可观察集合的 C# wpf listview 绑定问题

Question

我按照本教程创建日历/时间表：https://www.codeproject.com/Articles/35490/Creating-the-Microsoft-Outlook-Appointment-View-in Listview 包含 5 个项目，来源

<ListView.Items>
    <local:Termin Start="10/28/2021 6:00 AM" Finish="10/28/2021 4:00 PM" Subject="Meet with John" Location="Southwest Meeting Room" Organizer="Jim Smith" />
    <local:Termin Start="10/29/2021 6:00 AM" Finish="10/29/2021 4:00 PM" Subject="Meet with Rick" Location="Southwest Meeting Room" Organizer="Jim Smith" />
    <local:Termin Start="10/30/2021 6:00 AM" Finish="10/30/2021 6:00 PM" Subject="Meet with Dave" Location="Southwest Meeting Room" Organizer="Jim Smith" />
    <local:Termin Start="10/31/2021 6:00 AM" Finish="10/31/2021 6:00 PM" Subject="Meet with Larry" Location="Southwest Meeting Room" Organizer="Jim Smith" />
    <local:Termin Start="10/31/2021 6:00 AM" Finish="10/31/2021 6:00 PM" Subject="Meet with Jim" Location="Southwest Meeting Room" Organizer="Jim Smith" />
</ListView.Items>

现在，当我尝试用可观察的集合替换硬编码的项目时

<ListView  ItemsSource="{Binding Termine}">
    <ListView.View>
        <controls:CalendarView ItemBeginBinding="{Binding Start}" ItemEndBinding="{Binding Finish}">

public class KalenderVM : BewohnerVM
{
    public KalenderVM()
    {
        DateTime dateValue1;
        DateTime dateValue2;
        DateTime.TryParse("25.10.2021 6:00", out dateValue1);
        DateTime.TryParse("25.10.2021 16:00", out dateValue2);
        Termine.Add(new Termin(dateValue1, dateValue2, "Jan", "Anker"));
        DateTime.TryParse("26.10.2021 6:00", out dateValue1);
        DateTime.TryParse("26.10.2021 16:00", out dateValue2);
        Termine.Add(new Termin(dateValue1, dateValue2, "Jan", "Anker"));
        DateTime.TryParse("27.10.2021 6:00", out dateValue1);
        DateTime.TryParse("27.10.2021 18:00", out dateValue2);
        Termine.Add(new Termin(dateValue1, dateValue2, "Jan", "Frei"));
    }

    private ObservableCollection<Termin> _termine = new ObservableCollection<Termin>();
    public ObservableCollection<Termin> Termine
    {
        get { return _termine; }
        set { _termine = value; }
    }
...
}

public partial class Kalender : UserControl
{
    public Kalender()
    {
        InitializeComponent();
    }
}

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace IWHRManagment.Models
{
    public class Termin
    {
        public Termin(DateTime start, DateTime finish, string orga, string sub)
        {
            Start = start;
            Finish = finish;
            Organizer = orga;
            Subject = sub;
            Location = "Home";
        }
        public Termin() { }
        public DateTime Start { get; set; }
        public DateTime Finish { get; set; }
        public bool Recurring { get; set; }
        public object Interval { get; set; }
        public string Organizer { get; set; }
        public string Subject { get; set; }
        public string Location { get; set; }
    }
}

ListView 包含 2 个项目（我为测试目的创建了 2 个），但没有显示任何项目，因为“在 ViewModel 中找不到”“开始”和“完成”......我尝试了一个静态资源，几个相对源但我仍然很难以正确的方式做到这一点。

有人可以帮助我并告诉我正确的方法吗？

Answer 1

这是 MVVM 中的一个简单 LV。您的命名有点混乱：请保留xxxViewModel 等；不要走捷径。

我正在粘贴简单 ListView 的简单 MVVM 示例，它由 ItemViewModel 类包装并由 XAML 绑定。

如果您没有意识到危险，请不要从用户控件开始您的工作。它们需要不同的处理和绑定。

我有意用 ViewModel 包装了一个基本模型（数据库条目）对象。将来，更新属性会更容易，您不会为“如何将 inotifychanged 添加到实体框架”而烦恼。更多样板，但我希望它会起作用。

如果你不明白一些事情，那就试着去。有黑客。如果您像我在这里所做的那样从“xaml”初始化视图模型，那么不要声明datacontext = new AnyViewModel()，因为您将失败。

总的来说，我认为 MVVM 是一个糟糕的选择。绑定是 WinForms/QT 中一直缺少的东西，现在它们就在这里。但是，既然你有了绑定，你就开始在通信中挣扎和挣扎，然后你添加和添加类、数据类、服务和 bla bla。越有人进入模板和泛型，代码就越混乱。

VIEWMODEL（为简单起见集成）：

using Pjoter2000.View;
using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.ComponentModel;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Pjoter2000.ViewModel
{
    public class DatabaseEntry // EntityFramework as an example
    {
        public int ID { get; set; }
        public string DataName { get; set; }
    }

    // MVVM wrapper for single item, Inotifypropertychanged should be a class that simplifiesr wrapping
    public class SomeItemViewModel : INotifyPropertyChanged
    {
        public event PropertyChangedEventHandler? PropertyChanged;

        private DatabaseEntry _item;

        public string Name
        {
            get => _item.DataName;
            set
            {
                _item.DataName = value;
                PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(Name)));
            }
        }

        SomeItemViewModel() { } //wtf? :)

        public SomeItemViewModel(DatabaseEntry entry)
        {
            _item = entry;
        }
    }

    public class PoligonViewModel
    {
        ObservableCollection<SomeItemViewModel> _records;
        public ObservableCollection<SomeItemViewModel> Records
        {
            get => _records;
            set
            {
                _records = value;
            }
        }

        public PoligonViewModel()
        {
            // INIT Records
            Records = new ObservableCollection<SomeItemViewModel>();

            // Fetching data from model (DB), abstract
            for (int i = 0; i < 10; i++)
            {
                var item = new DatabaseEntry()
                {
                    DataName = "Name " + i.ToString()
                };

                // Wrapping database model data into itemviewmodel (some say it's more flexible and might be ok in future)
                Records.Add(new SomeItemViewModel(item));
            }
        }
    }
}

查看：

using System.Windows;

namespace Pjoter2000.View
{
    public partial class Poligon : Window
    {      
        public Poligon()
        {
            InitializeComponent(); // Current data context is poligonviewmodel, because it's set from xaml already           
        }
    }
}

XAML

<Window x:Class="Pjoter2000.View.Poligon"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:viewmodel="clr-namespace:Pjoter2000.ViewModel"
        mc:Ignorable="d"
        Title="Poligon" Height="400" Width="514">

    <Window.DataContext>
        <!-- THIS PART CREATES VIEW MODEL CLASS, DON'T CREATE IT IN CONSTRUCTOR -->
        <viewmodel:PoligonViewModel/>
    </Window.DataContext>
    <Grid>
        <ListView ItemsSource="{Binding Records}">
            <!-- This is the main view of the list, so I declare the view here -->
            <ListView.ItemTemplate>
                <DataTemplate>
                    <TextBlock Text="{Binding Name}"/>
                </DataTemplate>
            </ListView.ItemTemplate>
        </ListView>
    </Grid>
</Window>