Question

我得到的错误是

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

相关代码 -

public void delete(int position) {
SQLiteDatabase db = getWritableDatabase(); //this is null
db.execSQL("DELETE FROM LOGIN WHERE _ID=1;");
db.close();
}

这是DBHelper.class中的代码。数据添加和选择有效但删除仅导致错误。这有什么不对？

所有DBHelper代码

import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.util.Log;
import android.widget.Toast;

import java.util.ArrayList;
import java.util.List;

import static android.content.ContentValues.TAG;

public class DBHelper extends SQLiteOpenHelper {
    private Context context;
    private DBHelper dbHelper;

    public DBHelper(Context context, String name, SQLiteDatabase.CursorFactory factory, int version) {
        super(context, name, factory, version);
        this.context = context;
    }
    @Override public void onCreate(SQLiteDatabase db) {
        try {
            String DROP_SQL = "drop table if exists LOGIN";
            db.execSQL(DROP_SQL);
        } catch(Exception ex) {
            Log.e(TAG, "Exception in DROP_SQL", ex);
        }
        StringBuffer sb = new StringBuffer();
        sb.append(" CREATE TABLE LOGIN ( ");
        sb.append(" _ID INTEGER PRIMARY KEY AUTOINCREMENT, ");
        sb.append(" ID TEXT, ");
        sb.append(" PW TEXT ) ");
        try {
            db.execSQL(sb.toString());
        } catch(Exception ex) {
            Log.e(TAG, "Exception in CREATE_SQL", ex);
        }

        Toast.makeText(context, R.string.make, Toast.LENGTH_SHORT).show();
    }


    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        Toast.makeText(context, R.string.upgrade, Toast.LENGTH_SHORT).show();
    }


    public void addLogin(Login login) {
        SQLiteDatabase db = getWritableDatabase();
        StringBuffer sb = new StringBuffer();
        sb.append(" INSERT INTO LOGIN ( ");
        sb.append(" ID, PW ) ");
        sb.append(" VALUES ( ?, ? ) ");
        if(login.getId().equals("") || login.getPw().equals("")){
            Toast.makeText(context, R.string.nodata, Toast.LENGTH_SHORT).show();
        }else{
            db.execSQL(sb.toString(),
                    new Object[]{
                            login.getId(),
                            login.getPw(),
                    });;
            Toast.makeText(context, R.string.insert, Toast.LENGTH_SHORT).show();
        }

    }

    public void delete(int position) {
        SQLiteDatabase db = getWritableDatabase(); //this is null
        db.execSQL("DELETE FROM LOGIN WHERE _ID=1;");
        db.close();
        //????
          //db.execSQL("DELETE FROM LOGIN WHERE _ID=" + position + ";");
        //?? ???


    }


    public List getAllData() {
        StringBuffer sb = new StringBuffer();
        sb.append(" SELECT _ID, ID, PW FROM LOGIN ");
        SQLiteDatabase db = getReadableDatabase();
        Cursor cursor = db.rawQuery(sb.toString(), null);
        List list = new ArrayList();
        Login login = null;
        while (cursor.moveToNext()) {
            login = new Login();
            login.set_id(cursor.getInt(0));
            login.setId(cursor.getString(1));
            login.setPw(cursor.getString(2));
            list.add(login);
        }

        return list;

