Set button state base on the state of items in list

Question

Hi everyone,
I'm making an application that helps user to manages their file.
In my application, I have a list of files and a button Delete all.
I want the Delete all button to be disabled when all files in my list are hidden.
Can anyone help me please ?
Thank you :)

Answer 1

>>I want the Delete all button to be disabled when all files in my list are hidden.
Add a Hidden property to the class that represents a File in your application:
public class File : ViewModelBase
private bool _hidden;
public bool Hidden
get { return _hidden; }
set { _hidden = value; base.RaisePropertyChanged("Hidden"); }
...and bind the Command property of the Button to a RelayCommand (DeleteCommand) and make its CanExecute method return true only when there are at least one File object with the Hidden property set to false:
public class ViewModel
public ObservableCollection<File> Files { get; set; }
public RelayCommand DeleteCommand
get { return new RelayCommand(OnDelete, CanDelete); }
private bool CanDelete()
return Files.Any(f => !f.Hidden);
private void OnDelete()
//delete....
>>I wonder if the button state can be changed when an item state changes or not :)
Call the RaiseCanExecuteChanged() method of the DeleteCommand whenever the Hidden property of any File object in the Files collection is set to a new value.
You could do this by hooking up an event handler for the PropertyChanged event of each File object in the view model class like this:
public class ViewModel
public ViewModel()
this.Files = new ObservableCollection<File>();
//load files....
foreach (File file in this.Files)
(file as INotifyPropertyChanged).PropertyChanged
+= new PropertyChangedEventHandler(item_PropertyChanged);
this.Files.CollectionChanged += Files_CollectionChanged;
private void item_PropertyChanged(object sender, PropertyChangedEventArgs e)
if(e.PropertyName == "Hidden")
DeleteCommand.RaiseCanExecuteChanged();
private void Files_CollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
if (e.NewItems != null)
foreach (object file in e.NewItems)
(file as INotifyPropertyChanged).PropertyChanged
+= new PropertyChangedEventHandler(item_PropertyChanged);
if (e.OldItems != null)
foreach (object file in e.OldItems)
(file as INotifyPropertyChanged).PropertyChanged
-= new PropertyChangedEventHandler(item_PropertyChanged);
public ObservableCollection<File> Files { get; set; }
public RelayCommand DeleteCommand
get { return new RelayCommand(OnDelete, CanDelete); }
private bool CanDelete()
return Files.Any(f => !f.Hidden);
private void OnDelete()
//delete....
Note that this requires the File class to implement the INotifyPropertyChanged.
Hope that helps.
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