I use EditItem/CommitEdit for resorting (grouped) collection when some property of any item has changed. I do not want to call Refresh() because the collection contains a lot of items with relatively complicated visual tree so it slows down the application.
I faced some strange behavior when calling CommitEdit for current (selected) item - it will lost its currency during the process, of course I can still set it back through MoveCurrentTo(item) so everything looks fine at the moment. But... When for example a new item is added to the collection, the current item will automatically change with no reason to an item on the same index as was the edited item before the collection changed (added item) - it does not normally happen without calling CommitEdit in past.
I use master/detail model so properly set current item is very important for me. Did anyone went around it?
So I was digging around it, debugging ListCollectionView and found there a bug (in my opinion). When a CommitEdit is called for any item, the item needs to be removed from collection and again added into it so the item can lost its currency during the process - thats expected. But there is a special case when edit a current item, some private field called _currentElementWasRemoved is set to true. When the collection will change next time (add, remove...) it looks into this field and change the current item, but in that time the current item should have already changed (I can call f.e MoveCurrentTo multiple times meantime) so this behavior is completely useless in my eyes.
So the walk around can be following: before calling the Edit/Commit for current item, move current pointer into another item or "deselect all" via MoveCurrentTo(null). Right after the CommitEdit was called you can simply return the pointer to the origin item by calling MoveCurrentTo(item).
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Basically, I have a listview inside my form. In order to make the process of selecting the different items in the listview quicker, i have to add a "select all items" checkbox.
For Each lvItem As ListViewItem In Me.lvwDatos.Items
lvItem .Checked = True
Next
That's about it, very simple. Once i click on the select all checkbox, i can see clearly how all the elements go into checked state. However, on the next step, when i want to loop through the selected items in my code and do whatever tasks should be applied to them, i'm finding that ALL elements are unchecked. What's making them loose their state?
Ok, nevermind, i found the problem...that's how it is supposed to be, there's no problem in the listview, it's just the chain of events that were taking place that broke it all...legazy code, as usual...
This is why I have designed Better ListView component which have this behavior fixed (and many other quirks of .NET ListView).
There is also a free Better ListView Express, if you are interested.
The checked item collection is maintained separately and you always get its actual state.
I have a ListView and it's getting updated every 5 seconds.
The problem is that the selected item vanish. How can I obtain it ?
It depends what you're doing to update the list. If you're deleting and re-building the list willy-nilly (which isn't great), you'll need to store something which can uniquely identify the selected item before deleting the list and then use that stored value to select it again once the list is repopulated. A better solution is to use something like an ObservableCollection, and try not to wipe out anything in the list unless you really need to.
I appologize for the novel but I wanted to explain as much as I have done thus far.
Within my current project I have an application that consumes a service that provides a collection as a <List>. Due to how I am using this data in the application I have had to convert this data to an observable collection. This was done so that as the data was selected and moved about the application UI updates would be refreshed using INotifyPropertyChanged and INotifyCollectionChanged.
Where I am having a challenge now is I have a listbox that is bound to the observable collection within the listbox I have a datatemplate that renders out the items of the collection. This data template contains a button which needs to allow the user to click the button for each item to remove them from the collection.
The use case for this is a listbox that stores selected name as chosen from a gridview. Once the user has selected names from the gridview they are stored ( within the observable collection as a queue) and rendered out in the UI in a listbox control which shows all selected names. I need to provide the user with the ability to remove these names in any order selected.
From what I have been reading there is no means to enumerate / index an observable collection. For situations such as this you should use List or an Array. However in order for the items to refresh in the list view they need to be in an Observable Collection.
From what I have read it appears that when the event is triggered I need to convert the observable collection to an Array and then evaluate the array to determine the index and then remove the record accordingly?
I think I may be off base on this as it seems like I am over engineering this problem? The above scenario does not seem correct is because I fell as if I am doing a lot of converting to and from the collections to just remove a record?
Does anyone know of an efficient means to remove records from a collection ( in any order selected) when the collection is rendered out as an items control within a listbox?
I’ve been successful in removing the last record added to the collection using RemoveAt() however I have not had any success in randomly removing records.
Afterthought: Part of this issue could be related to the fact that I have a button inserted within the datatemplate (control item) and as a result the item is not actually being selected before the event is fired on the button event?
Sorry for the rambling on this but I have had my head in this for hours and made minor progress. Any tips or ideas would be appreciated!
ObservableCollection<T> inherits from Collection<T> which implements IList<T>, so you can certainly index and enumerate it. It has a Remove method that takes the object to remove and removes the first occurrence in the collection and a RemoveAt method that takes an index and removes the item at that index.
Based on your afterthought, it sounds like you have a WPF ListBox with an ItemTemplate that creates a Button. ListBox will set the DataContext of each instantiated template to the item in the list being bound to, so you can get a reference to the item that created a Button from the DataContext property on the Button or by using a Binding.
I populate a ListBox control with my own objects redefining ToString(). The objects are displayed correctly when I just add those objects using listBox1.Add(myObject). However, if I later change something in this object, no changes are displayed in the listbox. Debugging reveals that an object inside listBox1.Items is indeed changed, but it is not reflected on a screen.
Interestingly enough, if I reassign a particular listbox item to itself (sounds a bit weird, doesn't it?), like:
listBox1.Items[0] = listBox1.Items[0]
this line will display a correct value on screen.
What is going on here? Does it have anything to do with threading?
Since you're using ToString of the object to provide the text of the list box item, the ListBox has no idea that the value has changed. What you should do instead is have the object implement INotifyPropertyChanged then expose a public property such as Name or Text and return what you normally would have returned from ToString().
Then set the DisplayMember of the ListBox to the name of the new property.
Make sure you are correctly raising the PropertyChanged event in the object and the ListBox should be able to automatically pick up the changes.
Edit: Adrian's edit reminded me that I do believe you'll need to use a BindingList as your data source in order for the property change notifications to be picked up. A quick scan in Reflector looks like ListBox on its own will not pick up the property changes mentioned above. But INotifyPropertyChanged + BindingList should.
The ToString() value of each item is cached when the listbox is first displayed. If an item in the listbox's Items collection then changes, the listbox does not notice and still uses the cached ToString() values for display. To force the listbox to update, either call RefreshItems() to refresh all items, or call RefreshItem(int) specifying the index of the item to refresh.
From the MSDN docs for RefreshItems():
Refreshes all ListBox items and retrieves new strings for them.
EDIT: It turns out that both of these methods are protected, so cannot be called externally. In trying to find a solution, I came across this SO question that this question is basically a duplicate of.
Have you tried calling Refresh() on the ListBox? I think the problem is that the ListBox does not know your object changed. The reason reassigning the the item works is because the ListBox will repaint itself when the collection changes.
you could invalidate the control, forcing a re-paint... perhaps..
I'm using a TreeView to let the user navigate a complex data structure more easily. I'm trying to add a feature to my application so my users can add new items to the datastucture by clicking a button on a toolbar. This new item has 3 levels, each with 1 item. I would like to select the item in the lowest level.
Adding the data isn't a problem, I just add a new item to the collection that is bound to the TreeView in a specific. I can lookup the item by hand browsing the TreeView, so I know the adding works. Now, I want to set the selection of the new item programmaticly. So the user can change the default settings in the element right away.
I've done some testing and I've found that setting the selection is done with something like:
var obj = TreeView.ItemContainerGenerator
.ContainerFromItem(selectedObject) as TreeViewItem;
obj.IsSelected = true;
I've tried adding this code directly after my Add-method. The adding function returns the new object and places this in selectedObject. The Add-method adds a to an ObservableCollection, which raises the appropriate events.
But, obj is always null directly after adding.
I've tried setting the selection in the LayoutUpdated event, but in this case the obj variable from the earlier code always null again.
I think I might be missing something here. Does anyone have an idea on how to add a new item to the bounded collection and select that item in the TreeView?
You might want to read this article by Josh Smith on using the treeview in WPF. He demonstrates how to use an IsSelected property that could easily be adapted for your needs, using the MVVM pattern.