Android SQLitedatabase删除行NullPointerException

Question

当我尝试删除Admin类中的用户名/密码/电子邮件列表视图行之一时，我从DBAdapter类的deletePlayer中收到了NullPointerException。我知道自删除数据库以来，NPE来自我的delete方法。删除，打开和关闭我的吐司在onclick上起作用，但是当我实现它们时，我得到了NPE。我很确定这是我的delete方法，但是我尝试了遍地搜索可以使用的正确的delete方法，但是找不到与删除数据库中用户的USERNAME，PASSWORD和EMAIL列有关的内容。

更新：我包括了DBAdapter（context）并将光标包含到数据库的deletePlayer方法中，但是现在我得到了代码1语法错误，如LogCat所示

LogCat

    04-20 14:56:51.289: E/Trace(20896): error opening trace file: No such file or directory (2)
04-20 14:56:51.664: D/dalvikvm(20896): GC_FOR_ALLOC freed 78K, 11% free 8200K/9119K, paused 34ms, total 34ms
04-20 14:56:52.344: D/libEGL(20896): loaded /vendor/lib/egl/libEGL_POWERVR_SGX540_120.so
04-20 14:56:52.797: D/libEGL(20896): loaded /vendor/lib/egl/libGLESv1_CM_POWERVR_SGX540_120.so
04-20 14:56:52.805: D/libEGL(20896): loaded /vendor/lib/egl/libGLESv2_POWERVR_SGX540_120.so
04-20 14:56:53.360: D/OpenGLRenderer(20896): Enabling debug mode 0
04-20 14:57:00.000: D/dalvikvm(20896): GC_CONCURRENT freed 66K, 3% free 9899K/10147K, paused 14ms+2ms, total 86ms
04-20 14:59:07.102: E/Trace(21554): error opening trace file: No such file or directory (2)
04-20 14:59:07.164: D/dalvikvm(21554): GC_FOR_ALLOC freed 61K, 11% free 8200K/9119K, paused 29ms, total 29ms
04-20 14:59:07.696: D/libEGL(21554): loaded /vendor/lib/egl/libEGL_POWERVR_SGX540_120.so
04-20 14:59:07.891: D/libEGL(21554): loaded /vendor/lib/egl/libGLESv1_CM_POWERVR_SGX540_120.so
04-20 14:59:07.899: D/libEGL(21554): loaded /vendor/lib/egl/libGLESv2_POWERVR_SGX540_120.so
04-20 14:59:08.149: D/OpenGLRenderer(21554): Enabling debug mode 0
04-20 14:59:10.672: E/SQLiteLog(21554): (1) near ".": syntax error
04-20 14:59:10.672: D/AndroidRuntime(21554): Shutting down VM
04-20 14:59:10.672: W/dalvikvm(21554): threadid=1: thread exiting with uncaught exception (group=0x419742a0)
04-20 14:59:10.891: E/AndroidRuntime(21554): FATAL EXCEPTION: main
04-20 14:59:10.891: E/AndroidRuntime(21554): android.database.sqlite.SQLiteException: near ".": syntax error (code 1): , while compiling: DELETE FROM PLAYERS WHERE _id = android.database.sqlite.SQLiteCursor@4230c108
04-20 14:59:10.891: E/AndroidRuntime(21554):    at android.database.sqlite.SQLiteConnection.nativePrepareStatement(Native Method)
04-20 14:59:10.891: E/AndroidRuntime(21554):    at android.database.sqlite.SQLiteConnection.acquirePreparedStatement(SQLiteConnection.java:882)
04-20 14:59:10.891: E/AndroidRuntime(21554):    at android.database.sqlite.SQLiteConnection.prepare(SQLiteConnection.java:493)
04-20 14:59:10.891: E/AndroidRuntime(21554):    at android.database.sqlite.SQLiteSession.prepare(SQLiteSession.java:588)
04-20 14:59:10.891: E/AndroidRuntime(21554):    at android.database.sqlite.SQLiteProgram.<init>(SQLiteProgram.java:58)
04-20 14:59:10.891: E/AndroidRuntime(21554):    at android.database.sqlite.SQLiteStatement.<init>(SQLiteStatement.java:31)
04-20 14:59:10.891: E/AndroidRuntime(21554):    at android.database.sqlite.SQLiteDatabase.delete(SQLiteDatabase.java:1491)
04-20 14:59:10.891: E/AndroidRuntime(21554):    at com.fullfrontalgames.numberfighter.DBAdapter.deletePlayer(DBAdapter.java:106)
04-20 14:59:10.891: E/AndroidRuntime(21554):    at com.fullfrontalgames.numberfighter.Admin$MyListAdapter$1.onClick(Admin.java:66)
04-20 14:59:10.891: E/AndroidRuntime(21554):    at android.view.View.performClick(View.java:4106)
04-20 14:59:10.891: E/AndroidRuntime(21554):    at android.view.View$PerformClick.run(View.java:17052)
04-20 14:59:10.891: E/AndroidRuntime(21554):    at android.os.Handler.handleCallback(Handler.java:615)
04-20 14:59:10.891: E/AndroidRuntime(21554):    at android.os.Handler.dispatchMessage(Handler.java:92)
04-20 14:59:10.891: E/AndroidRuntime(21554):    at android.os.Looper.loop(Looper.java:137)
04-20 14:59:10.891: E/AndroidRuntime(21554):    at android.app.ActivityThread.main(ActivityThread.java:5059)
04-20 14:59:10.891: E/AndroidRuntime(21554):    at java.lang.reflect.Method.invokeNative(Native Method)
