我的代码中出现错误，这是不可理解的..请帮我找出它是什么问题。
我有数据库类和主要活动..它显示在日志中但是当它出现在我的模拟器屏幕上时它会给我错误。
我的数据库类：
package com.example.nearby_places;
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;
public class Database extends SQLiteOpenHelper {
//database name & version number
private static final String db_name = "nearby_places";
private static final int db_version = 1;
//tables
private static final String table_placetypes = "placetypes";
private static final String table_places = "table_places";
//column names
private static final String type_id = "type_id";
private static final String type_name = "type_name";
private static final String place_id = "place_id";
private static final String place_name = "place_name";
private static final String place_address = "place_address";
private static final String place_contact = "place_contact";
public Database(Context context) {
super(context, db_name, null, db_version);
// TODO Auto-generated constructor stub
}
// create table queries
String create_table_placetypes = "CREATE TABLE IF NOT EXISTS " + table_placetypes + "("
+ type_id + " INTEGER PRIMARY KEY NOT NULL," + type_name + " TEXT" + ")";
String create_table_places = "CREATE TABLE IF NOT EXISTS table_places (place_id INTEGER PRIMARY KEY NOT NULL, place_name TEXT, place_address TEXT, place_contact TEXT, type_id INTEGER, FOREIGN KEY (type_id) REFERENCES table_placetypes(type_id))";
@Override
public void onCreate(SQLiteDatabase db) {
// TODO Auto-generated method stub
db.execSQL(create_table_placetypes);
Log.d("creating", "placetypes created");
db.execSQL(create_table_places);
Log.d("creating", "places created");
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
// TODO Auto-generated method stub
db.execSQL("DROP TABLE IF EXISTS " + table_placetypes);
db.execSQL("DROP TABLE IF EXISTS " + table_places);
onCreate(db);
}
// add placetypes
void addplacetypes (placetypes pt) {
SQLiteDatabase db = getWritableDatabase();
ContentValues values = new ContentValues();
values.put(type_name, pt.getTypename());
db.insert(table_placetypes, null, values);
db.close();
}
// Getting single placetypes
placetypes getPlacetypes(int id) {
SQLiteDatabase db = this.getReadableDatabase();
Cursor cursor = db.query(table_placetypes, new String[] {type_id,
type_name }, type_id + "=?",
new String[] { String.valueOf(id) }, null, null, null, null);
if (cursor != null)
cursor.moveToFirst();
placetypes pt = new placetypes(Integer.parseInt(cursor.getString(0)),
cursor.getString(1));
// return contact
return pt;
}
// Getting All placetypes
public List<placetypes> getAllPlacetypes() {
List<placetypes> placetypesList = new ArrayList<placetypes>();
// Select All Query
String selectQuery = "SELECT * FROM " + table_placetypes;
SQLiteDatabase db = this.getWritableDatabase();
Cursor cursor = db.rawQuery(selectQuery, null);
// looping through all rows and adding to list
if (cursor.moveToFirst()) {
do {
placetypes pt = new placetypes();
pt.setTypeid(Integer.parseInt(cursor.getString(0)));
pt.setTypename(cursor.getString(1));
//String name = cursor.getString(1);
//MainActivity.ArrayofName.add(name);
// Adding contact to list
placetypesList.add(pt);
} while (cursor.moveToNext());
}
// return placetype list
return placetypesList;
}
// Getting placetypes Count
public int getPlacetypesCount() {
String countQuery = "SELECT * FROM " + table_placetypes;
SQLiteDatabase db = this.getReadableDatabase();
Cursor cursor = db.rawQuery(countQuery, null);
cursor.close();
// return count
return cursor.getCount();
}
public void addplaces(places p) {
SQLiteDatabase db = getWritableDatabase();
ContentValues values = new ContentValues();
values.put(place_name, p.getPlace_name());
values.put(place_address, p.getPlace_address());
values.put(place_contact, p.getPlace_contact());
values.put(type_id, p.getT_id());
Log.d("Type ID", String.valueOf(p.getT_id()));
db.insert(table_places, null, values);
db.close();
}
places getPlaces(int pid) {
SQLiteDatabase db = getReadableDatabase();
Cursor cursor = db.query(table_places, new String[] {place_id, place_name, place_address, place_contact,type_id}, place_id + "=?", new String[] { String.valueOf(pid) } , null, null, null, null);
