Question

我一直在研究sqlite数据库的android sdk的信息和文档，我仍然有点卡住了。我从我找到的here示例中检索了我的数据库类。这是我的班级：

package com.example.medtracker;

import java.sql.Timestamp;
import java.util.ArrayList;
import java.util.Calendar;

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.SQLiteDatabase.CursorFactory;
import android.database.sqlite.SQLiteOpenHelper;
import android.util.Log;

public class DBAdapter {
    private static final String DATABASE_NAME = "meds.db";
    private String DATABASE_TABLE;
    private static final int DATABASE_VERSION = 1;

    // Index Key column
    public static final String KEY_ID = "_id";

    // Name of the column index of each column in DB
    public ArrayList<String> TABLE_KEYS = new ArrayList<String>();
    public ArrayList<String> TABLE_OPTIONS = new ArrayList<String>();
    public final String KEY_TIMESTAMP = "timeStamp";
    public final int TIMESTAMP_COLUMN = 1;

    // Create new database
    private String DATABASE_CREATE;

    // Variable to hold database instant
    private SQLiteDatabase db;

    // Database open/upgrade helper
    private myDBHelper dbHelper;

    public DBAdapter(Context context, String table, ArrayList<String> keys,
            ArrayList<String> options) {
        // Start initializing all of the variables
        DATABASE_TABLE = table;
        TABLE_KEYS = (ArrayList<String>) keys.clone();
        TABLE_OPTIONS = options;

        String keyString = "";
        for (int i = 0; TABLE_KEYS.size() > i; i++) {

            // Add commas to the options elements if there is a next value.
            if (i + 1 < TABLE_OPTIONS.size() && TABLE_OPTIONS.get(i) != null) {
                TABLE_OPTIONS.set(i, TABLE_OPTIONS.get(i) + ",");
            } else if (i + 1 == TABLE_OPTIONS.size()
                    && TABLE_OPTIONS.get(i) != null) {
                if (i + 1 < TABLE_KEYS.size()) {
                    TABLE_OPTIONS.set(i, TABLE_OPTIONS.get(i) + ",");
                } else {
                    TABLE_KEYS.set(i, TABLE_KEYS.get(i) + "");
                }
            } else if (i + 1 != TABLE_KEYS.size()) {
                TABLE_KEYS.set(i, TABLE_KEYS.get(i) + ",");
            } else {
                TABLE_KEYS.set(i, TABLE_KEYS.get(i) + "");
            }

            System.out.println(TABLE_OPTIONS.toString());
            System.out.println(TABLE_KEYS.toString());

            if (i + 1 <= TABLE_OPTIONS.size() && TABLE_OPTIONS.get(i) != null)
                keyString = keyString + " " + TABLE_KEYS.get(i) + " "
                        + TABLE_OPTIONS.get(i);
            else if (i + 1 > TABLE_OPTIONS.size()
                    || TABLE_OPTIONS.get(i) == null) {
                keyString = keyString + " " + TABLE_KEYS.get(i);
            }
        }

        // Create the database creation string.
        DATABASE_CREATE = "CREATE TABLE IF NOT EXISTS " + DATABASE_TABLE + " ("
                + "_id" + " INTEGER PRIMARY KEY AUTOINCREMENT, "
                + KEY_TIMESTAMP + "," + keyString + ");";

        // Create a new Helper
        dbHelper = new myDBHelper(context, DATABASE_NAME, null,
                DATABASE_VERSION, DATABASE_TABLE, DATABASE_CREATE);
    }

    public DBAdapter open() throws SQLException {
        db = dbHelper.getWritableDatabase();
        return this;
    }

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

    public long insertEntry(ArrayList<String> key, ArrayList<String> value) {
        String timeStamp = new Timestamp(Calendar.getInstance()
                .getTimeInMillis()).toString();
        ContentValues contentValues = new ContentValues();
        for (int i = 0; key.size() > i; i++) {
            contentValues.put(key.get(i), value.get(i));
        }
        contentValues.put(KEY_TIMESTAMP, timeStamp);
        return db.insert(DATABASE_TABLE, null, contentValues);
    }

    public boolean removeEntry(long rowIndex) {
        return db.delete(DATABASE_TABLE, KEY_ID + "=" + rowIndex, null) > 0;
    }

    public Cursor getAllEntries(String[] columns, String selection,
            String[] selectionArgs, String groupBy, String having,
            String sortBy, String sortOption) {
        return db.query(DATABASE_TABLE, columns, selection, selectionArgs,
                groupBy, having, sortBy + " " + sortOption);
    }

    public int updateEntry(long rowIndex, ArrayList<String> key,
            ArrayList<String> value) {
        String timeStamp = new Timestamp(Calendar.getInstance()
                .getTimeInMillis()).toString();
        String where = KEY_ID + "=" + rowIndex;
        ContentValues contentValues = new ContentValues();
        for (int i = 0; key.size() > i; i++) {
            contentValues.put(key.get(i), value.get(i));
        }
        contentValues.put(KEY_TIMESTAMP, timeStamp);
        return db.update(DATABASE_TABLE, contentValues, where, null);
    }

    public boolean clearTable() {
        return db.delete(DATABASE_TABLE, null, null) > 0;
    }

    private static class myDBHelper extends SQLiteOpenHelper {
        private String creationString;
        private String tableName;
        @SuppressWarnings("unused")
        SQLiteDatabase db;

        /**
         * Creates a myDBHelper object.
         * 
         * @param context
         *            The context where the access is needed
         * @param name
         *            Name of database file
         * @param factory
         *            A CursorFactory, or null to use default CursorFactory
         * @param version
         *            Database version
         * @param tableName
         *            Name of table within database
         * @param creationString
         *            SQL String used to create the database
         */
        public myDBHelper(Context context, String name, CursorFactory factory,
                int version, String tableName, String creationString) {
            super(context, name, factory, version);
            this.creationString = creationString;
            this.tableName = tableName;
        }

        /**
         * Creates the database table.
         * 
         * @param db
         *            The database used by this helper to create the table in
         */
        @Override
        public void onCreate(SQLiteDatabase db) {
            db.execSQL(creationString);
        }

        /**
         * This method determines if the database needs to be updated or not.
         * 
         * @param db
         *            The database used by this helper
         * @param oldVersion
         *            The old database version
         * @param newVersion
         *            The new database version
         */
        @Override
        public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
            // Log the version upgrade
            Log.w("TaskDBAdapter", "Upgrading from version " + oldVersion
                    + " to " + newVersion + ", which will destroy all old data");
            db.execSQL("DROP TABLE IF EXISTS " + tableName);
            onCreate(db);

        }

        /**
         * Creates tables when the database is opened if the tables need to be
         * created.
         * 
         * @param db
         *            The database used by this helper
         */
        @Override
        public void onOpen(SQLiteDatabase db) {
            db.execSQL(creationString);
        }

    }
}

然后我创建了一个类来添加对象：公共类AddMed extends Activity实现了OnClickListener {

Button submit;
    EditText name, dossage;
    DBAdapter database;
    String names, amount;
    String total;
    ArrayList<String> btr;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        // TODO Auto-generated method stub
        super.onCreate(savedInstanceState);
        setContentView(R.layout.addmed);
        submit = (Button) findViewById(R.id.bSubmit);
        name = (EditText) findViewById(R.id.etNameOfMed);
        dossage = (EditText) findViewById(R.id.etHowMuch);
    }

    @Override
    public void onClick(View arg0) {
        // TODO Auto-generated method stub
        switch (arg0.getId()) {
        case R.id.bSubmit:
            names = name.getText().toString();
            amount = dossage.getText().toString();
            total = names + amount;
            btr.add(total);
            database.open();
            database.insertEntry(btr, btr);
            database.close();
            break;
        }
    }

}

然后我有另一个带有文本视图的类，我尝试创建一个新的DBAdatper实例并使用游标中的getAllEntries方法，但我对参数感到困惑。有人可以开导我吗？谢谢你的帮助。

Answer 1

您引用的示例似乎只是尝试充当SQLLiteDatabase类的包装器。该示例列出了getAllEntries中每个参数的用途。似乎有很多参数，但如果您不想对结果集进行分组或排序，则其中一些参数可能为空。以下列出了每个参数的作用，取自SQLLiteDatabase API：

enter image description here

Answer 2

你找到的教程提供了一个课程，它试图为你自动做很多事情：如果你得到它就很好，但如果不这样做则不是很好。

我建议你放弃这个非常复杂的例子，而是自己从头开始，使用更合适的教程。 http://www.vogella.com/有很多好的教程，包括SQLite数据库：SQLite

Answer 3

来自SQLiteDatabase documentation for query

public Cursor query (String table, String[] columns, String selection, String[]
selectionArgs, String groupBy, String having, String orderBy, String limit)

Added in API level 1

Query the given table, returning a Cursor over the result set.

Parameters

table       The table name to compile the query against.

columns     A list of which columns to return. Passing null will return all
            columns, which is discouraged to prevent reading data from storage
            that isn't going to be used.

selection   A filter declaring which rows to return, formatted as an SQL WHERE
            clause (excluding the WHERE itself). Passing null will return all rows for
            the given table.

selectionArgs   You may include ?s in selection, which will be replaced by the
                values from selectionArgs, in order that they appear in the
                selection. The values will be bound as Strings.

groupBy     A filter declaring how to group rows, formatted as an SQL GROUP BY 
            clause (excluding the GROUP BY itself). Passing null will cause the rows
            to not be grouped.

having      A filter declare which row groups to include in the cursor, if row
            grouping is being used, formatted as an SQL HAVING clause (excluding the
            HAVING itself). Passing null will cause all row groups to be included,
            and is required when row grouping is not being used.

orderBy     How to order the rows, formatted as an SQL ORDER BY clause (excluding
            the ORDER BY itself). Passing null will use the default sort order, which
            may be unordered.

limit       Limits the number of rows returned by the query, formatted as LIMIT
            clause. Passing null denotes no LIMIT clause.

假设您有一个名为table1的表，其中包含三个名为x，y，z的列。你想做以下声明：

SELECT x,y FROM table1 WHERE x = 'squirrels' AND y = 'cats';

表参数只是表的名称（“table1”）。 columns参数将是您有兴趣获取值的列（在本例中为“x”和“y”列）。选择参数是“x =？AND y =？”。 selectionArgs参数将是一个包含“squirrels”和“cats”的数组。如果你知道SQL，其余的都是非常自我解释的。

Android：如何从sqlite数据库中检索数据

3 个答案: