android中关于activity的返回键处理方法

/**
 * 菜单、返回键响应
 */
@Override
public boolean onKeyDown(int keyCode, KeyEvent event) {
// TODO Auto-generated method stub
Utiltools.printE("调用双击退出函数onKeyDown"+keyCode+ KeyEvent.KEYCODE_BACK);
if (keyCode == KeyEvent.KEYCODE_BACK) {
exitBy2Click(); // 调用双击退出函数
}
return false;
}
/**
 * 双击退出函数
 */
private static Boolean isExit = false;

private void exitBy2Click() {
Timer tExit = null;
if (isExit == false) {
isExit = true; // 准备退出
Toast.makeText(this, "再按一次退出程序", Toast.LENGTH_SHORT).show();
tExit = new Timer();
tExit.schedule(new TimerTask() {
@Override
public void run() {
isExit = false; // 取消退出
}
}, 2000); // 如果2秒钟内没有按下返回键，则启动定时器取消掉刚才执行的任务

} else {
//MyApplication.removeAll();
MyApplication application = (MyApplication) getApplication();
application.finishAllContext();
System.exit(0);
}
}