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WPF multiple Combobox binding with model

I have two comboboxes. One is grade category (e.g. elementary school, middle school, high school), and another for year. I want to make sure that the year combobox only shows the relevant ones, so that there there will be none of stuffs like 4th year of middle school. This is how I implemented my combobox.
Model
public class ComboBoxLogic {
private List<string> _Grade_category;
private List<string> _Year;
// There is no set property because all sets are done within the class.
public IList<string> public IList<string> Grade_category
{
get
{
return _Grade_category;
}
}
public IList<string> Year
{
get
{
return _Year;
}
}
public void Grade_category_selected(string s)
{
string temp;
_Grade.Clear();
if (s.Equals("Elementary"))
{
for (int i = 1; i <= 5; i++)
{
temp = i.ToString();
_Grade.Add(temp);
}
return;
}
else if (s.Equals("Middle"))
{
_Grade.Add("1");
_Grade.Add("2");
_Grade.Add("3");
return;
}
else if (s.Equals("High"))
{
_Grade.Add("1");
_Grade.Add("2");
_Grade.Add("3");
_Grade.Add("4");
return;
}
}
public ComboBoxLogic() {
_Grade_category = new List<string>() {"Elementary", "Middle", "High"}
_Year = new List<string>();
}
}
XAML
<Combobox
Name="Grade_category"
ItemsSource="{Bind Path=Grade_category}"
SelectedItem="{Bind Path=sGrade_category}" />
<Combobox
Name="Year"
ItemsSource="{Bind Path=Year}"
SelectedItem="{Bind Path=sYear}" />
View Model
class ComboBoxViewModel {
private ComboBoxLogic cbl;
public ComboBoxViewModel() {
cbl = new ComboBoxLogic();
}
public IList<string> Grade_category {
get { return cbl.Grade_category; }
}
public string Grade_category_selected {
set {cbl.Grade_category_selected(value);}
}
public IList<string> Year {
get { return cbl.Year; }
}
public string Year_selected {
set { }
}
}
There are 2 problems involved in this.
When I try this, it only works in the first time. From second selection of grade, year doesn't get updated properly. I'm thinking it's because I did not notify propertychanged for Year when grade_category changed. But, how do I do that?
In my project, I will have multiple of these comboboxes where one combobox depends on another. And, all implementation of dependency will be written in ComboboxLogic class. Is there a way to make this shorter instead of having to write every properties for ItemsSource and SelectedItem for every combobox?

"When I try this, it only works in the first time. From second
selection of grade, year doesn't get updated properly. I'm thinking
it's because I did not notify propertychanged for Year when
grade_category changed. But, how do I do that?"
Wrong, it's not about property changes. To propagate collection changes to the view the collection must implement INotifyCollectionChanged like ObservableCollection does. Replacing Years:IList with Years:ObservableCollection would do it.
"In my project, I will have multiple of these comboboxes where one
combobox depends on another. And, all implementation of dependency
will be written in ComboboxLogic class. Is there a way to make this
shorter instead of having to write every properties for ItemsSource
and SelectedItem for every combobox?"
In your specific case the trick is create a data model, that reflects the subject. All displayed data relates to a single object instance - the selected object (under different circumstances the solution would be to filter an ICollectionView).
A grade has a name and lasts a specific number of years.
The Grade class can look as follows:
Grade.cs
public class Grade : INotifyPropertyChanged
{
public string Name { get; set; }
public IEnumerable<int> Years { get; set; }
public event PropertyChangedEventHandler PropertyChanged;
protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null)
{
this.PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
}
}
ViewModel.cs
class ViewModel : INotifyPropertyChanged
{
public ObservableCollection<Grade> Grades { get; set; }
private Grade selectedGrade;
public Grade SelectedGrade
{
get => this.selectedGrade;
set
{
this.selectedGrade = value;
OnPropertyChanged();
}
}
public ViewModel()
{
this.Grades = new ObservableCollection<Grade>
{
new Grade() {Name = "Elementary", Years = Enumerable.Range(1, 4)},
new Grade() {Name = "Middle", Years = Enumerable.Range(1, 3)},
new Grade() {Name = "High", Years = Enumerable.Range(1, 4)},
};
}
public event PropertyChangedEventHandler PropertyChanged;
protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null)
{
this.PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
}
}
MainWindow.xaml
<Window>
<Window.DataContext>
<ViewModel />
</Window.DatContext>
<StackPanel>
<ComboBox ItemsSource="{Binding Grades}"
SelectedItem="{Binding SelectedGrade}"
DisplayMemberPath="Name" />
<ComboBox ItemsSource="{Binding SelectedGrade.Years}" />
</StackPanel>
</Window>

