如何刷新组合框在WPF

Question

在另一个组合框中切换选择后，我在我的窗口组合框：

<ComboBox x:Name="cbDeps" 
     ItemsSource="{Binding}" DisplayMemberPath="sName" SelectedValuePath="nDepartmentIdn" 
     Grid.Row="0" Margin="0,52,215,0" Grid.Column="1" SelectionChanged="cbUsers_SelectionChanged"/> 
<ComboBox x:Name="cbUsersDep" 
     ItemsSource="{Binding}" DisplayMemberPath="sUserName" SelectedValuePath="nUserIdn" 
     Grid.Row="0" Margin="218,52,0,0" Grid.Column="1"/> 

，我希望当我选择的第一个组合框的值，第二个由项目不仅填补的选定项目。我得到使用这种方法这些项目：

public ObservableCollection<DataModel.TB_USER> listUsersParDeps(int numDep) 
{ 
    var userDeps = (from DataModel.TB_USER ud in SessionContext.DBContext.TB_USER 
        where ud.nDepartmentIdn==numDep 
        select ud); 

    foreach (var userDep in userDeps) 
    { 
     userM.ListUserDep.Add(userDep); 
    } 

    return userM.ListUserDep; 
} 

，我把它们放在DataContext的：

cbUsersDep.DataContext = userVM.listUsersParDeps(int.Parse(cbDeps.SelectedValue.ToString())); 

Answer 1

除了手动设置每个组合框的数据上下文，你应该设置的数据上下文外部组件（通常是窗口，或其他一些“大”组件）到您的视图模型。然后，为两个组合框公开两个列表（理想情况下为ObservableCollection），并将组合框的ItemSource属性绑定到这些列表。然后，当你的第一个组合框的变化SelectedItem，你更新第二列表：

<StackPanel> 
    <ComboBox ItemsSource="{Binding Departments}" SelectedItem="{Binding SelectedDepartment}" /> 
    <ComboBox ItemsSource="{Binding Users}" /> 
</StackPanel> 

public class MainViewModel : INotifyPropertyChanged 
{ 
    // this holds the data 
    private Dictionary<string, List<string>> departmentUsers = new Dictionary<string,List<string>>(); 

    private List<string> departments; 
    public List<string> Departments 
    { 
     get { return departments; } 
     set 
     { 
      if (value != departments) 
      { 
       departments = value; 
       OnNotifyPropertyChanged("Departments"); 
      } 
     } 
    } 

    private string selectedDepartment; 
    public string SelectedDepartment 
    { 
     get { return selectedDepartment; } 
     set 
     { 
      if (value != selectedDepartment) 
      { 
       selectedDepartment = value; 
       OnNotifyPropertyChanged("SelectedDepartment"); 

       // update users list 
       Users = departmentUsers[selectedDepartment]; 
      } 
     } 
    } 

    private List<string> users; 
    public List<string> Users 
    { 
     get { return users; } 
     set 
     { 
      if (value != users) 
      { 
       users = value; 
       OnNotifyPropertyChanged("Users"); 
      } 
     } 
    } 

    public MainViewModel() 
    { 
     // sample data 
     departmentUsers = new Dictionary<string, List<string>>(); 
     departmentUsers.Add("Department 1", new List<string>() { "1.1", "1.2", "1.3" }); 
     departmentUsers.Add("Department 2", new List<string>() { "2.1", "2.2", "2.3", "2.4", "2.5" }); 
     departmentUsers.Add("Department 3", new List<string>() { "3.1", "3.2" }); 
     departmentUsers.Add("Department 4", new List<string>() { "4.1", "4.2", "4.3" }); 

     // initial state 
     Departments = new List<string>(departmentUsers.Keys); 
     SelectedDepartment = Departments[0]; 
    } 

    // simple INotifyPropertyChanged implementation 
    public event PropertyChangedEventHandler PropertyChanged; 
    private void OnNotifyPropertyChanged(string propertyName) 
    { 
     var handler = PropertyChanged; 
     if (handler != null) 
      handler(this, new PropertyChangedEventArgs(propertyName)); 
    } 
}