Jam*_*ees 12 .net c# sqlite dependency-injection xamarin.forms
我搜索了很多,我找不到任何答案.
我正在编写一个Xamarin Forms Mobile应用程序,似乎当我最小化应用程序然后重新打开它或我的一个活动启动时,会抛出以下异常:
SQLiteConnection.CreateCommand (System.String cmdText, System.Object[] ps)
SQLite.SQLiteException: Cannot create commands from unopened database
SQLiteConnection.CreateCommand (System.String cmdText, System.Object[] ps)
TableQuery`1[T].GenerateCommand (System.String selectionList)
TableQuery`1[T].GetEnumerator ()
System.Collections.Generic.List`1[T]..ctor (System.Collections.Generic.IEnumerable`1[T] collection) [0x00062] in :0
Enumerable.ToList[TSource] (System.Collections.Generic.IEnumerable`1[T] source)
AsyncTableQuery`1[T].<ToListAsync>b__9_0 ()
Task`1[TResult].InnerInvoke ()
Task.Execute ()
这是我的代码:
通用存储库(创建Sqlite实例的位置)
public class Repository<T> : IRepository<T> where T : Entity, new()
{
private readonly SQLiteAsyncConnection _db;
public Repository(string dbPath)
{
_db = new SQLiteAsyncConnection(dbPath);
_db.CreateTableAsync<T>().Wait();
}
}
国际奥委会注册
FreshIOC.Container.Register<IRepository<Settings>>(new Repository<Settings>(dbPath)); // FreshIOC is a wrapper around TinyIOC
在我的App.xaml.cs OnResume中
protected override void OnResume()
{
SQLiteAsyncConnection.ResetPool();
}
上面ResetPool我把它放进去看看它是否有所作为,但事实并非如此.
网址活动
protected override void OnCreate(Bundle bundle)
{
base.OnCreate(bundle);
var url = Intent.Data.ToString();
var split = url.Split(new[] { "ombi://", "_" }, StringSplitOptions.RemoveEmptyEntries);
if (split.Length > 1)
{
var dbLocation = new FileHelper().GetLocalFilePath("ombi.db3");
var repo = new Repository<OmbiMobile.Models.Entities.Settings>(dbLocation);
var settings = repo.Get().Result;
foreach (var s in settings)
{
var i = repo.Delete(s).Result;
}
repo.Save(new Settings
{
AccessToken = split[1],
OmbiUrl = split[0]
});
}
Intent startup = new Intent(this, typeof(MainActivity));
StartActivity(startup);
Finish();
}
我不知道还能做什么或寻找什么,我似乎无法找到有关此类错误的任何信息.
更新:
经过更多调试后,似乎只有在Url活动完成后才会发生.我已从活动中删除了数据库代码,但它似乎仍然存在.一旦Activity启动了main,App()然后运行以下代码:
var repo = FreshIOC.Container.Resolve<IRepository<Settings>>();
try
{
Task.Run(async () =>
{
settings = (await repo.Get()).FirstOrDefault();
}).Wait();
}
catch (Exception e)
{
Debug.WriteLine(e.Message);
throw;
}
这是错误发生的地方.当Get()调用调用时会发生这种情况return _db.Table<T>().ToListAsync();
我已经尝试使所有异步(没有帮助),使存储库,连接和我们做CreateTableAsync异步的地方仍然没有运气.
您正在进行同步阻塞调用,.Wait()并且.Result当与异步API混合时可能会导致死锁.
SQLiteAsyncConnection 意味着异步使用.
一个常见的工作是创建事件处理程序,以允许进行异步非阻塞调用.
例如,CreateTableAsync在存储库中调用时
public class Repository<T> : IRepository<T> where T : Entity, new() {
private readonly SQLiteAsyncConnection _db;
public Repository(string dbPath) {
_db = new SQLiteAsyncConnection(dbPath);
createTable += onCreateTable; //Subscribe to event
createTable(this, EventArgs.Empty); //Raise event
}
private event EventHandler createTable = delegate { };
private async void onCreateTable(object sender, EventArgs args) {
createTable -= onCreateTable; //Unsubscribe from event
await _db.CreateTableAsync<T>(); //async non blocking call
}
//...
