CODEWITHSUNDEEP
c#wpfcombobox
Marsh
Marsh

Reputation: 188

Binding a ComboBoxes itemssource with a Dictionary

Why would the first example not update the comboBoxes itemsSource, but the second would? As far as I knew, if I explicitly called OnPropertyChanged() then it would notify the GUI and get the new value from my VM.

example 1 - doesn't update in GUI (no items in cbo)

        // this is the property it's bound to
        this.AvailableSleepTimes = new Dictionary<string, int>();

        // gets a dictionary with values
        Dictionary<string, int> allTimes = ReminderTimesManager.GetReminderTimes();

        foreach(KeyValuePair<string,int> pair in allTimes)
        {
            // logic for adding to the dictionary
            this.AvailableSleepTimes.Add(pair.Key, pair.Value);

        }
        OnPropertyChanged(() => this.AvailableSleepTimes);

example 2 - updates in GUI (cbo is filled)

        // this is the property it's bound to
        this.AvailableSleepTimes = new Dictionary<string, int>();

        // gets a dictionary with values
        Dictionary<string, int> allTimes = ReminderTimesManager.GetReminderTimes();

        Dictionary<string, int> newList = new Dictionary<string, int>();

        foreach(KeyValuePair<string,int> pair in allTimes)
        {
            // logic for adding to the dictionary
            newList.Add(pair.Key, pair.Value);

        }
        this.AvailableSleepTimes = newList;
        OnPropertyChanged(() => this.AvailableSleepTimes);

Upvotes: 1

Views: 509

Answers (1)

JustinHui
JustinHui

Reputation: 729

No property changed notifications are created when you add/remove an item to the dictionary. However, when you reassign, the property, it fires the OnPropertyChanged and updates the GUI.

In order for the GUI to update when the collection is added to, you need to use the ObservableCollection class https://msdn.microsoft.com/en-us/library/ms668604(v=vs.110).aspx

http://www.c-sharpcorner.com/UploadFile/e06010/observablecollection-in-wpf/

Upvotes: 1

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