04-20 14:59:10.891: E/AndroidRuntime(21554):    at java.lang.reflect.Method.invoke(Method.java:511)
04-20 14:59:10.891: E/AndroidRuntime(21554):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:792)
04-20 14:59:10.891: E/AndroidRuntime(21554):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:555)
04-20 14:59:10.891: E/AndroidRuntime(21554):    at dalvik.system.NativeStart.main(Native Method)
04-20 14:59:10.961: D/dalvikvm(21554): GC_CONCURRENT freed 88K, 3% free 9886K/10147K, paused 13ms+5ms, total 75ms
04-20 14:59:13.172: I/Process(21554): Sending signal. PID: 21554 SIG: 9
04-20 15:03:13.141: E/Trace(22194): error opening trace file: No such file or directory (2)
04-20 15:03:13.399: D/dalvikvm(22194): GC_FOR_ALLOC freed 79K, 11% free 8200K/9119K, paused 57ms, total 58ms
04-20 15:03:13.844: D/libEGL(22194): loaded /vendor/lib/egl/libEGL_POWERVR_SGX540_120.so
04-20 15:03:13.883: D/libEGL(22194): loaded /vendor/lib/egl/libGLESv1_CM_POWERVR_SGX540_120.so
04-20 15:03:13.891: D/libEGL(22194): loaded /vendor/lib/egl/libGLESv2_POWERVR_SGX540_120.so
04-20 15:03:14.055: D/OpenGLRenderer(22194): Enabling debug mode 0
04-20 15:03:17.352: E/SQLiteLog(22194): (1) near ".": syntax error
04-20 15:03:17.375: D/AndroidRuntime(22194): Shutting down VM
04-20 15:03:17.375: W/dalvikvm(22194): threadid=1: thread exiting with uncaught exception (group=0x419742a0)
04-20 15:03:17.414: E/AndroidRuntime(22194): FATAL EXCEPTION: main
04-20 15:03:17.414: E/AndroidRuntime(22194): android.database.sqlite.SQLiteException: near ".": syntax error (code 1): , while compiling: DELETE FROM PLAYERS WHERE _id = android.database.sqlite.SQLiteCursor@4230c2a8
04-20 15:03:17.414: E/AndroidRuntime(22194):    at android.database.sqlite.SQLiteConnection.nativePrepareStatement(Native Method)
04-20 15:03:17.414: E/AndroidRuntime(22194):    at android.database.sqlite.SQLiteConnection.acquirePreparedStatement(SQLiteConnection.java:882)
04-20 15:03:17.414: E/AndroidRuntime(22194):    at android.database.sqlite.SQLiteConnection.prepare(SQLiteConnection.java:493)
04-20 15:03:17.414: E/AndroidRuntime(22194):    at android.database.sqlite.SQLiteSession.prepare(SQLiteSession.java:588)
04-20 15:03:17.414: E/AndroidRuntime(22194):    at android.database.sqlite.SQLiteProgram.<init>(SQLiteProgram.java:58)
04-20 15:03:17.414: E/AndroidRuntime(22194):    at android.database.sqlite.SQLiteStatement.<init>(SQLiteStatement.java:31)
04-20 15:03:17.414: E/AndroidRuntime(22194):    at android.database.sqlite.SQLiteDatabase.delete(SQLiteDatabase.java:1491)
04-20 15:03:17.414: E/AndroidRuntime(22194):    at com.fullfrontalgames.numberfighter.DBAdapter.deletePlayer(DBAdapter.java:106)
04-20 15:03:17.414: E/AndroidRuntime(22194):    at com.fullfrontalgames.numberfighter.Admin$MyListAdapter$1.onClick(Admin.java:66)
04-20 15:03:17.414: E/AndroidRuntime(22194):    at android.view.View.performClick(View.java:4106)
04-20 15:03:17.414: E/AndroidRuntime(22194):    at android.view.View$PerformClick.run(View.java:17052)
04-20 15:03:17.414: E/AndroidRuntime(22194):    at android.os.Handler.handleCallback(Handler.java:615)
04-20 15:03:17.414: E/AndroidRuntime(22194):    at android.os.Handler.dispatchMessage(Handler.java:92)
04-20 15:03:17.414: E/AndroidRuntime(22194):    at android.os.Looper.loop(Looper.java:137)
04-20 15:03:17.414: E/AndroidRuntime(22194):    at android.app.ActivityThread.main(ActivityThread.java:5059)
04-20 15:03:17.414: E/AndroidRuntime(22194):    at java.lang.reflect.Method.invokeNative(Native Method)
04-20 15:03:17.414: E/AndroidRuntime(22194):    at java.lang.reflect.Method.invoke(Method.java:511)
04-20 15:03:17.414: E/AndroidRuntime(22194):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:792)
04-20 15:03:17.414: E/AndroidRuntime(22194):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:555)
04-20 15:03:17.414: E/AndroidRuntime(22194):    at dalvik.system.NativeStart.main(Native Method)

