问安卓应用在启动时崩溃: ContactsFragment中的SQLite NullPointerException
EN

Stack Overflow用户

提问于 2015-05-06 06:07:52

回答 2查看 24.3K关注 0票数 10

我正在努力集成一个数据库，以保存和存储基本联系信息，以便在以后检索。然而，我的应用程序现在在启动时崩溃，所以我甚至不能验证表是否正在创建等。

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$MethodAndArgsCaller.run(ZygoteInit.java:794)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:610)
 Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.database.sqlite.SQLiteDatabase android.content.Context.openOrCreateDatabase(java.lang.String, int, android.database.sqlite.SQLiteDatabase$CursorFactory, 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说问题出在SQLiteDatabase db = this.getWriteableDatabase();上

这也是我令人不快的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, null, 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, null, null, 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, null, null, 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, dbPhone, status, 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，这里是ContactsDB类：

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

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

任何帮助都是非常感谢的--我认为问题出在我的上下文为null。我只是不确定为什么它会像我在MyDBHandler文件中定义的那样。到目前为止，我无法验证数据库是否正在创建，更不用说保存数据了。

干杯&谢谢你的时间和耐心，Shyam

android

sqlite

android-fragments

android-activity

android-sqlite

回答 2

Stack Overflow用户

回答已采纳

发布于 2015-05-06 06:33:06

看起来您意外地创建了一个context局部变量，而没有使用实例变量。

因此，当您将context传递给MyDBHandler时，它是空的，所以当您调用this.getWritableDatabase()时，this也是空的。因此，您将获得NullPointerException，如您在日志中所看到的：

Caused by: 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.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()，以确保拥有有效的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, 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);

    //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, layout, c, FROM, TO, flags);

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

    //context should now be valid:
    MyDBHandler dbHandler = new MyDBHandler(context, null, null, 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);

}
//........

票数 18

Stack Overflow用户

发布于 2018-07-30 06:22:50

在适配器中从onCreateViewHolder方法中的db类生成对象以解决此错误

票数 0

页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持

原文链接：

https://stackoverflow.com/questions/30064080

复制

相似问题

问安卓应用在启动时崩溃: ContactsFragment中的SQLite NullPointerException
EN

回答 2

Stack Overflow用户

Stack Overflow用户

社区

活动

资源

关于

腾讯云开发者

热门产品

热门推荐

更多推荐

问安卓应用在启动时崩溃: ContactsFragment中的SQLite NullPointerExceptionEN

回答 2

Stack Overflow用户

Stack Overflow用户

社区

活动

资源

关于

腾讯云开发者

热门产品

热门推荐

更多推荐

问安卓应用在启动时崩溃: ContactsFragment中的SQLite NullPointerException
EN