C# How to edit cell value in gridview?

I have a gridview shown as below in XAML
<ListView x:Name="listTasks">
<ListView.View>
<GridView x:Name="gridTasks">
<GridViewColumn Header="ID" HeaderStringFormat="Lowercase" Width ="26" DisplayMemberBinding="{Binding id}"/>
<GridViewColumn Header="Something" Width="113" DisplayMemberBinding="{Binding something}"/>
<GridViewColumn Header="State" Width="179" DisplayMemberBinding="{Binding currentState}"/>
</GridView>
</ListView.View>
</ListView>
and i have a button which adds to this gridview using the below
m.myList.Add(new mylistview.myitems
{
id = m.id,
something= m.something,
currentState = m.currentState,
});
This button works perfectly by adding the row into the gridview. However I would like to modify theCurrentState using a method that is running. How would I locate for example, ID = "8" and then modify theCurrentState for that row?
UPDATED CODE SHOWN
I've now replaced my list<Task> with ObservableCollection and managed to get it to add to my listview when I click onto my button. However, I am struggling to implement the iNotifyPropertyChanged into my code and getting it to work correctly... Below is my listview class
public class mylistview : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
protected void OnPropertyChanged([System.Runtime.CompilerServices.CallerMemberName] string propertyName = "")
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
}
private string _currentState;
public string currentState
{
get { return _currentState; }
set
{
_currentState = value;
OnPropertyChanged();
}
}
public ObservableCollection<myitems> _myList = new ObservableCollection<myitems>();
public ObservableCollection<myitems> myList
{
get { return _myList; }
}
private static int _id = 0;
public class myitems
{
public int id { get; set; }
public string something{ get; set; }
public string currentState { get; set; }
}
public int id
{
get { return _id; }
set { _id = value; }
}
}

So I see you're using data bindings already, that's good. But your question makes me think you haven't quite grasped everything it can do for you yet.
My recommendation would be to forget about adding items directly to listOfTasks.Items. Instead you should make an ObservableCollection to hold that list and bind the listOfTasks to it. Like so:
ObservableCollection tasks = new ObservableCollection<mylistview.myitems>();
ListOfTasks.ItemsSource = tasks;
With that binding in place you should be able to simply add new items to the tasks list when they click your button:
tasks.Add(new mylistview.myitems
{
id = theId,
something= something,
currentState = theCurrentState,
});
and it should automatically update the GUI.
The last step is to make sure that the class mylistview.myitems implements INotifyPropertyChanged. This is easier than it sounds; you just need to have it trigger an event any time the property is set. Something like so:
public class exampleProperties: INotifyPropertyChanged
{
//this is the event you have to emit
public event PropertyChangedEventHandler PropertyChanged;
//This is a convenience function to trigger the event.
//The CallerMemberName part will automatically figure out
//the name of the property you called from if propertyName == ""
protected void OnPropertyChanged([System.Runtime.CompilerServices.CallerMemberName] string propertyName = "")
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(propertyName);
}
}
//Any time this property is set it will trigger the event
private string _currentState = "";
public string currentState
{
get { return _currentState; }
set
{
if (_currentState != value)
{
_currentState = value;
OnPropertyChanged();
}
}
}
}
Now that the gridview is bound to an ObservableCollection and the items held in that collection can notify interested GUI controls that their properties have changed, you should simply be able to update the GUI simply by changing the appropriate item in the collection.
And here's an example of a form that uses the whole technique: https://msdn.microsoft.com/en-us/library/system.componentmodel.inotifypropertychanged(v=vs.110).asp
edit
I forgot that you specifically need to bind to the ItemSource property of the ListView. The way I have done it in the past is to set ItemsSource={binding} in the ListView's xaml and then assign an ObservableCollection to ListView.DataContext. However I have found an easier way and updated the original post with it. Here's a reference: http://www.wpf-tutorial.com/listview-control/listview-with-gridview/
Edit 2
Aha, you're adding the iPropertyChangedNotify to the wrong thing. It goes on the myitems class like so:
public class myitems : iNotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
protected void OnPropertyChanged([System.Runtime.CompilerServices.CallerMemberName] string propertyName = "")
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
}
private int _id;
public int id
{
get { return _id; }
set
{
_id = value;
OnPropertyChanged();
}
}
public string something{ get; set; }
public string currentState { get; set; }
}
I leave updating the current state and something properties as an excersize. They also need to trigger the OnPropertyChanged event when their value is set.

