在WPF中，如何将Checkbox的IsChecked绑定到List <>。Contains？

Question

Sorry if the wording of my question is not great or if this has been answered somewhere, I've searched, but I don't really know how well to explain what I am trying to do.

Here's a simple testbed I've partially set up to help explain:

MainWindow.xaml:

<Window x:Class="wpfExample.MainWindow"
    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:local="clr-namespace:wpfExample"
    mc:Ignorable="d"
    Title="MainWindow" Height="350" Width="525">
<Grid>
    <Grid.ColumnDefinitions>
        <ColumnDefinition Width="*"/>
        <ColumnDefinition Width="*"/>
    </Grid.ColumnDefinitions>

    <ListView Grid.Column="0" ItemsSource="{Binding People}" DisplayMemberPath="Name"/>

    <ListBox Grid.Column="1" ItemsSource="{Binding Interests}" Margin="0,4,4,4">
        <ListBox.ItemTemplate>
            <DataTemplate>
                <CheckBox Content="{Binding Name}"/>
            </DataTemplate>
        </ListBox.ItemTemplate>
    </ListBox>

</Grid>

MainWindow.xaml.cs:

using System;
using System.Collections.ObjectModel;
using System.Windows;

namespace wpfExample
{
    public class Person
    {
        public string Name { get; set; }
        public ObservableCollection<Guid> Interests { get; set; }
    }

    public class Interest
    {
        public Guid Id { get; set; }
        public string Name { get; set; }
    }

    public class Data
    {
        public ObservableCollection<Person> People { get; set; }
        public ObservableCollection<Interest> Interests { get; set; }
    }

    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            DataContext = new Data
            {
                People = new ObservableCollection<Person>
                {
                    new Person {Name="Fred", Interests=new ObservableCollection<Guid>() },
                    new Person {Name="Jane", Interests=new ObservableCollection<Guid>() },
                    new Person {Name="Zach", Interests=new ObservableCollection<Guid>() }
                },
                Interests = new ObservableCollection<Interest>
                {
                    new Interest {Name="Gardening", Id=Guid.NewGuid() },
                    new Interest {Name="Writing", Id=Guid.NewGuid() },
                    new Interest {Name="Avoiding Tax", Id=Guid.NewGuid() }
                }
            };

            InitializeComponent();
        }
    }
}

So I have a DataContext that contains two lists. One contains Interests, which have a name and an ID. The other contains People which have a name and a list of IDs of interests.

When a Person is selected in the UI, I want to be able to add and remove IDs of interests to their respective list, hence the ListView in column 1 is bound to the list of Interests, but how do I correctly bind up the IsChecked property of the checkboxes in the list?

In my full project, I've been able to successfully read properties of the selected Person's interest list by using a MultiBinding for IsChecked with a MultiValueConverter to pass both the Id of the Interest and the List of Interests of the Person through together (since you can't use binding with the parameter for a 'normal' value converter). I feel that this solution is a little bit of an abuse of the converter, but I'm happy to stick with it if necessary.

How do I implement a system that will allow me to add and remove Interest Guids to a Person's list of interests when the checkbox is toggled? Is there a cleaner way of doing this? I don't want to change the model if it can be avoided.

Answer 1

I wouldn't say your MultiConverter solution is an abuse at all; you are doing exactly what converters should (take a set of data and converting to the target type, then going back).

That being said; converters are a bit of a mess due to their generality (use of object ), and that goes double for Multi Converters, so if you want a different solution I would recommend creating a view model wrapper for Interest ; say Selectable<T> :

public class Selectable<T>
{
     public T Data {get; set;}
     public bool Selected {get; set;}
}

Then update your property

public ObservableCollection<Selectable<Interest>> Interests { get; set; }

And bind IsChecked directly to Selected

Then whenever the selected Person is changed you can update the Selected property appropriately; store the previous value to the other Person , etc. It somewhat depends on when the user action needs to be reflected in the model.

All that being said, both approaches will be perfectly valid, it just comes down to what you are most comfortable with.