I have a ListView and I'm subscribed to OnListKeyDown(). If I get any Left or Right inputs, I do some processing, effectively recreating the ItemsSource of the ListView.
When I say "recreating" I mean trigering this:
OnCollectionChanged(new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Reset));
I noticed, that after this, if I press up or down, the focused element will be reseted (instead of being the current one, it will be the 1st one). I tried logging the state during the input event, but everything looks correct.
After fighting for a few days I found how to reset my keyboard focus. First you need to cache the selected index, then, once done updating, reset the selected item and also focus it.
This is the code snipet for that:
View.EntriesView.SelectedItem = View.EntriesView.Items[cacheIdx];
View.EntriesView.UpdateLayout();
((ListViewItem)View.EntriesView.ItemContainerGenerator.ContainerFromIndex(cacheIdx)).Focus();
Thanks to #Alfie for his help.
Related
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 DataGridView bound to a List[of Parts]. The last item in the list is always a 'dummy part', which is there to create an extra row in the grid so the user can start typing into the first cell to add a part to the list.
As soon as the user types more than x characters into that particular cell, a new DataGridView with search results appears under the cell where he is typing (a bit look Google's suggestions), and he can select one of the matches to add the part to the list.
I do this by handling the EditControlShowing event, which assigns the 'editing control' to a TextBox variable which has a handler for TextChanged.
The bug:
I want the focus to change to the second DataGridView (search results) if the user hits the down arrow key.
The EditControlShowing handler works fine first time, moving the focus to the second DataGridView and leaves the first DataGridView in a 'seemingly' functional state, i.e. all other event handlers work. But the second time the EditControlShowing handler fires, the DataGridView throws the NullReferenceException on InitializeEditingControlValue.
Because it is the DataGridView's own call which throw the error, the debugger brings me to "Application.Run" in my code, which isn't helpful.
However, I determined that the call which causes the DataGridView to go into that state, and the point at which exception is thrown, is when I steal focus from the first DataGridView by calling Focus() on the second DataGridView (or any other control for that matter).
If however I let the user change focus to the DataGridView (e.g. by clicking with the mouse), then the DataGridView stays fine.
Does anyone know why stealing focus away from a DataGridView during a handler for EditControlShowing should result in it behaving differently afterwards?
I've tried CancelEdit, Refresh, Enable/Disable etc...
Any suggestions on helping me find out what is going on within the DataGridView? I can't spot anything obvious by inspecting it at breakpoints before and after. I don't even know how to find out what object is null as its the DataGridView's own code...
Many thanks.
OK, I resolved this using BeginInvoke in the TextChanged event handler (code is in Boo but should make sense):
//The event handler
private def CellAsTextBoxTextChanged(sender as object, e as EventArgs):
...
self.BeginInvoke(ShowPartSelectionArea, currentCell, _CellAsTextBox.Text)
//The method which amongst other things, sets the focus to another control
private def ShowPartSelectionArea(currentCell as DataGridViewCell, searchString as string):
...
AnotherDataGridView.Focus()
...
I had previously tried using BeginInvoke directly at the point of calling Focus() on the other control, like so:
private def CellAsTextBoxTextChanged(sender as object, e as EventArgs):
...
ShowPartSelectionArea(currentCell, _CellAsTextBox.Text)
private def ShowPartSelectionArea(currentCell as DataGridViewCell, searchString as string):
...
self.BeginInvoke(AnotherDataGridView.Focus())
...
But the latter didn't work, perhaps because the first way actually allows the DataGridView's cell to finish everything it does whereas the second way doesn't.
So for anyone facing the same problem, I'd advise playing about with where in the call stack you use BeginInvoke.
Found an interesting problem that I first found in WinForms, and found again in Silverlight, and more than likely WPF as well when it comes to databinding.
I have a tab control with several tabs. As users click across the tabs, each time should be valid before allowing the user to switch from the tab.
For example, user is in a text box which is updated. Binding of text boxes is not flushed until the control loses focus. Loss of focus occurs when the cursor is moved from the control, and focus is given to another control.
In this scenario, the user tabs into a control (let's use text box for this example), and updates the text box. At this point the databinding has not flushed the control, and hence the VM has not yet seen the change. The user then uses their mouse to click the next tab of the control.
At this point things get interesting. I used the PreviewSelectionChanged (Telerik RadTabControl), as I want to check things out before the jump to the next tab occurs, and it also gives me the ability to cancel the event.
However, when I look at the VM, in this event, it still does not have the updated data. I see the VM is clean, and go ahead and allow the jump to the next tab.
