Using NativeWindowEventFilter to Filter Multimodal Input Events (C/C++)

When to Use

You can use the capability provided by the NativeWindowEventFilter module to intercept key events so that they are not distributed to internal components of your application.

Available APIs

How to Develop

Linking the Dynamic Library in the CMake Script

target_link_libraries(entry PUBLIC libnative_window_manager.so libohinput.so)

Adding Header Files

#include "window_manager/oh_window_comm.h"
#include "window_manager/oh_window_event_filter.h"
#include "multimodalinput/oh_input_manager.h"
#include "multimodalinput/oh_key_code.h"

API Usage Description

• After an application window is created, bind a key event filter to the window specified by the window ID.
• The application window can trigger the key event interception only when it receives the key event.
• The application window intercepts the event when the return value of the key event filter is true. If the return value is false, it does not intercept the event.
• Only one key event filter can be registered for the same window ID. The last registered key event filter overwrites the previously registered one. To filter a multi-key event, you are advised to process the multi-key combination in a filter.

Example

The following sample code describes how to register and unregister a key event filter. The following uses the Esc key and number keys as an example.

#include "napi/native_api.h"
#include "window_manager/oh_window_comm.h"
#include "window_manager/oh_window_event_filter.h"
#include "multimodalinput/oh_input_manager.h"
#include "multimodalinput/oh_key_code.h"

// Set a filter.
static bool filterFunc(Input_KeyEvent *event) {
  auto keyCode = OH_Input_GetKeyEventKeyCode(event);
  auto action = OH_Input_GetKeyEventAction(event);
  // Case1: Implement the event filter for the Esc key.
  // return keyCode == Input_KeyCode::KEYCODE_ESCAPE;

  // Case 2: Implement the event filter for the number keys only when they are pressed.
  // return keyCode >= Input_KeyCode::KEYCODE_0 && keyCode <= Input_KeyCode::KEYCODE_9
  //  && action == Input_KeyEventAction::KEY_ACTION_DOWN;
  
  // Implement the event filter for the combination of the Esc key and a pressed-down number key. (Case1||Case2).
  return (keyCode >= Input_KeyCode::KEYCODE_0 && keyCode <= Input_KeyCode::KEYCODE_9
     && action == Input_KeyEventAction::KEY_ACTION_DOWN)||(keyCode == Input_KeyCode::KEYCODE_ESCAPE);
}

static napi_value registerFilter(napi_env env, napi_callback_info info) {
  size_t argc = 1;
  napi_value args[1] = {nullptr};
  napi_get_cb_info(env, info, &argc, args, nullptr, nullptr);
  
  int32_t windowId;
  napi_get_value_int32(env, args[0], &windowId);
  
  // Register the filter for the window specified by the window ID.
  auto res = OH_NativeWindowManager_RegisterKeyEventFilter(windowId, filterFunc);
  
  napi_value errCode;
  napi_create_int32(env, res, &errCode);
  return errCode;
}

static napi_value clearFilter(napi_env env, napi_callback_info info) {
  size_t argc = 1;
  napi_value args[1] = {nullptr};
  napi_get_cb_info(env, info, &argc, args, nullptr, nullptr);

  int32_t windowId;
  napi_get_value_int32(env, args[0], &windowId);

  auto res = OH_NativeWindowManager_UnregisterKeyEventFilter(windowId);
  napi_value errCode;
  napi_create_int32(env, res, &errCode);
  return errCode;

}

EXTERN_C_START
static napi_value Init(napi_env env, napi_value exports) {
  napi_property_descriptor desc[] = {
    {"registerFilter", nullptr, registerFilter, nullptr, nullptr, nullptr, napi_default, nullptr},
    {"clearFilter", nullptr, clearFilter, nullptr, nullptr, nullptr, napi_default, nullptr}};
  napi_define_properties(env, exports, sizeof(desc) / sizeof(desc[0]), desc);
  return exports;
}
EXTERN_C_END

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