Question

我有以下课程：
的档案

public class Item : INotifyPropertyChanged, IDataErrorInfo
{
    private int? id;
    public int? ID
    {
        get
        { return id; }
        set
        { id = value; }
    }

    private string name;
    public string Name
    {
        get
        { return name; }
        set
        {
            if (value != name)
            {
                ClearError("Name");
                if (string.IsNullOrEmpty(value) || value.Trim() == "")
                    SetError("Name", "Required Value");
                name = value;
            }
        }
    }
    private List<MedicineComposition> medicineCompositions;
    public List<MedicineComposition> MedicineCompositions
    {
        set { medicineCompositions = value; }
        get { return medicineCompositions; }
    }
}

MedicineComposition

public class MedicineComposition : INotifyPropertyChanged, IDataErrorInfo
{
    private int? id;
    public int? ID
    {
        get
        { return id; }
        set
        { id = value; }
    }

    private Item item;
    public Item Item
    {
        get
        { return item; }
        set
        {
            if (item != value)
            {
                ClearError("Item");
                if (value == null)
                    SetError("Item", "Required Value");
                item = value;
            }
        }
    }
    private Component component;
    public Component Component
    {
        get
        { return component; }
        set
        {
            if (component != value)
            {
                ClearError("Component");
                if (value == null)
                    SetError("Component", "Required Value");
                component = value;
            }
        }
    }
}

仅有id和Name的

组件以及从数据库中获取数据并生成我的对象列表的以下函数： Item类

中的 GetItems

public static List<Item> GetAllItems
{
get
{
    List<Item> MyItems = new List<Item>();
    SqlConnection con = new SqlConnection(BaseDataBase.ConnectionString);
    SqlCommand com = new SqlCommand("sp_Get_All_Item", con);
    com.CommandType = System.Data.CommandType.StoredProcedure;
    try
    {
        con.Open();
        SqlDataReader rd = com.ExecuteReader();
        while (rd.Read())
        {
            Item i = new Item();
            if (!(rd["ID"] is DBNull))
                i.ID = System.Int32.Parse(rd["ID"].ToString());
            i.Name = rd["Name"].ToString();
            i.MedicineCompositions = MedicineComposition.GetAllByItem(i);

            MyItems.Add(i);
        }
        rd.Close();
    }
    catch
    {
        MyItems = null;
    }
    finally
    {
        con.Close();
    }
    return MyItems;
}

MedicalCompositions

中的

GetAllByItem

public static List<MedicineComposition> GetAllByItem(Item i)
{
    List<MedicineComposition> MyMedicineCompositions = new List<MedicineComposition>();

    SqlConnection con = new SqlConnection(BaseDataBase.ConnectionString);
    SqlCommand com = new SqlCommand("sp_Get_ByItemID_MedicineComposition", con);
    com.CommandType = System.Data.CommandType.StoredProcedure;
    SqlParameter pr = new SqlParameter("@ID", i.ID);
    com.Parameters.Add(pr);
    try
    {
        con.Open();
        SqlDataReader rd = com.ExecuteReader();
        while (rd.Read())
        {
            MedicineComposition m = new MedicineComposition() { };
            if (!(rd["ID"] is DBNull))
                m.ID = Int32.Parse(rd["ID"].ToString());
            if (!(rd["ComponentID"] is DBNull))
                m.Component = Component.GetByID(Int32.Parse(rd["ComponentID"].ToString()));
            m.Item = i;
            MyMedicineCompositions.Add(m);
        }
        rd.Close();
    }
    catch
    {
        MyMedicineCompositions = null;
    }
    finally
    {
        con.Close();
    }
    return MyMedicineCompositions;
}

喜欢使用mvvm，因为它可以让你处理对象而不是datatable，但是当我使用以前的类结构形状时，我有以下问题：

我在数据库的Item表中至少有1000条记录，所以当我调用GetAllItems时，我的性能会很慢，尤其是当数据库不在本地计算机上时。
我尝试在启用启动画面时加载Items，需要时间但需要中等性能
在Item表格上的每次更新时，我都应该记得GetAllItems这么慢 我的问题是我在创建类时遇到的问题，这是在mvvm

Answer 1

我不认为你的用户需要一目了然地看到所有1000个项目，甚至没有相关的数千个组合和组件。

我这样的情况我会：

过滤数据。询问用户项目名称，类别或其他内容。
延迟加载。首先只加载（过滤的）项目。当用户选择项目切换到＆＃34;项目详细信息＆＃34;查看并加载相关数据（组合和组件）。

Answer 2

您可以在此处改进一些事项，例如：

鉴于我们在谈论MedicalComposition，拥有nullable唯一标识符
如果您有多个仅包含id和name的课程，则可以使用KeyValuePair<>或Tuple<>代替
实现一个基类，比如实现ModelBase

