This is the first experience with WPF so please forgive me, I know this is pretty basic but I can't get it to work. I'm simply trying to bind a combobox to an LINQ to EF populated ObservableCollection. When I step through the code I see that the collection is populated, but the combo box doesn't display the contents of the collection.
Here is my ViewModel:
public class MainWindowViewModel : ViewModelBase
{
# region ObservableCollections
private ObservableCollection<Site> _sitescollection;
public ObservableCollection<Site> SiteCollection
{
get { return _sitescollection;}
set {
if (value == _sitescollection) return;
_sitescollection = value;
RaisePropertyChanged("SiteCollection");
}
}
# endregion
public MainWindowViewModel()
{
this.PopulateSites();
}
// Get a listing of sites from the database
public void PopulateSites()
{
using (var context = new Data_Access.SiteConfiguration_Entities())
{
var query = (from s in context.SITE_LOOKUP
select new Site(){Name = s.SITE_NAME, SeqId = s.SITE_SEQ_ID });
SiteCollection = new ObservableCollection<Site>(query.ToList());
}
}
}
My Site Class:
public class Site : INotifyPropertyChanged
{
#region Properties
string _name;
public string Name
{
get
{
return _name;
}
set
{
if (_name != value)
{
_name = value;
RaisePropertyChanged("Name");
}
}
}
private int _seqid;
public int SeqId
{
get {
return _seqid;
}
set {
if (_seqid != value)
{
_seqid = value;
RaisePropertyChanged("SeqId");
}
}
}
#endregion
#region Constructors
public Site() { }
public Site(string name, int seqid)
{
this.Name = name;
this.SeqId = seqid;
}
#endregion
void RaisePropertyChanged(string prop)
{
if (PropertyChanged != null) { PropertyChanged(this, new PropertyChangedEventArgs(prop)); }
}
public event PropertyChangedEventHandler PropertyChanged;
}
And my XAML Bindings:
<ComboBox Margin="10"
ItemsSource="{Binding Sites}"
DisplayMemberPath="Name"
SelectedValuePath="SeqId" />
What am I doing wrong? Any assistance would be greatly appreciated.
You bound to path "Sites" but your property name was "SiteCollection".
You bind to properties, so the names have to match. Also make sure your data context is set to your view model object.
Related
I'm learning on how to implement inversion of control in the wpf application through the below link
https://www.codeguru.com/columns/experts/implementing-the-inversion-of-control-pattern-in-c.htm
The intent of the application is to load the data from table to combobox. The code works fine without any issue. So as a part of learning ooad design principle I thought below is the perfect case on which the highlevel module (Viewmodel) depend upon lowerlevel module (populatetab2combobox). I believe here we can apply dependency inversion. on reading online most of them started with inversion of control as a first step towards implementing Dependency inversion.
I just want to iterate that I don't have prior experience in oops principle. I might be wrong in my assumption. Please correct me if I'm wrong.
Window.xaml :
<ComboBox ItemsSource="{Binding populatecombobox.modeltogetusername}" Width="155" Margin="0,-20,-180,137">
<ComboBox.ItemTemplate>
<DataTemplate>
<TextBlock Text="{Binding username}"/>
</DataTemplate>
</ComboBox.ItemTemplate>
</ComboBox>
View Model :
Code without implementing inversion of control(This works fine without any issue):
//Class to populate the combobox
public class populatetab2combobox
{
public ObservableCollection<comboboxdata> modeltogetusername { get; set; }
public void getdatausinglinq()
{
using (Operations_Productivity_ToolEntities context = new Operations_Productivity_ToolEntities())
{
var a1 = from t1 in context.Test_ImportedAuditdata
select t1;
if (modeltogetusername == null)
modeltogetusername = new ObservableCollection<comboboxdata>();
foreach (var a in a1.GroupBy(x => x.username).Select(x => x.FirstOrDefault()))
{
modeltogetusername.Add(new comboboxdata
{
username = a.username.ToString()
});
}
}
}
}
public class ViewModel: INotifyPropertyChanged {
/** You can see that I'm calling viewModel class is depended with
populatetab2combobox. I believe this is the perfect case for implementing
Inversion of control **/
populatetab2combobox_populatecombobox = new populatetab2combobox();
