I have a WPF ComboBox which I'm using to search names. I use the MVVM pattern and it's all pretty simple:
The ComboBox Text property is bound to a "SearchString" property on the VM. The ComboBox ItemsSource is bound to a "SearchResult" property on the VM. This is a list of objects displayed using a DataTemplate. The ComboBox also triggers a "PreviewKeyDown" event and pressing enter selects the first item in the result set, with up and down arrow keys traversing the results. The SelectedItem is bound to the DataContext for a GroupBox. This part works really nicely.
When an item is selected in the ComboBox, WPF is automatically attempting to replace "Text" with my SelectedItem. This causes my results set to get emptied and "Text" to revert to an empty string.
The behaviour I'd like is that when an item is selected, the text in the ComboBox remains exactly the same, so that my user can continue to traverse the result set using up and down arrows.
Is there an elegant way to achieve this? I think that nothing will be added to the question with a code snippet, but happy to supply if wanted.
The behaviour I'd like is that when an item is selected, the text in the ComboBox remains exactly the same, so that my user can continue to traverse the result set using up and down arrows.
That's a requirement that's not built into the ComboBox control. If you want something like that, you'll have to build it yourself (and subclassing most likely won't help, you'll have to build most of a ComboBox from scratch for this).
In fact you shouldn't be binding the current item like that either, you should use the SelectedItem property, which doesn't do any conversions or copying, exactly what you want for an internal binding.
Related
So one particular behavior of the XAML combobox in WinRT is causing me a huge headache, because my client sees it as a defect, and doesn't care if it's the behavior of the control, he wants it changed. However, I cannot find anything that tells how to change it. The behavior I'm speaking of is that when nothing is selected the ComboBox popup opens displaying the ItemsSource in the middle of the list. I have a sorted list of countries, with the exception of US, UK, CAN being at the top. These 3 items are the most often selected items and the client wants them on top rather than having to scroll through the list to find them. That's easy enough, but because the list opens in the middle, you still have to scroll quite a bit to get to them. Is there some property I'm missing that turns this behavior off? I was able to finally convince them that the CarouselPanel wasn't a defect, but this one isn't going to fly.
Thanks in advance!
UPDATE:
So this combobox is databound through a ViewModel. in this instance, the ViewModel has no value (it is an empty string) for that particular property and so the Combobox shows empty, which is fine and desirable. When you click on the Combobox to select a value, it displays the list in the middle of the available values. this is the behavior that is undesirable. it should be showing the 1st value in the list at the top!
Well, one would think that the out of the box Combobox (there is no other built in dropdown control) would be able to work like any other combobox control in any other MS technology to date, but of course this is MS, so why should things be consistent. At any rate, I ended up having to create a "blank" entry and pre-select that item if the value in the VM is empty, and then write code in the setter of that property to ignore if "blank" item if it is selected. It's kludgy and wreaks of code smell, but it works
When you set the SelectedItem property to an object, the ComboBox attempts to make that object the currently selected one in the list. If the object is found in the list, it is displayed in the edit portion of the ComboBox and the SelectedIndex property is set to the corresponding index. If the object does not exist in the list, the SelectedIndex property is left at its current value.
I have a listbox bound to a List<object> as its DataSource. What I'm wanting to do is use the SelectedValue property of the Listbox (i.e the object corresponding to the current selection) as a DataSource for some textboxes that will display certain values of the object for editing.
I've tried
TextBox.DataBindings.Add(new Binding("Text", ListBox, "SelectedValue.name"));
and
TextBox.DataBindings.Add(new Binding("Text", ListBox.SelectedValue, "name"));
but as there is nothing selected in the ListBox (because the form hasn't been shown yet), I get an exception about "Value cannot be null".
Now I know that I can (re)bind to ListBox.SelectedValue in my form's SelectionChangeCommitted handler (that is, after a selection has been made), but if i have to do that I might as well just set the TextBox's value directly (admittedly I could just do this to resolve the issue, but I'd like to learn more about databinding).
So my question is, in short: Is it possible to bind to ListBox.SelectedValue once (initially, before the ListBox has a selection) and avoid the null value exception, and if so, how?
I'm not sure which control your projectNameCtrl is, but you'll want to bind your TextBox. Something like this:
textBox1.DataBindings.Add(new Binding("Text", listBox1, "selectedvalue"));
Where:
textBox1 is your TextBox
listBox1 is your ListView
EDIT
You should be able to data bind a ListBox even if that ListBox has no selected items so your 'value cannot be null' must be for another reason. I suggest using the debugger to determine which object specifically is null.
You can ensure you don't data bind a control more than once by first checking the control's DataBindings.Count property; if it's equal to zero you haven't yet data bound that control:
if (textBox1.DataBindings.Count == 0) {
// OK to data bind textBox1.
