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私のアプリケーションのデータベースには、すべてのユーザーのデータを保持する「PLAYERS」と、登録されたすべてのアカウントの個人的な「友達」リストを意図した「FRIENDSLIST」という 2 つのテーブルがあります。プレーヤー (Joe) がユーザー名を登録すると、彼の情報は「PLAYERS」テーブルに送られ、FindFriends アクティビティに移動し、アプリで友人のユーザー名 (Bob) を検索し、[追加] ボタンをクリックします。

次に、友人 (ボブ) が「FRIENDSLIST」テーブルに追加されます。彼が PlayAFriend アクティビティに入ると、彼が追加した「友人」を示すリストがロードされます。友人のアカウント (Bob) は、(Joe) と同じリストを持っています。

(Joe) の友達リストを読み込むために使用しているカーソルは、(Bob) の友達リストを読み込むために使用しているカーソルと同じであることはわかっているので、質問は次のとおりです。

Joe と Bob に自分の個人的な友達リストを持たせるにはどうすればよいですか?

このウェブサイトで検索して、これを達成する方法の例を見つけようとしましたが、このタイプの練習が作成されたすべての人気のあるアプリで使用されているにもかかわらず、このテーマに関するチュートリアルや投稿が見つからないのはおかしいと思います.長い投稿で申し訳ありません。単純な質問ではないことはわかっているので、問題の詳細を説明する必要がありました。

DBAdapter クラスを投稿して、作成方法がこれに対応するかどうかを示し、PlayAFriend クラスを投稿して、Cursor と ListView が動作していることを示します。

DBAdapter クラス

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 = 4;

    static final String DATABASE_CREATE_TABLE1 = "create table PLAYERS ( _id integer primary key autoincrement, "
            + "USERNAME text not null unique,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 ,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 long 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);

        return db.insertWithOnConflict("PLAYERS", null, initialValues,
                SQLiteDatabase.CONFLICT_IGNORE);
    }

    public boolean deletePlayer(long id) {
        Log.d(TAG, "delete is working");
        return db.delete("PLAYERS", KEY_ROWID + " = " + id, 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(int _id) throws SQLException {
        Cursor mCursor = db.query(true, "PLAYERS", new String[] {
                "_id", "USERNAME"
        }, KEY_ROWID + " =  " + "_id", null, null, null, null, null);
        while (mCursor.moveToNext()) {
            int id = mCursor.getInt(mCursor.getColumnIndex("_id"));
        }
        return mCursor;
    }

    public String getUsername(String Username) {
        Cursor mCursor = db.query("Players", new String[] {
            "USERNAME"
        }, "USERNAME = ?", new String[] {
            Username
        }, null, null, null);
        if (mCursor.moveToNext())
            return mCursor.getString(0);
        else
            return "";
    }

    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, initialValues);
    }

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

    public Cursor getAllFriends() {
        return db.query(false, "FRIENDSLIST", 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;
    }

}

プレイアフレンド クラス

package com.fullfrontalgames.numberfighter;

import android.app.ListActivity;
import android.content.Context;
import android.database.Cursor;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.Button;
import android.widget.ListAdapter;
import android.widget.TextView;

public class PlayAFriend extends ListActivity {

    DBAdapter DBAdapter;

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

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

        getListView().setAdapter(new FriendsListAdapter(this, db.getAllFriends()));

    }

    private class FriendsListAdapter extends BaseAdapter implements OnClickListener, ListAdapter {
        private Cursor fFriends;

        private Context fContext;

        public FriendsListAdapter(Context context, Cursor friends) {
            // TODO Auto-generated constructor stub
            fContext = context;
            fFriends = friends;
        }

        @Override
        public int getCount() {
            // TODO Auto-generated method stub
            return fFriends.getCount();
        }

        @Override
        public FriendInfo getItem(int position) {
            // TODO Auto-generated method stub
            if (fFriends.moveToPosition(position)) {
                String name = fFriends.getString(fFriends.getColumnIndex("FRIENDS"));

                return new FriendInfo(name);
            }
            return null;
        }

        @Override
        public long getItemId(int position) {
            // TODO Auto-generated method stub
            fFriends.moveToPosition(position);
            return fFriends.getLong(fFriends.getColumnIndex("_id"));
        }

