key_down

event<control, key_event_handler> xtd::forms::control::key_down

Occurs when a key is pressed while the xtd::forms::control has focus.

Remarks

Key events occur in the following order:

1. xtd::forms::control::key_down event

1. xtd::forms::control::key_press event

1. xtd::forms::control::key_up event

To handle keyboard events only at the form level and not enable other controls to receive keyboard events, set the xtd::forms::key_press_event_args::handled property in your form's xtd::forms::control::key_press event-handling method to true. Certain keys, such as the TAB, RETURN, ESC, and arrow keys are handled by controls automatically. To have these keys raise the xtd::forms::control::key_down event, you must override the is_input_key method in each control on your form. The code for the override of the is_input_key would need to determine if one of the special keys is pressed and return a value of true. Instead of overriding the is_input_key method, you can handle the preview_key_down event and set the is_input_key property to true.

Examples

The following code example demonstrates the use of control keyboard events.

#define TRACE
#include <xtd/forms/application>
#include <xtd/forms/form>
#include <xtd/forms/trace_form>
#include <xtd/ctrace>
 
using namespace xtd;
using namespace xtd::forms;
 
class form1 : public form {
public:
  form1() {
    text("Key events example");
    
    control1.dock(dock_style::fill);
    control1.parent(*this);
    
    control1.key_down += [&](object & sender, key_event_args & e) {
      ctrace << string::format("key_down={{key_code={}, key_data=[{}], value=0x{:X4}, modifiers=[{}]}}", e.key_code(), e.key_data(), e.key_value(), e.modifiers()) << environment::new_line;
    };
    
    control1.key_press += [&](object & sender, key_press_event_args & e) {
      ctrace << string::format("key_press={{key_char={}}}", e.key_char() == 0 ? "[none]" : string::format("'{}'", e.key_char())) << environment::new_line;
    };
    
    control1.key_up += [&](object & sender, key_event_args & e) {
      ctrace << string::format("key_up={{key_code={}, key_data=[{}], value=0x{:X4}, modifiers=[{}]}}", e.key_code(), e.key_data(), e.key_value(), e.modifiers()) << environment::new_line;
      if (e.modifiers() == keys::none) ctrace << environment::new_line;
    };
  }
  
private:
  control control1;
};
 
auto main() -> int {
  trace_form trace_form;
  application::run(form1 {});
}

Remarks

For more information about handling events, see Handling and Raising Events.