WPF MVVM: ComboBox SelectedValue binding

Question

由于评论中的反馈，我已经更新了我的问题。

我正试图根据另一个ComboBox(cbLicenseHolder)中的SelectedValue/Item对ComboBox(cbVehicle)进行排序和填充。属性的绑定是通过BindableCollection完成的(基本上与ObservableCollection相同)。

下面你会看到我的ViewModel。

namespace Ridel.Hub.ViewModels {
public class TripViewModel : Conductor<IScreen>.StackNavigation {
private readonly IWindowManager windowManager;
private BindableCollection<LicenseHolder> _licenseHolders;
public BindableCollection<LicenseHolder> LicenseHolders {
get => _licenseHolders;
set => SetAndNotify(ref this._licenseHolders, value);
}
private BindableCollection<License> _licenses;
public BindableCollection<License> Licenses {
get => _licenses;
set => SetAndNotify(ref this._licenses, value);
}
#region Constructor
public TripViewModel(IWindowManager windowManager) {
this.windowManager = windowManager;
LicenseHolders = new BindableCollection<LicenseHolder>();
Licenses = new BindableCollection<License>();
}
#endregion // Constructor
#region ComboBoxes
public void FillComboBoxLicenseHolders() {
try {
DataSet ds = new DataSet();
using (SqlConnection sqlCon = new SqlConnection(ConnectionString.connectionString)) {
SqlDataAdapter sqlDA = new();
sqlDA.SelectCommand = new SqlCommand("select Foretaksnavn from tblLicenseHolder", sqlCon);
sqlDA.Fill(ds);
}
DataTable dt = new();
dt = ds.Tables[0];
for (int i = 0; i < dt.Rows.Count; i++) {
DataRow dr = dt.NewRow();
dr = dt.Rows[i];
LicenseHolder licenseHolder = new();
licenseHolder.Foretaksnavn = dr["Foretaksnavn"].ToString();
LicenseHolders.Add(licenseHolder);
}
} catch (Exception ex) {
MessageBox.Show(ex.Message, "Message", MessageBoxButton.OK, MessageBoxImage.Information);
}
}
public void FillComboBoxLicenses() {
Licenses.Clear();
try {
DataSet ds = new();
using (SqlConnection sqlCon = new SqlConnection(ConnectionString.connectionString)) {
SqlDataAdapter sqlDA = new();
sqlDA.SelectCommand = new SqlCommand("fillLicensesComboBox", sqlCon);
sqlDA.SelectCommand.CommandType = CommandType.StoredProcedure;
sqlDA.SelectCommand.Parameters.Add("@Foretaksnavn", SqlDbType.NVarChar).Value = CbLicenseHolderSelection.ToString();
sqlDA.Fill(ds);
}
DataTable dt = new();
dt = ds.Tables[0];
for (int i = 0; i < dt.Rows.Count; i++) {
DataRow dr = dt.NewRow();
dr = dt.Rows[i];
License license = new();
license.KjøretøyID = dr["KjøretøyID"].ToString();
Licenses.Add(license);
}
} catch (Exception ex) {
MessageBox.Show(ex.Message, "Message", MessageBoxButton.OK, MessageBoxImage.Information);
}
}
private string _cbLicenseHolderSelection;
public string CbLicenseHolderSelection {
get { return this._cbLicenseHolderSelection; }
set { SetAndNotify(ref this._cbLicenseHolderSelection, value);
if (value != null) {
FillComboBoxLicenses();
}
}
}

您可以看到，我有两个BindableCollection，一个名为LicenseHolders，另一个名为Licenses。LicenseHolders绑定cbLicenseHolder,Licenses绑定cbVehicle。

同样，你看到我已经添加了我的方法;FillComboBoxLicenses，到CbLicenseHolderSelection属性，在下面的XAML中，您将看到我已经尝试将该属性绑定到cbLicenseHolder的SelectedValue。

但很明显，我在这里遗漏了一部分内容。cbVehicle未被填充。

XAML如下:

<ComboBox Name="cbLicenseHolder" Canvas.Left="50" Canvas.Top="204" Width="291"               
ItemsSource="{Binding LicenseHolders, Mode=TwoWay}"                 
Loaded="{s:Action FillComboBoxLicenseHolders}"    
DisplayMemberPath="Foretaksnavn"
SelectedValue="{Binding CbLicenseHolderSelection, UpdateSourceTrigger=PropertyChanged}"
FontSize="12"
/>

<ComboBox Name="cbVehicle" Canvas.Left="381" Canvas.Top="204" Width="269"
ItemsSource="{Binding Licenses, Mode=TwoWay}"
DisplayMemberPath="KjøretøyID"
FontSize="12" 
IsEnabled="True"
IsSynchronizedWithCurrentItem="True"
/>

LicenseHolder.cs和License.cs都实现了PropertyChangedBase。它们的属性如下所示:

private string _foretaksnavn;
public string Foretaksnavn {
get { return this._foretaksnavn; }
set { SetAndNotify(ref this._foretaksnavn, value); }
}

SetAndNotify是一个框架函数——它的作用是:

"通过引用获取一个字段及其新值。如果field != value，将设置field = value并引发PropertyChanged通知。">

Mystored procedure:

SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
ALTER PROCEDURE [dbo].[getLicense]
@Foretaksnavn nvarchar(50)
AS 
SELECT tblLicense.ID, LøyvehaverID, KjøretøyID
FROM tblLicense
INNER JOIN tblLicenseHolder
ON tblLicense.LøyvehaverID = tblLicenseHolder.Foretaksnavn
WHERE tblLicense.LøyvehaverID = @Foretaksnavn

Answer 1

不要把这当作答案，而是作为澄清问题以更好地理解问题。
我只需要一些包含代码的解释，所以我必须以答案的形式给出它们。

1. 按如下方式更改属性、方法和绑定的实现，并报告结果:

private LicenseHolder _cbLicenseHolderSelection;
public LicenseHolder CbLicenseHolderSelection {
get { return this._cbLicenseHolderSelection; }
set { SetAndNotify(ref this._cbLicenseHolderSelection, value);
if (value != null) {
FillComboBoxLicenses();
}
}
}

<ComboBox Name="cbLicenseHolder" Canvas.Left="50" Canvas.Top="204" Width="291"               
ItemsSource="{Binding LicenseHolders, Mode=TwoWay}"                 
Loaded="{s:Action FillComboBoxLicenseHolders}"    
DisplayMemberPath="Foretaksnavn"
SelectedItem="{Binding CbLicenseHolderSelection, UpdateSourceTrigger=PropertyChanged}"
FontSize="12"
/>

public ObservableCollection<License> Licenses {get;}
= new ObservableCollection<License>();

public void FillComboBoxLicenses() {
try {
DataSet ds = new();
using (SqlConnection sqlCon = new SqlConnection(ConnectionString.connectionString)) {
SqlDataAdapter sqlDA = new();
sqlDA.SelectCommand = new SqlCommand("fillLicensesComboBox", sqlCon);
sqlDA.SelectCommand.CommandType = CommandType.StoredProcedure;
sqlDA.SelectCommand
.Parameters
.Add("@Foretaksnavn", SqlDbType.NVarChar)
// It is necessary to specify a specific property for the Value.
.Value = CbLicenseHolderSelection.SomeProperty.ToString();
sqlDA.Fill(ds);
}
DataTable dt = new();
dt = ds.Tables[0];
Licenses.Clear();
for (int i = 0; i < dt.Rows.Count; i++) {
DataRow dr = dt.NewRow();
dr = dt.Rows[i];
License license = new();
license.KjøretøyID = dr["KjøretøyID"].ToString();
Licenses.Add(license);
}
} // On this line (after the for loop), set a breakpoint.
catch (Exception ex) {
MessageBox.Show(ex.Message, "Message", MessageBoxButton.OK, MessageBoxImage.Information);
}
}

还告诉在循环后的行中FillComboBoxLicenses方法停止后，许可证集合中有多少项。