Maybe with
listOfTasks.Items.Cast<ListViewItem>().First(item => item.ID == "8").theCurrentState = newState;
//I'm not sure about the Cast stuff, because I don't know what types the ListView uses for its items
Of course you could iterate through the items with a loop and check manually for the ID as well.

WPF Databind control in write-only mode

I'm trying to fiddle a little with WPF bindings, so I created a simple project.
Here's the code:
public class Person : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
public int Age {
get { return age; }
set {
age = value;
FirePropertyChanged("Age");
}
}
public string Name
{
get { return name; }
set
{
name = value;
FirePropertyChanged("Name");
}
}
private void FirePropertyChanged(string v)
{
if(PropertyChanged !=null)
PropertyChanged(this, new PropertyChangedEventArgs(v));
}
private int age;
private string name;
}
My viewmodel contains ObservableCollection of Person, and single Person to track selected Person.
I've bound listbox's ItemsSource to ObservableCollection, and SelectedItem to single Person, called CurrentPerson. Also, I've bound TextBox to CurrentPerson.Name.
Code works fine, but whenever I change content of TextBox - my listbox also changes. And no matter what combination of "OneWay, TwoWay, OneWayToSource" binding modes on listbox\selecteditem I cannot prevent listbox from updating from CurrentPerson.
How can I prevent this behavior? I'd like to update listbox from CurrentPerson only by using ICommand interface from VM.

There is only one copy of the Person object which is being used in both ListBox.ItemsSource and TextBox.Text, so naturally updating that object from one location will reflect the change in the other as well.
Two easy solutions would be
Change the BindingMode on TextBox.Text to Explicit, so it doesn't update the Person object until you tell it to
Use a separate string property for TextBox.Text and copy it over to your SelectedPerson.Name whenever the command executes
Personally I prefer the second option because I'm not a big fan of bindings that don't accurately reflect the data object behind the UI component, and it would allow the user to change the SelectedItem without resetting the TextBox value.
For an example of the second option, your ViewModel might look like this :
public class MyViewModel()
{
ObservableCollection<Person> People { get; set; }
Person SelectedPerson { get; set; }
string NewPersonName { get; set; }
ICommand UpdatePersonName { get; }
}
where the UpdatePersonName command would execute
SelectedPerson.Name = NewPersonName;
and the CanExecute would only return true if
SelectedPerson != null
&& !NewPersonName.IsNullOrWhiteSpace()
&& NewPersonName != SelectedPerson.Name

