WPF ComboBox selectedValue绑定失败 [英] WPF ComboBox selectedValue binding fails

问题描述

我有一个 ObservableCollection< Employee> ... ， ObservableCollection< Departments> 和 Enployee 定义为

  public class Employee 
 {
 [ Key] 
 public int Id {get;组; } 
 public string FirstName {get;组; } 
 public string LastName {get;组; } 
 public DateTime Birthday {get;组; } 
 public int DepId {get;组; } 
 
 [ForeignKey（DepId）] 
 public virtual Departments Departments {get;组; } 
 
} 
  

和部门定义为

  public class Departments 
 {
 [Key] 
 public int Id {get;组; } 
 public string Name {get;组; } 
 public virtual IEnumerable< Employee>员工{get;组; } 
} 
  

在数据库中我有

看起来最后ComboBox无法找到属于相应Employee的DepId！

 < DataGrid Name =DataGrid1Grid.Row =3Margin =10,0， 10,10
 RenderOptions.ClearTypeHint =Enabled
 TextOptions.TextFormattingMode =Display
 CanUserAddRows =False
 CanUserDeleteRows =False
 SelectionUnit = FullRow
 AutoGenerateColumns =false
 SelectedItem ={Binding CurrentSelectedEmployee，Mode = TwoWay}
 ItemsSource ={Binding Employees，Mode = TwoWay}> 
< DataGrid.Columns> 
<！ - 第1列：员工ID  - > 
< DataGridTextColumn Header =Emplyee IdBinding ={Binding Id}/> 
 
<！ - 第2列：名字 - > 
< DataGridTextColumn Header =First NameBinding ={Binding FirstName}/> 
 
<！ - 第3列：姓氏 - > 
< DataGridTextColumn Header =Last NameBinding ={Binding LastName}/> 
 
<！ - 第4栏：出生日 - > 
< DataGridTemplateColumn Header =Birth Day> 
< DataGridTemplateColumn.CellTemplate> 
< DataTemplate> 
< DatePicker SelectedDate ={Binding Birthday}BorderThickness =0/> 
< / DataTemplate> 
< /DataGridTemplateColumn.CellTemplate> 
< / DataGridTemplateColumn> 
 
<！ - 第5栏：部门ID  - > 
< DataGridTemplateColumn Header =Department> 
< DataGridTemplateColumn.CellTemplate> 
< DataTemplate> 
< ComboBox ItemsSource ={Binding Departments}
 DisplayMemberPath =NameSelectedValuePath =IdSelectedValue ={Binding DepId}/> 
< / DataTemplate> 
< /DataGridTemplateColumn.CellTemplate> 
< / DataGridTemplateColumn> 
 
< /DataGrid.Columns> 
< / DataGrid> 
  

看起来最后ComboBox找不到属于相应Employee的DepId！ ？

UPDATE：My viewModel

  public class MainViewModel：ViewModelBase 
 {
 private readonly ManagerDbContext _context = new ManagerDbContext 
 public MainViewModel（）
 {
 
} 
 private IEnumerable< Departments> _departments; 
 public ObservableCollection< Departments> Departments 
 {
 get 
 {
 return 
 new ObservableCollection< Departments>（_ context.Departments）; 
} 
 set 
 {
 _departments = value; 
 RaisePropertyChanged（Departments）; 
} 
} 
 
 private IEnumerable< Employee> _雇员; 
 
 public IEnumerable< Employee> Employees 
 {
 get 
 {
 return 
 new ObservableCollection< Employee>（_ context.Employees.Include（e => e.Department））; 
} 
 set 
 {
 _employee = value; 
 RaisePropertyChanged（Employees）; 
} 
} 
 private Employee _currentSelectedEmployee; 
 public Employee CurrentSelectedEmployee 
 {
 get 
 {
 return _currentSelectedEmployee; 
} 
 set 
 {
 _currentSelectedEmployee = value; 
 RaisePropertyChanged（CurrentSelectedEmployee）; 
} 
} 
 
