创建SQLite数据库时发生异常

Question

I develop a Universal app that use a local SQLite database. As I need to know the database version, I store an additional information that contains this information.

At the application startup, I check if the database exists, and if the database version has changed.

public sealed partial class App : Application
{
    // DB Name
    public static string DBFileName = "myDb.sqlite";
    public static string DBpath;

    // DB Version
    public static string DBVersionFilename = "myDb.version";
    public static string DBVersionPath;
    public static string DBVersion = "1.1.0";

    public App()
    {
        this.InitializeComponent();
        this.Suspending += this.OnSuspending;
        ManageDB();
    }

    private async Task ManageDB()
    {
        if (!CheckDbExist().Result)
        {
            CreateDb();
        }
        else
        {
            if (CheckDbVersionUpdated().Result)
            {
                await DeleteDb();
                CreateDb();
            }
        }
    }

    private async Task<bool> CheckDbExist()
    {
        try
        {
            StorageFile storageFile = await ApplicationData.Current.LocalFolder.GetFileAsync(DBFileName);
            DBpath = storageFile.Path;
            return true;
        }
        catch { }
        return false;
    }

    private void CreateDb()
    {
        try
        {
            StorageFile storageFile = ApplicationData.Current.LocalFolder.CreateFileAsync(DBFileName, CreationCollisionOption.OpenIfExists).GetResults();
            DBpath = storageFile.Path;
            var dbconnection = new SQLiteAsyncConnection(DBpath, false);
            dbconnection.CreateTableAsync<Article>();
            //...

            StorageFile file = ApplicationData.Current.LocalFolder.CreateFileAsync(DBVersionFilename, CreationCollisionOption.ReplaceExisting).GetResults();
            FileIO.WriteTextAsync(file, DBVersion);
        }
        catch (Exception e)
        { }
    }

    private async Task<bool> DeleteDb()
    {
        try 
        {
            StorageFile storageFile = ApplicationData.Current.LocalFolder.CreateFileAsync(DBFileName, CreationCollisionOption.OpenIfExists).GetResults();
            await storageFile.DeleteAsync(StorageDeleteOption.PermanentDelete);
            return true;
        }
        catch { }
        return false;
    }

    private async Task<bool> CheckDbVersionUpdated()
    {
        try
        {
            string userDBVersion;
            StorageFile file = await ApplicationData.Current.LocalFolder.GetFileAsync(DBVersionFilename);
            userDBVersion = await FileIO.ReadTextAsync(file);
            if (userDBVersion != DBVersion)
                return true;
            else
                return false;
        }
        catch { }
        return false;
    }
}

There is a problem on CreateDB() :

• if I browse this code step by step, with breakpoint, there is no problem
• but if I don't place breakpoint I meet an exception after calling var dbconnection = new SQLiteAsyncConnection(DBpath, false); :

System.InvalidOperationException: A method was called at an unexpected time. A method was called at an unexpected time. at Windows.Foundation.IAsyncOperation`1.GetResults() at TestRating.App.CreateDb()}

Would you have an idea about the encountered problem? Is there another way to do this?

Answer 1

When I remove " .Results()" it seems that the " CreateDb() " function works correctly:

 private async Task<bool> CreateDb() { try { StorageFile storageFile = await ApplicationData.Current.LocalFolder.CreateFileAsync(DBFileName, CreationCollisionOption.OpenIfExists); DBpath = storageFile.Path; var dbconnection = new SQLiteAsyncConnection(DBpath, false); dbconnection.CreateTableAsync<Article>(); //... StorageFile file = await ApplicationData.Current.LocalFolder.CreateFileAsync(DBVersionFilename, CreationCollisionOption.ReplaceExisting); FileIO.WriteTextAsync(file, DBVersion); return true; } catch (Exception e) { } return false; } 

Do you have an explanation?