    }

}

完整错误

08-01 11：14：34.094 23589-23589 / com.yonoo.naverloginhelper D / ViewRootImpl：ViewPostImeInputStage processPointer 0 08-01 11：14：34.134 23589-23589 / com.yonoo.naverloginhelper D / ViewRootImpl：ViewPostImeInputStage processPointer 1 08-01 11：24：33.866 23589-23589 / com.yonoo.naverloginhelper W / IInputConnectionWrapper：getTextBeforeCursor on inactive InputConnection 08-01 11：24：33.916 23589-23589 / com.yonoo.naverloginhelper V / ActivityThread：updateVisibility：ActivityRecord {a6dc7d0 token=android.os.BinderProxy@5f1945b {com.yonoo.naverloginhelper / com.yonoo.naverloginhelper.DBActivity} } show：true 08-01 11：24：33.916 23589-23589 / com.yonoo.naverloginhelper W / IInputConnectionWrapper：getSelectedText在非活动的InputConnection上 08-01 11：24：33.916 23589-23589 / com.yonoo.naverloginhelper W / IInputConnectionWrapper：getTextAfterCursor on inactive InputConnection 08-01 11：24：39.086 23589-23589 / com.yonoo.naverloginhelper D / ViewRootImpl：MSG_RESIZED_REPORT：ci = Rect（0,96 - 0,0）vi = Rect（0,96 - 0,0）或= 1 08-01 13：36：26.303 23589-23589 / com.yonoo.naverloginhelper D / ViewRootImpl：MSG_RESIZED：ci = Rect（0,96-0,1000）vi = Rect（0,96-0,1000）或= 1 08-01 13：36：26.373 23589-23589 / com.yonoo.naverloginhelper I / Timeline：Timeline：Activity_idle id：android.os.BinderProxy@5f1945b time：11500752 08-01 13：36：27.323 23589-23589 / com.yonoo.naverloginhelper D / ViewRootImpl：ViewPostImeInputStage processPointer 0 08-01 13：36：27.463 23589-23589 / com.yonoo.naverloginhelper D / ViewRootImpl：ViewPostImeInputStage processPointer 1 08-01 13：36：27.963 23589-23589 / com.yonoo.naverloginhelper D / ViewRootImpl：ViewPostImeInputStage processPointer 0 08-01 13：36：28.063 23589-23589 / com.yonoo.naverloginhelper D / ViewRootImpl：ViewPostImeInputStage processPointer 1 08-01 13：36：28.073 23589-23589 / com.yonoo.naverloginhelper D / AndroidRuntime：关闭虚拟机

java.lang.NullPointerException：尝试调用虚方法＆＃39; android.database.sqlite.SQLiteDatabase android.content.Context.openOrCreateDatabase（java.lang.String，int，android.database.sqlite.SQLiteDatabase $ CursorFactory ，android.database.DatabaseErrorHandler）＆＃39;在null对象引用上在android.content.ContextWrapper.openOrCreateDatabase（ContextWrapper.java:283）在android.database.sqlite.SQLiteOpenHelper.getDatabaseLocked（SQLiteOpenHelper.java:223）在android.database.sqlite.SQLiteOpenHelper.getWritableDatabase（SQLiteOpenHelper.java:163）在com.yonoo.naverloginhelper.DBHelper.delete（DBHelper.java:71）在com.yonoo.naverloginhelper.DBActivity.DeleteList（DBActivity.java:70）在com.yonoo.naverloginhelper.LoginListAdapter $ 1.onClick（LoginListAdapter.java:76）在android.view.View.performClick（View.java:5702）在android.widget.TextView.performClick（TextView.java:10888）在android.view.View $ PerformClick.run（View.java:22541）在android.os.Handler.handleCallback（Handler.java:739）在android.os.Handler.dispatchMessage（Handler.java:95）在android.os.Looper.loop（Looper.java:158）在android.app.ActivityThread.main（ActivityThread.java:7229） at java.lang.reflect.Method.invoke（Native Method）在com.android.internal.os.ZygoteInit $ MethodAndArgsCaller.run（ZygoteInit.java:1230）在com.android.internal.os.ZygoteInit.main（ZygoteInit.java:1120）

Answer 1

检查您的应用权限。清单和运行时。

您在哪里设置数据库名称和版本？

您可以像这样创建构造函数。您的数据库名称和版本始终相同。

// Database version
private static final int DATABASE_VERSION = 1;
// Database name
private static final String DATABASE_NAME = MyDatabase.db;

public DBHelper(Context context) {
        super(context, DATABASE_NAME, null, DATABASE_VERSION);
        this.context = context;
}

NullPointerException：尝试调用虚方法＆＃39; android.database.sqlite.SQLiteDatabase android.content.Context.openOrCreateDatabase

1 个答案: