WPF/MVVM: Refactoring Code-Behind to make it ready for MVVM binding

I have this code in my code-behind file of my View:

private string GetSelectedSchoolclassCode()
    {
        return ((SchoolclassCode)cboSchooclassCodeList.SelectedItem).SchoolclassCodeName;
    }

    private void dgTimeTable_MouseLeftButtonDown(object sender, MouseButtonEventArgs e)
    {        
        var columnNumber = dgTimeTable.CurrentCell.Column.DisplayIndex;
        var timetable = dgTimeTable.CurrentItem as TimeTableViewModel;

        switch (columnNumber)
        {
            case 0: timetable.SchoolclassCodeMonday = GetItemValue(timetable.SchoolclassCodeMonday); break;
            case 1: timetable.SchoolclassCodeTuesday = GetItemValue(timetable.SchoolclassCodeTuesday); break;
            case 2: timetable.SchoolclassCodeWednesday = GetItemValue(timetable.SchoolclassCodeWednesday); break;
            case 3: timetable.SchoolclassCodeThur开发者_JAVA百科sday = GetItemValue(timetable.SchoolclassCodeThursday); break;
            case 4: timetable.SchoolclassCodeFriday = GetItemValue(timetable.SchoolclassCodeFriday); break;
            case 5: timetable.SchoolclassCodeSaturday = GetItemValue(timetable.SchoolclassCodeSaturday); break;
            case 6: timetable.SchoolclassCodeSunday = GetItemValue(timetable.SchoolclassCodeSunday); break;
        }
    }

    private string GetItemValue(string schoolclassCodeWeekDay)
    {
        if (schoolclassCodeWeekDay == null)
            schoolclassCodeWeekDay = GetSelectedSchoolclassCode();
        else
            schoolclassCodeWeekDay = null;

        return schoolclassCodeWeekDay;
    }

I would like to put all this code in the ViewModel. The problem already starts with the CurrentColumn.DisplayIndex in XAML. I can not declare it with binding as the syntax is not allowed. WPF thinks that DisplayIndex is an attached property...

What would you do?

It can be tricking and quite complex to get pure XAML / ViewModel separation when dealing with complex controls such as a data grid. In some cases it might be best to have a little code behind to achieve cleaner XAML and code.

perhaps try

private void dgTimeTable_MouseLeftButtonDown(object sender, MouseButtonEventArgs e)
{        
    var columnNumber = dgTimeTable.CurrentCell.Column.DisplayIndex;
    ((YourViewModel)DataContext).SetDisplayIndex(columnNumber);
}

and in your view model have the rest of the code

private string GetSelectedSchoolclassCode()
{
    return ((SchoolclassCode)SelectedSchooclass).SchoolclassCodeName;
}

public int SetDisplayIndex(int columnNmber)
{        
         var timetable = CurrentItem as TimeTableViewModel;

        switch (columnNumber)
        {
            case 0: timetable.SchoolclassCodeMonday = GetItemValue(timetable.SchoolclassCodeMonday); break;
            case 1: timetable.SchoolclassCodeTuesday = GetItemValue(timetable.SchoolclassCodeTuesday); break;
            case 2: timetable.SchoolclassCodeWednesday = GetItemValue(timetable.SchoolclassCodeWednesday); break;
            case 3: timetable.SchoolclassCodeThursday = GetItemValue(timetable.SchoolclassCodeThursday); break;
            case 4: timetable.SchoolclassCodeFriday = GetItemValue(timetable.SchoolclassCodeFriday); break;
            case 5: timetable.SchoolclassCodeSaturday = GetItemValue(timetable.SchoolclassCodeSaturday); break;
            case 6: timetable.SchoolclassCodeSunday = GetItemValue(timetable.SchoolclassCodeSunday); break;
        }
    }

private string GetItemValue(string schoolclassCodeWeekDay)
{
    if (schoolclassCodeWeekDay == null)
        schoolclassCodeWeekDay = GetSelectedSchoolclassCode();
    else
        schoolclassCodeWeekDay = null;

    return schoolclassCodeWeekDay;
}

Provided you include bindings for the combobox to SelectedSchooclass and the currentitem on the data grid to the view model