/**
 * 雙擊退出功能是否生效（預設ture）
 */

private boolean DOUBLECLICK_EXIT = true;

/**
 * 雙擊退出函式
 */
private long firstTime = 0;

@Override
public boolean onKeyDown(int keyCode, KeyEvent event) {
    if (DOUBLECLICK_EXIT) {
        if (keyCode == KeyEvent.KEYCODE_BACK && event.getAction() == KeyEvent.ACTION_DOWN
 
) {
            if (System.currentTimeMillis() - firstTime > 2000) {
                Toast.makeText(mContext, "再按一次退出程式", Toast.LENGTH_SHORT).show();
                firstTime = System.currentTimeMillis();
            } else {
                finish();
                System.exit(0);
            }
            return true
 
;
        }
    }
    return super.onKeyDown(keyCode, event);
}