        @Override
        public View getView(int position, View convertView, ViewGroup parent) {
            // TODO Auto-generated method stub
            if (convertView == null) {
                convertView = LayoutInflater.from(fContext).inflate(R.layout.playafriendlistitems,
                        parent, false);
            }
            FriendInfo friendinfo = getItem(position);
            TextView friendTV = ViewHolder.get(convertView, R.id.textview_friends);
            Button playbutton = ViewHolder.get(convertView, R.id.playbutton, position);
            playbutton.setOnClickListener(this);

            friendTV.setText(friendinfo.getName());

            return convertView;
        }

        @Override
        public void onClick(View v) {
            // TODO Auto-generated method stub
            DBAdapter db = new DBAdapter(fContext);
            db.open();
            int position = (Integer)v.getTag();
            fFriends.moveToPosition(position);
            long id = fFriends.getLong(fFriends.getColumnIndex("_id"));
            fFriends = db.getAllFriends();
            db.close();
        }

    }

}

新しい DB アダプタ

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 = 9;

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

    static final String DATBASE_CREATE_TABLE2 = "create table FRIENDSLIST (_id integer primary key autoincrement,"
            + "player_id integer not null references PLAYERS(_id) on update cascade on delete cascade,"
            + "FRIENDS text ,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();
        db.execSQL("PRAGMA foreign_keys=ON;");
        return this;
    }

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

    // PLAYERS TABLE CRUD

    public long 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);

        return db.insertWithOnConflict("PLAYERS", null, initialValues,
                SQLiteDatabase.CONFLICT_IGNORE);
    }

    public boolean deletePlayer(long id) {
        Log.d(TAG, "delete is working");
        return db.delete("PLAYERS", KEY_ROWID + " = " + id, 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(int _id) throws SQLException {
        Cursor mCursor = db.query(true, "PLAYERS", new String[] {
                "_id", "USERNAME"
        }, KEY_ROWID + " =  " + "_id", null, null, null, null, null);
        while (mCursor.moveToNext()) {
            int id = mCursor.getInt(mCursor.getColumnIndex("_id"));
        }
        return mCursor;
    }

    public String getUsername(String Username) {
        Cursor mCursor = db.query("Players", new String[] {
            "USERNAME"
        }, "USERNAME = ?", new String[] {
            Username
        }, null, null, null);
        if (mCursor.moveToNext())
            return mCursor.getString(0);
        else
            return "";
    }

    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(long playerId, String Friend) {
        ContentValues initialValues = new ContentValues();
        initialValues.put("player_id", playerId);
        initialValues.put("FRIENDS", Friend);
        db.insertWithOnConflict("FRIENDSLIST", null, initialValues, SQLiteDatabase.CONFLICT_IGNORE);
    }

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

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

    public Cursor getFriend(long player_id) throws SQLException {
        Cursor mCursor = db.query(true, "FRIENDSLIST", new String[] {
                "_id", "FRIENDS"
        }, "player_id" + " =  " + "player_id", null, null, null, null, null);
        // cursor from query is never null,
        // should just check for if (cursor.moveToFirst()) in the calling
        // activity
        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;
    }

    public long getPlayerId(String Username) {
        // TODO Auto-generated method stub
        long id = 0;
        Cursor c = db.query("PLAYERS", new String[] {
            KEY_ROWID
        }, KEY_USERNAME + "=?", new String[] {
            Username
        }, null, null, null);
        if (c.moveToFirst()) {
            id = c.getLong(0);
        }
        c.close();
        return id;
    }

}


New PlayAFriend




package com.fullfrontalgames.numberfighter;

import android.app.ListActivity;
import android.content.Context;
import android.database.Cursor;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.Button;
import android.widget.ListAdapter;
import android.widget.TextView;

public class PlayAFriend extends ListActivity {

    DBAdapter DBAdapter;

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

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

        long player_id = 0;
        getListView().setAdapter(new FriendsListAdapter(this, db.getFriend(player_id)));