} 
  

方案

现在我看到了问题。当您使用ItemsSource时，ComboBox的每个项目都获得绑定到Department实体，而不是Employee。 Department实体是否具有属性DepId？可能不是，这是问题。如果你需要引用Employee，你需要这样做。

  {Binding RelativeSource = {RelativeSource Mode = FindAncestor，AncestorType = { x：Type DataGrid}}，Path = DepId} 
  
 
 
 
 
 
 
 Employee.Departments是什么？您确定它已初始化吗？
 
 
 
这对我有用：
  {
 public partial class MainWindow：Window 
 {
 public ObservableCollection< Employee>员工{get;组; } 
 
 public MainWindow（）
 {
 InitializeComponent（）; 
 Department dept1 = new Department（）{Id = 1，Name =aaa}; 
 Department dept2 = new Department（）{Id = 2，Name =bbb}; 
 Department dept3 = new Department（）{Id = 3，Name =ccc}; 
 
 ObservableCollection< Department> depts = new ObservableCollection< Department>（）; 
 depts.Add（dept1）; 
 depts.Add（dept2）; 
 depts.Add（dept3）; 
 
 this.Employees = new ObservableCollection< Employee>（）; 
 this.Employees.Add（new Employee（）{Id = 1，Birthday = DateTime.Now，FirstName =aaa，LastName =aaaa，DepId = 1，Departments = depts}）; 
 this.Employees.Add（new Employee（）{Id = 2，Birthday = DateTime.Now，FirstName =aaa，LastName =bbbb，DepId = 2，Departments = depts} 
 this.Employees.Add（new Employee（）{Id = 3，Birthday = DateTime.Now，FirstName =aaa，LastName =cccc，DepId = 3，Departments = depts} 
 this.Employees.Add（new Employee（）{Id = 4，Birthday = DateTime.Now，FirstName =aaa，LastName =dddd，DepId = 2，Departments = depts} 
 
 this.DataContext = this; 
} 
} 
} 
 
 public class Employee 
 {
 public int Id {get;组; } 
 public string FirstName {get;组; } 
 public string LastName {get;组; } 
 public DateTime Birthday {get;组; } 
 public int DepId {get;组; } 
 
 public virtual ObservableCollection< Department>部门{get;组; } 
} 
 
 public class Department 
 {
 public int Id {get;组; } 
 public string Name {get;组; } 
} 
  
这是XAML：
 < DataGrid Name =DataGrid1Grid.Row =3Margin =10,0,10,10
 RenderOptions.ClearTypeHint =Enabled 
 TextOptions.TextFormattingMode =Display
 CanUserAddRows =False
 CanUserDeleteRows =False
 SelectionUnit =FullRow
 AutoGenerateColumns =false
 SelectedItem ={Binding CurrentSelectedEmployee，Mode = TwoWay}
 ItemsSource ={Binding Employees，Mode = TwoWay}> 
< DataGrid.Columns> 
<！ - 第1列：员工ID  - > 
< DataGridTextColumn Header =Emplyee IdBinding ={Binding Id}/> 
 
<！ - 第2列：名字 - > 
< DataGridTextColumn Header =First NameBinding ={Binding FirstName}/> 
 
<！ - 第3列：姓氏 - > 
< DataGridTextColumn Header =Last NameBinding ={Binding LastName}/> 
 
<！ - 第4栏：出生日 - > 
< DataGridTemplateColumn Header =Birth Day> 
< DataGridTemplateColumn.CellTemplate> 
< DataTemplate> 
< DatePicker SelectedDate ={Binding Birthday}BorderThickness =0/> 
< / DataTemplate> 
< /DataGridTemplateColumn.CellTemplate> 
< / DataGridTemplateColumn> 
 
<！ - 第5栏：部门ID  - > 
< DataGridTemplateColumn Header =Department> 
< DataGridTemplateColumn.CellTemplate> 
< DataTemplate> 
< ComboBox ItemsSource ={Binding Departments}
 DisplayMemberPath =NameSelectedValuePath =IdSelectedValue ={Binding DepId}/> 
< / DataTemplate> 
< /DataGridTemplateColumn.CellTemplate> 
< / DataGridTemplateColumn> 
 
