[JAVA] Note that I touched Android's SQLiteOpenHelper lightly

constructor

java In java call super in constructor super(context, DATABASE_NAME, null, DATABASE_VERSION); kotlin Since the name of super is different from java, you need to be careful about how to write it. Describe as follows class DatabaseHelper(context : Context) : SQLiteOpenHelper(context, DATABASE_NAME, null, DATABASE_VERSION)

Caution

If the Context is null when calling the constructor, a NullPointerException will occur.

Unit test

When doing unit tests using Mockito, pay attention to the Context. RuntimeEnvironment.application To the constructor of DatabaseHelper, You can access, write, and read the DB in the unit test.

sample

    @Mock
    private DatabaseHelper mDatabaseHelper;
    private Context mContext;

    @Before
    public void setUp() {
        MockitoAnnotations.initMocks(this);
        mContext = RuntimeEnvironment.application;
        mDatabaseHelper = spy(new DatabaseHelper(mContext));
    }

Sample code

sample

    static class DatabaseHelper extends SQLiteOpenHelper {
        private static final String DATABASE_NAME = "Test.db";
        private static final int DATABASE_VERSION = 1;
        private static final String TABLE_NAME = "tablename";
        private static final String COLUMN_KEY = "name";

        public DatabaseHelper(Context context) {
            super(context, DATABASE_NAME, null, DATABASE_VERSION);
        }

        private void createTable(SQLiteDatabase db) {
            db.execSQL("CREATE TABLE " + TABLE_NAME + " ("
                    + COLUMN_KEY + " TEXT NOT NULL);");
        }

        /**
         * This call needs to be made while the mCacheLock is held. The way to
         * ensure this is to get the lock any time a method is called ont the DatabaseHelper
         * @param db The database.
         */
        @Override
        public void onCreate(SQLiteDatabase db) {
            createTable(db);
        }

        @Override
        public void onOpen(SQLiteDatabase db) {
        }

        @Override
        public void onConfigure(SQLiteDatabase db) {
        }

        @Override
        public void onUpgrade(SQLiteDatabase db, int oldVersion, int currentVersion) {
        }

        @Override
        public void onDowngrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        }
    }

MainActivity.kt

/*
 * Copyright (C) 2018 Sacred Sanctuary Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package jp.sacredsanctuary.databasesample

import android.content.ContentValues
import android.content.Context
import android.database.DatabaseUtils
import android.database.sqlite.SQLiteDatabase
import android.database.sqlite.SQLiteException
import android.database.sqlite.SQLiteOpenHelper
import android.support.v7.app.AppCompatActivity
import android.os.Bundle

class MainActivity : AppCompatActivity() {
    companion object {
        const val DATABASE_NAME = "Test.db"
        const val DATABASE_VERSION = 1
        const val TABLE_NAME = "tablename"
        const val COLUMN_KEY = "name"
        const val QUERY = "SELECT * FROM " + COLUMN_KEY + " limit 1"
    }

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
    }

    override fun onResume() {
        super.onResume()
        try {
            val db = DatabaseHelper(this).writableDatabase
            if (null != db) {
                try {
                    val values = ContentValues()
                    values.put(COLUMN_KEY, "TEST")
                    db.delete(TABLE_NAME, null, null)
                    db.insert(TABLE_NAME, null, values)
                } catch (e: SQLiteException) {
                    //Occurs due to failure to write to DB
                } finally {
                    db.close()
                }
            }
        } catch (e: SQLiteException) {
            //Occurs when the DB cannot be opened
        } catch (e: NullPointerException) {
            //Occurs in the SQLiteOpenHelper constructor when Context is null
        }
    }

    override fun onPause() {
        super.onPause()
        try {
            val db = DatabaseHelper(this).readableDatabase
            try {
                val name = DatabaseUtils.stringForQuery(db, QUERY, null)
            } catch (e: SQLiteException) {
                //Occurs when the query statement is invalid
            } finally {
                db.close()
            }
        } catch (e: SQLiteException) {
            //Occurs when the DB cannot be opened
        } catch (e: NullPointerException) {
            //Occurs in the SQLiteOpenHelper constructor when Context is null
        }
    }

    class DatabaseHelper(context : Context) : SQLiteOpenHelper(context, DATABASE_NAME, null, DATABASE_VERSION) {
        fun createTable(db: SQLiteDatabase?) {
            db?.execSQL("CREATE TABLE " + TABLE_NAME + " ("
                    + COLUMN_KEY + " TEXT NOT NULL);")
        }

        /**
         * This call needs to be made while the mCacheLock is held. The way to
         * ensure this is to get the lock any time a method is called ont the DatabaseHelper
         * @param db The database.
         */
        override fun onCreate(db: SQLiteDatabase?) {
            createTable(db)
        }

        override fun onOpen(db: SQLiteDatabase) {
        }

        override fun onConfigure(db: SQLiteDatabase) {
        }

        override fun onUpgrade(db: SQLiteDatabase?, oldVersion: Int, newVersion: Int) {
        }
    }
}