我试图创建一个应用程序，从数据库中获取数据并设置任务提醒，但是调用提醒函数获取NullPointerException时，我是Android新手，请帮帮我。log-cat和相关程序代码如下
LogCat
04-16 21:09:12.199: E/AndroidRuntime(1389): FATAL EXCEPTION: main
04-16 21:09:12.199: E/AndroidRuntime(1389): java.lang.NullPointerException
04-16 21:09:12.199: E/AndroidRuntime(1389): at com.examples.TaskRemainderActivity.remind(TaskRemainderActivity.java:49)
04-16 21:09:12.199: E/AndroidRuntime(1389): at com.examples.ReminderView$MyListAdapter.bindView(ReminderView.java:123)
04-16 21:09:12.199: E/AndroidRuntime(1389): at android.widget.CursorAdapter.getView(CursorAdapter.java:250)
04-16 21:09:12.199: E/AndroidRuntime(1389): at android.widget.AbsListView.obtainView(AbsListView.java:2267)
04-16 21:09:12.199: E/AndroidRuntime(1389): at android.widget.ListView.measureHeightOfChildren(ListView.java:1244)
04-16 21:09:12.199: E/AndroidRuntime(1389): at android.widget.ListView.onMeasure(ListView.java:1156)
04-16 21:09:12.199: E/AndroidRuntime(1389): at android.view.View.measure(View.java:15172)
04-16 21:09:12.199: E/AndroidRuntime(1389): at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4814)
04-16 21:09:12.199: E/AndroidRuntime(1389): at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1390)
04-16 21:09:12.199: E/AndroidRuntime(1389): at android.widget.LinearLayout.measureVertical(LinearLayout.java:681)
04-16 21:09:12.199: E/AndroidRuntime(1389): at android.widget.LinearLayout.onMeasure(LinearLayout.java:574)
04-16 21:09:12.199: E/AndroidRuntime(1389): at android.view.View.measure(View.java:15172)
04-16 21:09:12.199: E/AndroidRuntime(1389): at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4814)
04-16 21:09:12.199: E/AndroidRuntime(1389): at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
04-16 21:09:12.199: E/AndroidRuntime(1389): at android.view.View.measure(View.java:15172)
04-16 21:09:12.199: E/AndroidRuntime(1389): at android.widget.LinearLayout.measureVertical(LinearLayout.java:833)
04-16 21:09:12.199: E/AndroidRuntime(1389): at android.widget.LinearLayout.onMeasure(LinearLayout.java:574)
04-16 21:09:12.199: E/AndroidRuntime(1389): at android.view.View.measure(View.java:15172)
04-16 21:09:12.199: E/AndroidRuntime(1389): at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4814)
04-16 21:09:12.199: E/AndroidRuntime(1389): at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
04-16 21:09:12.199: E/AndroidRuntime(1389): at com.android.internal.policy.impl.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2148)
04-16 21:09:12.199: E/AndroidRuntime(1389): at android.view.View.measure(View.java:15172)
04-16 21:09:12.199: E/AndroidRuntime(1389): at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:1848)
04-16 21:09:12.199: E/AndroidRuntime(1389): at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1100)
04-16 21:09:12.199: E/AndroidRuntime(1389): at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1273)
04-16 21:09:12.199: E/AndroidRuntime(1389): at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:998)
04-16 21:09:12.199: E/AndroidRuntime(1389): at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:4212)
04-16 21:09:12.199: E/AndroidRuntime(1389): at android.view.Choreographer$CallbackRecord.run(Choreographer.java:725)
04-16 21:09:12.199: E/AndroidRuntime(1389): at android.view.Choreographer.doCallbacks(Choreographer.java:555)
04-16 21:09:12.199: E/AndroidRuntime(1389): at android.view.Choreographer.doFrame(Choreographer.java:525)
04-16 21:09:12.199: E/AndroidRuntime(1389): at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:711)
04-16 21:09:12.199: E/AndroidRuntime(1389): at android.os.Handler.handleCallback(Handler.java:615)
04-16 21:09:12.199: E/AndroidRuntime(1389): at android.os.Handler.dispatchMessage(Handler.java:92)
04-16 21:09:12.199: E/AndroidRuntime(1389): at android.os.Looper.loop(Looper.java:137)
04-16 21:09:12.199: E/AndroidRuntime(1389): at android.app.ActivityThread.main(ActivityThread.java:4745)
04-16 21:09:12.199: E/AndroidRuntime(1389): at java.lang.reflect.Method.invokeNative(Native Method)
04-16 21:09:12.199: E/AndroidRuntime(1389): at java.lang.reflect.Method.invoke(Method.java:511)
04-16 21:09:12.199: E/AndroidRuntime(1389): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
04-16 21:09:12.199: E/AndroidRuntime(1389): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
04-16 21:09:12.199: E/AndroidRuntime(1389): at dalvik.system.NativeStart.main(Native Method)