    }

    private class FriendsListAdapter extends BaseAdapter implements OnClickListener, ListAdapter {
        private static final long player_id = 0;

        private Cursor fFriends;

        private Context fContext;

        public FriendsListAdapter(Context context, Cursor friends) {
            // TODO Auto-generated constructor stub
            fContext = context;
            fFriends = friends;
        }

        @Override
        public int getCount() {
            // TODO Auto-generated method stub
            return fFriends.getCount();
        }

        @Override
        public FriendInfo getItem(int position) {
            // TODO Auto-generated method stub
            if (fFriends.moveToPosition(position)) {
                String name = fFriends.getString(fFriends.getColumnIndex("FRIENDS"));

                return new FriendInfo(name);
            }
            return null;
        }

        @Override
        public long getItemId(int position) {
            // TODO Auto-generated method stub
            fFriends.moveToPosition(position);
            return fFriends.getLong(fFriends.getColumnIndex("_id"));
        }

        @Override
        public View getView(int position, View convertView, ViewGroup parent) {
            // TODO Auto-generated method stub
            if (convertView == null) {
                convertView = LayoutInflater.from(fContext).inflate(R.layout.playafriendlistitems,
                        parent, false);
            }
            FriendInfo friendinfo = getItem(position);
            TextView friendTV = ViewHolder.get(convertView, R.id.textview_friends);
            Button playbutton = ViewHolder.get(convertView, R.id.playbutton, position);
            playbutton.setOnClickListener(this);

            friendTV.setText(friendinfo.getName());

            return convertView;
        }

        @Override
        public void onClick(View v) {
            // TODO Auto-generated method stub
            DBAdapter db = new DBAdapter(fContext);
            db.open();
            int position = (Integer)v.getTag();
            fFriends.moveToPosition(position);
            long id = fFriends.getLong(fFriends.getColumnIndex("_id"));
            fFriends = db.getFriend(id);
            db.close();
        }

    }

}

友達を探す活動

package com.fullfrontalgames.numberfighter;

import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.FrameLayout;
import android.widget.TextView;
import android.widget.Toast;

public class Findfriends extends Activity {
    DBAdapter db;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        // TODO Auto-generated method stub
        super.onCreate(savedInstanceState);
        setContentView(R.layout.findfriends);

        final EditText sbar = (EditText)findViewById(R.id.PlayerSeachBar);
        Button search = (Button)findViewById(R.id.Search);
        Button Add = (Button)findViewById(R.id.Add);
        final TextView ResultText = (TextView)findViewById(R.id.ResultTextView);
        final FrameLayout ResultFrame = (FrameLayout)findViewById(R.id.ResultFrameLayout);

        ResultFrame.setVisibility(View.GONE);

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

        search.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View v) {
                // TODO Auto-generated method stub
                String Username = sbar.getText().toString();
                String foundplayer = db.getUsername(Username);

                if (Username.equals(foundplayer)) {

                    ResultFrame.setVisibility(View.VISIBLE);
                    ResultText.setText(foundplayer);
                    Toast.makeText(getApplicationContext(), "Player Found", Toast.LENGTH_LONG)
                            .show();

                } else {
                    Toast.makeText(getApplicationContext(), "Username Not Found", Toast.LENGTH_LONG)
                            .show();
                }
            }

        });

        Add.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View v) {
                // TODO Auto-generated method stub
                String Friends = sbar.getText().toString();
                long playerId = db.getPlayerId(Friends);
                db.insertFriend(playerId, Friends);
                Toast.makeText(getApplicationContext(), "Player Has Been Added", Toast.LENGTH_LONG)
                        .show();

            }
        });
    }
}

LogCat

 04-22 21:11:37.834: E/SQLiteDatabase(15862): Error inserting player_id=0 FRIENDS=null
    04-22 21:11:37.834: E/SQLiteDatabase(15862): android.database.sqlite.SQLiteConstraintException: foreign key constraint failed (code 19)
    04-22 21:11:37.834: E/SQLiteDatabase(15862):    at android.database.sqlite.SQLiteConnection.nativeExecuteForLastInsertedRowId(Native Method)
    04-22 21:11:37.834: E/SQLiteDatabase(15862):    at android.database.sqlite.SQLiteConnection.executeForLastInsertedRowId(SQLiteConnection.java:775)
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