设置SelectedIndex时取消ListBox.SelectedItem绑定

Question

I have some problems with databinding... here is the situation:

my View:

<Window x:Class="Shifter.Forms.Employee.frmEditEmployee"
        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"
        mc:Ignorable="d"
        Title="frmEditEmployee" Height="350.141" Width="497.195" WindowStyle="None" ResizeMode="NoResize" Foreground="Blue" WindowStartupLocation="CenterScreen">        

    <Grid>    
        <ListBox x:Name="lstEmployee" IsEnabled="{Binding NoEditMode}" SelectedItem="{Binding MasterEmployee}" ItemsSource="{Binding Path=ListOfEmployees}" HorizontalAlignment="Left" Height="276" Margin="25,19,0,0" VerticalAlignment="Top" Width="217" />
        <TextBox x:Name="txtForename" Text="{Binding SelectedItem.Forname, ElementName=lstEmployee}" Margin="342,21,0,0" GotFocus="SelectText"/>
        <TextBox x:Name="txtLastname" Text="{Binding SelectedItem.Lastname, ElementName=lstEmployee}" Margin="342,47,0,0" GotFocus="SelectText"/>
        <TextBox x:Name="txtShowingname" Text="{Binding SelectedItem.Showingname, ElementName=lstEmployee}" Margin="342,74,0,0" GotFocus="SelectText"/>
        <TextBox x:Name="txtPersonelNumber" Text="{Binding SelectedItem.EmployeeID, ElementName=lstEmployee}" Margin="342,99,0,0" GotFocus="SelectText"/>
        <DatePicker x:Name="dtpBirthday" SelectedDate="{Binding SelectedItem.Birthday, ElementName=lstEmployee}" HorizontalAlignment="Left" Margin="342,125,0,0" VerticalAlignment="Top" RenderTransformOrigin="0.256,0.417" SelectedDateFormat="Short"/>
        <TextBox x:Name="txtLoan" Text="{Binding SelectedItem.Loan, ElementName=lstEmployee}" Margin="342,151,0,0" TextWrapping="Wrap" GotFocus="SelectText"/>
        <TextBox x:Name="txtPhone" Text="{Binding SelectedItem.Telephone, ElementName=lstEmployee}" Margin="342,229,0,0" TextWrapping="Wrap" GotFocus="SelectText"/>
        <TextBox x:Name="txtEMail" Text="{Binding SelectedItem.EMail, ElementName=lstEmployee}" Margin="342,255,0,0" TextWrapping="Wrap" GotFocus="SelectText"/>
        <ComboBox x:Name="cmbContract" ItemsSource="{Binding ListOfContracts, Mode=TwoWay}" SelectedItem="{Binding SelectedItem.Contract, ElementName=lstEmployee, Mode=TwoWay}" HorizontalAlignment="Left" Margin="342,179,0,0" VerticalAlignment="Top" Width="130"/>
        <ComboBox x:Name="cmbGroup" ItemsSource="{Binding ListOfGroups, Mode=TwoWay}" SelectedItem="{Binding SelectedItem.Group, ElementName=lstEmployee, Mode=TwoWay}" HorizontalAlignment="Left" Margin="342,204,0,0" VerticalAlignment="Top" Width="130"/>
        <CheckBox x:Name="chkHide" Content="MA im Dienstplan ausblenden" IsChecked="{Binding SelectedItem.isHiding, ElementName=lstEmployee}" HorizontalAlignment="Left" Margin="259,280,0,0" VerticalAlignment="Top" ToolTip="Der Mitarbeiter wird nicht im Dienstplan angezeigt (beispielsweise wegen längerer Abwesenheit)" Width="211"/>            

        <Button x:Name="btnAdd" Content="Add" Command="{Binding Path=cmdAdd, Mode=TwoWay}" HorizontalAlignment="Left" Height="35" Margin="25,303,0,0" VerticalAlignment="Top" Width="35">
        </Button>
        <Button x:Name="btnEdit" Content="Edit" Command="{Binding Path=cmdEdit}" HorizontalAlignment="Left" Height="35" Margin="70,303,0,0" VerticalAlignment="Top" Width="35">
        </Button>
        <Button x:Name="btnDelete" Content="Delete" Command="{Binding Path=cmdDelete}" HorizontalAlignment="Left" Height="35" Margin="115,303,0,0" VerticalAlignment="Top" Width="35">
        </Button>
        <Button x:Name="btnCancel" Content="Cancel" Command="{Binding Path=cmdCancel}" HorizontalAlignment="Left" Height="35" Margin="391,303,0,0" VerticalAlignment="Top" Width="35">
        </Button>
        <Button x:Name="btnOK" Content="OK" Command="{Binding Path=cmdOK}" HorizontalAlignment="Left" Height="35" Margin="436,303,0,0" VerticalAlignment="Top" Width="35">
        </Button>
    </Grid>
</Window>

my ViewModel:

namespace Models
{
    public class VM_EditEmployee : INotifyPropertyChanged
    {
        #region Propertys
        private ObservableCollection<Common.Employee> mListOfEmployees;
        private ObservableCollection<Common.EmployeeContract> mListOfContracts;
        private ObservableCollection<Common.EmployeeGroup> mListOfGroups;
        private Common.Employee mMasterEmployee;
        private bool isNew;
        private Employee.frmEditEmployee EmpoyeeView;

