Xamarin.Forms学习系列之SQLite

在App中我们通常不会实时获取服务器数据，会在用户手机中保存历史数据，这个时候就需要用到数据库SQLite，由于微软的封装，在Xamarin中操作SQLite非常简单，类似EF的操作。

1、我们需要在共享项目的nuget中引用 sqlite-net-pcl 和 SQLitePCLRaw.core  

2、由于Android和IOS的SQLite数据库存放位置不一样，所以我们需要在共享项目中抽象一个接口ISQLite，然后分别在Android和IOS项目中实现接口，初始化数据库连接

共享项目代码如下：

public interface ISQLite
    {
        SQLiteAsyncConnection GetAsyncConnection();
    }

Android项目代码如下：

[assembly: Xamarin.Forms.Dependency(typeof(SQLiteAndroid))]//注入SQLiteAndroid
namespace Mobile.Droid.Helpers
{
    public class SQLiteAndroid : ISQLite
    {
        private static string path;

        private static SQLiteAsyncConnection connectionAsync;

        private static readonly object locker = new object();
        private static readonly object pathLocker = new object();

        private static string GetDatabasePath()
        {
            lock (pathLocker)
            {
                if (path == null)
                { 
                    string documentsPath = Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments); // Documents folder
                    path = Path.Combine(documentsPath, GlobalSetting.SqliteFilename);
                }
            }
            return path;
        }

        public SQLiteAsyncConnection GetAsyncConnection()
        {
            lock (locker)
            {
                if (connectionAsync == null)
                {
                    var dbPath = GetDatabasePath();
                    connectionAsync = new SQLiteAsyncConnection(dbPath);
                }
            }
            return connectionAsync;
        }
    }
}

IOS项目代码如下：

[assembly: Xamarin.Forms.Dependency(typeof(SQLiteIOS))]
namespace Mobile.iOS.Helpers
{
    public class SQLiteIOS : ISQLite
    {
        private static string path;

        private static SQLiteAsyncConnection connectionAsync;

        private static readonly object locker = new object();
        private static readonly object pathLocker = new object();

        private static string GetDatabasePath()
        {
            lock (pathLocker)
            {
                if (path == null)
                { 
                    var documentsPath = Environment.GetFolderPath(Environment.SpecialFolder.Personal); // Documents folder
                    var libraryPath = Path.Combine(documentsPath, "..", "Library"); // Library folder
                    path = Path.Combine(libraryPath, GlobalSetting.SqliteFilename);
                }
            }
            return path;
        }

        public SQLiteAsyncConnection GetAsyncConnection()
        {
            lock (locker)
            {
                if (connectionAsync == null)
                {
                    var dbPath = GetDatabasePath();
                    connectionAsync = new SQLiteAsyncConnection(dbPath);
                }
            }
            return connectionAsync;
        }
    }
}

3、在共享项目中创建SqliteHelper 

using Microsoft.AppCenter.Crashes;
using Mobile.Interfaces;
using SQLite;
using System;
using Xamarin.Essentials;
using Xamarin.Forms;

namespace Mobile.Helpers
{
    public class SqliteHelper
    {
        static SqliteHelper baseSqlite;
        public static SqliteHelper Current
        {
            get { return baseSqlite ?? (baseSqlite = new SqliteHelper()); }
        }
        public SQLiteAsyncConnection db;
        public SqliteHelper()
        {
            if (db == null)
                db = DependencyService.Get().GetAsyncConnection();
        }

        /// 

        /// 创建或者更新Sqlite数据库表
        /// 在App启动的时候执行该方法，sqlite-net-pcl会根据实体类创建对应的表，如果实体类有更新，表结构也会更新，如果表结构没变，则不进行操作，sqlite-net-pcl会自动判断
        /// 
        public async void CreateOrUpdateAllTablesAsync()
        {
            await db.CreateTablesAsync();
        }

    }
}

4、Sqlite的增删改查操作

public async Task QueryNew(int id)
        {
            return await db.Table().Where(a => a.Id == id).FirstOrDefaultAsync();
        }
        public async Task> QueryNews(int pageSize)
        {
            return await db.Table().OrderByDescending(a => a.DateAdded).Skip(0).Take(pageSize).ToListAsync();
        }
        public async Task> QueryNewsByRecommend(int pageSize)
        {
            return await db.Table().Where(a => a.IsRecommend).OrderByDescending(a => a.DateAdded).Skip(0).Take(pageSize).ToListAsync();
        }
        public async Task> QueryNewsByWorkHot(int pageSize, DateTime startdate)
        {
            return await db.Table().Where(a => a.IsHot && a.DateAdded > startdate).OrderByDescending(a => a.DateAdded).Skip(0).Take(pageSize).ToListAsync();
        }
        public async Task UpdateNews(List lists)
        {
            foreach (var item in lists)
            {
                await QueryNew(item.Id).ContinueWith(async (results) =>
                {
                    if (results.Result == null)
                    {
                        try
                        {
                            await db.InsertAsync(item);
                        }
                        catch (Exception ex)
                        {
                            Crashes.TrackError(ex);
                        }
                    }
                    else
                    {
                        await UpdateNew(item);
                    }
                });
            }
        }
        public async Task UpdateNew(Model.News model)
        {
            try
            {
                await db.UpdateAsync(model);
            }
            catch (Exception ex)
            {
                Crashes.TrackError(ex);
            }
        }

参考代码： https://github.com/JoesWeek/XamCnblogs