我正在 xamarin 表单中使用 sqlite 创建一个项目，我遇到一个问题，在保存新项目页面上，我创建了我的 ITEM 模型的实例，并且在 ITEM 中引用了另一个模型，该模型是 PRIORITY，当我单击保存项目并将其保留在调试模式下，我可以接收所有项目，包括保存的优先级，但在我在 SQLite 中添加项目的变量中，它返回优先级，如下所示： ItemPriority = {CrudTasks.Models.Priority}
当我尝试在查看页面上访问这些项目时，我没有得到任何响应。
//Function SaveItems
private async void ExecuteSaveItemsCommand()
{
try
{
Item itemSaved = new Item
{
Name = NameSave,
Description = DescriptionSave,
ItemPriority = new Priority()
{
PriorityName = PrioritySave,
PriorityColor = "#ccc"
}
};
_itemsService.InsertItem(itemSaved);
ExecuteBackProductPageCommand();
}
catch (Exception ex)
{
await Shell.Current.DisplayAlert("Error", ex.Message, "OK");
}
}
//Model Item
namespace CrudTarefas.Models
{
[Table("Items")]
public class Item
{
[PrimaryKey, AutoIncrement]
public int Id { get; set; }
public string Name { get; set; }
public string Description { get; set; }
[ManyToOne]
public Priority ItemPriority { get; set; }
}
}
//Model Priority
namespace CrudTarefas.Models
{
[Table("Priorities")]
public class Priority
{
[PrimaryKey, AutoIncrement]
public int Id { get; set; }
public string PriorityName { get; set; }
public string PriorityColor { get; set; }
}
}
//CollectionView ListItemsPage
<ScrollView VerticalScrollBarVisibility="Never">
<StackLayout>
<CollectionView ItemsSource="{Binding ItemsList}">
<CollectionView.ItemsLayout>
<LinearItemsLayout ItemSpacing="20" Orientation="Vertical" />
</CollectionView.ItemsLayout>
<CollectionView.ItemTemplate>
<DataTemplate>
<StackLayout>
<Grid
Margin="0,0,0,20"
Padding="10"
xct:CornerRadiusEffect.CornerRadius="12"
BackgroundColor="{Binding ItemPriority.PriorityColor}"
RowDefinitions="*,20,20"
RowSpacing="10">
<Frame
Grid.Row="0"
Padding="5"
HorizontalOptions="Start">
<Label Text="{Binding ItemPriority.PriorityName}" />
</Frame>
<Label
Grid.Row="1"
Text="{Binding Name}"
TextColor="Black" />
<Label
Grid.Row="2"
Text="{Binding Description}"
TextColor="Black" />
</Grid>
</StackLayout>
</DataTemplate>
</CollectionView.ItemTemplate>
</CollectionView>
</StackLayout>
</ScrollView>
//Viewmodel ListItems
-> In the LOADITEMS method in the commented code, I can access the static item with the collectionView
#region constructor
public ListItemsViewmodel(INavigation navigation)
{
Navigation = navigation;
_itemsService = new ItemsService();
LoadItems();
GoAddItemPageCommand = new Command(ExecuteGoAddItemPageCommand);
LoadItemsCommand = new Command(ExecuteLoadItemsCommand);
}
#endregion
#region commands
public ICommand GoAddItemPageCommand { get; set; }
public ICommand LoadItemsCommand { get; set; }
#endregion
#region methods
-> private void LoadItems()
{
var items = _itemsService.GetAllItems();
ItemsList = new ObservableCollection<Item>(items);
}
我无法访问其他模型的表格
您可以尝试按如下方式修改您的代码：
1.为
public int ItemId { get; set; }添加外键（
Priority.cs）
[Table("Priorities")]
public class Priority
{
[PrimaryKey, AutoIncrement]
public int Id { get; set; }
public string PriorityName { get; set; }
public string PriorityColor { get; set; }
[ForeignKey(typeof(Item))]
public int ItemId { get; set; }
}
将
[ManyToOne]OneToOneItem.cs[表（“项目”）] 公开课项目 { [主键、自动增量] 公共 int Id { 得到;放; } 公共字符串名称{获取;放; } 公共字符串描述{获取;放; }
//add attribute OneToOne
[OneToOne]
public Priority ItemPriority { get; set; }
}
为
InsertPriority添加几个方法（
UpdatePriority和
IItemsService.cs）
public interface IItemsService
{
List<Item> GetAllItems();
void InsertItem(Item item);
//add method InsertPriority
void InsertPriority(Priority item);
//add method UpdatePriority
void UpdatePriority(Priority item);
void UpdateItem(Item item);
void DeleteItem(int id);
bool ExistsItem(string name, string description, string priorityName);
}
4.为类
InsertPriority实现上述接口
UpdatePriority和
ItemsService.cs
public class ItemsService : IItemsService
{
private SQLiteConnection _connection;
public ItemsService()
{
SetupDb();
}
private void SetupDb()
{
if(_connection == null)
{
string dbPath = Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.LocalApplicationData), "ItemsDb.db3");
_connection = new SQLiteConnection(dbPath);
_connection.CreateTable<Item>();
_connection.CreateTable<Priority>();
}
}
public void InsertItem(Item item)
{
_connection.Insert(item);
}
public void UpdateItem(Item item)
{
// _connection.Update(item);
// replace above code with the following code
_connection.UpdateWithChildren(item);
}
public void DeleteItem(int id)
{
_connection.Delete(id);
}
public List<Item> GetAllItems()
{
//var items = _connection.Table<Item>().ToList();
// replace above code with the following code
var items = _connection.GetAllWithChildren<Item>();
return items;
}
public bool ExistsItem(string name, string description, string priorityName)
{
var existsItem = _connection.Table<Item>().FirstOrDefault(it => it.Name == name && it.Description == description
&& it.ItemPriority.PriorityName == priorityName);
return existsItem != null;
}
public void InsertPriority(Priority item)
{
_connection.Insert(item);
}
public void UpdatePriority(Priority item)
{
_connection.Update(item);
}
}
5.修改命令
ExecuteSaveItemsCommandAddItemViewmodel.cspublic class AddItemViewmodel : BaseViewmodel
{
//For the sake of simplicity, omit the other codes
#region methods
//Function SaveItems
private async void ExecuteSaveItemsCommand()
{
try
{
Item itemSaved = new Item()
{
Name = NameSave,
Description = DescriptionSave,
//ItemPriority = new Priority
//{
// PriorityName = PrioritySave,
// PriorityColor = "#ccc"
//}
};
// _itemsService.InsertItem(itemSaved);
Priority ItemPriority = new Priority
{
PriorityName = PrioritySave,
PriorityColor = "#ccc"
};
_itemsService.InsertItem(itemSaved);
_itemsService.InsertPriority(ItemPriority);
itemSaved.ItemPriority = ItemPriority;
_itemsService.UpdateItem(itemSaved);
_itemsService.UpdatePriority(ItemPriority);
ExecuteBackProductPageCommand();
}
catch (Exception ex)
{
await Shell.Current.DisplayAlert("Error", ex.Message, "OK");
}
}
private async void ExecuteBackProductPageCommand()
{
await Navigation.PopAsync();
}
#endregion
}