}
存储库抽象似乎有一个异步API,但有同步调用.
再次,这可能会导致死锁,不建议.
如果意图是具有响应式UI或使用非同步版本的SQLite.Net来进行同步调用,则需要将代码重构为异步 .
将URL活动重构为异步将按照与上面相同的格式进行重构.
protected override void OnCreate(Bundle bundle) {
base.OnCreate(bundle);
creating += onCreateCore; //subscribe to event
creating(this, EventArgs.Empty); //raise event
}
private event EventHandler creating = delegate { };
private async void onCreateCore(object sender, EventArgs args) {
creating -= onCreateCore; //unsubscribe to event
var url = Intent.Data.ToString();
var split = url.Split(new[] { "ombi://", "_" }, StringSplitOptions.RemoveEmptyEntries);
if (split.Length > 1) {
var dbLocation = new FileHelper().GetLocalFilePath("ombi.db3");
var repo = new Repository<OmbiMobile.Models.Entities.Settings>(dbLocation);
var settings = await repo.Get();
foreach (var s in settings) {
var i = await repo.Delete(s);
}
repo.Save(new Settings {
AccessToken = split[1],
OmbiUrl = split[0]
});
}
Intent startup = new Intent(this, typeof(MainActivity));
StartActivity(startup);
Finish();
}
同样从设计角度来看,连接的初始化应该从存储库中反转出来并在外部进行管理(SRP).
public interface ISQLiteAsyncProvider {
SQLiteAsyncConnection GetConnection();
}
public class DefaultSQLiteAsyncProvider : ISQLiteAsyncProvider {
private readonly Lazy<SQLiteAsyncConnection> connection;
public DefaultSQLiteAsyncProvider(string path) {
connection = new Lazy<SQLiteAsyncConnection>(() => new SQLiteAsyncConnection(path));
}
public SQLiteAsyncConnection GetConnection() {
return connection.Value;
}
}
使用的连接的异步延迟初始化的想法
/// <summary>
/// Provides support for asynchronous lazy initialization.
/// </summary>
/// <typeparam name="T"></typeparam>
public class LazyAsync<T> : Lazy<Task<T>> {
/// <summary>
/// Initializes a new instance of the LazyAsync`1 class. When lazy initialization
/// occurs, the specified initialization function is used.
/// </summary>
/// <param name="valueFactory">The delegate that is invoked to produce the lazily initialized Task when it is needed.</param>
public LazyAsync(Func<Task<T>> valueFactory) :
base(() => Task.Run(valueFactory)) { }
}
这使得现在可以重构存储库以使用延迟初始化,这允许删除存储库中的事件处理程序
public class Repository<T> : IRepository<T> where T : Entity, new() {
public Repository(ISQLiteAsyncProvider provider) {
this.connection = new LazyAsync<SQLiteAsyncConnection>(await () => {
var db = provider.GetConnection();
await db.CreateTableAsync<T>();
return db;
});
}
private readonly LazyAsync<SQLiteAsyncConnection> connection;
public async Task<List<T>> Get() {
var _db = await connection.Value;
return await _db.Table<T>().ToListAsync();
}
public async Task<T> Get(int id) {
var _db = await connection.Value;
return await _db.Table<T>().Where(x => x.Id == id).FirstOrDefaultAsync();
}
public async Task<int> Save(T entity) {
var _db = await connection.Value;
return entity.Id == 0
? await _db.InsertAsync(entity)
: await_db.UpdateAsync(entity);
}
public async Task<int> Delete(T entity) {
var _db = await connection.Value;
return await _db.DeleteAsync(entity);
}
public void Dispose() {
Dispose(true);
GC.SuppressFinalize(this);
}
protected virtual void Dispose(bool disposing) {
if (disposing) {
// get rid of managed resources
}
// get rid of unmanaged resources
}
}
并注册了
// same instance should be used for other repositories
var provider = new DefaultSQLiteAsyncProvider(dbPath);
var settingsRepository = new Repository<Settings>(provider);
FreshIOC.Container.Register<IRepository<Settings>>(settingsRepository);