INotifyPropertyChanged

为数据库相关操作实施repository pattern，如果可能，实施缓存/页面结果
如果尚未完成，请将数据和/或时间密集型操作移至单独的线程
有一点令人困惑的是，Item你有MedicineComposition的IEnumerable，但MedicineComposition你也有Item吗？也许你根本不需要它或相关Item.Id就足够了？
您可以向存储库添加一个方法，仅返回自<timestamp>以来已添加/修改/删除的项目，并仅更新Items集合中所需的内容
您可以制作一些属性Lazy<>
利用TAP（基于任务的异步模式）

以下是您的问题的“一气呵成”，无法阻止UI线程。它远非完整但仍然存在。存储库中的Thread.Sleep正在模仿您的数据库查询延迟

imgur

查看\ MainWindow.xaml

Codebehind仅包含InitializeComponents。

<Window x:Class="WpfApplication1.View.MainWindow" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:viewModel="clr-namespace:WpfApplication1.ViewModel" Title="MainWindow" Height="300" Width="250"> <Window.DataContext> <viewModel:MainViewModel /> </Window.DataContext>  <Grid x:Name="ContentPanel" Margin="12,0,12,0"> <Grid.ColumnDefinitions> <ColumnDefinition Width="*" /> </Grid.ColumnDefinitions> <Grid.RowDefinitions> <RowDefinition Height="Auto" /> <RowDefinition Height="*" /> </Grid.RowDefinitions>  <Label Grid.Row="0" HorizontalAlignment="Stretch" VerticalAlignment="Top" Background="Bisque" Margin="0,3,0,3" Content="{Binding Status}" />  <StackPanel Grid.Row="1"> <Label Content="Items" />  <ComboBox HorizontalAlignment="Stretch" MaxDropDownHeight="120" VerticalAlignment="Top" Width="Auto" Margin="0,0,0,5" ItemsSource="{Binding Items}" SelectedItem="{Binding SelectedItem}" DisplayMemberPath="Name" />  <ItemsControl ItemsSource="{Binding SelectedItem.MedicineCompositions}"> <ItemsControl.ItemTemplate> <DataTemplate> <StackPanel> <TextBlock Text="{Binding Name}" />  <ItemsControl ItemsSource="{Binding Components}"> <ItemsControl.ItemTemplate> <DataTemplate> <TextBlock> <Run Text=" * " /> <Run Text="{Binding Name}" /> </TextBlock> </DataTemplate> </ItemsControl.ItemTemplate> </ItemsControl> </StackPanel> </DataTemplate> </ItemsControl.ItemTemplate> </ItemsControl> </StackPanel> </Grid> </Window>

<强>视图模型\ MainViewModel

public class MainViewModel : ViewModelBase { private string _status; private Item _selectedItem; private ObservableCollection<Item> _items; public MainViewModel() :this(new ItemRepository(), new MedicineCompositionRepository()) {} public MainViewModel(IRepository<Item> itemRepository, IRepository<MedicineComposition> medicineCompositionRepository) { ItemRepository = itemRepository; MedicineCompositionRepository = medicineCompositionRepository; Task.Run(() => LoadItemsData()); } public IRepository<Item> ItemRepository { get; set; } public IRepository<MedicineComposition> MedicineCompositionRepository { get; set; } public Item SelectedItem { get { return _selectedItem; } set { _selectedItem = value; OnPropertyChanged(); Task.Run(() => LoadMedicineCompositionsData(_selectedItem)); } } public ObservableCollection<Item> Items { get { return _items; } set { _items = value; OnPropertyChanged(); } } public string Status { get { return _status; } set { _status = value; OnPropertyChanged(); } } private async Task LoadItemsData() { Status = "Loading items..."; var result = await ItemRepository.GetAll(); Items = new ObservableCollection<Item>(result); Status = "Idle"; } private async Task LoadMedicineCompositionsData(Item item) { if (item.MedicineCompositions != null) return; Status = string.Format("Loading compositions for {0}...", item.Name); var result = await MedicineCompositionRepository.GetById(item.Id); SelectedItem.MedicineCompositions = result; Status = "Idle"; } }

<强>模型

public class Component : ModelBase {} public class MedicineComposition : ModelBase { private IEnumerable<Component> _component; public IEnumerable<Component> Components { get { return _component; } set { _component = value; OnPropertyChanged(); } } } public class Item : ModelBase { private IEnumerable<MedicineComposition> _medicineCompositions; public IEnumerable<MedicineComposition> MedicineCompositions { get { return _medicineCompositions; } set { _medicineCompositions = value; OnPropertyChanged(); } } } public abstract class ModelBase : INotifyPropertyChanged { public event PropertyChangedEventHandler PropertyChanged; private int _id; private string _name; public int Id { get { return _id; } set { _id = value; OnPropertyChanged(); } } public string Name { get { return _name; } set { _name = value; OnPropertyChanged(); } } [NotifyPropertyChangedInvocator] protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null) { var handler = PropertyChanged; if (handler != null) handler(this, new PropertyChangedEventArgs(propertyName)); } }

