Is there a way to add an item which has no text and even if that item selected it would be shown that nothing selected at all or SelectedIndex would be smaller than zero?
No, the combo box does not support this. There is no built-in logic for treating an item as non-selectable.
Sounds like you will need to either implement an owner draw combo box, or perhaps even a new control from scratch to make this work. I'm sure there are third-party controls that would do what you need as well.
Depending on what you are trying to accomplish (you didn't provide much detail), the ListView control might also provide some options for you.
You can add an item that is represented by an empty string, sure.
But SelectedIndex will return the selected index of the item.
Excerpt from MSDN: A value of negative one (-1) is returned if no item is selected.
You should consider working with the value of the item instead of its index.
Related
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.
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.
How to disable editing or hide text edit field, when DropDownStyle = Simple for Combo Box control?
MSDN on ComboBox.DropDownStyle:
The DropDownStyle property specifies whether the list is always displayed or whether the list is displayed in a drop-down. The DropDownStyle property also specifies whether the text portion can be edited.
Docs on ComboBoxStyle.Simple:
Specifies that the list is always visible and that the text portion is editable. This means that the user can enter a new value and is not limited to selecting an existing value in the list.
So, ComboBoxStyle.Simple suggests that list can be edited by user and it's confusing to disable edit with this DropDownStyle selected. Alternatives:
If you are ok with drop-down list use ComboBoxStyle.DropDownList
If you want to display a non-editable list with a view similar to ComboBoxStyle.Simple consider using ListBox
If you really need to achieve this effect on Combox you can just catch the events like "TextChanged" and then setting it back to "" and asking if (!comboBox1.DropDownStyle == ComboBoxStyle.Simple) before adding items to Items collection. Although it seems there are better ways to achive similar functionality using listbox as suggested before.
I have a combobox that displays a list of 'active' objects the user can select from. However, if the user goes into some older data screens, the selected values of some of the comboboxes might be old and 'inactive' objects that aren't in the current list.
I want the combobox to just display the old value even though it is not in the list. And I don't want the user to be able to manually edit it either.
Any suggestions?
Thanks!
Isaac
I would assume that it's your code that is removing the objects from the ComboBox in the first place, so you just... don't do that. To disallow typing into the ComboBox set its DropDownStyle property to ComboBoxStyle.DropDownList.
hey,
Does anybody knows a way to set a hidden value to a ListBox Item.
As an alternative i can use another listbox simultaneously.
Thanks.
You are probably looking for the Tag property. It holds an object type, which means you can save a reference to anything in there.
Although before setting on using the tag property, take a look at ItemsSource. Basically you can tie a collection of things to be the provider for your listbox, it's usually a superior alternative to dealing with Listbox items individually.