ReminderView。爪哇
package com.examples;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Date;
import android.app.AlarmManager;
import android.app.AlertDialog;
import android.app.ListActivity;
import android.app.PendingIntent;
import android.content.Context;
import android.content.DialogInterface;
import android.content.Intent;
import android.database.Cursor;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.AdapterView;
import android.widget.Button;
import android.widget.EditText;
import android.widget.LinearLayout;
import android.widget.ListView;
import android.widget.ResourceCursorAdapter;
import android.widget.TextView;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.Toast;
public class ReminderView extends ListActivity implements OnClickListener {
Button add;
private String TitleName[]={"Edit","Delete"};
private ArrayList<String> array_sort;
int textlength=0;
private AlertDialog myalertDialog=null;
Reminder_DB ex1 = new Reminder_DB(this);
public String event, venue, date, time, row_id, remind;
public String revent, rvenue, remind_on;
int flag =0;
@Override
protected void onCreate(Bundle savedInstanceState) {
// TODO Auto-generated method stub
super.onCreate(savedInstanceState);
setContentView(R.layout.sqlist);
add = (Button) findViewById(R.id.baddContact);
add.setOnClickListener(this);
Reminder_DB dbHelper = new Reminder_DB(this);
dbHelper.open();
// Get a Cursor for the list items
Cursor listCursor = dbHelper.fetchListItems();
startManagingCursor(listCursor);
setListAdapter(new MyListAdapter(this, listCursor));
//dbHelper.close();
// TaskRemainderActivity.remind(revent, rvenue, remind_on );
// Log.e("Remind_On ==>",remind_on);
}
private class MyListAdapter extends ResourceCursorAdapter{
public MyListAdapter(Context context, Cursor cursor) {
super(context, R.layout.list_item, cursor);
}
@Override
public void bindView(View view, Context context, final Cursor cursor) {
TextView tvevent = (TextView) view.findViewById(R.id.levent);
StringBuffer eventText = new StringBuffer();
eventText.append(cursor.getString(cursor.getColumnIndex(Reminder_DB.KEY_EVENT)));
tvevent.setText(eventText.toString());
TextView tvvenue = (TextView) view.findViewById(R.id.lvenue);
StringBuffer venueText = new StringBuffer();
venueText.append(cursor.getString(cursor.getColumnIndex(Reminder_DB.KEY_VENUE)));
tvvenue.setText(venueText.toString());
TextView tvdate = (TextView) view.findViewById(R.id.ldate);
StringBuffer dateText = new StringBuffer();
dateText.append(cursor.getString(cursor.getColumnIndex(Reminder_DB.KEY_DATE)));
tvdate.setText(dateText.toString());
TextView tvtime = (TextView) view.findViewById(R.id.ltime);
StringBuffer timeText = new StringBuffer();
timeText.append(cursor.getString(cursor.getColumnIndex(Reminder_DB.KEY_TIME)));
tvtime.setText(timeText.toString());
StringBuffer idText = new StringBuffer();
idText.append(cursor.getString(cursor.getColumnIndex(Reminder_DB.KEY_ROWID)));
StringBuffer remindText = new StringBuffer();
remindText.append(cursor.getString(cursor.getColumnIndex(Reminder_DB.KEY_REM)));
if(flag==0){
revent=eventText.toString();
rvenue=venueText.toString();
remind_on=remindText.toString();
Log.e( "View_Date ==>",dateText.toString());
Log.e( "View_Time ==>",timeText.toString());
Log.e( "View_Venue ==>",rvenue);
Log.e( "View_Event ==>",revent);
Log.e( "View_ID ==>",idText.toString());
Log.e("View_Remind_On ==>",remind_on);
flag=1;
}
//TaskRemainderActivity.remind(revent, rvenue, remind_on );
final ListView list = (ListView) findViewById(android.R.id.list);
TaskRemainderActivity.remind(revent, rvenue, remind_on );
// listening to single list item on click
list.setOnItemClickListener(new OnItemClickListener() {
public void onItemClick(AdapterView<?> parent, View view,
int position, long id) {
event = cursor.getString(cursor.getColumnIndex(Reminder_DB.KEY_EVENT));
venue = cursor.getString(cursor.getColumnIndex(Reminder_DB.KEY_VENUE));
date = cursor.getString(cursor.getColumnIndex(Reminder_DB.KEY_DATE));
time = cursor.getString(cursor.getColumnIndex(Reminder_DB.KEY_TIME));
row_id = cursor.getString(cursor.getColumnIndex(Reminder_DB.KEY_ROWID));
remind = cursor.getString(cursor.getColumnIndex(Reminder_DB.KEY_REM));
AlertDialog.Builder myDialog = new AlertDialog.Builder(ReminderView.this);
final EditText editText = new EditText(ReminderView.this);
