Xamarin C#在ViewModels上的数据绑定，数据模型中有多个外键关系:Picker和labels

Question

Oke这里是上下文：我有一个连接到ASP.NET rest服务的Xamarin应用程序。目前我正在对我的观点进行数据绑定

有一个称为presatie的特定数据模型，它有一个对Trainer模型类的外键引用，另一个对Getuigschrift类的外键参考。

public class Prestatie : INotifyPropertyChanged
{
[Key]
private Guid _PrestatieID;
public Guid PrestatieID
{
get => _PrestatieID;
set
{
_PrestatieID = value;
RaisePropertyChanged(nameof(PrestatieID));
}
}
private string _Rekeningnummer;
public string Rekeningnummer
{
get => _Rekeningnummer;
set
{
_Rekeningnummer = value;
RaisePropertyChanged(nameof(Rekeningnummer));
}
}
private string _Rijksregisternummer;
public string Rijksregisternummer
{
get => _Rijksregisternummer;
set
{
_Rijksregisternummer = value;
RaisePropertyChanged(nameof(Rijksregisternummer));
}
}


[ForeignKeyAttribute("Trainer")]
public Guid? TrainerID
{
get;
set;
}
public Trainer Trainer
{
get;
set;
}


public event PropertyChangedEventHandler PropertyChanged;
public void RaisePropertyChanged(string propertyName)
{
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
}
}

培训师类别：

public class Trainer : Persoon
{
private Guid _TrainerID;
public Guid TrainerID
{
get => _TrainerID;
set
{
_TrainerID = value;
RaisePropertyChanged(nameof(TrainerID));
}
}
public ICollection<Prestatie> Prestaties
{
get;
set;
}
public Getuigschrift Getuigschriften
{
get;
set;
}
private Guid _GetuigschriftID;
public Guid? GetuigschriftID
{
get => _GetuigschriftID;
set
{
_GetuigschriftID = (Guid)value;
RaisePropertyChanged(nameof(GetuigschriftID));
}
}

}

现在，我有两个ViewModels设置来表示这些数据，一个用于概述，另一个用于详细信息/编辑/添加。项目的数据绑定在视图模型上，所以理论上我应该在视图模型中建立这些关系，但我不确定如何做到这一点。一方面，我只需要在ItemViewModel中返回一些标签，另一方面，为了获得Foregin密钥，我需要对数据输入进行某种comobox/list/picker。

解决方案我试过这样的方法，但似乎不起作用。Xamarin ListView MVVM数据绑定

这是我的视图模型的一小部分，由于字符限制，我无法发布更多。

public class PrestatieViewModel : BaseViewModel
{
private ObservableCollection<Prestatie> _prestaties;
private readonly IPrestatieDataService _prestatieDataService;
private readonly INavigationService _navigationService;

public ObservableCollection<Prestatie> Prestaties
{
get => _prestaties;
set
{
_prestaties = value;
OnPropertyChanged("Prestaties");
}
}

public class PrestatieDetailViewModel : BaseViewModel
{
private Prestatie _selectedPrestatie;
private readonly IPrestatieDataService _prestatieDataService;
private readonly INavigationService _navigationService;

public Prestatie SelectedPrestatie
{
get => _selectedPrestatie;
set
{
_selectedPrestatie = value;
OnPropertyChanged(nameof(SelectedPrestatie));
}
}

Answer 1

您可以将选择器的selectedItem与trainer绑定，以便选择并设置值。这是你可以参考的代码

xmal:

<ContentPage.BindingContext>
<local:PeopleViewModel/>
</ContentPage.BindingContext>
<CollectionView x:Name="mycol">
<CollectionView.ItemTemplate>
<DataTemplate>
<Grid ColumnDefinitions="100,* "
RowDefinitions="*,*">
<Label Text="{Binding Name}" BackgroundColor="LightBlue"/>
<Picker x:Name="mypicker"  Grid.Column="1" Title="Select a Trainer"
TitleColor="Red"
ItemsSource="{Binding pgs}"
ItemDisplayBinding="{Binding Name}"
SelectedItem="{Binding Trainer}">
</Picker>
<Label Text="Trainer:" Grid.Row="1" Grid.Column="0" BackgroundColor="AliceBlue"/>
<Label
Grid.Row="1"
Grid.Column="1"
Text="{Binding Trainer.Name}"/>
</Grid>
</DataTemplate>
</CollectionView.ItemTemplate>
</CollectionView>

视图模型：

public class PeopleViewModel:INotifyPropertyChanged
{
string name;
People trainer;
public List<People> pgs { get; private set; } = new List<People>{new People{Name="Trainer1" },
new People{ Name="Trainer2"} ,
new People{ Name="Trainer3"} };
public string Name {
get { return name; }
set { if (name != value)
{ name = value;
OnPropertyChanged();
}
} }
public People Trainer
{
get { return trainer; }
set
{
if (trainer != value)
{
trainer = value;
OnPropertyChanged();
}
}
}
#region INotifyPropertyChanged
void OnPropertyChanged(string name=null)
{
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(name));
}
#endregion

public event PropertyChangedEventHandler PropertyChanged;

}}