我无法从我的数据库中显示一个事件信息。在 DayPlan.java 中的事件列表中单击我的事件后，它应该向我显示有关此事件的一些信息，但它只会使整个应用程序崩溃并出现错误：Nullpointer exception :( 我使用了 thiscodeasa base: Database example
错误出现在 ViewEvent 的 OnPostExecute 中，有人可以帮我吗？
我的数据库连接器：
package com.examples.android.calendar;
import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;
public class DatabaseConnector {
private static final String DB_NAME = "watchaday";
private SQLiteDatabase database;
private DatabaseOpenHelper dbOpenHelper;
public DatabaseConnector(Context context) {
dbOpenHelper = new DatabaseOpenHelper(context, DB_NAME, null, 1);
}
public void open() throws SQLException
{
//open database in reading/writing mode
database = dbOpenHelper.getWritableDatabase();
}
public void close()
{
if (database != null)
database.close();
}
public void insertContact(String date, String hour_from, String hour_to, String event, String colour)
{
ContentValues newCon = new ContentValues();
newCon.put("date", date);
newCon.put("hour_from", hour_from);
newCon.put("hour_to", hour_to);
newCon.put("event", event);
newCon.put("colour", colour);
open();
database.insert("calendar_events", null, newCon);
close();
}
public void updateContact(long id, String date, String hour_from, String hour_to, String event, String colour)
{
ContentValues editCon = new ContentValues();
;
editCon.put("date", date);
editCon.put("hour_from", hour_from);
editCon.put("hour_to", hour_to);
editCon.put("event", event);
editCon.put("colour", colour);
open();
database.update("calendar_events", editCon, "_id=" + id, null);
close();
}
public Cursor getAllContacts()
{
return database.query("calendar_events", new String[] {"_id", "event"},
null, null, null, null, "date");
}
public Cursor getOneContact(long id)
{
return database.query("calendar_events", null, "_id=" + id, null, null, null, null);
}
public void deleteContact(long id)
{
open();
database.delete("calendar_events", "_id=" + id, null);
close();
}
}
我的数据库助手：
package com.examples.android.calendar;
import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteDatabase.CursorFactory;
import android.database.sqlite.SQLiteOpenHelper;
public class DatabaseOpenHelper extends SQLiteOpenHelper {
public DatabaseOpenHelper(Context context, String name,
CursorFactory factory, int version) {
super(context, name, factory, version);
}
@Override
public void onCreate(SQLiteDatabase db) {
String createQuery = "CREATE TABLE calendar_events (_id integer primary key autoincrement,date, hour_from, hour_to, event, colour);";
db.execSQL(createQuery);
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
}
}
我的事件列表代码：
package com.examples.android.calendar;
import android.os.AsyncTask;
import android.os.Bundle;
import android.app.ListActivity;
import android.content.Intent;
import android.database.Cursor;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.view.View;
import android.widget.AdapterView;
import android.widget.CursorAdapter;
import android.widget.ListView;
import android.widget.SimpleCursorAdapter;
import android.widget.AdapterView.OnItemClickListener;
public class DayPlan extends ListActivity {
public static final String ROW_ID = "row_id";
private ListView conListView;
private CursorAdapter conAdapter;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
conListView=getListView();
conListView.setOnItemClickListener(viewConListener);
// map each name to a TextView
String[] from = new String[] { "event" };
int[] to = new int[] { R.id.countryTextView };
conAdapter = new SimpleCursorAdapter(DayPlan.this, R.layout.day_plan, null, from, to);
setListAdapter(conAdapter); // set adapter
}
@Override
protected void onResume()
{
super.onResume();
new GetContacts().execute((Object[]) null);
}
@Override
protected void onStop()
{
Cursor cursor = conAdapter.getCursor();
if (cursor != null)
cursor.deactivate();
conAdapter.changeCursor(null);
super.onStop();
}
private class GetContacts extends AsyncTask<Object, Object, Cursor>
{
DatabaseConnector dbConnector = new DatabaseConnector(DayPlan.this);
@Override
protected Cursor doInBackground(Object... params)
{
dbConnector.open();
return dbConnector.getAllContacts();
}
@Override
protected void onPostExecute(Cursor result)
{
conAdapter.changeCursor(result); // set the adapter's Cursor
dbConnector.close();
}
}
@Override
public boolean onCreateOptionsMenu(Menu menu)
{
super.onCreateOptionsMenu(menu);
MenuInflater inflater = getMenuInflater();
inflater.inflate(R.menu.dayplan_menu, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item)
{
Intent addContact = new Intent(DayPlan.this, AddEvent.class);
startActivity(addContact);
return super.onOptionsItemSelected(item);
}
OnItemClickListener viewConListener = new OnItemClickListener()
{
public void onItemClick(AdapterView<?> arg0, View arg1, int arg2,long arg3)
{
