Why is my combobox failing to bind to my List<string> in my ViewModel? WPF-CodePudding

I have four Comboboxes in my XAML. It looks like this:

 <ComboBox Grid.Row="2" ItemsSource="{Binding VehiclesAvailable}"  DisplayMemberPath="FleetNumber"/>
 <ComboBox Grid.Row="3" ItemsSource="{Binding Employees_VehicleEligible}" DisplayMemberPath="FullName"/>
 <ComboBox Grid.Row="4" ItemsSource="{Binding Jobsites}" DisplayMemberPath="Name"/>
 <ComboBox Grid.Row="5" ItemsSource="{Binding Conditions}" SelectedItem="{Binding SelectedCondition}" />

The first three CBs are bound to ObservableCollection properties, and these work fine. The last is bound to a List, and it is not displaying any content.

In the VM, I declare the property and set its value in a LoadInitialData command.

    //PROPERTIES
    public ObservableCollection<VehicleModel> VehiclesAvailable { get; set; }
    public ObservableCollection<EmployeeModel> Employees_VehicleEligible { get; set; }
    public ObservableCollection<JobsiteModel> Jobsites { get; set; }
    public ConditionsModel Conditions { get; set; }
    public GenericCondition SelectedConditionOut { get; set; }
    public string SelectedCondition { get; set; }

    //COMMANDs
    public RelayCommand<object> LoadIntialDataCommand { get; set; }

    //METHODS
    public async void LoadInitialData(object e)
    {
        var vehiclesAvailable = await GetData.VehiclesAvailableQueryAsync();
        foreach (VehicleModel _vehicle in vehiclesAvailable)
            VehiclesAvailable.Add(_vehicle);
        var employees_VehiclesEligible = await GetData.Employees_VehiclesEligibleQueryAsync();
        foreach (EmployeeModel _employee in employees_VehiclesEligible)
            Employees_VehicleEligible.Add(_employee);
        Conditions = new ConditionsModel();
    }

And for what it's worth, this is where I define the ConditionsModel:

 class ConditionsModel
    {
        private List<string> _conditions;

        public List<string> Conditions
        {
            get { return new List<string>() { "New", "Excellent", "Good", "Fair", "Poor", "Unacceptable" }; }
            set { _conditions = value; }
        }

When I step through the code, placing a break point at the closing bracket of the LoadInitialData method, Conditions appears to have all the strings populated. And when I go to the XAML, sure enough, all the strings appear when I hover over the ItemsSource property. But when I run it, the combobox is empty. What might be my next step to debug this problem?

CodePudding user response：

It would appear that your binding to a ConditionsModel and not the ConditionsModel.Conditions property. Aside from that ObservableCollection will trigger a NotifyPropertyChange event when it is updated whereas a standard List won't.

Being triggered by a RelayCommand your LoadInitialData(...) function is going to be called after the View has been created and displayed. If you had created and populated your Conditions in your ViewModel constructor then it's possible that you would see some values.

In this situation you may be better off having a ConditionsViewModel Conditions instead of a ConditionsModel Conditions property, where the ConditionsViewModel uses an ObservableCollection<string> Conditions and then bind to ConditionsViewModel.Conditions

CodePudding user response：

The Conditions property that you currently bind to doesn't return an IEnumerable which is required for the ItemsSource property.

You should bind to the Conditions list property of the ConditionsModel:

<ComboBox Grid.Row="5" ItemsSource="{Binding Conditions.Conditions}" 
          SelectedItem="{Binding SelectedCondition}" />