摘要：
privatestaticsringGetDatabasePath（）｛lock（pathLocker）｛if（path＝＝null）｛stringdocumentsPath＝Environment.GetFolderPath（Environment.SpecialFolder.MyDocuments）；
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<ISQLite>().GetAsyncConnection(); } /// <summary> /// 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 /// </summary> public async void CreateOrUpdateAllTablesAsync() { await db.CreateTablesAsync<TestTable, UserInfo>(); } } }
4、Sqlite的增删改查操作
public async Task<Model.News> QueryNew(int id) { return await db.Table<Model.News>().Where(a => a.Id == id).FirstOrDefaultAsync(); } public async Task<List<Model.News>> QueryNews(int pageSize) { return await db.Table<Model.News>().OrderByDescending(a => a.DateAdded).Skip(0).Take(pageSize).ToListAsync(); } public async Task<List<Model.News>> QueryNewsByRecommend(int pageSize) { return await db.Table<Model.News>().Where(a => a.IsRecommend).OrderByDescending(a => a.DateAdded).Skip(0).Take(pageSize).ToListAsync(); } public async Task<List<Model.News>> QueryNewsByWorkHot(int pageSize, DateTime startdate) { return await db.Table<Model.News>().Where(a => a.IsHot && a.DateAdded > startdate).OrderByDescending(a => a.DateAdded).Skip(0).Take(pageSize).ToListAsync(); } public async Task UpdateNews(List<Model.News> 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