Android实现风蓝记事本（2）：数据库设计

骑猪看日落 2022-05-24 04:12 214阅读 0赞

Android实现风蓝记事本（2）：数据库设计：

要实现记事本记事能力，得设计一个数据库，要有一张表来保存记事记录。

package com.example.notes;
    
            import java.sql.SQLData;
    
            import android.content.Context;
            import android.database.DatabaseErrorHandler;
            import android.database.sqlite.SQLiteDatabase;
            import android.database.sqlite.SQLiteDatabase.CursorFactory;
            import android.database.sqlite.SQLiteOpenHelper;
    
    public class DatabaseHelper extends SQLiteOpenHelper{
    
        private String tableName="notes";//表名
        private Context mContext=null;
        private String sql="create table if not exists "+tableName+
                "( id Integer primary key autoincrement , "+
                "n_title varchar(30) NOT NULL,"+//标题
                "n_content text NOT NULL ,"+//内容
                "n_time varchar(30))";//时间
        public DatabaseHelper(Context context, String name, CursorFactory factory,
                              int version) {
            super(context, name, factory, version);
            // TODO Auto-generated constructor stub
        }
    
        @Override
        public void onCreate(SQLiteDatabase db) {
            // TODO Auto-generated method stub
            //创建表
            db.execSQL(sql);
        }
    
        @Override
        public void onUpgrade(SQLiteDatabase arg0, int arg1, int arg2) {
            // TODO Auto-generated method stub
    
        }
    
    }

把对数据表的增删改查操作封装在一个类：

package com.example.notes;
    
            import android.content.ContentValues;
            import android.content.Context;
            import android.database.Cursor;
            import android.database.sqlite.SQLiteDatabase;
            import android.database.sqlite.SQLiteException;
            import android.util.Log;
    
    public class DatabaseManage {
        private Context mContext = null;
    
        private SQLiteDatabase mSQLiteDatabase = null;// 用于操作数据库的对象
        private DatabaseHelper dh = null;// 用于创建数据库的对象
    
        private String dbName = "notes.db";
        private int dbVersion = 1;
    
        public DatabaseManage(Context context) {
            mContext = context;
        }
    
        public DatabaseManage() {
            // TODO Auto-generated constructor stub
        }
    
        /**
         * 打开数据库
         */
        public void open() {
    
            try {
                dh = new DatabaseHelper(mContext, dbName, null, dbVersion);
                if (dh == null) {
                    // Log.v("msg", "is null");
                    return;
                }
                mSQLiteDatabase = dh.getWritableDatabase();
                // dh.onOpen(mSQLiteDatabase);
    
            } catch (SQLiteException se) {
                se.printStackTrace();
            }
        }
    
        /**
         * 关闭数据库
         */
        public void close() {
    
            mSQLiteDatabase.close();
            dh.close();
    
        }
    
        // 获取列表
        public Cursor selectAll(boolean sort_desc) {
            Cursor cursor = null;
            String sql = null;
            try {
                sql = "select * from notes order by n_time "
                        + (sort_desc != true ? "" : "desc");// 倒序
                cursor = mSQLiteDatabase.rawQuery(sql, null);
            } catch (Exception ex) {
                ex.printStackTrace();
                cursor = null;
            }
            return cursor;
        }
    
        public Cursor selectById(int id) {
    
            // String result[] = {};
            Cursor cursor = null;
            try {
                String sql = "select * from notes where id='" + id + "'";
                cursor = mSQLiteDatabase.rawQuery(sql, null);
            } catch (Exception ex) {
                ex.printStackTrace();
                cursor = null;
            }
    
            return cursor;
        }
    
        // 根据内容查找
        public Cursor selectWord(String word) {
            Cursor cursor = null;
            System.out.println("---data----word" + word);
            try {
                String sql = " select * from notes where n_title like '" + "%"
                        + word + "%' or n_content like '" + "%" + word
                        + "%' order by n_time desc";
                cursor = mSQLiteDatabase.rawQuery(sql, null);
            } catch (Exception e) {
                // TODO: handle exception
                e.printStackTrace();
                cursor = null;
            }
            return cursor;
        }
    
        // 插入数据
        public long insert(String title, String content, String time) {
    
            long flag = -1;
            try {
                ContentValues cv = new ContentValues();
                cv.put("n_title", title);
                cv.put("n_content", content);
                cv.put("n_time", time);
                System.out.println("----insert"+time);
                flag = mSQLiteDatabase.insert("notes", null, cv);
            } catch (Exception ex) {
                ex.printStackTrace();
            }
            return flag;
    
        }
    
        // 删除数据
        public int delete(long id) {
            int affect = 0;
            try {
                affect = mSQLiteDatabase.delete("notes", "id=?", new String[] { id
                        + "" });
            } catch (Exception ex) {
                ex.printStackTrace();
                affect = -1;
            }
    
            return affect;
        }
    
        // 修改数据
        public int update(int id, String title, String content, String time) {
            int affect = 0;
            try {
                ContentValues cv = new ContentValues();
    
                cv.put("n_title", title);
                cv.put("n_content", content);
                cv.put("n_time", time);
                String w[] = { id + "" };
                affect = mSQLiteDatabase.update("notes", cv, "id=?", w);
            } catch (Exception ex) {
                ex.printStackTrace();
                affect = -1;
            }
            return affect;
        }
    
    }

# 注：源码下载：[https://download.csdn.net/download/weixin\_39220472/10426057][https_download.csdn.net_download_weixin_39220472_10426057] #

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[https_download.csdn.net_download_weixin_39220472_10426057]: https://download.csdn.net/download/weixin_39220472/10426057