<强>存储库

public interface IRepository<T> where T : class { Task<IEnumerable<T>> GetAll(); Task<IEnumerable<T>> GetById(int id); } public class ItemRepository : IRepository<Item> { private readonly IList<Item> _mockItems; public ItemRepository() { _mockItems = new List<Item>(); for (int i = 0; i < 100; i++) _mockItems.Add(new Item { Id = i, Name = string.Format("Item #{0}", i), MedicineCompositions = null }); } public Task<IEnumerable<Item>> GetAll() { Thread.Sleep(1500); return Task.FromResult((IEnumerable<Item>) _mockItems); } public Task<IEnumerable<Item>> GetById(int id) { throw new NotImplementedException(); } } public class MedicineCompositionRepository : IRepository<MedicineComposition> { private readonly Random _random; public MedicineCompositionRepository() { _random = new Random(); } public Task<IEnumerable<MedicineComposition>> GetAll() { throw new NotImplementedException(); } public Task<IEnumerable<MedicineComposition>> GetById(int id) { // since we are mocking, id is actually ignored var compositions = new List<MedicineComposition>(); int compositionsCount = _random.Next(1, 3); for (int i = 0; i <= compositionsCount; i++) { var components = new List<Component>(); int componentsCount = _random.Next(1, 3); for (int j = 0; j <= componentsCount; j++) components.Add(new Component {Id = j, Name = string.Format("Component #1{0}", j)}); compositions.Add(new MedicineComposition { Id = i, Name = string.Format("MedicalComposition #{0}", i), Components = components }); } Thread.Sleep(500); return Task.FromResult((IEnumerable<MedicineComposition>) compositions); } }

Answer 3

将数据集分配到ObservableCollection属性的构造函数中。否则，您的视图将通过PropertyChanged通知更新ObservableCollection执行添加操作的每个项目。

试试这个：

var items = services.LoadItems();
myObservableCollection = new ObservableCollection<somedatatype>(items);

这种类型的分配将通知您的视图一次，而不是您的实现执行1000次的当前方式。

Answer 4

不是返回List，而是返回IEnumerable并在需要时生成结果。当你没有阅读所有结果时，显然它只会提高性能，这在大多数情况下都是如此。要做到这一点，你必须删除捕获，因为你不能有收益和集合。捕获可以绕过con.Open和ExecuteReader，在catch中你可以产生break：

        public static IEnumerable<MedicineComposition> GetAllByItem(Item i)
    {
        SqlConnection con = new SqlConnection(BaseDataBase.ConnectionString);
        SqlCommand com = new SqlCommand("sp_Get_ByItemID_MedicineComposition", con);
        com.CommandType = System.Data.CommandType.StoredProcedure;
        SqlParameter pr = new SqlParameter("@ID", i.ID);
        com.Parameters.Add(pr);
        try
        {
            SqlDataReader rd;
            try
            {
                con.Open();
                rd = com.ExecuteReader();
            }
            catch { yield break;}
            while (rd.Read())
            {
                MedicineComposition m = new MedicineComposition() { };
                if (!(rd["ID"] is DBNull))
                    m.ID = Int32.Parse(rd["ID"].ToString());
                if (!(rd["ComponentID"] is DBNull))
                    m.Component = Component.GetByID(Int32.Parse(rd["ComponentID"].ToString()));
                m.Item = i;
                yield return m;
            }
            rd.Close();
        }
        finally
        {
            con.Close();
        }
    }

现在，如果发生异常，则不再返回null，但可以返回少量项甚至空枚举。我宁愿把捕获物移动到这个吸气剂的来电者身上。如果由于某种原因需要返回项目的计数，请调用GetAllByItem（item）.ToArray（）。这将枚举所有项目并为您获取长度。绝对不要调用枚举两次来获取长度，然后枚举项目：

var length = GetAllByItem(item).Count();// this will get all the items from the db
foreach(var i in GetAllByItem(item)) // this will get all the items from the db again

而是这样做：

var list = GetAllByItem(item); // this will get all the items and now you have the length and the items.

显然，如果由于某种原因需要长度，那么改为IEnumerable没有意义，只是为了更好的抽象。

其他改进可能是，只创建一次连接，而不是每次调用getter。只有这样才有可能，如果你知道它不会造成任何伤害。

在mvvm问题中创建类结构

4 个答案: