Question

我目前有一个listview，它从SQL Lite数据库中获取数据。我无法弄清楚如何使数据显示在顶部的最新信息，最旧的信息显示在底部。这是我的主要类，它显示了listview和我的DBAdapter

主要：

package com.ArielR.Spot;

import java.util.ArrayList;
import java.util.Arrays;

import android.app.Activity;
import android.os.Bundle;
import android.view.Menu;
import android.view.View;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import android.content.Intent;
import android.widget.SimpleCursorAdapter;
import android.widget.Toast;
import android.database.Cursor;
import android.view.MenuInflater;
import android.view.MenuItem;

public class main extends Activity {
/** Called when the activity is first created. */

DBAdapter SpotDB;
String Name;
String URL;
String Description;

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    Bundle extras = getIntent().getExtras();
    openDB();
    if (extras != null) {
        Name= extras.getString("name");
        URL= extras.getString("url");
        Description= extras.getString("description");
        if(Name.equals("") || URL.equals("") || Description.equals("")){
            Toast.makeText(this, "Invalid Submission", Toast.LENGTH_LONG).show();
            populateListViewfromDB();
        }
        else{

            populateListViewfromDB();
        }
    }

    }

@Override
protected void onDestroy() {
    super.onDestroy();
    closeDB();
}

private void openDB() {
    SpotDB = new DBAdapter(this);
    SpotDB.open();
    addRow();
    populateListViewfromDB();
}
private void closeDB() {
    SpotDB.close();
}

public void addRow() {
    long newid = SpotDB.insertRow(Name, URL, Description);
    populateListViewfromDB();
}


public void AddNew() {
    Intent intent = new Intent();
    intent.setClass(this, AddNewItem.class);
    startActivity(intent);
}


public void populateListViewfromDB() {
    Cursor cursor = SpotDB.getAllRows();

    startManagingCursor(cursor);

    String[] FromFieldNames= new String[]
            {DBAdapter.KEY_NAME, DBAdapter.KEY_URL, DBAdapter.KEY_DESCRIPTION};
    int[] ToViewIDs= new int[]
            {R.id.Name, R.id.URL, R.id.Description};

    SimpleCursorAdapter myCursorAdapter =
            new SimpleCursorAdapter(
                    this,
                    R.layout.row,
                    cursor,
                    FromFieldNames,
                    ToViewIDs
            );

    ListView list = (ListView) findViewById(R.id.listView);
    list.setAdapter(myCursorAdapter);
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    MenuInflater inflater = getMenuInflater();
    inflater.inflate(R.menu.main, menu);
    return super.onCreateOptionsMenu(menu);
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    // Handle presses on the action bar items
    switch (item.getItemId()) {
        case R.id.action_search:
            AddNew();
            return true;
    }
    return true;
}
}

将对DBAdapter：

package com.ArielR.Spot;

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



public class DBAdapter {

/////////////////////////////////////////////////////////////////////
//  Constants & Data
/////////////////////////////////////////////////////////////////////
// For logging:
private static final String TAG = "DBAdapter";

// DB Fields
public static final String KEY_ROWID = "_id";
public static final int COL_ROWID = 0;
/*
 * CHANGE 1:
 */
// TODO: Setup your fields here:
public static final String KEY_NAME = "Name";
public static final String KEY_URL = "URL";
public static final String KEY_DESCRIPTION = "Description";

// TODO: Setup your field numbers here (0 = KEY_ROWID, 1=...)
public static final int COL_NAME = 1;
public static final int COL_URL = 2;
public static final int COL_DESCRIPTION = 3;


public static final String[] ALL_KEYS = new String[] {KEY_ROWID, KEY_NAME, KEY_URL,               KEY_DESCRIPTION};

// DB info: it's name, and the table we are using (just one).
public static final String DATABASE_NAME = "SpotDb";
public static final String DATABASE_TABLE = "main";
// Track DB version if a new version of your app changes the format.
public static final int DATABASE_VERSION = 2;

private static final String DATABASE_CREATE_SQL =
        "create table " + DATABASE_TABLE
                + " (" + KEY_ROWID + " integer primary key autoincrement, "

        /*
         * CHANGE 2:
         */
                // TODO: Place your fields here!
                // + KEY_{...} + " {type} not null"
                //  - Key is the column name you created above.
                //  - {type} is one of: text, integer, real, blob
                //      (http://www.sqlite.org/datatype3.html)
                //  - "not null" means it is a required field (must be given a value).
                // NOTE: All must be comma separated (end of line!) Last one must have NO comma!!
                + KEY_NAME + " text not null, "
                + KEY_URL + " text not null, "
                + KEY_DESCRIPTION + " text not null"

                // Rest  of creation:
                + ");";

// Context of application who uses us.
private final Context context;

private DatabaseHelper myDBHelper;
private SQLiteDatabase db;

/////////////////////////////////////////////////////////////////////
//  Public methods:
/////////////////////////////////////////////////////////////////////

public DBAdapter(Context ctx) {
    this.context = ctx;
    myDBHelper = new DatabaseHelper(context);
}

// Open the database connection.
public DBAdapter open() {
    db = myDBHelper.getWritableDatabase();
    return this;
}

// Close the database connection.
public void close() {
    myDBHelper.close();
}

// Add a new set of values to the database.
public long insertRow(String name, String url, String description) {
    /*
     * CHANGE 3:
     */
    // TODO: Update data in the row with new fields.
    // TODO: Also change the function's arguments to be what you need!
    // Create row's data:
    ContentValues initialValues = new ContentValues();
    initialValues.put(KEY_NAME, name);
    initialValues.put(KEY_URL, url);
    initialValues.put(KEY_DESCRIPTION, description);

    // Insert it into the database.
    return db.insert(DATABASE_TABLE, null, initialValues);
}

// Delete a row from the database, by rowId (primary key)
public boolean deleteRow(long rowId) {
    String where = KEY_ROWID + "=" + rowId;
    return db.delete(DATABASE_TABLE, where, null) != 0;
}

public void deleteAll() {
    Cursor c = getAllRows();
    long rowId = c.getColumnIndexOrThrow(KEY_ROWID);
    if (c.moveToFirst()) {
        do {
            deleteRow(c.getLong((int) rowId));
        } while (c.moveToNext());
    }
    c.close();
}

// Return all data in the database.
public Cursor getAllRows() {
    String where = null;
    Cursor c =  db.query(true, DATABASE_TABLE, ALL_KEYS,
            where, null, null, null, null, null);
    if (c != null) {
        c.moveToFirst();
    }
    return c;
}

// Get a specific row (by rowId)
public Cursor getRow(long rowId) {
    String where = KEY_ROWID + "=" + rowId;
    Cursor c =  db.query(true, DATABASE_TABLE, ALL_KEYS,
            where, null, null, null, null, null);
    if (c != null) {
        c.moveToFirst();
    }
    return c;
}

// Change an existing row to be equal to new data.
public boolean updateRow(long rowId, String name, String url, String description) {
    String where = KEY_ROWID + "=" + rowId;

    /*
     * CHANGE 4:
     */
    // TODO: Update data in the row with new fields.
    // TODO: Also change the function's arguments to be what you need!
    // Create row's data:
    ContentValues newValues = new ContentValues();
    newValues.put(KEY_NAME, name);
    newValues.put(KEY_URL, url);
    newValues.put(KEY_DESCRIPTION, description);

    // Insert it into the database.
    return db.update(DATABASE_TABLE, newValues, where, null) != 0;
}



/////////////////////////////////////////////////////////////////////
//  Private Helper Classes:
/////////////////////////////////////////////////////////////////////

/**
 * Private class which handles database creation and upgrading.
 * Used to handle low-level database access.
 */
private static class DatabaseHelper extends SQLiteOpenHelper
{
    DatabaseHelper(Context context) {
        super(context, DATABASE_NAME, null, DATABASE_VERSION);
    }

    @Override
    public void onCreate(SQLiteDatabase _db) {
        _db.execSQL(DATABASE_CREATE_SQL);
    }

    @Override
    public void onUpgrade(SQLiteDatabase _db, int oldVersion, int newVersion) {
        Log.w(TAG, "Upgrading application's database from version " + oldVersion
                + " to " + newVersion + ", which will destroy all old data!");

        // Destroy old database:
        _db.execSQL("DROP TABLE IF EXISTS " + DATABASE_TABLE);

        // Recreate new database:
        onCreate(_db);
    }
}
}

Answer 1

在getAllRows()来电db.query()，您可以提供orderBy参数。假设KEY_ROWID反映了从最旧到最新的顺序，orderBy参数可以是KEY_ROWID + " DESC"

Answer 2

将您的数据库数据放入列表或地图中，并将列表以相反的顺序放在listview适配器

中

显示数据库中的ListView数据，其中最高和最低的最新结果

2 个答案: