绑定不起作用 - 没有属性、可绑定属性或事件发现错误

Question

Am having an issue with binding, but I first searched with several questions on this, but no luck, below is the error am getting :

Error: Position 18:36. No property, bindable property, or event found for 'Lat', or mismatching type between value and property

Below is my xaml file :

<controls:MapView x:Name="map" VerticalOptions="FillAndExpand">
            <controls:MapView.Center>
                <controls:Position Lat="{Binding latitude}" Long="{Binding longitude}" />
            </controls:MapView.Center>
        </controls:MapView>

Then the c# code is as below :

public partial class DisplayMap : ContentPage
    {

        private double latitude { get; } 
        private double longitude { get; } 

        public DisplayMap()
        {

            InitializeComponent();

            this.latitude = 0.3476;
            this.longitude = 32.5825;

            BindingContext = this;

        }

What am I missing ?

Answer 1

The issue seems to be a lack of publicly-accessible bindable properties in the Position class (notice that the error mentions Lat which is a member of Position ). Position should look something like this:

public class Position : BindableObject
{
    public static readonly BindableProperty LatProperty = BindableProperty.Create(nameof(Lat), typeof(double), typeof(Position), 0);
    public double Lat
    {
        get { return (double)this.GetValue(LatProperty); }
        set { this.SetValue(LatProperty, value); }
    } 

    public static readonly BindableProperty LongProperty = BindableProperty.Create(nameof(Long), typeof(double), typeof(Position), 0);
    public double Long
    {
        get { return (double)this.GetValue(LongProperty); }
        set { this.SetValue(LongProperty, value); }
    }

    // ...

I suggest you take a look at the official documentation for Bindable Properties . Essentially, the error message you are getting is because it is looking for LatProperty when trying to bind using the accessor Lat .

Answer 2

The reason why you are not able to use the Lat and Long property is that if you check the Position class there is no Bindable Property defined for them in it which means you cannot access them in XAML,

A possible solution is to download the Sample project and take the code and make the respective changes for it to have Bindable Properties.

For that, you can check @Aaron's answer