private PopulateDatagrid _populatedatagridwithobservablecollection = new PopulateDatagrid();
private Loadfileintodatabase loaddata = new Loadfileintodatabase();
public PopulateDatagrid Populatedatagridwithobservablecollection {
get {
return _populatedatagridwithobservablecollection;
}
set {
if (value != _populatedatagridwithobservablecollection) {
_populatedatagridwithobservablecollection = value;
OnPropertyChanged("Populatedatagridwithobservablecollection");
}
}
}
DataModel dm = new DataModel();
public ViewModel() {
_populatecombobox.getdatausinglinq();
DoSomeThingCmd = new RelayCommand(o = >search());
_populatedatagridwithobservablecollection.getdatausinglinq();
}
#region INotifyPropertyChanged Members
public event PropertyChangedEventHandler PropertyChanged;
private void OnPropertyChanged(string propertyName) {
if (PropertyChanged != null) {
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
}
#endregion
}
}
Code with implementation of inversion of control(The issue is combobox is empty when i run when IOC implemented):
public interface INofificationAction
{
void getdatausinglinq();
}
public class populatetab2combobox : INofificationAction
{
public ObservableCollection<comboboxdata> modeltogetusername { get; set; }
public void getdatausinglinq()
{
using (Operations_Productivity_ToolEntities context = new Operations_Productivity_ToolEntities())
{
var a1 = from t1 in context.Test_ImportedAuditdata
select t1;
if (modeltogetusername == null)
modeltogetusername = new ObservableCollection<comboboxdata>();
foreach (var a in a1.GroupBy(x => x.username).Select(x => x.FirstOrDefault()))
{
modeltogetusername.Add(new comboboxdata
{
username = a.username.ToString()
});
}
}
}
}
public class implementingabstraction
{
INofificationAction _an;
public implementingabstraction(INofificationAction action)
{
this._an = action;
}
public void getdatausinglinq()
{
_an.getdatausinglinq();
}
}
public class ViewModel: INotifyPropertyChanged
{
INofificationAction getdata123 = new populatetab2combobox();
populatetab2combobox _populatecombobox = new populatetab2combobox();
public populatetab2combobox populatecombobox {
get {
return _populatecombobox;
}
set {
if (value != _populatecombobox) {
_populatecombobox = value;
OnPropertyChanged("populatetab2combobox");
}
}
}
public RelayCommand DoSomeThingCmd {
get;
set;
}
DataModel dm = new DataModel();
public ViewModel() {
implementingabstraction abs = new implementingabstraction(getdata123);
abs.getdatausinglinq();
DoSomeThingCmd = new RelayCommand(o = >search());
_populatedatagridwithobservablecollection.getdatausinglinq();
}
}
questions:
1) since I'm very new to oops based approach.Whether the above usecase is correct.
2) The above code is not working correctly. Can you please point out the mistake in my approach.
MyProduct is the model that has HasError boolean property (with OnPropertyChanged ...) that can change.
MyProductDialogViewModel is:
class ProductDialogViewModel : Notifier
{
public ProductDialogViewModel() { }
public MyProduct Product { get; set; }
public bool HasError
{
get { return Product.HasError; }
}
}
I have assigned MyProductDialogViewModel instance to BaseContentControl.DataContext to inflate a ContentControl.
This View can be inflated with different ViewModels all having HasError property using template binding.
<ContentControl x:Name="BaseContentControl" Content="{Binding}" ... >
Then I try to extract informations directly from its DataContext.
This don't work:
<Label Content="{Binding ElementName=BaseContentControl, Path=DataContext.HasError}"/>
But this works perfectly.
<Label Content="{Binding ElementName=BaseContentControl, Path=DataContext.Product.HasError}"/>
I tought it ca be a notifiy problem in the ViewModel so I have changed to this:
class ProductDialogViewModel : Notifier
{
public ProductDialogViewModel() { }
public MyProduct Product { get; set; }
public bool HasError
{
get { return Product.HasError; }
set
{
if (Product.HasError != value)
{
Product.HasError = value;
OnPropertyChanged("HasError");
}
}
}
}
but to no avail (in fact the set method is never called so it never notifies).
I don't want to directly refer to the specific Model instance cause the View can be inflated with different ViewModels.
How can I do ?