< /DataGrid.Columns> 
< / DataGrid> 
  
  
 
I have an ObservableCollection<Employee>..., an ObservableCollection<Departments> and Enployee is defined as 
public class Employee
{
    [Key]
    public int Id { get; set; }
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public DateTime Birthday { get; set; }
    public int DepId { get; set; }

    [ForeignKey("DepId")]
    public virtual Departments Departments { get; set; } 

}
and Departmentis defined as 
public class Departments
{
    [Key]
    public int Id { get; set; }
    public string Name { get; set; }
    public virtual IEnumerable<Employee> Employees { get; set; } 
}
In the database I have 



It looks like last ComboBox fails to locate the DepId which belongs to the corresponding Employee！！ Any ideas guys?
    <DataGrid  Name="DataGrid1" Grid.Row="3" Margin="10,0,10,10"
               RenderOptions.ClearTypeHint="Enabled"
               TextOptions.TextFormattingMode="Display"
               CanUserAddRows="False"
               CanUserDeleteRows="False"
               SelectionUnit="FullRow" 
               AutoGenerateColumns="false"
               SelectedItem="{Binding CurrentSelectedEmployee, Mode=TwoWay}"
               ItemsSource="{Binding Employees, Mode=TwoWay}">
        <DataGrid.Columns>
            <!--Column 1: Employee Id-->
            <DataGridTextColumn Header="Emplyee Id" Binding="{Binding Id}"/>

            <!--Column 2: First Name-->
            <DataGridTextColumn Header="First Name" Binding="{Binding FirstName}"/>

            <!--Column 3: Last Name-->
            <DataGridTextColumn Header="Last Name" Binding="{Binding LastName}"/>

            <!--Column 4: Birth Day-->
            <DataGridTemplateColumn Header="Birth Day" >
                <DataGridTemplateColumn.CellTemplate>
                    <DataTemplate>
                        <DatePicker SelectedDate="{Binding Birthday}"  BorderThickness="0" />
                    </DataTemplate>
                </DataGridTemplateColumn.CellTemplate>
            </DataGridTemplateColumn>

            <!--Column 5: Department Id-->
            <DataGridTemplateColumn Header="Department" >
                <DataGridTemplateColumn.CellTemplate>
                    <DataTemplate>
                        <ComboBox ItemsSource="{Binding Departments}"
                                  DisplayMemberPath="Name" SelectedValuePath="Id" SelectedValue="{Binding DepId}" />
                    </DataTemplate>
                </DataGridTemplateColumn.CellTemplate>
            </DataGridTemplateColumn>

        </DataGrid.Columns>
    </DataGrid>
It looks like last ComboBox fails to locate the DepId which belongs to the corresponding Employee！！ Any ideas guys?



UPDATE: My viewModel
public class MainViewModel : ViewModelBase
{
    private readonly ManagerDbContext _context = new ManagerDbContext();
    public MainViewModel()
    {

    }
    private IEnumerable<Departments> _departments;
    public ObservableCollection<Departments> Departments
    {
        get
        {
            return
                new ObservableCollection<Departments>(_context.Departments);
        }
        set
        {
            _departments = value;
            RaisePropertyChanged("Departments");
        }
    }

    private IEnumerable<Employee> _employee;

    public IEnumerable<Employee> Employees
    {
        get
        {
            return
                new ObservableCollection<Employee>(_context.Employees.Include(e => e.Department));
        }
        set
        {
            _employee = value;
            RaisePropertyChanged("Employees");
        }
    }
    private Employee _currentSelectedEmployee;
    public Employee CurrentSelectedEmployee
    {
        get
        {
            return _currentSelectedEmployee;
        }
        set
        {
            _currentSelectedEmployee = value;
            RaisePropertyChanged("CurrentSelectedEmployee");
        }
    }

}

解决方案
now I see the problem. When you use the ItemsSource, then each item of ComboBox gets the binding to Department entity, not to Employee. Does Department entity has a property DepId? Probably not, and that's is the problem. If you need to refer to Employee  you need to do this.
{Binding RelativeSource={RelativeSource Mode=FindAncestor, AncestorType={x:Type DataGrid}}, Path=DepId}




Employee.Departments what is this? Are you sure it's initialized?

