TIWCGJQComboBoxEx causes AV during lookup

[dfields]

The TIWCGJQComboBoxEx component causes an access violation when calling the ItemsByValue method with a value that is not in the list.

I populate the items with 3 entries where the Caption and Value properties are set to the same value: "aaa", "bbb" and "ccc". I add an IWCGJQEdit on the form. Next, I drop a button on the form and set its OnChange event to a single line of code:

{code}
procedure TIWForm1.Button1JQButtonOptionsClick(Sender: TObject; AParams: TStringList);
begin
ComboBoxEx1.SelectedIndex := ComboBoxEx1.Items.ItemsByValue[IWCGJQEdit1.Text].Index;
end;
{code}

If the value in the Edit is set to any of the values in the list, everything works fine. If I enter any value that is not in the items, such as "123", the error is generated.

Is there a property that can be set to prevent this?

[ScottWGast]

It's my guess that the value of .Index is -1.

Scott

[Jorge Sousa]

Hello Daniel

Can you please submit a test case please? t.i.a.

Is AV an Access Violation? or any other exception?

[dfields]

Here is the test case I used. I did mean "access violation" by AV.

[Jorge Sousa]

Hi Daniel

What happens if there are no items for

ComboBoxEx1.Items.ItemsByValue[IWCGJQEdit1.Text]?

Do you imagine what is the return?

[ScottWGast]

If IWCGJQEdit1.Text does not contain a valid ComboBoxEx1.Items.ItemsByValue "value", then I'm not surprised if you get an AV when you hit this line:

ComboBoxEx1.SelectedIndex := ComboBoxEx1.Items.ItemsByValue[IWCGJQEdit1.Text].Index;

because

ComboBoxEx1.Items.ItemsByValue[IWCGJQEdit1.Text].Index;

will fail.

[Jorge Sousa]

Hi Scott

I'm not surprised if you get an AV when you hit this line

Exactly!

ComboBoxEx1.Items.ItemsByValue[IWCGJQEdit1.Text]

will return nil

if there are no items for value IWCGJQEdit1.Text

[dfields]

What? Are you saying that the designed behavior is to generate the error when searching for a value that is not in the list? I expect that it would it to return -1 or nil, but the error is completely unexpected.

When I use a normal ComboBox I can use a similar call without getting the error. If there is not a match I get -1 without an error.

Code: Select all

ComboBox1.ItemIndex := ComboBox1.Items.IndexOf(IWCGJQEdit1.Text);

Based upon what you are telling me I would have to add extra code any place I want to use a ComboBoxEx.

Code: Select all

try
  ComboBoxEx1.SelectedIndex := ComboBoxEx1.Items.ItemsByValue[IWCGJQEdit1.Text].Index;
except
  ComboBoxEx1.SelectedIndex := -1;
end;


So you are saying it is not a bug, but designed behavior that the control should function this way?

[ScottWGast]

The error is not caused by the .ItemsByValue "search", per se. The AV comes from attempting to access .Index when the search fails.

ComboBox1.Items.IndexOf method automagically returns -1 if the string is not found.

ComboBoxEx1.Items.ItemsByValue[IWCGJQEdit1.Text] returns nil if the string is not found; if the string is found, then it returns an instance of TIWCGJQComboBoxExItem.

You will need to check to see if ComboBoxEx1.Items.ItemsByValue[IWCGJQEdit1.Text] is nil before attempting to check the .Index property.
If it returns nil, my suggestion would be to add the manually entered string to the items list and then set the .SelectedIndex:

Code: Select all

if (ComboBoxEx1.Items.ItemsByValue[IWCGJQEdit1.Text] = nil) then
    ComboBoxEx1.Items.AddOption(IWCGJQEdit1.Text, IWCGJQEdit1.Text));

ComboBoxEx1.SelectedIndex := ComboBoxEx1.Items.ItemsByValue[IWCGJQEdit1.Text].Index;


HTH!

Scott

[Jorge Sousa]

Hi Daniel

property Items is a collection

Items.ItemsByValue returns the collection Item class TIWCGJQComboBoxExItem if found if not, returns nil

so you will have to do

var
Item: TIWCGJQComboBoxExItem;
begin
Item:= ComboBoxEx1.Items.ItemsByValue[IWCGJQEdit1.Text];
if Assigned(Item) then
ComboBoxEx1.SelectedIndex := Item.Index
else
ComboBoxEx1.SelectedIndex := -1;
end;

or just...

ComboBoxEx1.SelectByValue(IWCGJQEdit1.Text);

and we don't care how other controls work, because we know that we are doing right.