java - Android ListView 与详细信息页空对象

Question

我正在从 api 的内容创建一个 ListView ，如果我单击一个 ListView 项目，我想显示一个新 View ，其中包含该单击项目的更多详细信息，当前 ListView 可以正确显示，但如果我单击一个项目，应用程序崩溃，并且收到此错误消息:

> java.lang.RuntimeException: Unable to start activity
> ComponentInfo{de.dev.app/de.dev.app.ui.quote.ArticleDetailActivity}:
> java.lang.NullPointerException: Attempt to invoke virtual method
> 'java.lang.String de.dev.app.jokeapp.entities.Joke.getTitle()' on a null
> object reference  ...  Caused by: java.lang.NullPointerException:
> Attempt to invoke virtual method 'java.lang.String
> de.dev.app.entities.Joke.getTitle()' on a null object reference
>                                                                       at
> de.dev.app.ui.quote.ArticleDetailFragment.onCreateView(ArticleDetailFragment.java:100)

错误指向我的 ArticleDetailFragment.java 中的这一行:

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    View rootView = inflateAndBind(inflater, container, R.layout.fragment_article_detail);
    if (!((BaseActivity) getActivity()).providesActivityToolbar()) {
        ((BaseActivity) getActivity()).setToolbar((Toolbar) rootView.findViewById(R.id.toolbar));
    }
    collapsingToolbar.setTitle(jokeItem.getTitle()); // points here
    author.setText(jokeItem.getTitle());
    quote.setText(jokeItem.getTitle());
    jokeHeader.setText(jokeItem.getTitle());
    jokeContent.setText(jokeItem.getContent());

    return rootView;
}

这是我的 onAttach 方法:

@Override
public void onAttach(Context context) {
    super.onAttach(context);
    Bundle bundle = getArguments();
    if(bundle == null) {
        getActivity().finish();
        return;
    }
    jokeItem = (Joke)bundle.getSerializable("joke");
}

这是我的 ArticleDetailFragment 看起来像:

public class ArticleDetailFragment extends BaseFragment {



    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        if (getArguments().containsKey(ARG_ITEM_ID)) {
            // load dummy item by using the passed item ID.
            dummyItem = DummyContent.ITEM_MAP.get(getArguments().getString(ARG_ITEM_ID));
        }

        SharedPreferences preferences = this.getActivity().getSharedPreferences("pref", Context.MODE_PRIVATE);
        tokenManager = TokenManager.getInstance(preferences);
        service = RetrofitBuilder.createServiceWithAuth(ApiService.class, tokenManager);

        setHasOptionsMenu(true);
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View rootView = inflateAndBind(inflater, container, R.layout.fragment_article_detail);
        if (!((BaseActivity) getActivity()).providesActivityToolbar()) {
            // No Toolbar present. Set include_toolbar:
            ((BaseActivity) getActivity()).setToolbar((Toolbar) rootView.findViewById(R.id.toolbar));
        }
        collapsingToolbar.setTitle(jokeItem.getTitle());
        author.setText(jokeItem.getTitle());

        return rootView;
    }


    @Override
    public void onCreateOptionsMenu(Menu menu, MenuInflater inflater) {
        inflater.inflate(R.menu.sample_actions, menu);
        super.onCreateOptionsMenu(menu, inflater);
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        switch (item.getItemId()) {
            case R.id.action_settings:
                // your logic
                return true;
        }
        return super.onOptionsItemSelected(item);
    }


    @Override
    public void onAttach(Context context) {
        super.onAttach(context);
        Bundle bundle = getArguments();
        if(bundle == null) {
            getActivity().finish();
            return;
        }
        jokeItem = (Joke)bundle.getSerializable("joke");
    }

}

我的文章详情 Activity

public class ArticleDetailActivity extends BaseActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_detail);

        if (getSupportActionBar() != null) {
            getSupportActionBar().setDisplayHomeAsUpEnabled(true);
        }

        ArticleDetailFragment fragment =  ArticleDetailFragment.newInstance(getIntent().getStringExtra(ArticleDetailFragment.ARG_ITEM_ID));
        getFragmentManager().beginTransaction().replace(R.id.article_detail_container, fragment).commit();
    }

    @Override
    public boolean providesActivityToolbar() {
        return false;
    }
}

在我的 ListActivit 中调用 ArticleDetailActivity，如下所示:

public class ListActivity extends BaseActivity implements ArticleListFragment.Callback {
...
    @Override
    public void onItemSelected(Joke joke) {

            Intent detailIntent = new Intent(this, ArticleDetailActivity.class);
            // detailIntent.putExtra(ArticleDetailFragment.ARG_ITEM_ID, id);
            startActivity(detailIntent);
    }
    ...

Answer 1

从 ListActivity 中像这样调用 DetailActivity，

Intent detailIntent = new Intent(this, ArticleDetailActivity.class);
// detailIntent.putExtra(ArticleDetailFragment.ARG_ITEM_ID, id);
Bundle bundle = new Bundle();
bundle.putSerializable("joke", joke);
detailIntent.putExtras(bundle);
startActivity(detailIntent);

并像这样更改您的 ArticleDetailActivity 更改，我们需要将数据发送到 fragment

public class ArticleDetailActivity extends BaseActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_detail);

        // Show the Up button in the action bar.
        if (getSupportActionBar() != null) {
            getSupportActionBar().setDisplayHomeAsUpEnabled(true);
        }

        ArticleDetailFragment fragment =  new ArticleDetailFragment();

        fragment.setArguments(getIntent().getExtras());

        getFragmentManager().beginTransaction().replace(R.id.article_detail_container, fragment).commit();
    }

    @Override
    public boolean providesActivityToolbar() {
        return false;
    }
}