I'm not sure if I've followed the question properly.
So, we have a class Person as
public class Person : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
public int Age
{
get { return age; }
set
{
age = value;
FirePropertyChanged("Age");
}
}
public string Name
{
get { return name; }
set
{
name = value;
FirePropertyChanged("Name");
}
}
private void FirePropertyChanged(string v)
{
if (PropertyChanged != null)
PropertyChanged(this, new PropertyChangedEventArgs(v));
}
private int age;
private string name;
}
And we have a view model as
public class ViewModel : INotifyPropertyChanged
{
public ObservableCollection<Person> List { get; set; }
Person currentPerson;
public Person CurrentPerson {
get { return currentPerson; }
set { currentPerson = value;
FirePropertyChanged("CurrentPerson");
}
}
private void FirePropertyChanged(string v)
{
if (PropertyChanged != null)
PropertyChanged(this, new PropertyChangedEventArgs(v));
}
public event PropertyChangedEventHandler PropertyChanged;
}
The xaml is
<ListBox ItemsSource="{Binding List}" SelectedItem="{Binding CurrentPerson}">
<ListBox.ItemTemplate>
<DataTemplate>
<TextBox Text="{Binding Name}" Width="100" />
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>
And I bind the view model to the view via
ViewModel vm = new ViewModel();
vm.List = new ObservableCollection<Person>();
foreach (var i in Enumerable.Range(1,10))
{
vm.List.Add(new Person() { Name = "Test" + i.ToString(), Age= i });
}
vm.CurrentPerson = null;
this.DataContext = vm;
Whenever I change the value at textbox, it updates the name properly. I tried to add a handler for list changed, but it doesn't happen to get triggered.
vm.List.CollectionChanged += List_CollectionChanged;
void List_CollectionChanged(object sender, System.Collections.Specialized.NotifyCollectionChangedEventArgs e)
{
MessageBox.Show(e.Action.ToString());
}
Can you comment if it isn't the same as your problem statement?

If you want to control when and what is saved/updated, you obviously need is a ViewModel for editing your Person model.
When selecting a person in your Listbox, you have to pass the person's id (avoid passing the object itself) to the PersonEditViewModel which is bound to the properties that shall be edited, load the persons data into the PersonEditViewModel and then edit. Once you hit the "Save" button, it should commit the change and update the database or whatever you are using for persistence.
Use either events/messages to pass values/events back and forth, or use a navigation approach (like INavigationAware interface in Prism).

How to bind ComboBox properly in WPF?