Thanks
You have to propagate the PropertyChanged event of MyProduct, i.e. subscribe to it and invoke OnPropertyChanged(nameof(HasError)) if HasError property of MyProduct being changed:
public class ProductDialogViewModel : Notifier
{
public ProductDialogViewModel() { }
private MyProduct _product = null;
public MyProduct Product
{
get { return _product; }
set
{
if (_product!=null)
{
_product.PropertyChanged -= Product_PropertyChanged;
}
_product = value;
if (_product != null)
{
_product.PropertyChanged += Product_PropertyChanged;
}
}
}
private void Product_PropertyChanged(object sender, PropertyChangedEventArgs e)
{
if (e.PropertyName==nameof(MyProduct.HasError))
{
OnPropertyChanged(nameof(HasError));
}
}
public bool HasError => Product.HasError;
}
why does not working the following code?
I have this class:
public class ExportSetting : INotifyPropertyChanged
{
public Guid Guid { get; set; }
public string Name { get; set; }
private bool export;
public bool Export
{
get { return export; }
set
{
export = value;
NotifyPropertyChanged();
}
}
public event PropertyChangedEventHandler PropertyChanged;
protected void NotifyPropertyChanged([CallerMemberName]string propertyName = null)
{
if (!string.IsNullOrEmpty(propertyName) && PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
}
}
And I created collection by using command yield:
public IEnumerable<ExportSetting> SequencesToExport
{
get { return sequencesToExport; }
set { sequencesToExport = value; }
}
...
sequencesToExport = FillSequencesSetting(sequences);
private IEnumerable<ExportSetting> FillSequencesSetting(List<MTFSequence> sequences)
{
foreach (var item in sequences)
{
yield return new ExportSetting(item.Id, item.Name, true);
}
}
When the property Export (from class ExportSetting) is changed from UI should be raised the event PropertyChanged but this event is null.
(ListBox in XAML has ItemsSource binding to property SequenceToExport)
When I modified creation of collection like this everything is working properly:
private IEnumerable<ExportSetting> FillSequencesSetting(List<MTFSequence> sequences)
{
List<ExportSetting> tmp = new List<ExportSetting>();
foreach (var item in sequences)
{
tmp.Add(new ExportSetting(item.Id, item.Name, true));
}
return tmp;
}
Why the command yield causes the event PropertyChanged isn't registered and is null and when i create collection by using the generic List the event is working properly?
Thanks for your answers.
You need to materialize the enumerable. With your current code, the foreach loop is run every time the enumerable is enumerated, creating new ExportSetting objects every single time.
Fix:
sequencesToExport = FillSequencesSetting(sequences).ToArray();
Or:
sequencesToExport = FillSequencesSetting(sequences);
private IEnumerable<ExportSetting> FillSequencesSetting(List<MTFSequence> sequences)
{
return sequences.Select(x => new ExportSetting(x.Id, x.Name, true)).ToArray();
}
You miss notification for when SequencesToExport property is changed:
public bool Export
{
get { return export; }
set
{
export = value;
NotifyPropertyChanged();
NotifyPropertyChanged(nameof(SequencesToExport));
}
}
I am new in WPF I have implemented INotifyPropertyChanged interface. I have one viewmodel containing the property "TeamMemberList". The control executes the setter part, changes the property value but the PropertyChanged event remains null.
Here is code:
ViewModelBase:
public class ViewModelBase : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
protected void NotifyPropertyChanged(string propertyName)
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
}
}
ViewModel:(Which inherits the viewmodelbase)
Property is
public List<Employee> TeamMemberList
{
get
{
return _teamMemberList;
}
set
{
_teamMemberList = value;
NotifyPropertyChanged("TeamMemberList");
}
}
Binding
<ListBox Margin="10" ItemsSource="{Binding TeamMemberList, Mode=TwoWay,
UpdateSourceTrigger=PropertyChanged}" >
when new employee added to the DB, model reads it & creates List for all emplyee then the TeamMeberList property gets updated. This is updation method for TeamMemberList
var qryEmp = from employee in ClientModel.EmployeeList
where employee.ReportingManager == UserProfile.EmployeeId
select new Employee
{
EmployeeId = employee.EmployeeId,
EmployeeName = employee.EmployeeName,
Designation = employee.Designation,
ProfilePic = employee.ProfilePic,
};
TeamMemberList = qryEmp.ToList();
And implementation of Employee
public class Employee : ViewModelBase
{
private string _employeeName;
private string _employeeId;
private string _profilePic;
private string _designation;
private string _reportinManager;
public string EmployeeName
{
get
{
return _employeeName;
}
set
{
_employeeName = value;
NotifyPropertyChanged("EmployeeName");
}
}
public string EmployeeId
{
get
{
return _employeeId;
}
set
{
_employeeId = value;
NotifyPropertyChanged("EmployeeId");
}
}
public string ProfilePic
{
get
{
return _profilePic;
}
set
{
_profilePic = value;
NotifyPropertyChanged("ProfilePic");
}
}
public string Designation
{
get
{
return _designation;
}
set
{
_designation = value;
NotifyPropertyChanged("Designation");
}
}
public string ReportingManager
{
get
{
return _reportinManager;
}
set
{
_reportinManager = value;
NotifyPropertyChanged("ReportingManager");
}
}
}
It's hard to say what the problem is when we don't see more code (eg: how you are setting the DataContext etc...).
