启动时Android应用程序崩溃：ContactsFragment中的SQLite NullPointerException

我正在集成数据库来保存和存储以后要检索的基本联系信息.但是,我的应用程序现在在启动时崩溃,所以我甚至无法验证是否正在创建表等.

05-05 16:39:50.671  11631-11631/treehouse.greenlight E/AndroidRuntime﹕   FATAL EXCEPTION: main
Process: treehouse.greenlight,PID: 11631
java.lang.RuntimeException: Unable to start activity ComponentInfo{treehouse.greenlight/treehouse.greenlight.Home_screen}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.database.sqlite.sqliteDatabase android.content.Context.openOrCreateDatabase(java.lang.String,int,android.database.sqlite.sqliteDatabase$CursorFactory,android.database.DatabaseErrorHandler)' on a null object reference
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2205)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2255)
        at android.app.ActivityThread.access$800(ActivityThread.java:142)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1203)
        at android.os.Handler.dispatchMessage(Handler.java:102)
        at android.os.Looper.loop(Looper.java:136)
        at android.app.ActivityThread.main(ActivityThread.java:5118)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:794)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:610)
 Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.database.sqlite.sqliteDatabase android.content.Context.openOrCreateDatabase(java.lang.String,android.database.DatabaseErrorHandler)' on a null object reference
        at android.database.sqlite.sqliteOpenHelper.getDatabaseLocked(sqliteOpenHelper.java:224)
        at android.database.sqlite.sqliteOpenHelper.getWritableDatabase(sqliteOpenHelper.java:164)
        at treehouse.greenlight.MyDBHandler.addContact(MyDBHandler.java:54)
        at treehouse.greenlight.ContactsFragment.onCreateLoader(ContactsFragment.java:117)
        at android.support.v4.app.LoaderManagerImpl.createLoader(LoaderManager.java:490)
        at android.support.v4.app.LoaderManagerImpl.createAndInstallLoader(LoaderManager.java:499)
        at android.support.v4.app.LoaderManagerImpl.initLoader(LoaderManager.java:553)
        at treehouse.greenlight.ContactsFragment.onActivityCreated(ContactsFragment.java:71)
        at android.support.v4.app.Fragment.performActivityCreated(Fragment.java:1797)
        at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:979)
        at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1138)
        at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1120)
        at android.support.v4.app.FragmentManagerImpl.dispatchActivityCreated(FragmentManager.java:1929)
        at android.support.v4.app.FragmentActivity.onStart(FragmentActivity.java:547)
        at android.app.Instrumentation.callActivityOnStart(Instrumentation.java:1171)
        at android.app.Activity.performStart(Activity.java:5285)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2178)

数据库处理程序代码：

public class MyDBHandler extends sqliteOpenHelper {

private static final int DATABASE_VERSION = 1;
private static final String DATABASE_NAME = "contactsDB.db";
public static final String TABLE_CONTACTS = "contacts";
private Context context;
public static final String COLUMN_ID = "_id";
public static final String COLUMN_NAME = "name";
public static final String COLUMN_PHONE = "phone";
public static final String COLUMN_STATUS = "status";
public static final String COLUMN_BLURB = "blurb";

public MyDBHandler(Context context,String name,CursorFactory factory,int version)  {
    super(context,DATABASE_NAME,factory,DATABASE_VERSION);

}
    @Override
    public void onCreate (sqliteDatabase db){

        String CREATE_CONTACTS_TABLE = "CREATE TABLE " +
                TABLE_CONTACTS + "("
                + COLUMN_ID + " INTEGER PRIMARY KEY," + ContactsContract.CommonDataKinds.Phone.DISPLAY_NAME
                + " TEXT," + ContactsContract.CommonDataKinds.Phone.NUMBER + " INTEGER,"
                + COLUMN_STATUS + " TEXT," + COLUMN_BLURB
                + " TEXT" + ");";
        db.execsql(CREATE_CONTACTS_TABLE);
    }

    @Override
    public void onUpgrade (sqliteDatabase db,int oldVersion,int newVersion){
        db.execsql("DROP TABLE IF EXISTS " + TABLE_CONTACTS);
        onCreate(db);
    }
public void addContact(ContactsDb contacts) {

    ContentValues values = new ContentValues();
    values.put(COLUMN_NAME,contacts.getName());
    values.put(COLUMN_PHONE,contacts.getPhone());
    values.put(COLUMN_STATUS,contacts.getStatus());
    values.put(COLUMN_BLURB,contacts.getBlurb());

    sqliteDatabase db = this.getWritableDatabase();
    db.insert(TABLE_CONTACTS,null,values);

}

logcat说问题是sqliteDatabase db = this.getWriteableDatabase();

这也是我违规的Contactsfragment：

public class ContactsFragment extends ListFragment implements LoaderManager.LoaderCallbacks<Cursor> {

private CursorAdapter mAdapter;
private Context context;
TextView idView;
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    // create adapter once
    Context context = getActivity();
    int layout = R.layout.activity_list_item_1;
    Cursor c = null; // there is no cursor yet
    int flags = 0; // no auto-requery! Loader requeries.
    mAdapter = new SimpleCursorAdapter(context,layout,c,FROM,TO,flags);

}


public void ContactsDb(Context context) {
    this.context=context;


}
Uri contentUri = ContactsContract.CommonDataKinds.Phone.CONTENT_URI;

