Flex 实现全屏后无法捕获键盘事件

private function changeScreen():void {if ( stage.displayState == StageDisplayState.FULL_SCREEN ) {stage.displayState = StageDisplayState.NORMAL;                  // other handlenormalscreen.play([main]);} else if ( stage.displayState ==  StageDisplayState.NORMAL ) {stage.displayState = StageDisplayState.FULL_SCREEN;                  // other handlefullscreen.play([main]);}}