CODEWITHSUNDEEP
c#xamlxamarinxamarin.forms
Ajit Hegde
Ajit Hegde

Reputation: 550

Xamarin Forms Bindable Object Value Changed Event

I have created a custom map using Xamarin Forms Map. I want to access updated VisibleRegion when VisibleRegion is changed.

Custom Renderer

protected override void OnElementPropertyChanged(object sender, PropertyChangedEventArgs e)
{
    base.OnElementPropertyChanged(sender, e);

    if (Element == null)
        return;

    var map = (CustomMap)sender;
    if(map.VisibleRegion==null)
        return;

    map.OnMapRegionUpdated();
}

In Custom Control I created a bindable property

public MapCenterPosition MapCenter { get; set; }
public static readonly BindableProperty MapCenterProperty = BindableProperty.Create(
            nameof(MapCenter),
            typeof(MapCenterPosition),
            typeof(CustomMap),
            null);


public void OnMapRegionUpdated()
{
   MapCenter = new MapCenterPosition {Position = VisibleRegion.Center};
}

MapCenterPosition.cs

public class MapCenterPosition: INotifyPropertyChanged
{
    private Position _position;

    public event PropertyChangedEventHandler PropertyChanged;

    public void RaisePropertyChange([CallerMemberName]string propertyname = null)
    {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyname));
    }

    public Position Position
    {
        get => _position;
        set 
        { 
            _position = value;
            RaisePropertyChange();
        }

    }
}

Now I have the CustomMap & binded it to ViewModel code. But how can I trigger some method in my ViewModel when MapCenter is updated ?

Upvotes: 0

Views: 1011

Answers (1)

Ajit Hegde
Ajit Hegde

Reputation: 550

I made a simple mistake

All I have to do was to set binding mode as TwoWay in xaml.

And in custom control, I should replace this 

public MapCenterPosition MapCenter { get; set; }

with

public MapCenterPosition MapCenter
{
    get => (MapCenterPosition) GetValue(MapCenterProperty);
    set => SetValue(MapCenterProperty,value);
}

Now I can trigger method in view model every time MapCenter got updated.

Upvotes: 1

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