final ListView listview=new ListView(ReminderView.this);
array_sort=new ArrayList<String> (Arrays.asList(TitleName));
LinearLayout layout = new LinearLayout(ReminderView.this);
layout.setOrientation(LinearLayout.VERTICAL);
layout.addView(listview);
myDialog.setView(layout);
CustomAlertAdapter arrayAdapter=new CustomAlertAdapter(ReminderView.this, array_sort);
listview.setAdapter(arrayAdapter);
myDialog.setNegativeButton("cancel", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
dialog.dismiss();
}
});
listview.setOnItemClickListener(new OnItemClickListener() {
public void onItemClick(AdapterView<?> parent, View view,
int position, long id) {
myalertDialog.dismiss();
if(position==0){
Toast.makeText(ReminderView.this,
"Edit is pressed", Toast.LENGTH_SHORT)
.show();
Intent i = new Intent(getApplicationContext(), ReminderSingleView.class);
// sending data to new activity
i.putExtra("event_name", event);
i.putExtra("event_venue", venue);
i.putExtra("event_date", date);
i.putExtra("event_time", time);
i.putExtra("rowid", row_id);
i.putExtra("remind", remind);
startActivity(i);
// int t = 1+ position;
Toast.makeText(ReminderView.this,
event, Toast.LENGTH_SHORT)
.show();
}
if(position==1){
Toast.makeText(ReminderView.this,
"Delete is pressed", Toast.LENGTH_SHORT)
.show();
alertMessage();
}
}
});
myalertDialog=myDialog.show();
}
});
}
}
public void alertMessage() {
DialogInterface.OnClickListener dialogClickListener = new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int which) {
switch (which) {
case DialogInterface.BUTTON_POSITIVE:
// Yes button clicked
long lRow1 = Long.parseLong(row_id);
ex1.open();
ex1.deleteEntry(lRow1);
ex1.close();
Toast.makeText(ReminderView.this,
"DELETED!" , Toast.LENGTH_SHORT)
.show();
finish();
Intent intent = new Intent(ReminderView.this, ReminderView.class);
startActivity(intent);
break;
case DialogInterface.BUTTON_NEGATIVE:
// No button clicked
// do nothing
Toast.makeText(ReminderView.this, "No Clicked", Toast.LENGTH_LONG).show();
break;
}
}
};
AlertDialog.Builder builder = new AlertDialog.Builder(this); builder.setMessage("Are you sure?")
.setPositiveButton("Yes", dialogClickListener)
.setNegativeButton("No", dialogClickListener).
show();
}
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
Intent intent = new Intent(ReminderView.this, Remainder.class);
startActivity(intent);
}
}
TaskRemainderActivity.java
package com.examples;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;
import android.app.AlarmManager;
import android.app.PendingIntent;
import android.content.Context;
import android.content.Intent;
import android.util.Log;
import android.widget.Toast;
public class TaskRemainderActivity {
/** Called when the activity is first created. */
private static Context mContext;
private static String Rtime,Revent,Rvenue;
public static int notificationCount;
public static void remind(String event, String venue, String remind ){
Rtime=remind;
Revent=event;
Rvenue=venue;
Log.e( "Rem_Event ==>",Revent);
Log.e( "Rem_Venue ==>",Rvenue);
Log.e( "Rem_timet ==>",Rtime);
notificationCount = notificationCount+1;
SimpleDateFormat df = new SimpleDateFormat("yyyy-MM-dd hh-mm");
Date dt = null;
try {
dt = df.parse(Rtime);
Log.e( "Rem_dt ==>",dt.toString());
} catch (ParseException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
long rem_when = dt.getTime();
Log.e( "Rem_rem_when ==>",Long.toString(rem_when));
AlarmManager mgr = (AlarmManager) mContext.getSystemService(Context.ALARM_SERVICE);
Log.e( "Rem_Alaram ==>",Integer.toString(1));
Intent notificationIntent = new Intent(mContext, ReminderAlarm.class);
notificationIntent.putExtra("Name",Revent );
notificationIntent.putExtra("Description",Rvenue );
notificationIntent.putExtra("NotifyCount",notificationCount );
Log.e( "Rem_Alaram ==>",Integer.toString(2));
PendingIntent pi = PendingIntent.getBroadcast(mContext, notificationCount, notificationIntent, PendingIntent.FLAG_UPDATE_CURRENT);
mgr.set(AlarmManager.RTC_WAKEUP,rem_when, pi);
Toast.makeText(mContext, "Your Reminder Activated", Toast.LENGTH_LONG).show();
}
}
试试这个。
您mContext在TaskRemainderActivity.class具有以下构造函数的send Context中为null 。
TaskRemainderActivity.remind(revent, rvenue, remind_on, ReminderView.this);
变得像下面
public static void remind(String event, String venue, String remind, Context context ){
mContext = context;
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我来说两句