But there is an easy way to debug your bindings by adding the following attribute to it:
<ListBox Margin="10" ItemsSource="{Binding TeamMemberList, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"
PresentationTraceSources.TraceLevel=High>
Adding this attribute will output the whole binding sequence to the Output window of Visual Studio. That should point out what is going wrong.
If you want to enable this for all bindings, you can also use the Visual Studio options:
Use ObserveableCollection instead of a list
My project ViewModel elements are not being found. I'm trying to implement a ViewModel within my WPF Usercontrol. However, the binding isn't working properly and there appears to be no data. I'm trying to create a ViewModel to interact with, putting generic string arrays into, and various other bits of data.
MainWindow.xaml - (Usercontrol declaration)
<panels:FilterLister Grid.Column="0" x:Name="filter1FilterLister" />
MainWindows.cs - (Within the constructor, call to usercontrol
filter1FilterLister.Initialise(typeof(Genre));
FilterListViewModel.cs
public class FilterListViewModel
{
MyEntities context = new MyEntities();
ObservableCollection<string> entries = new ObservableCollection<string>();
public Type SelectedType;
private string p_TypeName;
public string TypeName
{
get { return p_TypeName; }
set {
//p_TypeName = value;
p_TypeName = SelectedType.Name.ToString();
}
}
public FilterListViewModel() { }
public FilterListViewModel(Type selectedType)
{
if (selectedType == typeof(Artist))
{
returnedArray = Artist.ReturnArtistNames(context);
}
// put together ObservableCollection
foreach (var str in returnedArray)
{
entries.Add(str);
}
SelectedType = selectedType;
}
}
FilterLister.xaml
<Label Name="labelToBind" Content="{Binding TypeName}" Grid.Row="0" />
FilterLister.cs
public partial class FilterLister : UserControl
{
FilterListViewModel filterListViewModel;
private MyEntities context;
public FilterLister()
{
InitializeComponent();
context = new MyEntities();
}
public void Initialise(Type objectType)
{
filterListViewModel = new FilterListViewModel(objectType);
this.DataContext = filterListViewModel;
}
}
Based on your code, TypeName is null so you saw nothing on the Label. From your code, I think you want to describe like:
public string TypeName
{
get{ return SelectedType.Name.ToString();}
}
As deryck suggested, you should add INotifyPropertyChanged interface for notification, but it should not affect binding at first time. If you believe ViewModel's data is correct but not populated on UI, you should check DataContext and Binding.
You've missed implement the INotifyPropertyChanged interface in your ViewModel, it's needed to the binded property can send "refresh message" to a UI.
Here is the interface, and how you can implement this:
http://msdn.microsoft.com/en-us/library/system.componentmodel.inotifypropertychanged.aspx
public class FilterListViewModel : INotifyPropertyChanged
{
MyEntities context = new MyEntities();
ObservableCollection<string> entries = new ObservableCollection<string>();
public Type SelectedType;
private string p_TypeName;
public string TypeName
{
get { return p_TypeName; }
set {
//p_TypeName = value;
p_TypeName = SelectedType.Name.ToString();
NotifyPropertyChanged();
}
}
public FilterListViewModel() { }
public FilterListViewModel(Type selectedType)
{
if (selectedType == typeof(Artist))
{
returnedArray = Artist.ReturnArtistNames(context);
}
// put together ObservableCollection
foreach (var str in returnedArray)
{
entries.Add(str);
}
SelectedType = selectedType;
}
private void NotifyPropertyChanged([CallerMemberName] String propertyName = "")
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
}
}