When working with Windows applications, particularly when handling text inputs in controls like Edit or TextBox, developers often encounter a challenge related to the EN_CHANGE notification message. This message gets sent whenever the text in the control changes, which can happen both through user input and programmatic changes. If you're using the WM_SETTEXT message to update text, you might want to suppress the EN_CHANGE notification. In this article, we will explore how to do just that.
Understanding the Problem
When you send the WM_SETTEXT message to a control, you are programmatically updating the text. However, this action triggers the EN_CHANGE notification, which may not always be desired—especially if the change does not require any additional handling or processing. This can lead to unnecessary function calls, performance hits, or even unintended behavior if your application relies heavily on handling EN_CHANGE.
Original Code Example
Here’s a basic example of using WM_SETTEXT to update the text of a control:
SendMessage(hEditControl, WM_SETTEXT, 0, (LPARAM)"New Text");
In this case, sending WM_SETTEXT causes an EN_CHANGE notification to be sent.
Solutions to Suppress EN_CHANGE Notifications
Method 1: Subclassing the Control
One effective way to suppress the EN_CHANGE notification is to subclass the control. By intercepting the messages sent to the control, you can filter out EN_CHANGE before it gets processed.
Here’s a simplified version of how to do this:
LRESULT CALLBACK SubclassProc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam) {
if (uMsg == WM_SETTEXT) {
// Prevent EN_CHANGE from being sent
// Store the original text if needed
// Call the original window procedure
return DefWindowProc(hwnd, uMsg, wParam, lParam);
}
return CallWindowProc(OldProc, hwnd, uMsg, wParam, lParam);
}
// Inside your initialization function
OldProc = (WNDPROC)SetWindowLongPtr(hEditControl, GWLP_WNDPROC, (LONG_PTR)SubclassProc);
Method 2: Temporarily Disabling the Control
Another simple technique is to disable the control temporarily before sending the text, and then re-enabling it afterward. This approach effectively prevents EN_CHANGE notifications from being sent during the update.
EnableWindow(hEditControl, FALSE);
SendMessage(hEditControl, WM_SETTEXT, 0, (LPARAM)"New Text");
EnableWindow(hEditControl, TRUE);
However, note that this method may not be suitable if the control is user-interactive or if it disrupts the user experience.
Method 3: Using a Custom Notification Flag
If subclassing or disabling the control is too complex or not practical for your application, consider implementing a custom notification flag. By using a boolean variable to indicate whether you're programmatically setting the text, you can skip processing during your EN_CHANGE handler:
bool isProgrammaticChange = false;
void OnTextChanged() {
if (isProgrammaticChange) return;
// Handle normal text change operations
}
void UpdateText() {
isProgrammaticChange = true;
SendMessage(hEditControl, WM_SETTEXT, 0, (LPARAM)"New Text");
isProgrammaticChange = false;
}
Conclusion
Suppressing EN_CHANGE notifications when sending WM_SETTEXT can help maintain application performance and behavior, especially in larger applications where many text changes might occur in response to various events. By using techniques such as subclassing, temporarily disabling controls, or implementing a notification flag, you can control when your application reacts to changes in the text input controls.
Additional Resources
For further reading on managing Windows messages and notifications, you might find the following resources useful:
By following these methods and practices, developers can improve the efficiency and robustness of their applications. If you encounter any specific issues or need further clarification, feel free to reach out or comment below!
