Updating a ListView with Xamarin.Forms

Question

I am having an issue with list views on in a couple of my Xamarin Forms applications. One form is within a tabbed page setup, the other is a normal content page (different apps)

I have a class like this

public class SomeClass
{
    public string StringOne {get;set;}
    public string StringTwo {get;set;}
    public int IntOne {get;set;}
}

In my Content page, I set up an ObservableCollection and add some data in. I then tell the list that SomeClass is my ItemSource. This produces the ListView correctly on all of my devices.

The problem is that when I change one of the properties, nothing on the ListView changes (so if say I have 3 objects in the Observable and remove one, the list still says 3 - or if I change a property in my second object, the second item on the ListView doesn't change either).

I have also tried to solve the problem by using a standard List and implement INotifyChanged within the class. Again though, the ListView doesn't alter when the List changes.

I know the data has altered as if I make a change to the object, come out and go back in, the data has changed in the UI.

Am I doing something wrong or is this a bug I need to putting into Bugzilla?

An ObservableCollection should update when an item is added or removed - but it will not force an update if an item is modified, unless that item implements INotifyPropertyChanged. — Jason
So I need both the observable and inotifypropertychanged in order for the list view to update? — Nodoid

eakgul eakgul · Accepted Answer · 2015-10-16T07:10:49

It will not change if you don't bind it and implement INotifyPropertyChanged interface.

Sample Code:

public class ObservableProperty : INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;

    protected void OnPropertyChanged(string propertyName)
    {
        var handler = PropertyChanged;
        if (handler != null)
            handler(this, new PropertyChangedEventArgs(propertyName));
    }
}

public class SomeClass:ObservableProperty
{
    string stringOne;
    string stringTwo;
    int intOne;
    public string StringOne 
    {
        get{return stringOne;}
        set
        {
            stringOne = value;
            OnPropertyChanged("StringOne");
        }
    }

    public string StringTwo 
    {
        get{ return stringTwo;}
        set
        {
            stringTwo = value;
            OnPropertyChanged("StringTwo");
        }
    }

    public int IntOne 
    {
        get{ return intOne;}
        set
        {
            intOne = value;
            OnPropertyChanged("IntOne");
        }
    }
}

public class MainVM:ObservableProperty
{
    ObservableCollection<SomeClass> items;

    public ObservableCollection<SomeClass> items
    {
        get{return items;}
        set
        {
            items = value;
            OnPropertyChanged("Items");
        }
    }

    public MainVM()
    {
        Items = new ObservableCollection<SomeClass>();

        Items.Add(new SomeClass(){StringOne = "123", StringTwo = "test", IntOne =12});
    }

    public void CallMeForChangingProperty()
    {
        SomeClass item = Items[0];
        item.StringOne = "Test1";
    }
}


public class MainView
{
    public MainView()
    {
        this.BindingContext=  new MainVM()
    }
} 


< ListView ItemsSource="{Binding Items}" RowHeight="120">
 < ListView.ItemTemplate>
   < DataTemplate>
     < ViewCell>
       < ViewCell.View>
        < StackLayout>
            < Label Text= "StringOne" />
            < Label Text= "StringTwo" />
            < Label Text= "IntOne" />
        </ StackLayout>
       </ ViewCell.View>
     </ ViewCell>
   </ DataTemplate>
 </ ListView.ItemTemplate>
</ ListView>

Updating a ListView with Xamarin.Forms

2 Answers