I have a Combobox with several items (C# Labels because I want to change individual text colors). Within callbacks, when editing some textboxes, I change the color and/or text of the items. When I click on the combobox I see that the items in the list have the correct color/text. However, the color/text changes of the selected item are not directly reflected in the shown combobox text. How can I achieve that?
I tried to set the Text property of the combobox itself: no effect. Also setting the selected item to an empty Label and then set it back to the correct Label has no effect. If I set SelectedIndex to -1 and then back to the correct selected index it works and the shown text is updated, but this triggers the SelectionChanged callback which I do not want. I could first detach the SelectionChanged callback from the combobox and then attach it again, but this is in my opinion very ugly programming.
Maybe I am missing something simple...
Edit
I tried binding, following the suggestion of SLak:
List<Label> labels;
MyComboBox.ItemsSource = labels;
The result is still the same. Suppose index 0 is selected. When I change the corresponding Label:
labels[0].Contents = "new content";
then it is not reflected in the selected text of the combobox. When I click the combobox I can see the new text in the unfolded list, but only when I change the selection and then go back to index 0 the new text is shown by the combobox as the selected item. That synchronization should be autmatically.
I cannot seem to figure out how to dynamically change the selected item in a combo box. I am trying this:
myComboBox.SelectedItem = item.Id;
Here item.Id is a int that corresponds to valid ValueMember that is bound to the combobox. However the combobox remains unchanged. I have trying invalidating the control after changing the selected item. What's the trick?
Thanks
try SelectedValue instead..
myComboBox.SelectedValue = item.Id;
You can use either of these:
SelectedIndex Property
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.
SelectedItem Property
Get or Set A zero-based index of the for selected item.
How to allow Combobox placed inside Datagrid to type text.
It just binding the values already stored in the database. but i need to type the value in the Combobox which is not shown in the bound values.
How to make the Combobox as editable column?
You can set ComboBoxStyle to DropDown
Specifies that the list is displayed by clicking the down arrow 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.
How can I make a listbox dropdown like a combobox?
Or is it possible to configure a combobox so that the user can't add values but rather only select from the available list of values?
This is for a desktop application.
The ComboBox control has a DropDownStyle property used to set this. Set it to DropDownList.
Set the DropDownStyle to DropDownList:
Specifies that the list is displayed by clicking the down arrow and that the text portion is not editable. This means that the user cannot enter a new value. Only values already in the list can be selected. The list displays only if AutoCompleteMode is Suggest or SuggestAppend.
like:
DropDownStyle = DropDownList;
Set the ComboBox.DropDownStyle property to DropDownList - that should give you the behaviour you need
I have an interesting data binding question related to combobox. Hope someone has some good suggestion.
I have a simple form, it contains a file picker and a comboxbox. Every time a file is picked, I read a list of strings from the file to a List object and I set comboBox.DataSource = listOfStrings.
In the form load event, I set comboBox.DataBindings.Add("SelectedItem", myObject, "PickedValue");
The purpose is clear: every time a string is selected from the combobox, I want to write the string to myObject.PickedValue.
That is the whole story.
Now I launch the form, rather than go pick a file, I check the combobox first. Of course, at this point, comboBox.DataSource is null, comboBox.SelectedItem is null, too. But the data binding on the comboBox is already setup (since the setting is in form load event). Now my focus cannot be moved from the combobox to anywhere else.
I think the reason is, when I try to check the combobox, it has null as SelectedItem. When I try to move the focus to somewhere else, the data binding of the combobox is triggered. Underlying, it tries to convert the selected item to string and update myObject.PickedValue with that converted string. Since you cannot convert a null to a string, the data binding validation fails, and the validation mechanism doesn't allow my focus to be moved elsewhere and I am sucked at this moment, cannot even move to pick a file.
My question is, what is the normal binding setup work-flow for my application scenario to prevent this trap? What is the correct order of setting up such a data binding so I can check my combobox before its data source is filled by something?
FYI, I tried to bind myObject.PickedValue to SelectedText property of the combobox (I noticed that SelectedText is a string and never be null, even when SelectedItem is null). But interestingly, even if I select something from the combobox, SelectedText is still empty string when data binding is triggered. What's wrong here?
Thanks for any help.
The failure is a little simpler than you describe: Your ComboBox will fail just because there is no selected item, because there's nothing to select from.
I would just disable the ComboBox if there's nothing to select from. It's pretty easy to do. Remember to hook up a PropertyChanged event in your data object; the binding source will find it automatically with reflection.
class MyData
{
public event PropertyChangedEventHandler PropertyChanged;
// ...
public HasListOfStrings { get { return ListOfStrings != null && 0 < ListOfStrings.Count; } }
private void LoadListOfStrings
{
// ... load the list of strings ...
if ( PropertyChanged) {
PropertyChanged(this, "ListOfStrings");
PropertyChanged(this, "HasListOfStrings");
}
}
}
In the designer, bind the 'Enabled' property of the 'ComboBox' to the HasListOfStrings property. You can do it in code with:
listOfStringsComboBox.Bindings.Add ("Enabled", bindingSource, "HasListOfStrings");
I also recommend you change the AutoValidate property of the container (or container's container) to EnableAllowFocusChange.
This doesn't seem right; it should be possible to set a string property to null. Possibly the focus problem lies elsewhere. Have you tried setting a breakpoint on your property setter to confirm your theory?
The SelectedText property of a combo box refers to text that has been selected in the text portion of the combobox. This only works if the dropdown style is set to combo. Basically it's the selected text of the text box portion of the combo control (the reason a combobox is called "combo" is because it is a combination of a textbox and a selection list). You would ordinarily expect this property to be empty unless the user was editing the text portion of the combo.
If you want a workaround for this problem that is consistent with a good user experience, try disabling the combo box on form load, then enabling it when a file is picked.