- 1 year ago
How to UPDATE_COMMAND_UI with SendMessage
In MFC (Microsoft Foundation Classes), the UPDATE_COMMAND_UI
mechanism is typically used with message maps to update the state and appearance of user interface elements (such as menu items, toolbar buttons, etc.) based on the current application state. While SendMessage
can be used to send messages between windows, it is not the appropriate method to implement UPDATE_COMMAND_UI
functionality.
To implement UPDATE_COMMAND_UI
in MFC using message maps, follow these steps:
Define the message handler: In your C++ class derived from
CWnd
orCFrameWnd
, add a message handler for theUPDATE_COMMAND_UI
message. This message handler will be responsible for updating the user interface elements.cppON_UPDATE_COMMAND_UI(ID_MYCOMMAND, OnUpdateMyCommand)
Implement the message handler: Implement the
OnUpdateMyCommand
function to update the state and appearance of the user interface element. This function is called when theUPDATE_COMMAND_UI
message is sent.cppvoid CMyWnd::OnUpdateMyCommand(CCmdUI* pCmdUI)
{
// Update the user interface element based on the application state
if (IsCommandEnabled())
{
pCmdUI->Enable(TRUE);
pCmdUI->SetCheck(IsCommandChecked());
pCmdUI->SetText(GetCommandText());
}
else
{
pCmdUI->Enable(FALSE);
}
}
In this example,
IsCommandEnabled()
,IsCommandChecked()
, andGetCommandText()
are placeholder functions that determine the state and appearance of the user interface element.Trigger the update: When the application state changes, you can trigger the update of the user interface elements associated with the
UPDATE_COMMAND_UI
message by calling theUpdateAllViews
function.cppGetActiveDocument()->UpdateAllViews(NULL);
This will notify all the views associated with the document and trigger the
UPDATE_COMMAND_UI
mechanism.
By following these steps, you can implement the UPDATE_COMMAND_UI
mechanism in MFC to update the state and appearance of user interface elements dynamically. The ON_UPDATE_COMMAND_UI
macro associates a user-defined message handler with the UPDATE_COMMAND_UI
message, and the message handler is responsible for updating the user interface elements based on the application state.