How to display “default” selected item - Combobox C# WPF

Question

I populated combobox using an IEnumerable<string>Variables . The items are displayed correctly and allows user to select an option.

 <ComboBox Grid.Row="0" Grid.Column="1" HorizontalAlignment="Center" VerticalAlignment="Center"
     x:Name="ofmvar"  IsTextSearchEnabled="True" Width="150" Margin="2,2,2,2"
     ItemsSource="{Binding Variables}" SelectionChanged="log_SelectionChanged"
     SelectedItem="{Binding SelectedVar, NotifyOnValidationError=True, UpdateSourceTrigger=PropertyChanged, ValidatesOnDataErrors=True, ValidatesOnExceptions=True}"/>

Most of the time (98%) user selects one specific option from the list; lets call it "A_Variable". but occasionally he may select a different variable from the combobox; lets call it "B_Variable" .

When the program launches, he expects the combobox to display "A_Variable" by default as selection.. Is this possible to do?

This is how the SelectedVar is defined:

public string SelectedVar
        {
            get { return _SelectedVar; }
            set
            {
                if (_SelectedVar == value) return;
                _SelectedVar = value;

                OnPropertyChanged("SelectedVar");
            }
        }               
        public string _SelectedVar;

Answer 1

由于SelectedItem已绑定到ViewModel的SelectedVar ，因此只需在ViewModel的构造函数中将SelectedVar设置为默认值即可。

Answer 2

Set the value of the SelectedVar property to "A_Variable" or whatever value in the Variables collection that you want to select in your view model class:

class ViewModel
{
    public ViewModel()
    {
        Variables = new List<string> { "A_Variable", "B_Variable" };

        SelectedVar = "A_Variable"; //default selected value...
    }

    public IEnumerable<string> Variables { get; private set; }

    private string _SelectedVar;
    public string SelectedVar
    {
        get { return _SelectedVar; }
        set
        {
            if (_SelectedVar == value) return;
            _SelectedVar = value;

            OnPropertyChanged("SelectedVar");
        }
    }

    //...
}