- Qt 5.15
- Qt Core
- C++ Classes
- QAbstractNativeEventFilter
- Qt 5.15.18 Reference Documentation

# QAbstractNativeEventFilter Class

The QAbstractNativeEventFilter class provides an interface for receiving native events, such as MSG or XCB event structs. More...

Header: | #include <QAbstractNativeEventFilter>
qmake: | QT += core
Since: | Qt 5.0

This class was introduced in Qt 5.0.

- List of all members, including inherited members

## Public Functions

| QAbstractNativeEventFilter()
virtual | ~QAbstractNativeEventFilter()
virtual bool | nativeEventFilter(const QByteArray &eventType, void *message, long *result) = 0

## Detailed Description

## Member Function Documentation

### QAbstractNativeEventFilter::QAbstractNativeEventFilter()

Creates a native event filter.

By default this doesn't do anything. Remember to install it on the application object.

### `[virtual]` QAbstractNativeEventFilter::~QAbstractNativeEventFilter()

Destroys the native event filter.

This automatically removes it from the application.

### `[pure virtual]` bool QAbstractNativeEventFilter::nativeEventFilter(const QByteArray &eventType, void *message, long *result)

This method is called for every native event.

Note: The filter function here receives native messages, for example, MSG or XCB event structs.

It is called by the QPA platform plugin. On Windows, it is called by the event dispatcher.

The type of event eventType is specific to the platform plugin chosen at run-time, and can be used to cast message to the right type.

On X11, eventType is set to "xcb_generic_event_t", and the message can be casted to a xcb_generic_event_t pointer.

On Windows, eventType is set to "windows_generic_MSG" for messages sent to toplevel windows, and "windows_dispatcher_MSG" for system-wide messages such as messages from a registered hot key. In both cases, the message can be casted to a MSG pointer. The result pointer is only used on Windows, and corresponds to the LRESULT pointer.

On macOS, eventType is set to "mac_generic_NSEvent", and the message can be casted to an NSEvent pointer.

In your reimplementation of this function, if you want to filter the message out, i.e. stop it being handled further, return true; otherwise return false.

Linux example

     class MyXcbEventFilter : public QAbstractNativeEventFilter
     {
     public:
         bool nativeEventFilter(const QByteArray &eventType, void *message, long *) override
         {
             if (eventType == "xcb_generic_event_t") {
                 xcb_generic_event_t* ev = static_cast<xcb_generic_event_t *>(message);
                 // ...
             }
             return false;
         }
     };

macOS example

mycocoaeventfilter.h:

     #include <QAbstractNativeEventFilter>

     class MyCocoaEventFilter : public QAbstractNativeEventFilter
     {
     public:
         bool nativeEventFilter(const QByteArray &eventType, void *message, long *) override;
     };

mycocoaeventfilter.mm:

     #include "mycocoaeventfilter.h"

     #import <AppKit/AppKit.h>

     bool CocoaNativeEventFilter::nativeEventFilter(const QByteArray &eventType, void *message, long *)
     {
         if (eventType == "mac_generic_NSEvent") {
             NSEvent *event = static_cast<NSEvent *>(message);
             if ([event type] == NSKeyDown) {
                 // Handle key event
                 qDebug() << QString::fromNSString([event characters]);
             }
         }
         return false;
     }

myapp.pro:

     HEADERS += mycocoaeventfilter.h
     OBJECTIVE_SOURCES += mycocoaeventfilter.mm
     LIBS += -framework AppKit