Bind observerbaleCollection to wpf combo box - wpf

I'm having Class call Apps. It has Observable collection called AvailableTypes. I want to bind this AvailableTypes observable collection to the wpf ComboBox. When form is loaded these AppId should loaded into comboBox.. Would you give me a solution to this one?
class Apps: INotifyPropertyChanged{
ServiceReference1.AssetManagerServiceClient client;
ObservableCollection<string> availableType;
public ObservableCollection<string> AvailableTypes
{
get
{
if (availableType == null)
{
availableType = new ObservableCollection<string>();
}
client = new ServiceReference1.AssetManagerServiceClient();
List<string> AssestList = client.GetAppIds().ToList<string>();
foreach (string appid in AssestList)
{
availableType.Add(appid);
}
return availableType;
}
set
{
availableType = value;
NotifyPropertyChanged("AvailableTypes");
}
}
public event PropertyChangedEventHandler PropertyChanged;
private void NotifyPropertyChanged(string propertyName)
{
if (PropertyChanged != null)
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
}
}

In your xaml code, this is a simple example of how you can bind to your combobox.
<ComboBox ItemsSource={Binding Path=AvailableTypes} />
You will also need to load your viewmodel into the DataContext of your window too.
var window = new MainWindow
{
DataContext = new Apps()
};
window.Show();
If you want open the window on App startup, you can do this instead
public partial class App : Application
{
protected override void OnStartup(StartupEventArgs e)
{
base.OnStartup(e);
var window = new MainWindow
{
DataContext = new Apps()
};
window.Show();
}
}

Don't overload property getters/setters. Make it simplier.
I recommend to use auto properties and NotifyPropertyWeaver or use PostSharp post build compile-time injected instuctions to support INotifyPropertyChanged interface.
This makes your view model more readable and easy to manage/understand.
In your form 'Loaded' event or 'NavigatedTo' in SL you can start loading your data from anywhere you want and set corresponding properties after loading completed (in callbacks/events handlers, don't forget about using UI dispatcher while updating binded properties)

Related

SelectedItem not shown in ComboBox

I am using MVVM in a WPF application with C# and got a problem binding a ComboBox correctly.
This is my ComboBox line in the XAML:
<ComboBox ItemsSource="{Binding Repository.Models}" SelectedValue="{Binding Repository.SelectedModel}" DisplayMemberPath="Name"></ComboBox>
This is the interesting part of my Repository:
class Repository : INotifyPropertyChanged
{
//init MVVM pattern
public event PropertyChangedEventHandler PropertyChanged;
private void NotifyPropertyChanged(string propertyName)
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
}
private ObservableCollection<Model> _models;
public ObservableCollection<Model> Models
{
get
{
return _models;
}
set
{
_models = value;
NotifyPropertyChanged("Models");
}
}
private Model _selectedModel;
public Model SelectedModel
{
get
{
return _selectedModel;
}
set
{
_selectedModel = value;
NotifyPropertyChanged("SelectedModel");
}
}
This is the interesting part of my Model class:
abstract class Model : INotifyPropertyChanged
{
//init MVVM pattern
public event PropertyChangedEventHandler PropertyChanged;
private void NotifyPropertyChanged(string propertyName)
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
}
private string _name;
public string Name
{
get
{
return _name;
}
set
{
_name = value;
NotifyPropertyChanged("Name");
}
}
So when I select/change different items of the combobox a DataGrid that is binded to Repository.SelectedModel.Parameters does update just as i want it to.
Because of that I know, that the binding does work!
When I restart the application and debug into my Repository, I see that there is a SelectedModel (deserialised on startup) but the ComboBox stays blank. The DataGrid though does show the right data.
So the binding itself does work, but the binding to the ComboBoxLabel somehow fails.
I tried a lot of things like switching between SelectedItem and SelectedValue, between Binding and Binding Path, between IsSynchronizedWithCurrentItem true and false, but nothing worked so far.
Do you see my mistake?
Thanks in advance!
EDIT
Here is the interesting part of my MainWindowViewModel:
class MainWindowViewModel : INotifyPropertyChanged
{
//init MVVM pattern
public event PropertyChangedEventHandler PropertyChanged;
private void NotifyPropertyChanged(string propertyName)
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
}
private Repository _repository;
public Repository Repository
{
get
{
return _repository;
}
set
{
_repository = value;
NotifyPropertyChanged("Repository");
}
}
And here is my App.xaml.cs where I init my DataContext:
//init point of app
public partial class App : Application
{
private MainWindowViewModel mainWindowViewModel;
//gets fired as the app starts
protected override void OnStartup(StartupEventArgs e)
{
//create the ViewModel
mainWindowViewModel = new MainWindowViewModel();
//create the mainWindow
var mainWindow = new MainWindow();
mainWindow.DataContext = mainWindowViewModel;
//show the mainWindow
mainWindow.Show();
}
When I restart the application and debug into my Repository, I see that there is a SelectedModel (deserialised on startup) but the ComboBox stays blank. The DataGrid though does show the right data.
Looks like the deserialization is the problem.
You have a selected item which was deserialized. That means that a new Model instance was created which has a Name of whatever, and Properties that are whatever. And you have a list of Model instances in an ObservableCollection<Model> which are displayed in a ComboBox.
And you assure us that at least sometimes, you have ComboBox.SelectedItem bound to SelectedModel, though for some reason the code in your question binds ComboBox.SelectedValue instead. That's not going to work. Here's how ComboBox.SelectedValue would be used:
<ComboBox
ItemsSource="{Binding Repository.Models}"
SelectedValuePath="Name"
SelectedValue="{Binding SelectedModelName}"
/>
...and you would have to have a String SelectedModelName { get; set; } property on your viewmodel. The Name property of the selected Model would be assigned to that by the ComboBox when the selection changed. But you don't have SelectedModelName, and you don't want it, so forget about SelectedValue.
Back to SelectedItem. The ComboBox gets the value of SelectedModel from the binding, and tries to find that exact object in its list of Items. Since that exact object is not in that list, it selects nothing. There is probably an item in Repository.Models that has the same name and has identical Properties, but it is not the same actual instance of the Model class. ComboBox doesn't look for an identical twin of the value in SelectedItem; it looks for the same object.
SelectedModel.Properties works in the DataGrid because the DataGrid doesn't know or care what's in Models. You give it a collection, it's good.
So: If you want to deserialize a SelectedModel and have it mean anything, what you need to do is go ahead and deserialize, but then find the equivalent item in Repository.Models (same Name, same Properties), and assign that actual object instance to SelectedModel.
You may be tempted to overload Model.Equals(). Don't. I've done that to solve the same problem. The resulting behavior is not expected in C# and will bite you, hard, and when you least expect it, because you are invisibly altering behavior that happens in framework code. I've spent days tracking down bugs I created that way, and I'll never do it to myself again.
Try SelectedItem instead of SelectedValue in ComboBox.

