() > 0) {
while (cursor.moveToNext()) {
NameCard card = new NameCard();
card.setId(cursor.getLong(cursor.getColumnIndex(CardDBOpenHelper.COLUMN_ID)));
card.setName(cursor.getString(cursor.getColumnIndex(CardDBOpenHelper.COLUMN_NAME)));
card.setCompany(cursor.getString(cursor.getColumnIndex(CardDBOpenHelper.COLUMN_COMPANY)));
card.setEmail(cursor.getString(cursor.getColumnIndex(CardDBOpenHelper.COLUMN_EMAIL)));
card.setFavourite(1 == cursor.getInt(cursor.getColumnIndex(CardDBOpenHelper.COLUMN_FAVOURITE)));
card.setOccupation(cursor.getString(cursor.getColumnIndex(CardDBOpenHelper.COLUMN_OCCUPATION)));
card.setPhone(cursor.getString(cursor.getColumnIndex(CardDBOpenHelper.COLUMN_NUMBER)));
card.setUrl(cursor.getString(cursor.getColumnIndex(CardDBOpenHelper.COLUMN_URL)));
card.setSummary(cursor.getString(cursor.getColumnIndex(CardDBOpenHelper.COLUMN_SUMMARY)));
cards.add(card);
}
}
Log.i(LOGTAG, "Going to return cards now");
return cards;
}
public boolean removeCard(Long id) {
String where = CardDBOpenHelper.COLUMN_ID + "=" +id ;
int result = database.delete(CardDBOpenHelper.TABLE_CARDS, where, null);
return (result == 1);
}
}
list_card.xml：
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent" >
<Listview
android:id="@+id/listview"
android:layout_width="wrap_content"
android:layout_height="wrap_content" />
</RelativeLayout>
答案 0 :(得分：2)
setContentView()中缺少onCreate()方法。