Question

我在zip文件中使用了Google的示例here中的代码。

当我运行它时，一切顺利。

如果我删除了支持库并将FragmentActivity更改为Activity并支持.Fragment到Fragment（还有gertsupportFragmentManager（）到FragmentManager（）），并且Manifest指向api 17，如下所示： <uses-sdk android:minSdkVersion="11" android:targetSdkVersion="17" />

单击列表项时，我收到NPE。我不明白发生了什么变化，无法找到R.id.article。

由于我没有更改布局文件，因此我并没有太多地使用代码，我猜测它与API和/或活动/片段的生命周期有关代替FragmentActivity和support.Fragment。

错误是：

11-07 18:30:20.397: E/AndroidRuntime(1266): FATAL EXCEPTION: main
11-07 18:30:20.397: E/AndroidRuntime(1266): java.lang.NullPointerException
11-07 18:30:20.397: E/AndroidRuntime(1266):     at com.example.android.fragments.ArticleFragment.updateArticleView(ArticleFragment.java:63)
11-07 18:30:20.397: E/AndroidRuntime(1266):     at com.example.android.fragments.MainActivity.onArticleSelected(MainActivity.java:70)
11-07 18:30:20.397: E/AndroidRuntime(1266):     at com.example.android.fragments.HeadlinesFragment.onListItemClick(HeadlinesFragment.java:75)

ArticleFragment代码在这里：

public class ArticleFragment extends android.app.Fragment {
final static String ARG_POSITION = "position";
int mCurrentPosition = -1;

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, 
    Bundle savedInstanceState) {

    // If activity recreated (such as from screen rotate), restore
    // the previous article selection set by onSaveInstanceState().
    // This is primarily necessary when in the two-pane layout.
    if (savedInstanceState != null) {
        mCurrentPosition = savedInstanceState.getInt(ARG_POSITION);
    }

    // Inflate the layout for this fragment
    return inflater.inflate(R.layout.article_view, container, false);
}

@Override
public void onStart() {
    super.onStart();

    // During startup, check if there are arguments passed to the fragment.
    // onStart is a good place to do this because the layout has already been
    // applied to the fragment at this point so we can safely call the method
    // below that sets the article text.
    Bundle args = getArguments();
    if (args != null) {
        // Set article based on argument passed in
        updateArticleView(args.getInt(ARG_POSITION));
    } else if (mCurrentPosition != -1) {
        // Set article based on saved instance state defined during onCreateView
        updateArticleView(mCurrentPosition);
    }
}

public void updateArticleView(int position) {
    TextView article = (TextView) getActivity().findViewById(R.id.article);
    article.setText(Ipsum.Articles[position]);
    mCurrentPosition = position;
}

@Override
public void onSaveInstanceState(Bundle outState) {
    super.onSaveInstanceState(outState);

    // Save the current article selection in case we need to recreate the fragment
    outState.putInt(ARG_POSITION, mCurrentPosition);
}
}

Ipsum课程：

package com.example.android.fragments;

public class Ipsum {

static String[] Headlines = {
    "Article One",
    "Article Two"
};

static String[] Articles = {
    "Article One\n\nExcepteur pour-over occaecat squid biodiesel umami gastropub, nulla laborum salvia dreamcatcher fanny pack. Ullamco culpa retro ea, trust fund excepteur eiusmod direct trade banksy nisi lo-fi cray messenger bag. Nesciunt esse carles selvage put a bird on it gluten-free, wes anderson ut trust fund twee occupy viral. Laboris small batch scenester pork belly, leggings ut farm-to-table aliquip yr nostrud iphone viral next level. Craft beer dreamcatcher pinterest truffaut ethnic, authentic brunch. Esse single-origin coffee banksy do next level tempor. Velit synth dreamcatcher, magna shoreditch in american apparel messenger bag narwhal PBR ennui farm-to-table.",
    "Article Two\n\nVinyl williamsburg non velit, master cleanse four loko banh mi. Enim kogi keytar trust fund pop-up portland gentrify. Non ea typewriter dolore deserunt Austin. Ad magna ethical kogi mixtape next level. Aliqua pork belly thundercats, ut pop-up tattooed dreamcatcher kogi accusamus photo booth irony portland. Semiotics brunch ut locavore irure, enim etsy laborum stumptown carles gentrify post-ironic cray. Butcher 3 wolf moon blog synth, vegan carles odd future."
};
}

Answer 1

标记为已接受的答案对我不起作用。我最终在这里找到了详细的答案（http://marksunghunpark.blogspot.com/2015/04/googles-fragment-example-error.html）

来自Sunghun的博客：

当您点击标题中的项目时，它会加载新闻内容。 MainActivity切换片段以将其显示在手机中但是它在表格设备的第二个窗格中显示新闻内容。错误来自ArticleFragment课程。当MainActivity加载两个窗格时 news_articles.xml中的/res/layout-large，找不到ID为'article'的视图，因为它试图通过调用查找视图 getActivity().findViewById()。这不起作用。你必须阅读来自'article'的{{1}}的{{1}} TextView。

Answer 2

将TextView声明为类成员

在onCreateView

中对其进行初始化

TextView article; 
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, 
    Bundle savedInstanceState) {

    // If activity recreated (such as from screen rotate), restore
    // the previous article selection set by onSaveInstanceState().
    // This is primarily necessary when in the two-pane layout.
    if (savedInstanceState != null) {
        mCurrentPosition = savedInstanceState.getInt(ARG_POSITION);
    }
    View view =inflater.inflate(R.layout.article_view, container, false); 
     article = (TextView) view.findViewById(R.id.article);
    // Inflate the layout for this fragment
    return view;
}

findViewById查找当前的infalted布局中提到的视图。如果没有找到，你会得到NPE。因此，使布局使用视图对象初始化textview。

FragmentBasics给出空指针异常

2 个答案: