问题
I want to implement LoaderManager in my application in order to reduce the startup time As you can see here but after implementing the suggestion in that thread i was getting the following error initLoader(int, Bundle, LoaderManager.LoaderCallbacks) in the type LoaderManager is not applicable for the arguments (int, null, MainActivity). After searching on here i found the solution for that second error here. But after implementing the suggestion from later, now i am getting the error java.lang.NullPointerException
at android.support.v4.content.Loader. I am putting up the code which i currently have, can anyone tell me, how can i solve this problem
FULL CODE CAN BE SEEN HERE
Log Cat
10-03 20:11:34.849: E/AndroidRuntime(2968): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.test.sms.it/com.test.sms.it.MainActivity}: java.lang.NullPointerException
10-03 20:11:34.849: E/AndroidRuntime(2968): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1647)
10-03 20:11:34.849: E/AndroidRuntime(2968): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1663)
10-03 20:11:34.849: E/AndroidRuntime(2968): at android.app.ActivityThread.access$1500(ActivityThread.java:117)
10-03 20:11:34.849: E/AndroidRuntime(2968): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:931)
10-03 20:11:34.849: E/AndroidRuntime(2968): at android.os.Handler.dispatchMessage(Handler.java:99)
10-03 20:11:34.849: E/AndroidRuntime(2968): at android.os.Looper.loop(Looper.java:123)
10-03 20:11:34.849: E/AndroidRuntime(2968): at android.app.ActivityThread.main(ActivityThread.java:3683)
10-03 20:11:34.849: E/AndroidRuntime(2968): at java.lang.reflect.Method.invokeNative(Native Method)
10-03 20:11:34.849: E/AndroidRuntime(2968): at java.lang.reflect.Method.invoke(Method.java:507)
10-03 20:11:34.849: E/AndroidRuntime(2968): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
10-03 20:11:34.849: E/AndroidRuntime(2968): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
10-03 20:11:34.849: E/AndroidRuntime(2968): at dalvik.system.NativeStart.main(Native Method)
10-03 20:11:34.849: E/AndroidRuntime(2968): Caused by: java.lang.NullPointerException
10-03 20:11:34.849: E/AndroidRuntime(2968): at android.support.v4.content.Loader.<init>(Loader.java:91)
10-03 20:11:34.849: E/AndroidRuntime(2968): at android.support.v4.content.AsyncTaskLoader.<init>(AsyncTaskLoader.java:92)
10-03 20:11:34.849: E/AndroidRuntime(2968): at com.test.sms.it.MainActivity$ContactsDataLoader.<init>(MainActivity.java:104)
10-03 20:11:34.849: E/AndroidRuntime(2968): at com.test.sms.it.MainActivity.onCreateLoader(MainActivity.java:496)
10-03 20:11:34.849: E/AndroidRuntime(2968): at android.support.v4.app.LoaderManagerImpl.createLoader(LoaderManager.java:487)
10-03 20:11:34.849: E/AndroidRuntime(2968): at android.support.v4.app.LoaderManagerImpl.createAndInstallLoader(LoaderManager.java:496)
10-03 20:11:34.849: E/AndroidRuntime(2968): at android.support.v4.app.LoaderManagerImpl.initLoader(LoaderManager.java:550)
10-03 20:11:34.849: E/AndroidRuntime(2968): at com.test.sms.it.MainActivity.onCreate(MainActivity.java:91)
10-03 20:11:34.849: E/AndroidRuntime(2968): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
10-03 20:11:34.849: E/AndroidRuntime(2968): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1611)
MainActivity.java
import java.util.ArrayList;
import java.util.HashMap;
import java.util.Map;
import android.app.AlertDialog;
import android.app.ProgressDialog;
import android.content.Context;
import android.content.DialogInterface;
import android.content.Intent;
import android.content.SharedPreferences;
import android.database.Cursor;
import android.graphics.Color;
import android.net.ConnectivityManager;
import android.net.NetworkInfo;
import android.net.Uri;
import android.os.AsyncTask;
import android.os.Bundle;
import android.preference.PreferenceManager;
import android.provider.ContactsContract;
import android.support.v4.app.FragmentActivity;
import android.support.v4.app.LoaderManager;
import android.support.v4.content.AsyncTaskLoader;
import android.support.v4.content.Loader;
import android.view.KeyEvent;
import android.view.Menu;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.Window;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.AutoCompleteTextView;
import android.widget.Button;
import android.widget.EditText;
import android.widget.SimpleAdapter;
import android.widget.Spinner;
import android.widget.Toast;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
this.requestWindowFeature(Window.FEATURE_NO_TITLE);
setContentView(R.layout.activity_main);
editUser1UserName = (EditText) findViewById(R.id.editTextUser1UserName);
editUser1Password = (EditText) findViewById(R.id.editTextUser1Password);
editUser2UserName = (EditText) findViewById(R.id.editTextUser2UserName);
editUser2Password = (EditText) findViewById(R.id.editTextUser2Password);
editUser3UserName = (EditText) findViewById(R.id.editTextUser3UserName);
editUser3Password = (EditText) findViewById(R.id.editTextUser3Password);
editUser4UserName = (EditText) findViewById(R.id.editTextUser4UserName);
editUser4Password = (EditText) findViewById(R.id.editTextUser4Password);
editUser5UserName = (EditText) findViewById(R.id.editTextUser5UserName);
editUser5Password = (EditText) findViewById(R.id.editTextUser5Password);
mTxtPhoneNo = (AutoCompleteTextView) findViewById(R.id.mmWhoNo);
mTxtPhoneNo.setThreshold(1);
mTxtPhoneNo.setTextColor(Color.BLACK);
editText = (EditText) findViewById(R.id.editTextMessage);
spinner1 = (Spinner) findViewById(R.id.spinnerGateway);
btnsend = (Button) findViewById(R.id.btnSend);
btnContact = (Button) findViewById(R.id.btnContact);
btnClear = (Button) findViewById(R.id.btnClear);
btnClear.setOnClickListener(this);
btnsend.setOnClickListener(this);
btnContact.setOnClickListener(this);
mPeopleList = new ArrayList<Map<String, String>>();
getSupportLoaderManager().initLoader(0, null, this);
mTxtPhoneNo.setOnItemClickListener(this);
readPerson();
Panel panel;
topPanel = panel = (Panel) findViewById(R.id.mytopPanel);
panel.setOnPanelListener(this);
panel.setInterpolator(new BounceInterpolator(Type.OUT));
getLoginDetails();
}
public class ContactsDataLoader extends
AsyncTaskLoader<ArrayList<Map<String, String>>> {
public ContactsDataLoader(Context context) {
super(context);
}
@Override
public ArrayList<Map<String, String>> loadInBackground() {
mPeopleList.clear();
Cursor people = getContentResolver().query(
ContactsContract.Contacts.CONTENT_URI, null, null, null,
null);
while (people.moveToNext()) {
String contactName = people
.getString(people
.getColumnIndex(ContactsContract.Contacts.DISPLAY_NAME));
String contactId = people.getString(people
.getColumnIndex(ContactsContract.Contacts._ID));
String hasPhone = people
.getString(people
.getColumnIndex(ContactsContract.Contacts.HAS_PHONE_NUMBER));
if ((Integer.parseInt(hasPhone) > 0)) {
Cursor phones = getContentResolver().query(
ContactsContract.CommonDataKinds.Phone.CONTENT_URI,
null,
ContactsContract.CommonDataKinds.Phone.CONTACT_ID
+ " = " + contactId, null, null);
while (phones.moveToNext()) {
String phoneNumber = phones
.getString(phones
.getColumnIndex(ContactsContract.CommonDataKinds.Phone.NUMBER));
String numberType = phones
.getString(phones
.getColumnIndex(ContactsContract.CommonDataKinds.Phone.TYPE));
Map<String, String> NamePhoneType = new HashMap<String, String>();
NamePhoneType.put("Name", contactName);
NamePhoneType.put("Phone", phoneNumber);
if (numberType.equals("0"))
NamePhoneType.put("Type", "Work");
else if (numberType.equals("1"))
NamePhoneType.put("Type", "Home");
else if (numberType.equals("2"))
NamePhoneType.put("Type", "Mobile");
else
NamePhoneType.put("Type", "Other");
mPeopleList.add(NamePhoneType);
}
phones.close();
}
}
people.close();
startManagingCursor(people);
return mPeopleList;
}
@Override
protected void onStartLoading() {
super.onStartLoading();
forceLoad();
}
}
public Loader<ArrayList<Map<String, String>>> onCreateLoader(int id,
Bundle args) {
return new ContactsDataLoader(context);
}
public void onLoadFinished(Loader<ArrayList<Map<String, String>>> loader,
ArrayList<Map<String, String>> data) {
mPeopleList = data;
mAdapter = new SimpleAdapter(this, mPeopleList, R.layout.custcontview,
new String[] { "Name", "Phone", "Type" }, new int[] {
R.id.ccontName, R.id.ccontNo, R.id.ccontType });
mTxtPhoneNo.setAdapter(mAdapter);
}
public void onLoaderReset(Loader<ArrayList<Map<String, String>>> loader) {
mPeopleList = new ArrayList<Map<String, String>>();
mAdapter = new SimpleAdapter(this, mPeopleList, R.layout.custcontview,
new String[] { "Name", "Phone", "Type" }, new int[] {
R.id.ccontName, R.id.ccontNo, R.id.ccontType });
mTxtPhoneNo.setAdapter(mAdapter);
}
回答1:
RC's comment is the answer of your problem. You pass a null Context(as I don't see anywhere in the code you posted the context variable being initialized with a valid reference) to your custom loader and the code will fail with a NullPointerException. If you used my code from my previous answer then those callbacks are implemented in your Activity. In this case just pass this, the reference to your current Activity instance, to your custom loader:
public Loader<ArrayList<Map<String, String>>> onCreateLoader(int id,
Bundle args) {
return new ContactsDataLoader(this);
}
Also, if you close the cursor, there is no need to use startManagingCursor() for that Cursor as you might get in trouble.
来源：https://stackoverflow.com/questions/12792953/error-java-lang-nullpointerexception-at-android-support-v4-content-loader