Android:NullPointerException当更改片段时

我的活动中有两个片段。我正在实现actionbarsherlock选项卡导航，每个选项卡都有单独的片段。我正在执行网络操作，并将结果放在

TextView

中

如果我在当前片段完全加载后更改片段，它可以正常工作。

NullPointerException

只有在当前片段仍在加载时更改片段时才会发生。请帮忙

片段1：

public class Fragment1 extends SherlockFragment {

public static Fragment1 newInstance() {
    Fragment1 f = new Fragment1 ();
    return f;
}

private static LinearLayout mainll;

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
        Bundle savedInstanceState) {
    // TODO Auto-generated method stub4

    final View V = inflater.inflate(R.layout.fragment_1, container, false);

    AsyncHttpClient client = new AsyncHttpClient();
    client.get(((MainActivity) act).getUrl(), new AsyncHttpResponseHandler() {
        @Override
        public void onSuccess(String response) {
            Document document = Jsoup.parse(response);

            Element results = document.getElementById("search_results");

            mainll = (LinearLayout) V.findViewById(R.id.content);

            LayoutParams mainllParams = new LayoutParams(LayoutParams.WRAP_CONTENT, LayoutParams.WRAP_CONTENT);
            mainllParams.setMargins(10, 5, 0, 0);

            if(results != null) {
                TextView tv= new TextView(getActivity());  //NPE occurs here
                tv.setLayoutParams(mainllParams);
                tv.setText(results.ownText());
                tv.setGravity(Gravity.CENTER_HORIZONTAL);
                mainll.addView(tv);
            }
    });

    return V;
}
}

片段2：

public class Fragment2 extends SherlockFragment {

public static Fragment2 newInstance() {
    Fragment2 f = new Fragment2 ();
    return f;
}

private static LinearLayout mainll;

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
        Bundle savedInstanceState) {
    // TODO Auto-generated method stub4

    final View V = inflater.inflate(R.layout.fragment_1, container, false);

    AsyncHttpClient client = new AsyncHttpClient();
    client.get(((MainActivity) act).getUrl(), new AsyncHttpResponseHandler() {
        @Override
        public void onSuccess(String response) {
            Document document = Jsoup.parse(response);

            Element results2 = document.getElementById("more_results");

            mainll = (LinearLayout) V.findViewById(R.id.content);

            LayoutParams mainllParams = new LayoutParams(LayoutParams.WRAP_CONTENT, LayoutParams.WRAP_CONTENT);
            mainllParams.setMargins(10, 5, 0, 0);

            if(results2 != null) {
                TextView tv2 = new TextView(getActivity());  //NPE Occurs here
                tv2.setLayoutParams(mainllParams);
                tv2.setText(results.ownText());
                tv2.setGravity(Gravity.CENTER_HORIZONTAL);
                mainll.addView(tv2);
            }
    });

    return V;
}
}

---

提前感谢

好吧，您已经回答了自己的问题：NPE的发生是因为当前片段处于分离状态，这意味着它已从活动中分离，并且没有链接->

getActivity（）

返回

null

您可以为检查添加几个额外选项，以验证您的片段是否仍然可见和附着：

if(results2 != null && getActivity()!=null && isVisible()) {
            TextView tv2 = new TextView(getActivity());  //NPE Occurs here
            tv2.setLayoutParams(mainllParams);
            tv2.setText(results.ownText());
            tv2.setGravity(Gravity.CENTER_HORIZONTAL);
            mainll.addView(tv2);
        }

---

我怎么看不出来！！。非常感谢。