DBAdapter类

package com.fullfrontalgames.numberfighter;

import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteException;
import android.database.sqlite.SQLiteOpenHelper;
import android.util.Log;

public class DBAdapter {
    static final String KEY_ROWID = "_id";

    static final String KEY_USERNAME = "USERNAME";

    static final String KEY_PASSWORD = "PASSWORD";

    static final String KEY_EMAIL = "EMAIL";

    static final String KEY_NUMBERINPUT = "NUMBERINPUT";

    static final String KEY_SCORE = "SCORE";

    static final String KEY_FRIENDS = "FRIENDS";

    static final String TAG = "DBAdapter";

    static final String DATABASE_NAME = "NFDatabase";

    static final String DATABASE_TABLE1 = "PLAYERS";

    static final String DATABASE_TABLE2 = "FRIENDSLIST";

    static final int DATABASE_VERSION = 2;

    static final String DATABASE_CREATE_TABLE1 = "create table PLAYERS ( _id integer primary key autoincrement, "
            + "USERNAME text not null,PASSWORD text not null,EMAIL text,NUMBERINPUT text,SCORE text);";

    static final String DATBASE_CREATE_TABLE2 = "create table FRIENDSLIST (_id integer primary key autoincrement,"
            + "FRIENDS text not null,USERNAME text not null,NUMBERINPUT text,SCORE text);";

    final Context context;

    DatabaseHelper DBHelper;

    static SQLiteDatabase db;

    public DBAdapter(Context ctx) {
        this.context = ctx;
        DBHelper = new DatabaseHelper(context);
    }

    private static class DatabaseHelper extends SQLiteOpenHelper {

        public DatabaseHelper(Context context) {
            // TODO Auto-generated constructor stub
            super(context, DATABASE_NAME, null, DATABASE_VERSION);
        }

        @Override
        public void onCreate(SQLiteDatabase db) {
            // TODO Auto-generated method stub
            try {
                db.execSQL(DATABASE_CREATE_TABLE1);
                db.execSQL(DATBASE_CREATE_TABLE2);
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }

        @Override
        public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
            // TODO Auto-generated method stub
            Log.w(TAG, "Upgrading database from version " + oldVersion + " to " + newVersion
                    + ", which will destroy all old data");
            db.execSQL("DROP TABLE IF EXISTS PLAYERS");
            db.execSQL("DROP TABLE IF EXISTS FRIENDSLIST");
            onCreate(db);
        }

    }

    public DBAdapter open() throws SQLiteException {
        db = DBHelper.getWritableDatabase();
        return this;
    }

    public void close() {
        DBHelper.close();
    }

    // PLAYERS TABLE CRUD

    public void insertPlayer(String Username, String Password, String Email) {
        ContentValues initialValues = new ContentValues();
        initialValues.put("USERNAME", Username);
        initialValues.put("PASSWORD", Password);
        initialValues.put("EMAIL", Email);

        db.insert("PLAYERS", null, initialValues);
    }

    public boolean deletePlayer(Cursor playeraccounts) {
        return db.delete("PLAYERS", KEY_ROWID + " = " + playeraccounts, null) > 0;
    }

    public Cursor getAllPlayers() {
        return db.query(false, "Players", new String[] {
                "_id", "USERNAME", "PASSWORD", "EMAIL"
        }, null, null, null, null, null, null);

