private CountryChooseDialog mCountryChooseDialog;
private void showCountryChooseDialog() {
    if (mCountryChooseDialog == null) {
      mCountryChooseDialog = CountryChooseDialog.newInstance();
    }
    if (mCountryChooseDialog.isAdded()) {　　//解决方法就是添加这行代码，如果已经添加了，就移除掉然后再show，就不会出现Fragment already added的错误了。
      getSupportFragmentManager().beginTransaction().remove(mCountryChooseDialog).commit();
    }
    mCountryChooseDialog.show(getSupportFragmentManager(), mCountryChooseDialog.getClass().getName());
}