We Keep Coding

Text property of Listbox control returns string when nothing is selected

listBox_groupmakingrepairs is a listbox control on my form. When first loading the form, nothing is selected in the listbox and the code in the following 'if' statement will run because the condition is true.
if (listBox_groupmakingrepairs.Text == "")
{
Error = "You must indicate what group will be making the repairs.";
Con = listBox_groupmakingrepairs;
}
But, if I run the following code...
listBox_groupmakingrepairs.Text = "Cell";
Followed by this code...
listBox_groupmakingrepairs.ClearSelected();
The listbox will not have anything selected, yet it will cause the first code snippet above to be false and not run the code in the 'if' block. When I step through and check the value of 'listBox_groupmakingrepairs.Text' it is "Cell". Yet on the form, the listbox clearly has nothing selected.
Am I using the Text property of the Listbox control incorrectly? Or is this a bug? Or am I missing something altogether obvious?
The way I see it I have a property (Text) that seems to work well most of the time. But under certain conditions it returns a value that isn't the correct value anymore. Why is the Text property returning an old value that has since changed? Does this make logical sense to anyone who can explain it to me?

That is because the ListBox control of C# winform control handles both the Text property and the SelectedItem separately, but in a way together.
It works in the following way:
IF [SelectedItem is True i.e. Item is selected] THEN
Text property = SelectedItem.ToString()
ELSE IF [SelectedItem is False i.e. No Item is selected] THEN
Text Property will still assume its current value (or in a way previous value) unless its manually reset
So always in such cases donot forget resetting the Text property. Hope this helps...

Maybe I am a bit slow, but eventually I realized that Microsoft is the creator, so to them I will go for the answer.
Here is what I found:
According to Microsoft, the following code I was using is a correct way of selecting text in a listbox control.
listBox_groupmakingrepairs.Text = "Cell";
Then, also according to Microsoft, the following code I was using is a correct way of deselecting all items in a listbox.
listBox_groupmakingrepairs.ClearSelected();
Finally, also according to Bill Gates (see two links above) the Text property is also a correct way to retrieve the text of the first selected item.
string SelectedText = listBox_groupmakingrepairs.Text;
But, as I described in my original question above, when I evaluated the Text property WHEN NOTHING WAS SELECTED IN THE LISTBOX, it contained text. But Microsoft says "this property returns the text of the first selected item." WHICH IS FALSE. It should have returned null because there was nothing selected...yet it returned text which was NOT SELECTED.
So to answer my two questions in my original post:
"Am I using the Text property of the Listbox control incorrectly?" -- The answer is YES.
"Or is this a bug?" -- Yes, it is.

C# Combobox Displaying Blank Items

I'm coding a combobox in C# and for some reason the items in the drop down don't have text. When I have selected an item, it is shown in the combo box text field (the drop down list is always blank whenever I click the drop down button). The datasource seems bound properly because the proper values are being returned when I select items, and the size of the drop down list will change depending on how many items the datasource has. Everything looks fine except for the fact that it seems like my drop down is populated with a bunch of empty strings, which it clearly isn't since as soon as an item is selected the proper text will display.
This is the relevant code:
if (list.Count > 0)
{
cboCustomers.DisplayMember = "Name";
cboCustomers.DataSource = list;
cboCustomers.ValueMember = "ID";
cboCustomers.SelectedIndex = 0;
}
I have looked for an answer to this but can't find it anywhere...I'm sure it's something really simple, but I can't figure it out. The closest problem I found had an answer suggested to set the display member before the data source, which clearly didn't work.
The list is populated from a database query. This will run on keyUp, the idea is that the list is populated as the person is typing based on the info given. So if I wrote 'S' I'd get a combobox with a dropdown that had all the clients starting with 'S'.

Given you don't have any anomalies in your binding, you are probably being affected by DrawMode property of your ComboBox, which may be set to OwnerDrawFixed or OwnerDrawVariable. Set it to Normal and things should get better.

as soon as an item is selected the proper text will display.
A foreground color the same as the background color will produce the same results you are seeing.

Combobox SelectedItem does not work

I have the code below
FooCB.DisplayMember = "FooNome";
FooCB.ValueMember = "Foo";
FooCB.DataSource = FooRepository.Instance.All();
FooCB.DataBindings.Add("SelectedItem", Bar, "Foo");
but when I display the form the SelectedItem is always the first.
What am I doing wrong?