if(cursor != null)
cursor.moveToFirst();
places p = new places(Integer.parseInt(cursor.getString(0)),
Integer.parseInt(cursor.getString(1)),
cursor.getString(2),
cursor.getString(3),
cursor.getString(4)
);
cursor.close();
return p;
}
public List<places> getAllPlaces(String typeName) {
List<places> placeList = new ArrayList<places>();
//String selectQuery = "SELECT * FROM table_places INNER JOIN placetypes ON placetypes.type_id=table_places.type_id ";
//String selectQuery = "SELECT * FROM table_places WHERE table_places.type_id="+Integer.toString(typeid);
String selectQuery ="SELECT * FROM table_places WHERE placetypes.place_name="+typeName+" INNER JOIN placetypes ON placetypes.type_id=table_places.type_id";
SQLiteDatabase db = this.getWritableDatabase();
Cursor cursor = db.rawQuery(selectQuery, null);
if(cursor.moveToFirst() )
{
do{
places p = new places();
/*p.setT_id(cursor.getColumnIndex(type_id));
p.setPlace_id(cursor.getColumnIndex(place_id));
p.setPlace_name(cursor.getColumnIndex(place_name));
*/
p.setT_id(cursor.getInt(0));
p.setPlace_id(cursor.getInt(1));
p.setPlace_name(cursor.getString(2));
p.setPlace_address(cursor.getString(3));
p.setPlace_contact(cursor.getString(4));
/*String t_id = cursor.getString(4);
String p_name = cursor.getString(2);
String p_address = cursor.getString(3);
String p_contact = cursor.getString(1);*/
placeList.add(p);
}while(cursor.moveToNext());
}
cursor.close();
return placeList;
}
public int getPlaceCount () {
String selectQuery = "SELECT * FROM " +table_places;
SQLiteDatabase db = getReadableDatabase();
Cursor cursor = db.rawQuery(create_table_places, null);
cursor.close();
return cursor.getCount();
}
}
MainActivity
package com.example.nearby_places;
import java.util.ArrayList;
import java.util.List;
import android.os.Bundle;
import android.app.Activity;
import android.content.Intent;
import android.util.Log;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import android.widget.TextView;
import android.widget.Toast;
import android.widget.AdapterView.OnItemClickListener;
public class MainActivity extends Activity {
private ListView listView;
public static ArrayList<String> ArrayofName = new ArrayList<String>();
public static final String PLACETYPE = "com.example";
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Database db = new Database(this);
if(db.getAllPlacetypes().isEmpty())
{
/**
* CRUD Operations
* */
// Inserting Places
Log.d("Insert: ", "Inserting ..");
db.addplacetypes(new placetypes("RESTURAUNTS"));
db.addplacetypes(new placetypes("MALLS"));
db.addplacetypes(new placetypes("GAS STATIONS"));
db.addplacetypes(new placetypes("HOTELS"));
db.addplacetypes(new placetypes("MOTELS"));
}
// Reading all Places
Log.d("Reading: ", "Reading all placetypes..");
if(ArrayofName.isEmpty())
{
List<placetypes> placetypes = db.getAllPlacetypes();
for (placetypes pt : placetypes)
{
String log = "Id: "+pt.getTypeid()+" ,Name: " + pt.getTypename();
// Writing Places to log
Log.d("Name: ", log);
System.out.println(log);
ArrayofName.add(pt.getTypename());
}
}
listView = (ListView) findViewById(R.id.listView1);
ArrayAdapter<String> adapter = new ArrayAdapter<String>(this,
android.R.layout.simple_list_item_1, ArrayofName);
int pos = listView.getAdapter().getCount() -1;
listView.getAdapter().getItemId(pos);
listView.setAdapter(adapter);
listView.setOnItemClickListener(new OnItemClickListener()
{
public void onItemClick(AdapterView<?> parent, View v, int position, long id)
{
String type = ((TextView) v).getText().toString();
Toast.makeText(getApplicationContext(), type, Toast.LENGTH_SHORT).show();
Intent i = new Intent(getApplicationContext(),MainActivity2.class);
i.putExtra(PLACETYPE, type);
startActivity(i);
/*Cursor cursor = (Cursor) parent.getItemAtPosition(position);
Toast.makeText(getApplicationContext(), "id: " +id+ "position: " +position+ "row id: " +(cursor.getColumnIndex("" +
"")), Toast.LENGTH_LONG).show();
*/
Intent intent = new Intent(MainActivity.this, MainActivity2.class);
startActivity(intent);
}
}
);
}
}
logcat的
10-11 17:21:51.871: D/Reading:(4932): Reading all placetypes..