This is what works for me:
{
    public partial class MainWindow : Window
    {
        public ObservableCollection<Employee> Employees { get; set; }

        public MainWindow()
        {
            InitializeComponent();
            Department dept1 = new Department() { Id = 1, Name = "aaa" };
            Department dept2 = new Department() { Id = 2, Name = "bbb" };
            Department dept3 = new Department() { Id = 3, Name = "ccc" };

            ObservableCollection<Department> depts = new ObservableCollection<Department>();
            depts.Add(dept1);
            depts.Add(dept2);
            depts.Add(dept3);

            this.Employees = new ObservableCollection<Employee>();
            this.Employees.Add(new Employee() { Id = 1, Birthday = DateTime.Now, FirstName = "aaa", LastName = " aaaa", DepId = 1, Departments = depts });
            this.Employees.Add(new Employee() { Id = 2, Birthday = DateTime.Now, FirstName = "aaa", LastName = " bbbb", DepId = 2, Departments = depts });
            this.Employees.Add(new Employee() { Id = 3, Birthday = DateTime.Now, FirstName = "aaa", LastName = " cccc", DepId = 3, Departments = depts });
            this.Employees.Add(new Employee() { Id = 4, Birthday = DateTime.Now, FirstName = "aaa", LastName = " dddd", DepId = 2, Departments = depts });

            this.DataContext = this;
        }
    }
}

public class Employee
{
    public int Id { get; set; }
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public DateTime Birthday { get; set; }
    public int DepId { get; set; }

    public virtual ObservableCollection<Department> Departments { get; set; }
}

public class Department
{
    public int Id { get; set; }
    public string Name { get; set; }
}
and this is XAML:
<DataGrid  Name="DataGrid1" Grid.Row="3" Margin="10,0,10,10"
       RenderOptions.ClearTypeHint="Enabled"
       TextOptions.TextFormattingMode="Display"
       CanUserAddRows="False"
       CanUserDeleteRows="False"
       SelectionUnit="FullRow" 
       AutoGenerateColumns="false"
       SelectedItem="{Binding CurrentSelectedEmployee, Mode=TwoWay}"
       ItemsSource="{Binding Employees, Mode=TwoWay}">
    <DataGrid.Columns>
        <!--Column 1: Employee Id-->
        <DataGridTextColumn Header="Emplyee Id" Binding="{Binding Id}"/>

        <!--Column 2: First Name-->
        <DataGridTextColumn Header="First Name" Binding="{Binding FirstName}"/>

        <!--Column 3: Last Name-->
        <DataGridTextColumn Header="Last Name" Binding="{Binding LastName}"/>

        <!--Column 4: Birth Day-->
        <DataGridTemplateColumn Header="Birth Day" >
            <DataGridTemplateColumn.CellTemplate>
                <DataTemplate>
                    <DatePicker SelectedDate="{Binding Birthday}"  BorderThickness="0" />
                </DataTemplate>
            </DataGridTemplateColumn.CellTemplate>
        </DataGridTemplateColumn>

        <!--Column 5: Department Id-->
        <DataGridTemplateColumn Header="Department" >
            <DataGridTemplateColumn.CellTemplate>
                <DataTemplate>
                    <ComboBox ItemsSource="{Binding Departments}"
                          DisplayMemberPath="Name" SelectedValuePath="Id" SelectedValue="{Binding DepId}" />
                </DataTemplate>
            </DataGridTemplateColumn.CellTemplate>
        </DataGridTemplateColumn>

    </DataGrid.Columns>
</DataGrid>


                        
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