I am facing some problems using GalaSoft's RelayCommand.
I have a NextCommand property that works, but only several times.
Afterwards, it stops working completely.
You can try this out with the sample project:
http://s000.tinyupload.com/?file_id=65828891881629261404
The behaviour is as follows:
- NextCommand:
- pops all items until the active index
- if there are less than 50 items left, pushes 1 new item
- marks new item as active
- BackCommand:
- moves the active index back by 1 position
Steps to replicate:
- the '+' (OemPlus) key has been bound to NextCommand
- the '-' (OemMinus) key has been bound to BackCommand
- Hold the '+' key until the list stops growing (50 items limit)
- Hold the '-' key until the first item in the list is the active
- Repeat
The number of repetitions needed (to replicate the bug) is inconsistent.
Sometimes I get it after 4 repetitions; other times up till 9.
// Items Collection
public class ItemCollection : ViewModelBase
{
// List of Items
private readonly ObservableCollection<Item> _items = new ObservableCollection<Item>();
public ObservableCollection<Item> Items
{
get { return _items; }
}
// Constructor
public ItemCollection()
{
BackCommand = new RelayCommand(
() =>
{
// Go to previous page
var index = Items.IndexOf(ActiveItem);
if (index > 0)
{
ActiveItem = Items[index - 1];
}
},
() => ActiveItem != null && Items.IndexOf(ActiveItem) > 0);
}
// Back command
public RelayCommand BackCommand { get; set; }
// Next command
public RelayCommand NextCommand { get; set; }
// The currently-active item
private Item _activeItem;
public Item ActiveItem
{
get { return _activeItem; }
set
{
Set(() => ActiveItem, ref _activeItem, value);
}
}
}
// Item
public class Item : ViewModelBase
{
public string Title { get; set; }
}
When I stepped into the RelayCommand's code, the execute action's isAlive flag was false. But I can't seem to figure out how that might happen.
why dont you simply use the methods from ICollectionView? there you have:
something like this
Two words: Garbage Collector
In your example project--which you should post the relevant bits of to make your question future-proof--you set the
DataContext
on your window like this:Because nothing else retains a reference to the
LogicObject
created here, it will be collected at the next opportunity.The command stops functioning because in
LogicObject
, you set theNextCommand
of theItemCollection
to use private members of the soon-to-be-collectedLogicObject
:Once
LogicObject
is collected, the command can no longer work because it no longer has references to valid methods (AddItem
andCanAddItem
). This is why theisAlive
field on both of theRelayCommand
's weak references to the methods is false.You can fix this by just hanging on to the
LogicObject
, or by moving theAddItem
andCanAddItem
methods into the collection.To get in the spirit of GIFs for this question, here's one that shows the button stop working as soon as a Gen 0 collection occurs.