    }

    public String getData() {
        String[] columns = new String[] {
                "_id", "USERNAME", "PASSWORD"
        };
        Cursor mCursor = db.query("PLAYERS", columns, null, null, null, null, null);
        String result = "";
        int iRow = mCursor.getColumnIndex(KEY_ROWID);
        int iName = mCursor.getColumnIndex(KEY_USERNAME);

        for (mCursor.moveToFirst(); !mCursor.isAfterLast(); mCursor.moveToNext()) {
            result = mCursor.getString(iRow) + " " + mCursor.getString(iName) + "/n";
        }
        return result;
    }

    public Cursor getPlayer(long rowid) throws SQLException {
        Cursor mCursor = db.query(true, "PLAYERS", new String[] {
                "_id", "USERNAME"
        }, KEY_ROWID + " =  " + "_id", null, null, null, null, null);
        if (mCursor != null) {
            mCursor.moveToFirst();
        }
        return mCursor;
    }

    public String getUsername(String username) {
        // TODO Auto-generated method stub
        String[] columns = new String[] {
                "_id", "USERNAME"
        };
        Cursor mCursor = db.query("PLAYERS", columns, null, null, null, null, null);
        String result = "";
        int iRow = mCursor.getColumnIndex(KEY_ROWID);
        int iName = mCursor.getColumnIndex(KEY_USERNAME);

        for (mCursor.moveToFirst(); !mCursor.isAfterLast(); mCursor.moveToNext()) {
            result = mCursor.getString(iRow) + " " + mCursor.getString(iName) + "/n";
        }
        return result;
    }

    public String getSinlgeEntry(String Username) {
        Cursor cursor = db.query("PLAYERS", null, " USERNAME=?", new String[] {
            Username
        }, null, null, null);
        if (cursor.getCount() < 1) // UserName Not Exist
        {
            cursor.close();
            return "NOT EXIST";
        }
        cursor.moveToFirst();
        String password = cursor.getString(cursor.getColumnIndex("PASSWORD"));
        cursor.close();
        return password;
    }

    public boolean updatePlayer(long _id, String Username, String Password, String Email) {
        ContentValues args = new ContentValues();
        args.put("USERNAME", Username);
        args.put("PASSWORD", Password);
        args.put("EMAIL", Email);
        return db.update("PLAYERS", args, KEY_ROWID + " = " + _id, null) > 0;
    }

    // FRIENDS TABLE CRUD

    public void insertFriend(String Friend) {
        ContentValues initialValues = new ContentValues();
        initialValues.put("FRIENDS", Friend);
        db.insert("FRIENDSLIST", null, null);
    }

    public boolean deleteFriend() {
        return db.delete("FRIENDSLIST", KEY_ROWID + " = " + "_id", null) > 0;
    }

    public Cursor getAllFriends() {
        return db.query(null, new String[] {
                "_id", "FRIENDS"
        }, null, null, null, null, null, null);
    }

    public Cursor getFriend(long rowid) throws SQLException {
        Cursor mCursor = db.query(true, "FRIENDSLIST", new String[] {
                "_id", "FRIENDS"
        }, KEY_ROWID + " =  " + "_id", null, null, null, null, null);
        if (mCursor != null) {
            mCursor.moveToFirst();
        }
        return mCursor;
    }

    public boolean updateFriend(long _id, String Friends) {
        ContentValues args = new ContentValues();
        args.put("FRIENDS", Friends);

        return db.update("FRIENDSLIST", args, KEY_ROWID + " = " + _id, null) > 0;
    }

}

管理员班

package com.fullfrontalgames.numberfighter;

import android.app.ListActivity;
import android.content.Context;
import android.database.Cursor;
import android.os.Bundle;
import android.support.v4.widget.ResourceCursorAdapter;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.ListView;
import android.widget.TextView;
import android.widget.Toast;

public class Admin extends ListActivity {

    DBAdapter db;

    @SuppressWarnings("deprecation")
    @Override
    public void onCreate(Bundle savedInstanceState) {
        // TODO Auto-generated method stub
        super.onCreate(savedInstanceState);
        setContentView(R.layout.admin);

