C# 为什么绑定不更新选取器选定项

我有一个Xamarin表单中的

选择器

，绑定到一个模型（代码如下）

Load

方法设置

SelectedVehicle

，但选择器不显示所选车辆。第一次加载页面时，选择器会在列表中显示正确的项。但是在

App.VehicleId

更改后重新加载页面上，选择器显示为空白

即使我在出现时在选择器上显式设置了SelectedIndex，选择器也会显示为空，并且当我稍后查看时，

SelectedIndex

已被设置回

-1

重新加载页面时，如何正确更新选择器选择

Xaml：

---

原来问题是创建了一个新的

可观察集合

。我改了密码

Vehicles = new ObservableCollection<Vehicle>(await App.Database.ReadAsync<Vehicle>().ToListAsync());

Vehicles=newobserveCollection（等待App.Database.ReadAsync（）.ToListAsync（））；

而是清除现有集合，并向其中添加新记录

public partial class MainPage : ContentPage {
    public class VehicleInfo : Model {
        public async void Load() {
            Vehicles = new ObservableCollection<Vehicle>(await App.Database.ReadAsync<Vehicle>().ToListAsync());
            SelectedVehicle = Vehicles.FirstOrDefault(v => v.DeviceRecordId == App.VehicleId) ?? Vehicles.FirstOrDefault();
            System.Diagnostics.Debug.WriteLine("App.VehicleId = " + App.VehicleId);
            System.Diagnostics.Debug.WriteLine("SelectedVehicle.Id = " + selectedVehicle.DeviceRecordId);
        }

        private Vehicle selectedVehicle;

        public Vehicle SelectedVehicle {
            get { return selectedVehicle; }
            set {
                if (selectedVehicle != value) {
                    selectedVehicle = value;
                    OnPropertyChanged("SelectedVehicle");
                }
            }
        }

        private ObservableCollection<Vehicle> vehicles;

        public ObservableCollection<Vehicle> Vehicles {
            get { return vehicles; }
            set {
                if (vehicles != value) {
                    vehicles = value;
                    OnPropertyChanged("Vehicles");
                }
            }
        }

    }
    VehicleInfo data;
    public MainPage() {
        data = new VehicleInfo();
        BindingContext = data;
        InitializeComponent();
    }

    protected override void OnAppearing() {
        base.OnAppearing();
        data.Load();
    }

public class Model : System.ComponentModel.INotifyPropertyChanged {
    public void OnPropertyChanged(string name) {
        if (PropertyChanged != null)
            PropertyChanged(this, new PropertyChangedEventArgs(name));
    }

    public event PropertyChangedEventHandler PropertyChanged;
}

Vehicles = new ObservableCollection<Vehicle>(await App.Database.ReadAsync<Vehicle>().ToListAsync());