I have WPF listview bound to collection of objects. Objects are continuously added in to collection from remote server and same is reflecting in to listview. Now we have requirement that we should be able to freeze listview for some time,
That is objects should still get added in to collection but should not appear in listview till we unfreeze it ( we have button to freeze and unfreeze) . What is the best way to do it, when listview is bound to collection ? How to unbind collection and rebind it ? and Will i still able to filter and sort when collection is unbound from listview ? Waiting for answer please reply
Regards
Sandeep
You can just break the binding. In your freeze button handler say:
listView = _list
Which will freeze it at that point. Then in your unfreeze handler set the binding back up:
listView.SetBinding(ListView.ItemsSourceProperty, New Binding("_list"))
I hope this helps.
You should just stop updating the collection when the list is frozen, if you must keep adding to the collection even when the list is frozen (if the same collection is used somewhere else that shouldn't be frozen) then consider having two collections, one always updated and the other one bound to the listview.
What is the list type you are using as the data-source? Can you use BindingList<T>? If so, this has a settable RaiseListChangedEvents property, allowing you to turn off notifications. This will probably get very messy re your last points, though (sort/filter).
Personally, I'd work with 2 lists - the bound one, and the one that the server is updating. When paused, simply stop pumping data between the two. This should leave the paused view free for sorting / filtering etc.
Related
With Dev Express I have a treelist whose datasource is a bindinglist
at some point during an update of the underlying data we manually call:
treeList.LockReloadNodes();
list.Clear(); // binding list that is bound to the treelist
treeList.UnlockReloadNodes();
The problem is that calling clear is extremely slow, since a "element deleted" event is sent to the treelist for each of the elements in the list, so the treelist has to recompute its state as many times as there are elements in the binding list
Do you know if this is the correct way to do this? This obviously gets very slow when I have lots of nodes
I guess you dont't use the MVVM, otherwise you can bind to a List with your Models and than just Control your PropertyChanged Events.
I have a DevExpress GridControl bound to a BindingList. I used a BindingList so that changes are automatically applied to the bound control.
It works perfectly when I add or remove items from the list, but when I change an item, it doesn't quit work the way I want it.
I created a foreach loop that runs in another thread (to keep the UI thread free to update) that iterates thru all the objects in the BindingList and changes some of their properties.
The way I expect it to work is that each property updated updates on the GridControl in real time. However the updating is very "chunky". Sometimes it updates 2 rows at a time, sometimes I have to click the GridControl to get the new values.
Why does this happen?
Is it a good solution to call DataControl.RefreshDataSource() after each item?
but when I change an item, it doesn't quit work the way I want it.
Becasue changes within an item are not somethign the BindingList cares about -that is why the items should implement INotifyPropertyChanged.
Basically the binding list says when the LIST has changed, but if you update a property - how should the list know ;) And why should it care - every item is separately responsible for publishing updates to its properties using said interface.
Is it a good solution to call DataControl.RefreshDataSource() after each item?
Worst way. Make sure the items implement INotifyPropertyChange and raise the PropertyChanged event accordingly.
The objects in your BindingList should implement the INotifyPropertyChanged interface and raise the PropertyChanged event when the value of their properties change.
For some reason when adding or remove items from the DataSource (a simple BindingList) the ComboBox updates accordingly but if I edit an item like this, it doesn't update automatically:
myBindingList[index].Name = "NewName";
myBindingList[index].Value = newValue;
In order to get it to update when I edit an item as opposed to creating or removing an item I have to do this after the change is made:
myComboBox.DataSource = null;
myComboBox.DataSource = myBindingList;
This fixes the problem but it seems like a rather messy solution. Also with large lists it may become slow (premature optimization I know) but still is there a way to force the ComboBox to update without completely re-assigning its DataSource?