How to update observable collection on property change and also store it on every change?

I have dynamic listbox contains textbox to display list items and so I can edit listbox item. My application setting file contains string collection which I want to bind for that listbox. I also want to update that setting files on every change of listbox item, I created class which implements INotifyProprtyChanged. I have converted string collection from settings file into observable collection of custom type which has string property. I bind textbox to property of that custom class and update source property on property change. I want to update observable collection as well. and that updates my app setting file as well. Please help me on this. Any help would be really appreciated. My code:
public class WindowViewModel : INotifyPropertyChanged
{
private ObservableCollection<UrlModel> customcollection;
public ObservableCollection<UrlModel> CustomCollection
{
get { return customcollection; }
set
{
customcollection = value;
NotifyPropertyChanged("CustomCollection");
}
}
public event PropertyChangedEventHandler PropertyChanged;
protected void NotifyPropertyChanged(string property)
{
if (PropertyChanged != null)
PropertyChanged(this, new PropertyChangedEventArgs(property));
}
public WindowViewModel()
{
List<string> customlist = Properties.Settings.Default.CustomList.Cast<string>().ToList();
List<UrlModel> urllist = new List<UrlModel>();
urllist = customlist.Select(item => new UrlModel() { urlString = item }).ToList();
CustomCollection = new ObservableCollection<UrlModel>(urllist);
}
}
public class UrlModel : INotifyPropertyChanged
{
private string url;
public string urlString
{
get { return url; }
set
{
url = value;
NotifyPropertyChanged("urlString");
}
}
public event PropertyChangedEventHandler PropertyChanged;
protected void NotifyPropertyChanged(string property)
{
if (PropertyChanged != null)
PropertyChanged(this, new PropertyChangedEventArgs(property));
}
}
/// <summary>
/// Interaction logic for MainWindow.xaml
/// </summary>
public partial class MainWindow : Window
{
public MainWindow()
{
InitializeComponent();
ViewModel = new WindowViewModel();
ListTwo.ItemsSource = ViewModel.CustomCollection;
}
private WindowViewModel viewModel;
public WindowViewModel ViewModel
{
get { return viewModel; }
set{
viewModel = value;
DataContext = value;
}
}
}
}
Add property changed event handler for each url when inserting into ObservableCollection
public WindowViewModel()
{
List<string> customlist = Properties.Settings.Default.CustomList.Cast<string>().ToList();
List<UrlModel> urllist = new List<UrlModel>();
urllist = customlist.Select(item => new UrlModel() { urlString = item }).ToList();
CustomCollection = new ObservableCollection<UrlModel>(urllist);
foreach(var model in CustomCollection)
{
model.PropertyChaged += SettingsUpdater; //Settings update fucntion
}
}
A naive implementation of SettingsUpdater would just update the whole list of urls in settings whenever one of them changes.
I believe you are using data template to make your listbox editable. If that is the case, while binding the text, include Text="{Binding urlString,UpdateSourceTrigger=PropertyChanged}" in the Xaml code.
<ListBox.ItemTemplate>
<DataTemplate>
<TextBox Name="EditableText" Text="{Binding urlString,UpdateSourceTrigger=PropertyChanged}"/>
</DataTemplate>
</ListBox.ItemTemplate>

