按俩下退出

    private long timeExit = 0;

    @Override
    public boolean onKeyDown(int keyCode, KeyEvent event) {
        if (keyCode == KeyEvent.KEYCODE_BACK && event.getAction() == KeyEvent.ACTION_DOWN) {
            if (System.currentTimeMillis() - timeExit > 2000) {
                timeExit = System.currentTimeMillis();
                Toast.makeText(getApplicationContext(), "再按一下退出", Toast.LENGTH_SHORT).show();
            } else {
                System.exit(0);
            }
            return true;
        } else {
            return super.onKeyDown(keyCode, event);
        }

    }