}
Off the top of my head, I think you'd need to do something on each selectedItemChanged event...
I know this doesn't answer your question, but I'd look at using WPF instead since this is so much more elegant to do in WPF, and let's face it, by not creating a GUI in code (using XAML instead) your sanity will be much more intact when you finish your project. I don't recall enough windows forms, but in WPF, you just implement INotifyPropertyChanged on your back-end object that you're binding to, and then when you bind to the SelectedItem property of that ListBox, you automatically get updates since the SelectedItem property is a DependencyProperty.
I have a ComboBox whose ItemSource is bound to a list of strings (idealy i would use an Enum), this is done using the MVVM pattern.
Now i want to bind an object to the ComboBox, it's called SelectedUser and i want to bind its property: UserType, which is a string.
So i have got this:
<ComboBox ItemsSource="{Binding Path=Usertypes}" SelectedValue="{Binding Mode=TwoWay, Path=SelectedUser.UserType}" />
It works and it does change the value of the selected user if i play with it, but the problem is, that it does not display anything in the ComboBox unless i select a user, and then change the ComboBox selection, then it works, but only for that user.
I tried playing around with DisplayMemberPath, SelectedValuePath and SelectedItem,
when i added those the ComboBox did not show anything in it (there were still options to select from, but they were invisible or something).
So what should i do? Is this a bug?
I have to mention that i have got another ComboBox that has a list of ints, and it works fine.
Update:
I was informed that I'm getting this issue because the string I'm comparing to the string in the comboBox, are not actually the same.
My string comes from the Entity Framework via Ria Services. (User.UserType)
And when it compares it to the list of strings in the ComboBox ItemSource, they are not equal, for some strange reason.
And i also heard, i might have to override Equal method for that check.
but I'm not sure where and how to do so.
Is the view notified if the SelectedUser changes? I could imagine that this might be the problem; if there is no such notification the ComboBox will not reload the SelectedValue if another user is selected, it will only update the binding if you make changes yourself.
If that is not it, you also need to consider that no selected value will be displayed unless the current value exactly matches one of values in the source list.
I am having trouble setting the Selected Item of a Listbox I am populating and adding to the LayoutRoot's children in code.
I am creating the ListBox over when going back to the page, so I am saving a variable which will tell me what the selected item was before the user clicked.
I tried setting SelectedIndex, but that did not seem to work. That selects the item and calls SelectionChanged, but the item does not come into focus.
I also tried the combination of MyListBox.ScrollIntoView(MyListBox.Items[MyListBox.SelectedIndex]) and MyListBox.UpdateLayout(), but that did not seem to work either. The item does not seem to come into focus.
Try MyListBox.SelectedItem.EnsureVisible().
(If it doesn't have SelectedItem (ListBox on the desktop CLR doesn't), then use SelectedItems[0] instead)
E: Okay, looks like Windows Phone doesn't support that. However, it does support MyListBox.EnsureVisible(MyListBox.SelectedItems[0])
I ended up fixing this by Adding the UserControl that had the ListBox into the Page's XAML, and the ListBox into the UserControl's XAML.
Then, I was able to use the ScrollIntoView(MyListBox.Items[mySavedSelectedItem]);
I simply saved this value when the user made the selection.
mySavedSelectedItem = ((ListBox)sender).SelectedIndex;
I'm certain this has come up before, but I haven't been able to find the answer.
I made a basic ViewModel that contains a list of People (an array of Person) with a property called SelectedPerson, which naturally points to the currently selected Person in the list of People. I also have a ListBox and a TreeView that are databound to the ViewModel's People list.
What I'd like to do is to keep the ListBox's SelectedValue and TreeView's SelectedItem in sync with with the ViewModel's SelectedPerson. The idea is that no matter how the SelectedPerson is modified (through a control, through code, etc), all the controls should update themselves properly. I can get it to work with two ListBoxes, which is nice, but I can't get it to work with a ListBox and a TreeView because the TreeView's SelectedItem is readonly and apparently unavailable through XAML.
Where should I look to get ideas on making this work?
Also note that I'm trying to make this work in pure XAML. No code-behind as XAML files in my application can be loaded and changed dynamically.
Thanks!
You can Use Selector.IsSyncronizedWithCurrentItem.
You can bind both thye listbox and treeview to the same datasource and make sure that the IsSyncronized parameter is set to true. Then any changes to the current item in one will be reflected in the other.
More information can be found here:
link text
I asked around and the best solution I could find was here
http://social.msdn.microsoft.com/Forums/en-US/wpf/thread/cc73893a-3383-4328-a002-ed8fb002a19d
It works for me but it's not the most optimal solution at this point.