Thanks for reading.
this is stated in the MSDN forums:
The IBindingList interface contains the ListChanged event where
controls like the combobox hook up into if the underlying datasource
assigned to it implements the said interface. your datasource must
raise the corresponding ListChanged with proper ListChangeEventArgs if
ever you add, remove, change, etc. your IBindingList implementor.
this way, whenever the underlying source you used to bind to your
combobox is changed, the corresponding UI control (combobox) is
refreshed.
you say you are using BindingList and in fact you do get the combobox to reflect add or remove items events. I think you should do the update of the items already inside your BindingList in another way because looks like the proper BindingList events are not firing.
you could either investigate into that or simply live with reset and reassign the DataSource, I don't think is too bad, you are in Statefull Windows Forms application not in SatetLess Webforms so you do have your objects there all the time :)
You need observable collections and IPropertyChange implementation:
ComboBox bound to a ObservableCollection does not update
Basically, I'm wondering how it is actually efficient here.
Sample code:
void GetItems()
{
foreach (var item in items)
myObservableCollection.Add(item);
}
Won't this fire off the CollectionChanged event every time causing the UI to have to refresh everytime? Or does it do it so that it waits til the GetItems function is done?
Basically, it seems that WPF handles it very well, and I'm wondering how they did that.
Optimizing Performance: Data Binding provides some background on how data bindings are resolved, including the performance implications of different items sources. Take a look at the Binding to an ItemsSource section.
Consider a scenario in which you have a CLR List object that holds
a list of employees that you want to display in a ListBox. To create a
correspondence between these two objects, you would bind your employee
list to the ItemsSource property of the ListBox. However, suppose you
have a new employee joining your group. You might think that in order
to insert this new person into your bound ListBox values, you would
simply add this person to your employee list and expect this change to
be recognized by the data binding engine automatically.
That assumption would prove false; in actuality, the change will not
be reflected in the ListBox automatically. This is because the CLR
List object does not automatically raise a collection changed
event. In order to get the ListBox to pick up the changes, you would
have to recreate your list of employees and re-attach it to the
ItemsSource property of the ListBox. While this solution works, it
introduces a huge performance impact. Each time you reassign the
ItemsSource of ListBox to a new object, the ListBox first throws away
its previous items and regenerates its entire list. The performance
impact is magnified if your ListBox maps to a complex DataTemplate.
A very efficient solution to this problem is to make your employee
list an ObservableCollection. An ObservableCollection object
raises a change notification which the data binding engine can
receive. The event adds or removes an item from an ItemsControl
without the need to regenerate the entire list.
Update time for 1 item (ms)
To a CLR List object = 1656 ms
To an ObservableCollection = 20 ms
WPF never binds directly to a collection. If you specify a collection as a binding source, WPF actually binds to the collection's default view.
A collection view is a layer on top of a binding source collection
that allows you to navigate and display the source collection based on
sort, filter, and group queries, without having to change the
underlying source collection itself. A collection view also maintains
a pointer to the current item in the collection. If the source
collection implements the INotifyCollectionChanged interface, the
changes raised by the CollectionChanged event are propagated to the
views.
The event will fire for every change.
The GUI does not have to react and refresh every time, it can postpone that.
I know WinForms will optimize this, I think WPF has a similar approach.
If you want to see how often the UI requests the fresh results expose it as a public property and put a debug line in the get (assessor) of the public property for myObservableCollection.
I have a ListBox that is bound to a List. Every-time the ListBox updates to reflect the collection, the SelectedIndex changes to the top item. How can stop this behavior and retain the current SelectedIndex?
[UPDATE]
I found a better collection to use for this kind of functionality - the 'BindingList': http://msdn.microsoft.com/en-us/library/ms132679(v=VS.90).aspx.
WulfgarPro.
When [...] updates to reflect the collection
Does that mean there is a new collection? If so what does "the same position" mean?
When re-binding to a(nother) list, you will have to save & restore the index position. Just write code around the place where you update the DataSource.
Using the BindingList collection rather than a List remedied a lot of my problems. I was originally using a Thread and a Delegate to query the collection and call ListBox.DataSource=[..] to update the binding. This was slow, cumbersome and error prone. Not to mention my original problem of not being able to easily retain the SelectedItem. Changing to to the BindingList allowed me to remove the thread and delegate and now everything works as intended. Assigning the desired display property for the ListBox can be achieved using ListBox.DisplayMember=[..].
WulfgarPro.