MVVM Light pass parameters to child view model

I am new to MVVM and WPF.
I am using MVVM Light to make an application which contains a DataGrid within a window, which has a view model (MainViewModel) and another window for adding and editing records in the DataGrid, that also has its own view model (EditViewModel).
What I am worried about is the approach I am using to open the Add/Edit window from the MainViewModel. In the MainViewModel I have a property SelectedItem, which is bound to the SelectedItem property of the DataGrid and an IsEdit boolean property that indicates if the Add/Edit window should be launched in Add or Edit mode.
When the Add/Edit window gets opened in edit mode, in the constructor of its view model I have the following line:
MainViewModel mainViewModel = ServiceLocator.Current.GetInstance<MainViewModel>();
That obviously retrieves the current instance of the MainViewModel, which works perfectly fine, but I am not really sure it is the best way to do this.
Also if I have more than one instances of the Main window, that use the same MainViewModel instance and I open an instance of the Add/Edit window from both of them, the Add/Edit windows are going to get data from the same instance of the MainViewModel which may be a problem.
If I try to create a new instance of MainViewModel for each MainWindow I open, then I don't know how to pass the instance of the currently used MainViewModel to the EditViewModel.
I hope I made clear what I need to do. Tell me if I have missed something and I will add it:)
Thanks in advance
Hi if I havent misunderstood your problem incorrect you can do it this way:
Since i need IsRequired dependency Property in both MainView and EditView i created a class that extends Window class
public class ExtendedWindow:Window
{
public static readonly DependencyProperty IsRequiredProperty = DependencyProperty.Register("IsRequired", typeof(bool), typeof(ExtendedWindow));
public bool IsRequired
{
get { return (bool)GetValue(IsRequiredProperty); }
set { SetValue(IsRequiredProperty, value); }
}
}
MainView and ViewModel
public partial class MainWindow:ExtendedWindow
{
public MainWindow()
{
InitializeComponent();
DataContext = new MainViewModel();
}
private void Button_Click(object sender, RoutedEventArgs e)
{
EditView editView = new EditView();
**((EditViewModel)editView.DataContext).IsRequired = this.IsRequired;**
editView.Show();
}
}
public class MainViewModel : INotifyPropertyChanged
{
public MainViewModel()
{
IsRequired = true;
}
private bool isRequired;
public bool IsRequired
{
get { return isRequired; }
set { isRequired = value; Notify("IsRequired"); }
}
public event PropertyChangedEventHandler PropertyChanged;
private void Notify(string propName)
{
if (PropertyChanged != null)
PropertyChanged(this, new PropertyChangedEventArgs(propName));
}
}
EditView and ViewModel
public partial class EditView:ExtendedWindow
{
public EditView()
{
InitializeComponent();
DataContext = new EditViewModel();
}
}
public class EditViewModel : INotifyPropertyChanged
{
private bool isRequired;
public bool IsRequired
{
get { return isRequired; }
set { isRequired = value; Notify("IsRequired"); }
}
public event PropertyChangedEventHandler PropertyChanged;
private void Notify(string propName)
{
if (PropertyChanged != null)
PropertyChanged(this, new PropertyChangedEventArgs(propName));
}
}
This is just kind of dummy but can give you idea how you can do it. I have tried it in dummy and its working fine.

