how to use mxml component in another actionscript

how to use mxml component in another mxml component actionscript code

for ex. in my main mxml file

private var warningMessage:Warning;//this is variable

if (!_controller.flashVars.chatSession || _controller.flashVars.chatSession == "")
            {

                warningMessage.includeInLayout = true;
                warningMessage.visible = true;
            }
            else
            {
                _controller.flashVars.showWarningMessage = "2";
            }

private var warningMessage:Warning;(warning is external custom component)

warningMessage.visible=true (and i want use it like this in my actionscript code

but i am getting error saying "Type was not found or was not compile time constant:warning")

There are three things that jump out.

1. If this component is in another SWC file, make sure to reference it in the project settings
2. Import the namespace or call it directly (com.whatever.namespace.Warning)
3. Make sure to call new to generate a new object. In your code above, warningMessage is null.

private var warningMessage:Warning = new Warning();