10-11 17:21:51.871: D/Name:(4932): Id: 1 ,Name: RESTURAUNTS
10-11 17:21:51.875: I/System.out(4932): Id: 1 ,Name: RESTURAUNTS
10-11 17:21:51.875: D/Name:(4932): Id: 2 ,Name: MALLS
10-11 17:21:51.875: I/System.out(4932): Id: 2 ,Name: MALLS
10-11 17:21:51.875: D/Name:(4932): Id: 3 ,Name: GAS STATIONS
10-11 17:21:51.875: I/System.out(4932): Id: 3 ,Name: GAS STATIONS
10-11 17:21:51.875: D/Name:(4932): Id: 4 ,Name: HOTELS
10-11 17:21:51.875: I/System.out(4932): Id: 4 ,Name: HOTELS
10-11 17:21:51.875: D/Name:(4932): Id: 5 ,Name: MOTELS
10-11 17:21:51.875: I/System.out(4932): Id: 5 ,Name: MOTELS
10-11 17:21:51.887: D/AndroidRuntime(4932): Shutting down VM
10-11 17:21:51.887: W/dalvikvm(4932): threadid=1: thread exiting with uncaught exception (group=0x41c77300)
10-11 17:21:51.894: E/AndroidRuntime(4932): FATAL EXCEPTION: main
10-11 17:21:51.894: E/AndroidRuntime(4932): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.nearby_places/com.example.nearby_places.MainActivity}: java.lang.NullPointerException
10-11 17:21:51.894: E/AndroidRuntime(4932): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2059)
10-11 17:21:51.894: E/AndroidRuntime(4932): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2084)
10-11 17:21:51.894: E/AndroidRuntime(4932): at android.app.ActivityThread.access$600(ActivityThread.java:130)
10-11 17:21:51.894: E/AndroidRuntime(4932): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1195)
10-11 17:21:51.894: E/AndroidRuntime(4932): at android.os.Handler.dispatchMessage(Handler.java:99)
10-11 17:21:51.894: E/AndroidRuntime(4932): at android.os.Looper.loop(Looper.java:137)
10-11 17:21:51.894: E/AndroidRuntime(4932): at android.app.ActivityThread.main(ActivityThread.java:4745)
10-11 17:21:51.894: E/AndroidRuntime(4932): at java.lang.reflect.Method.invokeNative(Native Method)
10-11 17:21:51.894: E/AndroidRuntime(4932): at java.lang.reflect.Method.invoke(Method.java:511)
10-11 17:21:51.894: E/AndroidRuntime(4932): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
10-11 17:21:51.894: E/AndroidRuntime(4932): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
10-11 17:21:51.894: E/AndroidRuntime(4932): at dalvik.system.NativeStart.main(Native Method)
10-11 17:21:51.894: E/AndroidRuntime(4932): Caused by: java.lang.NullPointerException
10-11 17:21:51.894: E/AndroidRuntime(4932): at com.example.nearby_places.MainActivity.onCreate(MainActivity.java:62)
10-11 17:21:51.894: E/AndroidRuntime(4932): at android.app.Activity.performCreate(Activity.java:5008)
10-11 17:21:51.894: E/AndroidRuntime(4932): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1079)
10-11 17:21:51.894: E/AndroidRuntime(4932): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2023)
10-11 17:21:51.894: E/AndroidRuntime(4932): ... 11 more
10-11 17:21:53.695: I/Process(4932): Sending signal. PID: 4932 SIG: 9
答案 0 :(得分：3)
你对getAdapter的调用返回null，因为你在setAdapter之前调用它，试试这个：
listView.setAdapter(adapter);
int pos = listView.getAdapter().getCount() -1;
listView.getAdapter().getItemId(pos);
答案 1 :(得分：0)
如果您有 NULLPOINTER异常，请深入了解您的LogCat。特别是在 Caused by 的行。
了解如何阅读和使用您的LogCat，并尝试找到提及您的类/包名称的行并分析此行。
Caused by: java.lang.NullPointerException
10-11 17:21:51.894: E/AndroidRuntime(4932): at com.example.nearby_places.MainActivity.onCreate(MainActivity.java:62)
答案 2 :(得分：0)
问题在于
List<placetypes> placetypes = db.getAllPlacetypes();
您使用的查询错误。它应该是
`SELECT * FROM table_places INNER JOIN placetypes ON placetypes.type_id=table_places.type_id WHERE placetypes.place_name="+typeName+`"