Intent viewCon = new Intent(DayPlan.this, ViewEvent.class);
viewCon.putExtra(ROW_ID, arg3);
startActivity(viewCon);
}
};
}
我的查看事件代码在 OnPostExecute 部分中使应用程序崩溃：
视图事件.java：
public class ViewEvent extends Activity {
private long rowID;
private TextView dateTv;
private TextView hourfromTv;
private TextView hourtoTv;
private TextView eventTv;
private TextView colourTv;
@Override
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.view_event);
setUpViews();
Bundle extras = getIntent().getExtras();
rowID = extras.getLong(DayPlan.ROW_ID);
}
private void setUpViews() {
dateTv = (TextView) findViewById(R.id.date);
hourfromTv = (TextView) findViewById(R.id.hour_fromText);
hourtoTv = (TextView) findViewById(R.id.hour_toText);
eventTv = (TextView) findViewById(R.id.eventText);
colourTv = (TextView) findViewById(R.id.colourText);
}
@Override
protected void onResume()
{
super.onResume();
new LoadContacts().execute(rowID);
}
private class LoadContacts extends AsyncTask<Long, Object, Cursor>
{
DatabaseConnector dbConnector = new DatabaseConnector(ViewEvent.this);
@Override
protected Cursor doInBackground(Long... params)
{
dbConnector.open();
return dbConnector.getOneContact(params[0]);
}
@Override
protected void onPostExecute(Cursor result)
{
super.onPostExecute(result);
result.moveToFirst();
// get the column index for each data item
int dateindex = result.getColumnIndex("date");
int hourfromIndex = result.getColumnIndex("hour_from");
int hourtoIndex = result.getColumnIndex("hour_to");
int eventIndex = result.getColumnIndex("event");
int colourIndex = result.getColumnIndex("colour");
dateTv.setText(result.getString(dateindex));
hourfromTv.setText(result.getString(hourfromIndex));
hourtoTv.setText(result.getString(hourtoIndex));
eventTv.setText(result.getString(eventIndex));
colourTv.setText(result.getString(colourIndex));
result.close();
dbConnector.close();
}
}
@Override
public boolean onCreateOptionsMenu(Menu menu)
{
super.onCreateOptionsMenu(menu);
MenuInflater inflater = getMenuInflater();
inflater.inflate(R.menu.view_event_menu, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item)
{
switch (item.getItemId())
{
case R.id.editItem:
Intent addEditContact =
new Intent(this, AddEvent.class);
addEditContact.putExtra(DayPlan.ROW_ID, rowID);
startActivity(addEditContact);
return true;
case R.id.deleteItem:
deleteContact();
return true;
default:
return super.onOptionsItemSelected(item);
}
}
private void deleteContact()
{
AlertDialog.Builder alert = new AlertDialog.Builder(ViewEvent.this);
alert.setTitle(R.string.confirmTitle);
alert.setMessage(R.string.confirmMessage);
alert.setPositiveButton(R.string.delete_btn,
new DialogInterface.OnClickListener()
{
public void onClick(DialogInterface dialog, int button)
{
final DatabaseConnector dbConnector =
new DatabaseConnector(ViewEvent.this);
AsyncTask<Long, Object, Object> deleteTask =
new AsyncTask<Long, Object, Object>()
{
@Override
protected Object doInBackground(Long... params)
{
dbConnector.deleteContact(params[0]);
return null;
}
@Override
protected void onPostExecute(Object result)
{
finish();
}
};
deleteTask.execute(new Long[] { rowID });
}
}
);
alert.setNegativeButton(R.string.cancel_btn, null).show();
}
}
错误 ：
12-30 17:52:29.334：E/AndroidRuntime(1173)：致命异常：主要
12-30 17:52:29.334: E/AndroidRuntime(1173): java.lang.NullPointerException
12-30 17:52:29.334: E/AndroidRuntime(1173): 在 com.examples.android.calendar.ViewEvent$LoadContacts.onPostExecute(ViewEvent.java:76)
12-30 17:52:29.334: E/AndroidRuntime(1173): 在 com.examples.android.calendar.ViewEvent$LoadContacts.onPostExecute(ViewEvent.java:1)
12-30 17:52:29.334: E/AndroidRuntime(1173): 在 android.os.AsyncTask.finish(AsyncTask.java:631)
12-30 17:52:29.334: E/AndroidRuntime(1173): 在 android.os.AsyncTask.access$600(AsyncTask.java:177)
12-30 17:52:29.334: E/AndroidRuntime(1173): 在 android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:644)
12-30 17:52:29.334: E/AndroidRuntime(1173): 在 android.os.Handler.dispatchMessage(Handler.java:99)
12-30 17:52:29.334: E/AndroidRuntime(1173): 在 android.os.Looper.loop(Looper.java:137)
12-30 17:52:29.334: E/AndroidRuntime(1173): 在 android.app.ActivityThread.main(ActivityThread.java:4745)
12-30 17:52:29.334: E/AndroidRuntime(1173): 在 java.lang.reflect.Method.invokeNative(Native Method)
12-30 17:52:29.334: E/AndroidRuntime(1173): 在 java.lang.reflect.Method.invoke(Method.java:511)
12-30 17:52:29.334: E/AndroidRuntime(1173): 在 com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
12-30 17:52:29.334: E/AndroidRuntime(1173): 在 com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
12-30 17:52:29.334: E/AndroidRuntime(1173): at dalvik.system.NativeStart.main(Native Method) 12-30 17:52:31.463: I/Process(1173): 发送信号。PID：1173 SIG：9 12-30 17:52:32.305：E/Trace(1191)：打开跟踪文件时出错：没有这样的文件或目录 (2)