I'm new to WPF and MVVM and I'm developing a test WPF application following the MVVM design pattern. My database has 2 entities, Cards and Departments. Any card can have only 1 department, so it's a one-to-many relationship.
I've created the following ViewModel in order to bind to the view:
public class CardViewModel : INotifyPropertyChanged
{
public CardViewModel(Card card)
{
this.Card = card;
SqlConnectionStringBuilder builder = new SqlConnectionStringBuilder();
builder.DataSource = ".\\SQLExpress";
builder.InitialCatalog = "TESTDB";
builder.IntegratedSecurity = true;
SybaseDatabaseContext myDB = new SybaseDatabaseContext(builder.ConnectionString);
var query = from d in myDB.Departments
select d;
this.Departments = new ObservableCollection<Department>(query);
}
private Card _Card;
private ObservableCollection<Department> _Departments;
public Card Card
{
get { return _Card; }
set
{
if (value != this._Card)
{
this._Card = value;
SendPropertyChanged("Card");
}
}
}
public ObservableCollection<Department> Departments
{
get { return _Departments; }
set
{
this._Departments = value;
SendPropertyChanged("Departments");
}
}
#region INPC
// Logic for INotify interfaces that nootify WPF when change happens
public event PropertyChangedEventHandler PropertyChanged;
protected virtual void SendPropertyChanged(String propertyName)
{
if ((this.PropertyChanged != null))
{
this.PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
}
#endregion
}
The CardForms' datacontext is currently being set to an instance of the CardViewModel in the code where the CardForm is being instantiated, but I'm going to create a IoC container or dependency injections down the line.
Everything binds correctly except for the ComboBox that should contain all departments and that has the current department in the Card instance selected (card.Department). Here's the XAML for the ComboBox:
<ComboBox Height="23" HorizontalAlignment="Left" Margin="350,64,0,0"
Name="comboBoxDepartment" VerticalAlignment="Top" Width="120"
IsSynchronizedWithCurrentItem="True"
ItemsSource="{Binding Path=Departments}"
DisplayMemberPath="DepartmentName"
SelectedItem="{Binding Path=Card.Department, Mode=TwoWay}" />
The departments are displayed in the combobox, but the current department of the card isn't and if I try to change it I get and error saying "Cannot add an entity with a key that is already in use".
So, my question is, how do I bind this combobox correctly to my ViewModel?
P.S. I know populating the ObservableCollection<Department> in the ViewModel is probably not the right way to do it, but I could not think of a better way at the time. If you have any suggestions for this also, please let me know.
Additionally, this is the Card model:
[Table(Name = "Card")]
public class Card : INotifyPropertyChanged, INotifyPropertyChanging
{
private string _CardID;
private string _Holder;
private Int16? _DepartmentNo;
[Column(UpdateCheck = UpdateCheck.WhenChanged)]
public string CardID
{
get
{
return this._CardID;
}
set
{
if (value != this._CardID)
{
SendPropertyChanging();
this._CardID = value;
SendPropertyChanged("CardID");
}
}
}
[Column(UpdateCheck = UpdateCheck.WhenChanged)]
public string Holder
{
get
{
return this._Holder;
}
set
{
if (value != this._Holder)
{
SendPropertyChanging();
this._Holder = value;
SendPropertyChanged("Holder");
}
}
}
[Column(CanBeNull = true, UpdateCheck = UpdateCheck.WhenChanged)]
public Int16? DepartmentNo
{
get
{
return this._DepartmentNo;
}
set
{
if (value != this._DepartmentNo)
{
SendPropertyChanging();
this._DepartmentNo = value;
SendPropertyChanged("DepartmentNo");
}
}
}
private EntityRef<Department> department;
[Association(Storage = "department", ThisKey = "DepartmentNo", OtherKey = "DepartmentNo", IsForeignKey = true)]
public Department Department
{
get
{
return this.department.Entity;
}
set
{
Department previousValue = this.department.Entity;
if (((previousValue != value)
|| (this.department.HasLoadedOrAssignedValue == false)))
{
this.SendPropertyChanging();
if ((previousValue != null))
{
this.department.Entity = null;
previousValue.Cards.Remove(this);
}
this.department.Entity = value;
if ((value != null))
{
value.Cards.Add(this);
this._DepartmentNo = value.DepartmentNo;
}
else
{
this._DepartmentNo = default(Nullable<short>);
}
this.SendPropertyChanged("Department");
}
}
}

I edited the constructor in the CardViewModel to take the DataContext as a parameter and that did it. This is the new CardViewModel constructor:
public CardViewModel(Card card, SybaseDatabaseContext myDB)
{
this.Card = card;
var query = from d in myDB.Departments
select d;
this.Departments = new ObservableCollection<Department>(query);
}