        DBAdapter db = new DBAdapter(this);
        db.open();

        ListView UsernameList = (ListView)findViewById(android.R.id.list);
        Button deleteplayer = (Button)findViewById(R.id.PlayerDelete);

        Cursor playeraccounts = db.getAllPlayers();
        startManagingCursor(playeraccounts);
        setListAdapter(new MyListAdapter(this, R.layout.admin, playeraccounts));

    }

    private class MyListAdapter extends ResourceCursorAdapter {
        DBAdapter db;

        public MyListAdapter(Context context, int layout, Cursor cursor) {
            super(context, R.layout.admin, cursor);
            // TODO Auto-generated constructor stub

        }

        @Override
        public void bindView(View view, final Context context, final Cursor playeraccounts) {

            final TextView PlayerName = (TextView)findViewById(R.id.AdminUsername);
            final TextView PlayerPass = (TextView)findViewById(R.id.AdminPassword);
            final TextView PlayerEmail = (TextView)findViewById(R.id.AdminEmail);

            PlayerName.setText(playeraccounts.getString(playeraccounts.getColumnIndex("USERNAME")));
            PlayerPass.setText(playeraccounts.getString(playeraccounts.getColumnIndex("PASSWORD")));
            PlayerEmail.setText(playeraccounts.getString(playeraccounts.getColumnIndex("EMAIL")));
            Button deleteplayer = (Button)findViewById(R.id.PlayerDelete);
            deleteplayer.setOnClickListener(new OnClickListener() {

                @Override
                public void onClick(View view) {
                    // TODO Auto-generated method stub
                    DBAdapter db = new DBAdapter(context);
                    db.open();
                    db.deletePlayer(playeraccounts);
                    Toast.makeText(getBaseContext(), "Player Deleted", Toast.LENGTH_SHORT).show();
                    MyListAdapter.this.notifyDataSetChanged();
                    db.close();

                }
            });

        }

    }

}

Answer 1

您的数据库，即DBAdapter为Null，

当您尝试对其进行操作时

即

db.open(); 将抛出NullPointerException

因此，尝试在适配器的构造函数中实例化db 。

db=new DBAdapter(context); when you are using them in separate classess.

或将db声明为字段，然后使用它。 在适配器中删除新对象。

Answer 2

您有两个DBAdapter db对象。 onCreate()中的一个被初始化，而MyListAdapter class的一个保持为空。

您应该仅维护一个db对象，或者同时初始化两者。

这应该工作。

public class Admin extends ListActivity {

DBAdapter db;

@SuppressWarnings("deprecation")
@Override
public void onCreate(Bundle savedInstanceState) {
    // TODO Auto-generated method stub
    super.onCreate(savedInstanceState);
    setContentView(R.layout.admin);

    db = new DBAdapter(this);
    db.open();

    ListView UsernameList = (ListView)findViewById(android.R.id.list);
    Button deleteplayer = (Button)findViewById(R.id.PlayerDelete);

    Cursor playeraccounts = db.getAllPlayers();
    startManagingCursor(playeraccounts);
    setListAdapter(new MyListAdapter(this, R.layout.admin, playeraccounts));

}

private class MyListAdapter extends ResourceCursorAdapter {


    public MyListAdapter(Context context, int layout, Cursor cursor) {
        super(context, R.layout.admin, cursor);
        // TODO Auto-generated constructor stub

    }

    @Override
    public void bindView(View view, Context context, Cursor playeraccounts) {

        final TextView PlayerName = (TextView)findViewById(R.id.AdminUsername);
        final TextView PlayerPass = (TextView)findViewById(R.id.AdminPassword);
        final TextView PlayerEmail = (TextView)findViewById(R.id.AdminEmail);

        PlayerName.setText(playeraccounts.getString(playeraccounts.getColumnIndex("USERNAME")));
        PlayerPass.setText(playeraccounts.getString(playeraccounts.getColumnIndex("PASSWORD")));
        PlayerEmail.setText(playeraccounts.getString(playeraccounts.getColumnIndex("EMAIL")));
        Button deleteplayer = (Button)findViewById(R.id.PlayerDelete);
        deleteplayer.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View view) {
                // TODO Auto-generated method stub
                db.open();
                db.deletePlayer(0);
                Toast.makeText(getBaseContext(), "Player Deleted", Toast.LENGTH_SHORT).show();
                MyListAdapter.this.notifyDataSetChanged();
                db.close();

            }
        });

    }

}

}