As soon as this event is over however, the databindings flush, and the VM gets updated. what now? The events are out of sync! When the mouse was used to click the next tab, the textbox should have lost focus, flushed it's bindings, before the Preview of the Tab click! It's to late to jump back and say oops we didn't catch that in time!
I think I found an interesting work around to this issue - but I'm not 100% sure it will work 100% of the time. I cancel the current event, but then I use the Dispatcher and create a delegate pointing to another method with the same signature as the current event. The Dispatcher will add this message to the message pump, which by this time will now (hopefully?) be behind the messages of the VM updating...
My two questions are:
1) I'm assuming that the textbox control either didn't flush when the mouse left the control, or the process that was fired was too slow and hence the preview message was on the pump before the databinding - either way I see this to be a major issue.
2) Is the workaround a good solution?
Ok, first to answer question 1:
Just because the mouse left the textbox area, doesn't mean that the textbox lost focus. It only loses focus once something else gets focus. For example, if you moved the mouse out of the textbox and click on some other control on your page (it can be anything from a scroll viewer to another textbox, etc.) then your textbox will lose focus.
Now, based on that, the events do not happen in the wrong order. What happens is; your click event on the other tab triggers both the textbox to lose focus (and the data binding to take place) and the move to the next frame, and based on that, you basically get a race condition where the moving to the next tab happens before the databinding takes place.
About question 2:
What you can do is, set the UpdateSourceTrigger to Explicit, you will however be forced to then have some kind of text_changed event and manually update the binding.
You can read more about that here. It might not be the most complete explanation but is a good place to start.
On the other hand, you can associate some events to the textbox and force the textbox to lose focus on those events (e.g. mouse out).
Just an idea: Why not do everything in the VM's PropertyChanged event?
protected override void OnThisViewModelPropertyChanged(object sender, PropertyChangedEventArgs e) {
if(e.PropertyName == "WhateverProperty") {
//Do your magic here for whatever you want to set
}
}
Have your TabItems bound to a collection that will control is being disabled or not.
<sdk:TabControl>
<sdk:TabItem IsEnabled="{Binding SomeProperty, Converter={AmIDisabledOrWhatConverter}}" />
</sdk:TabControl>
That way, everything is triggered whenever a property is chaned in the vm. No more timing issues since everything is on the vm.
Just my two cents.
There's a design defect here, and you're trying to work around the defect instead of fixing it. You shouldn't have to figure out how to cancel the Click event on the tab. The tab shouldn't be processing Click events in the first place.
Generally speaking, if it's not legal for the user to click on a control, the control shouldn't be enabled. The tab should be disabled until the state of the view model is valid.
Your view model should be exposing a command for navigating to the next tab, and the tab should be bound to the command. The command's CanExecute method should only return true when the state of the view model on the current tab is valid.
This doesn't fix your other problem, which is that Silverlight doesn't support UpdateSourceTrigger="PropertyChanged" out of the box. But that's a solved problem (here is one example).
Note that if you implement commands to handle this wizard-like navigation in your application, you can, down the road, change the view to use something other than a tab control (e.g. to use navigation buttons like an actual wizard, or something like Telerik's PanelBar) without having to screw around with event handlers.
Change your bindings to include UpdateSourceTrigger="PropertyChanged".
This will ensure that your data sources are updated on every key stroke, not just LostFocus.
MyOwnTextBox()
{
this.TextChanged += (s, e) => UpdateText();
}
private void UpdateText()
{
BindingExpression be = GetBindingExpression(TextProperty);
if (be != null && be.ParentBinding.Mode == BindingModes.TwoWay)
{
be.UpdateSource();
}
}
I am using this class it updates my binding on the fly, however there is issue with empty string and null values, if your destination property is nullable string then this will update empty string in your destination property. You can get workaround by using some sort of string converter which will use null instead of empty string in case of nullable strings.
I've done a lot of searching on SO and google around this problem, but can't seem to find anything else to try.
I have a MainView (window) that contains a tab control. The tab control binds to an ObservableCollection of ChildViews (user controls). The MainView's ViewModel has a method that allows adding to the collection of ChildViews, which then creates a new tab. When a new tab is created, it becomes the active tab, and this works fine. This method on the MainView is called from another ViewModel (OtherViewModel).
What I am trying to do is set the keyboard focus to the first control on the tab (an AutoCompleteBox from WPFToolkit*) when a new tab is created. I also need to set the focus the same way, but WITHOUT creating a new tab (so set the focus on the currently active tab).