Had to do a bit of research on this myself. Thought I would contribute with a self answered question, but found this open current question...
The ComboBox is designed to be a kind of textbox that restricts it's possible values to the contents of a given list. The list is provided by the ItemsSource attribute. The current value of the ComboBox is the SelectedValue property. Typically these attributes are bound to relevant properties of a corresponding ViewModel.
The following example shows wired ComboBox together with a TextBox control used to redundantly view the current value of the ComboBox by sharing a view model property. (It is interesting to note that when TextBox changes the shared property to a value outside the scope of the ComboBox's list of values, the ComboBox displays nothing.)
Note: the following WPF/C# example does does use code-behind and so presents the ViewModel as merely the datacontext of the view and not a partial class of it, a current implementation constraint when using WPF with F#.
WPF XAML
<Window
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:m="clr-namespace:WpfApplication1"
Title="MainWindow" Height="350" Width="525">
<Window.DataContext>
<m:MainWindowVM />
</Window.DataContext>
<StackPanel>
<TextBox Text="{Binding SelectedString}" />
<ComboBox ItemsSource="{Binding MyList}" SelectedValue="{Binding SelectedString}" />
</StackPanel>
</Window>
C# ViewModel
using System.Collections.Generic;
using System.ComponentModel;
namespace WpfApplication1
{
public class MainWindowVM : INotifyPropertyChanged
{
string selectedString;
void NotifyPropertyChanged(string propertyName)
{
if (PropertyChanged == null) return;
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
public string SelectedString
{
get { return selectedString; }
set
{
selectedString = value;
NotifyPropertyChanged("SelectedString");
}
}
public List<string> MyList
{
get { return new List<string> { "The", "Quick", "Brown", "Fox" }; }
}
public event PropertyChangedEventHandler PropertyChanged;
}
}
By default, ToString() is used to interpret the objects in the list. However, ComboBox offers DisplayMemberPath and SelectedValuePath attributes for specifying paths to specific object properties for corresponding displayed and stored values. These paths are relative to the list object element so a path of "Name" refers to Name on a list object item.
The "Remarks" section of this MSDN link explains the interpretations of the IsEditable and IsReadOnly ComboBox properties.

How to bind a combo-box to a collection of multi-language values in WPF?

I am trying to set up a multi-language application, so when the user changes the display language all the texts in all the open windows change automatically.
I am having issues through with binding combo-box control. The binding needs to be done in code-behind as I have dynamic content coming from a database, and sometimes I even have to create additional combo-boxes at runtime.
Also I do not want to keep the translations in the database because I do not want to query the database every time a user is changing the display language.
What I did until now:
in xaml:
<ComboBox x:Name="cmb"/>
and in C#:
public class MyCmbItem
{
public int Index { get; set; }
public string Text { get; set; }
}
private ObservableCollection<MyCmbItem> LoadText()
{
ObservableCollection<MyCmbItem> _result = new ObservableCollection<MyCmbItem>();
foreach (var _item in _list)
{
//the list is coming from a database read
_result.Add(new MyCmbItem { Index = _item.Value, Text = _res_man_global.GetString(_item.KeyText, _culture) });
}
return _result;
}
public ObservableCollection<MyCmbItem> MyTexts
{
get { return LoadText(); }
set {} //I do not have to add/remove items at runtime so for now I leave this empty
}
private void Window_Loaded(object sender, RoutedEventArgs e)
{
...
LoadList(); //this adds values in _list
cmb.ItemsSource = MyTexts; //this populates the combo-box
Here I got stuck and I do not know how to determine the combo-box to refresh the displayed texts. The method must achieve that if I have several windows opened each containing a random number of combo-boxes, when I change the current language all the combo-boxes in all the windows will refresh the displayed list, without affecting other values inside (like the selected item). Does anybody know how this can be done?
Many thanks.

For your xaml UI, the INotifyPropertyChanged interface indicates updates of the viewmodel. You can extend your class like this:
public class MyCmbItem : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
protected void NotifyPropertyChanged(string APropertyName)
{
var property_changed = PropertyChanged;
if (property_changed != null)
{
property_changed(this, new PropertyChangedEventArgs(APropertyName));
}
}
private string _Text;
private string _KeyText;
public int Index { get; set; }
public string Text
{
get { return _Text;}
set {
if (_Text != value)
{
_Text = value;
NotifyPropertyChanged("Text");
}
}
}
public MyCmbItem(string key_text, int index)
{
Index = index;
_KeyText = key_text;
RefreshText();
_res_man_global.LanguageChanged += () => RefreshText();
}
public void RefreshText()
{
Text = _res_man_global.GetString(_KeyText, _culture);
}
}
Your view can simply bind to the Text-property as following:
<DataTemplate DataType="{x:Type local:MyCmbItem}">
<TextBlock Text="{Binding Path=Text}"/>
</DataTemplate>
Note: I assumed that your language class is global and has some kind of language-changed notification event.