Default load up value in ComboBox - WPF MVVM

Question

I have a ComboBox and want to prepopulate the value in the ComboBox to a preset value.

I have a list of food categories, which is an ObservableCollection called ItemCategories, which is a property. The list has 5 different types.

I also have a selected category property called ItemCategory of type ItemCategory.

ItemCategory has two properties, Category and PK_ItemCategoryId.

So far this is what I have

ComboBox XAML

ComboBox Contents RunTime

The combobox's ItemSource is bound to a property in the ViewModel.

private ObservableCollection<ItemCategory> _itemCategories;
        public ObservableCollection<ItemCategory> ItemCategories
        {
            get
            { return _itemCategories; }
            set
            {
                _itemCategories = value;
                OnPropertyChanged("ItemCategories");
            }
        }

        private ItemCategory _itemCategory;
        public ItemCategory ItemCategory
        {
            get { return _itemCategory; }
            set
            {
                _itemCategory = value;
                OnPropertyChanged("ItemCategory");
            }
        }

What I want to do, when the user opens the app is to prepopulate the value in the combox witha an item in the list. Below is an example what I want to achieve.

Goal

How can I acheive this using MVVM and WPF?

c0nn1 c0nn1 · Accepted Answer · 2018-09-23T15:06:57

Since your SelectedItem property is set to Mode=TwoWay, you can set the property in your ViewModel like this:

//if you imported LINQ
if(ItemCategories != null && ItemCategories.Any())
    ItemCategory = ItemCategories.First();

//without LINQ
if(ItemCategories != null && ItemCategories.Count > 0)
    ItemCategory = ItemCategories[0];

This would take the first item in ItemCategories, if there is any, and set it as the SelectedItem.

The UI will be notified through OnPropertyChanged().

Default load up value in ComboBox - WPF MVVM

2 Answers