XAML data.binding-如何将方法中的属性绑定到视图中的经度/纬度？

Question

I'm using GeoLocator to find out my position. This is the method:

private async void GetCurrentLocation()
{
    Geolocator locationFinder = new Geolocator
    {
        DesiredAccuracyInMeters = 50,
        DesiredAccuracy = PositionAccuracy.Default
    };

    try
    {
        Geoposition currentLocation = await  locationFinder.GetGeopositionAsync(
            maximumAge: TimeSpan.FromSeconds(120),
            timeout: TimeSpan.FromSeconds(10));
        String longitude = currentLocation.Coordinate.Longitude.ToString("0.00");
        String latitude = currentLocation.Coordinate.Latitude.ToString("0.00");
        MyTextBlock.Text = "Long: " + longitude + "Lat: " + latitude;
    }
    catch (UnauthorizedAccessException)
    {
        MyTextBlock.Text = "some message";
    }
}

Now, I'm my view I have this code (here with hard-coded values that I would like to replace with longitude/latitude from the above method).

<bm:Map ZoomLevel="7.5" Credentials="my key" x:Name="myMap">
    <bm:Map.Center>
        <bm:Location Latitude="48" Longitude="-122.580489" />
    </bm:Map.Center>
</bm:Map>

I'm very new to this kind of developing and would like to know how I can bind the properties in the method to the long/lat in my view. Thank you!

Answer 1

This would require some sort of object (usually called a ViewModel) from which your Map control would get its DataContext . (DataContext moves down the visual tree, from parent to child, unless explicitly set on any child control.) The ViewModel exposes information you'd like the view (your Window/other visible control) to visually represent somehow to the user.

Note that one of the crucial components of ViewModels in the MVVM style for WPF is that it implements INotifyPropertyChanged . This interface allows an object to signal to the UI that the a value which is bound in the above fashion has changed, and the UI should be updated to reflect that.

Here's a really simple implementation of a ViewModel for your purposes:

// uses System.ComponentModel
public class YourViewModel : INotifyPropertyChanged
{
    private double longitude;
    public double Longitude
    { 
        get { return longitude; }
        set
        {
            longitude = value;
            NotifyPropertyChanged("Longitude");
        }
    } 

    private double latitude;
    public double Latitude
    { 
        get { return latitude; }
        set
        {
            latitude = value;
            NotifyPropertyChanged("Latitude");
        }
    } 

    public event PropertyChangedEventHandler PropertyChanged;
    protected void NotifyPropertyChanged(string propertyName)
    {
        if (PropertyChanged != null)
        {
            PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }
    }
}

This exposes a Longitude property and a Latitude property which you can use for binding in your XAML. If you're going to do true MVVM, those properties should probably be contained within a model object, and the ViewModel should in turn expose a collection of model objects to the View. As it stands, this is basically as simple an example as possible.

In general, you'd just use a simple binding to connect a control's property to your ViewModel's property, like so:

<TextBlock Text="{Binding Longitude}" />

where the TextBlock 's DataContext had been set to an instance of YourViewModel.

However, it looks like the Bing Map object isn't a FrameworkElement, so it doesn't have a DataContext property, and binding is a little more complicated because it needs StaticResource s. I don't really have the capacity to test out the Bing maps API, but this link on binding to non-FrameworkElements should help.