        public event PropertyChangedEventHandler PropertyChanged;

        public ObservableCollection<Common.Employee> ListOfEmployees
        {
            get
            {
                return mListOfEmployees;
            }

            set
            {
                mListOfEmployees = value;
                OnPropertyChanged("ListOfEmployees");
            }
        }
        public ObservableCollection<EmployeeContract> ListOfContracts
        {
            get
            {
                return mListOfContracts;
            }

            set
            {
                mListOfContracts = value;
                OnPropertyChanged("ListOfContracts");
            }
        }
        public ObservableCollection<EmployeeGroup> ListOfGroups
        {
            get
            {
                return mListOfGroups;
            }

            set
            {
                mListOfGroups = value;
                OnPropertyChanged("ListOfGroups");
            }
        }
        public Common.Employee MasterEmployee
        {
            get
            {
                return mMasterEmployee;
            }

            set
            {
                mMasterEmployee = value;
                OnPropertyChanged("MasterEmployee");
            }
        }


        public ICommand cmdAdd { get; set; }
        public ICommand cmdEdit { get; set; }
        public ICommand cmdDelete { get; set; }
        public ICommand cmdCancel { get; set; }
        public ICommand cmdOK { get; set; }

        #endregion

        public VM_EditEmployee(Employee.frmEditEmployee tmpView)
        {
            EmpoyeeView = tmpView;
            cmdAdd = new RelayCommand(o => AddEntry());
            cmdEdit = new RelayCommand(o => EditEntry());
            cmdDelete = new RelayCommand(o => DeleteEntry());
            cmdCancel = new RelayCommand(o => Cancel());
            cmdOK = new RelayCommand(o => SaveEntry());

            ListOfEmployees = Database_Employee.GetListOfEmployee();
            ListOfContracts = Database_Contract.GetListOfContract();
            ListOfGroups = Database_Group.GetListOfGroups();
        }

        protected internal void OnPropertyChanged(string propertyname)
        {
            if (PropertyChanged != null)
                PropertyChanged(this, new PropertyChangedEventArgs(propertyname));
        }

        private void DeleteEntry()
        {
            if (MessageBox.Show("Sure you want to delete?", "Question", MessageBoxButton.OKCancel) == MessageBoxResult.OK)
            {
                Database_Employee.DeleteEmployee(MasterEmployee);
                ListOfEmployees = Database_Employee.GetListOfEmployee();
            }
        }

        private void Cancel()
        {

        }

        private void AddEntry()
        {
            isNew = true;
            Common.Employee newEmployee = new Common.Employee()
            {
                Forname = "Max",
                Lastname = "Mustermann",
                Showingname = "Max",
                EmployeeID = 666,
                Birthday = new System.DateTime(1980, 5, 5),
                Loan = "9,50",
                Contract = Database_Contract.GetListOfContract()[0],
                Group = Database_Group.GetListOfGroups()[0],
                Telephone = "012456789",
                EMail = "chris@roedernet.de",
                isHiding = false
            };

            ListOfEmployees.Add(newEmployee);
            MasterEmployee = newEmployee;
        }

        private void EditEntry()
        {
            isNew = false;
        }

        private void SaveEntry()
        {
                if (isNew == true)
                {
                    Database_Employee.CreateEmployee(MasterEmployee);                    
                }
                else                    {
                    Database_Employee.EditEmployee(MasterEmployee);
                }
                ListOfEmployees = Database_Employee.GetListOfEmployee();
            }
            else // Wenn der EditMode nict aktiv ist
            {
                EmpoyeeView.Close();
            }


        }
    }
}

The "MasterEmployee" property is for getting access to the selected item in the ViewModel to save changes in the employee. Everything works fine, the ListBox is filled with data and the details of the selected employee in the ListBox is shown correctly in the textboxes (there are more then just this one, but its not necessary for this question).

When I create a new employee I create a new instance of the class employee, fill it with some placeholder-information and set the reference of the MasterEmployee to this new employee, because I want to edit the new employee in the textboxes of the view. Then I edit the new employee, save the changes and want to go to another employee in the ListView and nothing happens. I guess its because when I set the reference of the MasterEmployee, the binding with the ListBox is lost.

So my question is: How can I solve this problem? I want to keep the MVVM pattern, means, for setting the binding via code I need to access the view in the viewmodel and thats not MVVM.

Thanks a lot! Chris

Answer 1

I see several issues with the code posted, possibly because it is incomplete:

• SelectedItem : You're textboxes etc are binding to SelectedItem but there is no such property on your VM. You probably mean to bind to MasterEmployee . (note: I would rather name that SelectedItem instead). I think this is the root cause of what you are seeing.
• When you execute SaveEntry you're probably recreating the list completely. As such MasterEmployee won't be in that list anymore. I think this might lead to further bugs. You're showing a node that is not in the list.

If this doesn't help please provide a complete simple example because the code you posted is incomplete and won't compile. Try to narrow down your issue.

Answer 2

Problem solved, it was an issue with my employee class where i had overridden the GetHashCode function to return the employeeID. This makes the binding brake up when editing the employeeID... thanks for your efforts!