WPF : How do I implement Save button enabling

What would be the cleanest way to have a Save state for an application so that whenever a property or content was updated the "Save" options would become enabled.
For example, there is a menu and toolbar "Save" buttons. When the WPF app first opens both buttons are disabled. When the user updates the properties or document, the buttons become enabled until a "Save" is done, at which point they go back to disabled.
Bind IsEnabled to a ViewModel that exposes an "IsDirty" or "HasBeenModified" boolean property, or something of similar ilk. The ViewModel would watch for changes to the Model and set IsDirty to true if the Model is modified for any reason. When saved, the ViewModel can be told to set IsDirty to false, disabling the button.
You are using the Model-View-ViewModel pattern, right? Here are a few links on the pattern to help you on your way, just in case:
http://en.wikipedia.org/wiki/Model_View_ViewModel
http://msdn.microsoft.com/en-us/magazine/dd419663.aspx
http://www.wintellect.com/CS/blogs/jlikness/archive/2010/04/14/model-view-viewmodel-mvvm-explained.aspx
Are all the properties you wish to watch for in the same class? If so, something like this will work:
Have the class derive from INotifyPropertyChanged;
Watch for property changes from the class and set an IsDirty flag when there are changes
Set IsEnabled for the Save button based on the IsDirty flag
When the Save command is executed, set IsDirty=false
Notifying Class Example
public class NotifyingClass : INotifyPropertyChanged
{
private string Property1Field;
public string Property1
{
get { return this.Property1Field; }
set { this.Property1Field = value; OnPropertyChanged("Property1"); }
}
private string Property2Field;
public string Property2
{
get { return this.Property2Field; }
set { this.Property2Field = value; OnPropertyChanged("Property2"); }
}
#region INotifyPropertyChanged Members
public event PropertyChangedEventHandler PropertyChanged;
public void OnPropertyChanged(string propertyName)
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
}
#endregion
}
Watching for Property Changes
public partial class MainWindow : Window
{
private bool isDirty;
NotifyingClass MyProperties = new NotifyingClass();
public MainWindow()
{
InitializeComponent();
this.MyProperties.PropertyChanged += (s, e) =>
{
this.isDirty = true;
};
}
}
How you set the disabled/enabled state depends on what type of button/command implementation you are doing. If you would like further help just let me know how you are doing it (event handler, RoutedCommand, RelayCommand, other) and I'll check it out.

WPF Listbox not redrawing

I have a listbox defined in XAML as:
<ListBox x:Name="directoryList"
MinHeight="100"
Grid.Row="0"
ItemsSource="{Binding Path=SelectedDirectories}"/>
The SelectedDirectories is a property on the lists DataContext of type List<DirectoryInfo>
The class which is the datacontext for the listbox implements INotifyPropertyChanged. When the collection changes the items are added successfully to the list however the display does not update until I force the listbox to redraw by resizing it.
Any ideas why?
EDIT: INotifyPropertyChanged implementation
public class FileScannerPresenter : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
private FileScanner _FileScanner;
public FileScannerPresenter()
{
this._FileScanner = new FileScanner();
}
public List<DirectoryInfo> SelectedDirectories
{
get
{
return _FileScanner.Directories;
}
}
public void AddDirectory(string path)
{
this._FileScanner.AddDirectory(path);
OnPropertyChanged("SelectedDirectories");
}
public void OnPropertyChanged(string property)
{
if (this.PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(property));
}
}
}
Try
ObservableCollection<DirectoryInfo>
instead - you're triggering a refresh of the entire ListBox for no reason, and you don't need to make your hosting class implement INotifyPropertyChanged - it could easily just be a property of the window. The key is to never set the property to a new instance. So:
class SomeWindow : Window {
public ObservableCollection<DirectoryInfo> SelectedDirectories {get; private set;}
SomeWindow() { SelectedDirectories = new ObservableCollection<DirectoryInfo>(); }
public void AddDirectory(string path) {
SelectedDirectories.Add(new DirectoryInfo(path));
}
}
If you end up using that FileScanner class, you need to implement INotifyCollectionChanged instead - that way, the ListBox knows what to add/remove dynamically.
(See Update below). WPF seems to be working alright. I put your code into a new project. The listbox updates whenever I click the button to invoke AddDirectory. You should not need any more code changes.
The problem seems to be something else.. Are there multiple threads in your UI?
I didnt have the FileScanner type. So I created a dummy as follows.
public class FileScanner
{
string _path;
public FileScanner()
{ _path = #"c:\"; }
public List<DirectoryInfo> Directories
{
get
{
return Directory.GetDirectories(_path).Select(path => new DirectoryInfo(path)).ToList();
}
}
internal void AddDirectory(string path)
{ _path = path; }
}
No changes to your FileScannerPresenter class. Or your listbox XAML. I created a Window with a DockPanel containing your listbox, a textbox and a button.
Update: Paul Betts is right. It works because I return a new list each time from the Bound property. Data binding with lists always messes me up.
With more tinkering, the easy way to do this is:
Make FileScanner#Directories return an ObservableCollection<DirectoryInfo> (which implements INotifyCollectionChanged for you). Change all signatures all the way up to return this type instead of a List<DirectoryInfo>
FileScanner and FileScannerPresenter themselves do not have to implement any INotifyXXX interface.
// in FileScanner class def
public ObservableCollection<DirectoryInfo> Directories
{
get
{ return _DirList; }
}
internal void AddDirectory(string path)
{
_path = path;
//var newItems = Directory.GetDirectories(_path).Select(thePath => new DirectoryInfo(thePath)).ToList();
//_DirList.Concat( newItems ); -- doesn't work for some reason.
foreach (var info in Directory.GetDirectories(_path).Select(thePath => new DirectoryInfo(thePath)).ToList())
{
_DirList.Add(info);
}
}

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