I have been struggling a little with the behaviour of Winforms comboboxes and databinding recently and these are my observations (.Net4) when binding the ComboBox.DataSource to a list of items and also binding an object property to ComboBox.SelectedItem.
When binding a list of objects (in your case List<Foo>) to ComboBox.DataSource, the first object in the list is always shown in the combobox.
If you bind an object property to ComboBox.SelectedItem (in your case Bar.Foo) and that object property matches one of the combobox list objects then that object is displayed in the combobox. If the object property is null (Bar.Foo == null) or the object property is not in the combobox list then the first object is shown in the combobox.
Setting ComboBox.SelectedItem = null or ComboBox.SelectedIndex = -1 clears the displayed item on the combobox even though this seems to warn against it. And will set your bound object property to null.
If a user clears the combobox selection when using ComboBox.DropDownStyle == DropDown (with backspace) then the bound object property is set to null.
If you have implemented INotifyPropertyChanged on the object whose property is bound to Combobox.SelectedItem (Bar.Foo) and you programatically set the bound property to a value and that value appears in the combobox list then the changed value will be displayed. If you set the property to null or a value not in the list then the combobox displayed value will not change.
So what can you do about it? The only real issue I have is having no value displayed when my bound property is null so I have just been explicitly setting Combobox.SelectedItem = null as in point #3. You may be able to extend ComboBox and override the default behaviour but so far I have been content with an extra line of code here and there combined with using default values on non-nullable properties.

Probably you are missing some decleration. If you created the Combobox from the Tool Box, -I had the similar problem- you might want to add name of the Combobox's Name as a tag on XAML.
Other than that, if you created it dynamically by code, check if you are missing any decleration for class.

I can't tell from the OP's code whether I'm answering their question, but maybe this will help somebody reading this question. The ComboBox has four ways to set the current value:
SelectedIndex
SelectedItem
SelectedText
SelectedValue
You need to be consistent about what you're setting (and about which event handler you're using). You'll get an error if you set SelectedIndex to something dumb (less than -1 or longer than the list). However, you don't get errors setting the other three to something that doesn't exist for that type of selection.
Suppose you use a Dictionary (that's pseudo code) as a binding source and set DisplayMember = "Value" and ValueMember = "Key", the mapping would look like:
SelectedIndex - -1 to index of last item
SelectedItem - KeyValuePair<Key, Value>
SelectedText - Dictionary value
SelectedValue - Dictionary key
Supplying either value or key to SelectedItem will not generate an error, it will simply act like the OP has described. And that's why I thought this answer might help somebody.
I might also note that, if you're swapping out the contents of the ComboBox, it's not always safe to use SelectedIndex. Suppose the same basic kind of data is in the ComboBox, but selections are limited in some cases compared to others. Using SelectedIndex to persist a previous selection that was still valid in the new list of options is only going work if that previous selection held the exact same place in the list. You'd almost think this was the voice of very, very recent experience speaking...

Looping through Datagrid for checked Checkboxs to create a list

I have a Silverlight DataGrid, not an asp Gridview, that gets populated just fine. I have added a checkbox column for the user to select which items they want to download. My goal is to create a 'cart' where the user can select their items, then click a button to add them. Then they will go to a checkout page etc..
My problem so far is that I am having trouble checking to see if the user checked a check box or not. My foreach loops through fine I think, but I get a 'nullreferenceexception' in the bool IsChecked line. During a breakpoint, none of the values came back as null that I saw but it obviously isnt working the way I hoped.
foreach (var row in gridResults.ItemsSource)
{
bool IsChecked = (bool)((CheckBox)gridResults.Columns[8].GetCellContent(row)).IsChecked;
if (IsChecked)
{
List<string> lstFile = new List<string>();
string fileName = (gridResults.SelectedItem as JobSearchResult).FileName;
lstFile.Add(fileName);
}
}
Through the filename, I can find the files on the server for them to download, but How can i check if they checked the ones they wanted or not?

Without knowing precisely how you are populating your datagrid, it is difficult to tell you what the exact cause of your issue is. But I will tell you how I would handle this situation.
Create an ObservableCollection of your object type. Set the ItemsSource of the DataGrid to the ObservableCollection. Then, in the data grid row, create a binding for the IsChecked property of the checkbox to some public boolean value on your object (perhaps call that IsSelected). Make sure to set the binding mode to TwoWay.
Then, all you have to do is use a linq query on the ObservableCollection. Remember that Silverlight is a presentation layer, and you should not rely upon it at all to perform business logic.

A ComboBox Data Binding Question

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.