如何通过WPF组合框选择来填充数据库中的列表集合

Question

I have Many-to-Many Tables and want to display some of the fields in WPF controls.

How can I fill the list collection List<Course> courses = new List<Course>() whenever I select the InstructorIDs in the combobox ? I want to display only the CourseID and Title from the List in the ListView control

Here're my codes:

public partial class MainWindow : Window
{
    SchoolEntities db = new SchoolEntities();
    public MainWindow()
    {
        InitializeComponent();
        var instructors = db.Instructors.Where(f => f.HireDate == 2011).ToList();

        this.comboBox1.ItemsSource = instructors;
        this.comboBox1.DisplayMemberPath = "LastName";
        this.comboBox1.SelectedValuePath = "InstructorID";           
    }
    List<Course> courses = new List<Course>();

    private void comboBox1_SelectionChanged(object sender, SelectionChangedEventArgs e)
    {
        int S = (int)this.comboBox1.SelectedValue;
        var InstrSelection = db.Instructors.Include("CourseInstructors.Course").SingleOrDefault(f => f.InstructorID == S);


        foreach (var C in InstrSelection.CourseInstructors)
        {
            courses.Add(C.Course);
        }

        this.listView1.DataContext = null;
        this.listView1.DataContext = courses;
    }
}   

And the window xaml

<Window x:Class="School.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="MainWindow" Height="773" Width="677">

<Grid>        
    <ComboBox Height="23" HorizontalAlignment="Left" Name="comboBox1"  SelectionChanged="comboBox1_SelectionChanged"></ComboBox>
    <ListView  HorizontalAlignment="Left" Name="listView1">
        <ListView.View>
         <GridView>
            <GridViewColumn Width="140" Header= "CourseID" />
            <GridViewColumn Width="140" Header= "Title" />                
         </GridView>
        </ListView.View>
    </ListView>
</Grid>

Answer 1

I would make my parent data model contain a collection of the child data model, and bind the child ComboBox to the selected item in the parent ComboBox

For example, your Instructor model would contain

int InstructorId
string FirstName
string LastName
DateTime HireDate
List Courses

and you would bind your ComboBox of instructors to a List<Instructor> . Then you could bind your courses ComboBox to the instructor ComboBox's SelectedItem.Courses

<ComboBox x:Name="InstructorList" ... />

<ComboBox x:Name="CourseList"
          ItemsSource="{Binding ElementName=InstructorList, 
                                Path=SelectedItem.Courses}"
          DisplayMemberPath="Title"
          SelectedValuePath="CourseId" />

Answer 2

I am not sure I understand what you are asking. Are you just wondering why your current code is not displaying any courses in the ListView? If so then your problem is that you are setting the DataContext of the ListView when you should be setting the ItemsSource. You should likely also be clearing the list of courses before adding new ones:

private void comboBox1_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
    courses.Clear();
    ...

    this.listView1.ItemsSource = null; // ItemsSource instead of DataContext
    this.listView1.ItemsSource = courses;
}

Edit

You will also have to add the DisplayMemberBindings to your GridViewColumns:

<GridViewColumn 
    Width="140" 
    Header="CourseID" 
    DisplayMemberBinding="{Binding CourseID}" /> <!-- Here -->
<GridViewColumn 
    Width="140" 
    Header="Title" 
    DisplayMemberBinding="{Binding Title}" /> <!-- And Here -->