(*Note that there seem to be some focus problems with the AutoCompleteBox--even if it does have focus you need to send a MoveNext() to it to get the cursor in its window. I have worked around this already).
So here's the problem. The focusing works when I don't create a new tab, but it doesn't work when I do create a new tab. Both functions use the same method to set focus, but the create logic first calls the method that creates a new tab and sets it to active. Code that sets the focus (in the ChildView's Codebehind):
IInputElement element1 = Keyboard.Focus(autoCompleteBox);
//plus code to deal with AutoCompleteBox as noted.
In either case, the Keyboard.FocusedElement starts out as the MainView. After a create, calling Keyboard.Focus seems to do nothing (focused element is still the MainView). Calling this without creating a tab correctly sets the keyboard focus to autoCompleteBox.
Any ideas?
Update:
Bender's suggestion half-worked.
So now in both cases, the focused element is correctly the AutoCompleteBox. What I then do is MoveNext(), which sets the focus to a TextBox. I have been assuming that this Textbox is internal to the AutoCompleteBox, as the focus was correctly set on screen when this happened. Now I'm not so sure. This is still the behavior I see when this code gets hit when NOT doing a create. After a create, MoveNext() sets the focus to an element back in my MainView.
The problem must still be along the lines of Bender's answer, where the state of the controls is not the same depending on whether a new tab was created or not. Any other thoughts?
Final Update
As noted, majocha's suggestion worked.
I wanted to update this in case anyone happened upon this same problem with the AutoCompleteBox. It appears that setting focus does not activate it in the UI--you need to do a MoveNext on it to move focus forward once to the control's internal Textbox. This is based on my debugging experience, which may not be 100% scientific. If I have time, I will attempt to create a small repro project and submit it to the WPFToolkit team.
You can try defering the focus change with
Dispatcher.BeginInvoke(MyChangeFocusAction, DispatcherPriority.ContextIdle);
It will get queued after layout and properties updates are done.
I don't think it's best practice, but it works for me.
The control must be visible to be focused, you may try to defer focusing by subscribing to the IsVisibleChanged event, something similar to the following should work:
public static void setFocusLate(this Control control)
{
DependencyPropertyChangedEventHandler handler = null;
handler = delegate
{
control.Focus();
control.IsVisibleChanged -= handler;
};
control.IsVisibleChanged += handler;
}
I have a canvas inside a scrollview. I attached a keydown event handler to the scrollview. For most keys, the handler gets called.
However, for the arrow keys, the handler does not get called. Instead, the scrollview gets scrolled in the appropriate direction.
I also attached a keyup handler to the scrollview and the keyup does get called for the arrow keys.
Is there any way to get the arrow key down event here?
Just use the KeyUp event. Works like a charm.
I found this silly hack to make it work. Setting the scrollview to not be a tabstop keeps it from eating the key events.. but then I had another textbox on the page that all of a sudden ALWAYS had focus because the scrollview didn't anymore. So I fixed that by letting an invisible textbox get focus.
scrollView.IsTabStop = false;
invisibleTextBox.Foreground = new SolidColorBrush(Colors.Transparent);
invisibleTextBox.Background = new SolidColorBrush(Colors.Transparent);
Canvas.SetZIndex(invisibleTextBox, -1000);
invisibleTextBox.KeyDown += new KeyEventHandler(HandleKeyDown);
invisibleTextBox.KeyUp += new KeyEventHandler(HandleKeyUp);
Edit: I also had to move the text box off the canvas because despite being invisible, its outline still showed up.
2nd Edit: I used a textbox because that was the first thing I found that could capture KeyDown events. However, a UserControl can. So it would probably be better practice to use a UserControl instead of an invisible text box. You can call Focus() on the UserControl if needed.
This is a possible answer - I haven't had a chance to test this. I've had similar trouble in the past though, when a control is consuming the events before you can get at them. There's a few things you may be able to try:
Use the PreviewKeyDown event, I think that's what it's called. It may let you get at the event before it's consumed by the control.
Try mblandfo's suggestion, although if you do this you probably ant to wrap the whole thing up in a user control to hide what you're doing from the rest of your code.
Add a key handler to the Canvas object, you may be able to catch the event there, and "bubble" it up through your own event.
Except for 1) all of these count as hacks, really, but good luck, I hope one of them works for you!
"Use the PreviewKeyDown event, I think that's what it's called. It may let you get at the event before it's consumed by the control."
This works. Just set the event arguments "Handled = true" and the ScrollViewer (or ListBox) wont grab onto the event after you've already handled it. I didn't need to use the IsTabStop property for the ListBox though; that and it didn't seem to do anything anyways.