String[] PROJECTION = {
        ContactsContract.Contacts.HAS_PHONE_NUMBER,ContactsContract.Contacts._ID,// _ID is always required
        ContactsContract.CommonDataKinds.Phone.DISPLAY_NAME_PRIMARY,// that is what we want to display
        Contacts.TIMES_CONTACTED,ContactsContract.CommonDataKinds.Phone.NUMBER

};

@Override
public void onActivityCreated(Bundle savedInstanceState) {
    super.onActivityCreated(savedInstanceState);

    // each time we are started use our listadapter
    setListAdapter(mAdapter);
    // and tell loader manager to start loading
    getLoaderManager().initLoader(0,this);
}

// columns requested from the database


// and name should be displayed in the text1 textview in item layout

public String[] has_phone = {ContactsContract.Contacts.HAS_PHONE_NUMBER};

    String phone = "0";
    int dbPhone = 0;
private  final String[] FROM = {Contacts.DISPLAY_NAME_PRIMARY,ContactsContract.CommonDataKinds.Phone.NUMBER};
private final int[] TO = {android.R.id.text1,dbPhone};


public void newContact (View view) {
    MyDBHandler dbHandler = new MyDBHandler(context,1);

    String name = Contacts.DISPLAY_NAME_PRIMARY;
    int dbPhone =
    Integer.parseInt(phone);

    String status ="";
    String blurb ="";
    ContactsDb contacts =
            new ContactsDb(name,dbPhone,status,blurb);
    dbHandler.addContact(contacts);

}


@Override
public Loader<Cursor> onCreateLoader(int id,Bundle args) {
    Context context = this.context;
    // load from the "Contacts table"
    MyDBHandler dbHandler = new MyDBHandler(context,1);

    String name = Contacts.DISPLAY_NAME_PRIMARY;
    int phone = Integer.parseInt(ContactsContract.CommonDataKinds.Phone.NUMBER);

    String status ="Busy";
    String blurb ="N/A";

    ContactsDb contacts =
            new ContactsDb(name,blurb);
    dbHandler.addContact(contacts);

    // no sub-selection,no sort order,simply every row
    // projection says we want just the _id and the name column
    return new CursorLoader(getActivity(),contentUri,PROJECTION,ContactsContract.Contacts.HAS_PHONE_NUMBER + " =? AND " + Contacts.TIMES_CONTACTED + ">=?",// This is selection string,we're looking for records that HAS_PHONE_NUMBER is 1
            new String[]{"1","0"},// 1 means that contact has a phone number & 60 is the amount of times contacted (arbitrary - needs to be fixed before release)
            null);
}

最后,这是ContactsDB类：

public ContactsDb(String name,int phone,String status,String blurb) {

    this._name = name;
    this._phone = phone;
    this._status = status;
    this._blurb = blurb;

非常感谢任何帮助 – 我认为问题在于我的Context为null.我只是不确定为什么它会在我的MyDBHandler文件中定义它.截至目前,我无法验证是否正在创建数据库,更不用说保存数据了.

干杯&感谢您的时间和耐心,
希亚姆

解决方法

看起来你不小心创建了一个上下文局部变量而不是使用实例变量.

因此,当您将其传递给MyDBHandler时,context为null,因此当您调用this.getWritableDatabase()时,它为null.因此,您可以在日志中看到NullPointerException：

Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.database.sqlite.sqliteDatabase android.content.Context.openOrCreateDatabase(java.lang.String,android.database.DatabaseErrorHandler)' on a null object reference
        at android.database.sqlite.sqliteOpenHelper.getDatabaseLocked(sqliteOpenHelper.java:224)
        at android.database.sqlite.sqliteOpenHelper.getWritableDatabase(sqliteOpenHelper.java:164)

尝试将所有与Context相关的代码移动到onActivityCreated()以确保您具有有效的Context,并确保使用实例变量而不是局部变量：

public class ContactsFragment extends ListFragment implements LoaderManager.LoaderCallbacks<Cursor> {

private CursorAdapter mAdapter;
private Context context; //this is the Context you will use
TextView idView;
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    // create adapter once
    //Context context = getActivity(); //Here was the problem
    //int layout = R.layout.activity_list_item_1;
    //Cursor c = null; // there is no cursor yet
    //int flags = 0; // no auto-requery! Loader requeries.
    //mAdapter = new SimpleCursorAdapter(context,ContactsContract.CommonDataKinds.Phone.NUMBER

};

@Override
public void onActivityCreated(Bundle savedInstanceState) {
    super.onActivityCreated(savedInstanceState);

    //Add this here:
    context = getActivity(); //use the instance variable
    int layout = R.layout.activity_list_item_1;
    Cursor c = null; // there is no cursor yet
    int flags = 0; // no auto-requery! Loader requeries.
    mAdapter = new SimpleCursorAdapter(context,flags);

    // each time we are started use our listadapter
    setListAdapter(mAdapter);
    // and tell loader manager to start loading
    getLoaderManager().initLoader(0,dbPhone};


public void newContact (View view) {

    //context should now be valid:
    MyDBHandler dbHandler = new MyDBHandler(context,blurb);
    dbHandler.addContact(contacts);

}
//........

启动时Android应用程序崩溃：ContactsFragment中的SQLite NullPointerException

解决方法

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