Cannot resolve method ‘show(android.app.FragmentManager,java.lang.String)’

问题是我似乎无法从这个片段中引用android.support.v4.app.FragmentManager.负责这个片段的活动从FragmentActivity延伸,但显然这还不够.我也试过调用getSupportFragmentManager(),但这给了我这个错误：

Cannot resolve method ‘getSupportFragmentManager()’

我怎样才能做到这一点？

这是一些代码：

gPrefAcknowledgements.setOnPreferenceClickListener(new Preference.OnPreferenceClickListener()
{
    @Override
    public boolean onPreferenceClick(Preference preference)
    {
        DialogAcknowledgements dialogAck = new DialogAcknowledgements();
        dialogAck.show(getFragmentManager(),"acknowledgements");
        return true;
    }
});