如何将数据添加到SQLite离线数据库表并在listView Xamarin上显示

我正在Xamarin.Forms中进行Weather应用程序项目。在成功将用户添加到数据库并在“登录”上验证现有用户之后，现在我正在努力在SQLite数据库内部添加一个城镇（带有3个变量），然后在内容页面的ListView中显示信息。问题是当我单击“天气”按钮时，ListView中没有显示任何内容，并且还触发了第二个捕获-Temp =“无法获取天气”；

让我们从我的城镇模型开始：

public class Town {
[PrimaryKey] public int ID { get; set; } public string TownName { get; set; } public string Temp { get; set; } public string searchTime { get; set; }

public Town() { }

} 创建这个简单的类之后，我将实现一个控制器类来处理Town数据：

SQLiteConnection database;

public SearchHistoryDataController()
{

    database = DependencyService.Get<ISQLite>().GetConnection();

    database.CreateTable<Town>();

}

IEnumerable<Town> orderItemCollection;
public IEnumerable<Town> OrderItemCollection
{
    get
    {
        if (orderItemCollection == null)
            orderItemCollection = GetTowns();
        return orderItemCollection;
    }
}

public IEnumerable<Town> GetTowns()
{
    // Changing the database table items as ObservableCollection
    var table = (from i in database.Table<Town>() select i);
    ObservableCollection<Town> TownList = new ObservableCollection<Town>();
    foreach (var town in table)
    {
        TownList.Add(new Town()
        {
            ID = town.ID,
            TownName = town.TownName,
            Temp = town.Temp,
            searchTime = town.searchTime
        });
    }
    return TownList;
}

public Town GetTown(int id)
{

    return database.Table<Town>().FirstOrDefault(t => t.ID == id);

}


public void DeleteTown(int id)
{

    database.Delete<Town>(id);

}

public string AddTown(Town town)
{
    var data = database.Table<Town>();
    var d1 = data.Where(x => x.TownName == town.TownName && x.searchTime == town.searchTime).FirstOrDefault();

    if (d1 == null)
    {           

        database.Insert(town);

        return "Successfully Added";

    }
    else
    {
        return "Invalid Town id Exist";
    }
}

从这里开始，最后两件事是：创建城镇，插入一些信息，将城镇存储在数据库中，只要单击“显示天气”按钮，就可以在命令中完成。有代码：

             //Get weather information for the Weather view
        Temp = $"{weatherRoot?.MainWeather?.Temperature ?? 0}°C";
        Condition = $"{weatherRoot?.Weather?[0]?.Description ?? string.Empty}";
        Name = $"{weatherRoot.Name}, {weatherRoot.System.Country}";
        Humidity = $"{weatherRoot.MainWeather.Humidity}%";
        Pressure = $"{weatherRoot.MainWeather.Pressure} hpa";
        Clouds = $"{weatherRoot.Clouds.CloudinessPercent}%";
        Wind = $"{weatherRoot.Wind.Speed} m/s";


        town.TownName = $"{weatherRoot.Name}";
        town.Temp = Temp;
        town.searchTime = DateTime.Parse(weatherRoot.Date).ToLocalTime().ToString("g");;

        //history database push               
        try
        {
            SearchHistoryDataController searchHistoryDataController = new SearchHistoryDataController();
            var returnvalue = searchHistoryDataController.AddTown(town);

            if (returnvalue == "Sucessfully Added")
            {

                Console.WriteLine("Success");

            }
            else
            {
                Console.WriteLine("Fail");
            }
        }
        catch (Exception es)
        {
            Debug.WriteLine(es.Message);
        }


        await TextToSpeech.SpeakAsync(Temp + " " + Condition);
        IsBusy = false;

    }
    catch (Exception ex)
    {
        Temp = "Unable to get Weather";
        Debug.WriteLine(ex.Message);
    }
    finally
    {
        IsBusy = false;
    }
}

最终的XAML文件的结构如下：

<ListView.SeparatorColor> </ListView.SeparatorColor> <ListView.ItemTemplate> <Grid.ColumnDefinitions> </Grid.ColumnDefinitions> </ListView.ItemTemplate> 想法是当单击“天气”按钮时自动更新历史记录列表。历史记录将在文本字段中存储城镇名称，确切时间以及温度。该列表将不会用于其他任何事情，它是一个选项卡。

非常感谢你！

问题来源于stack overflow