我正在处理片段和库，如slidingMenu，pullToRefreshListViews和android Aquery。 在我的应用程序中，我想使用自定义适配器来填充我的ListView，该适配器包含我从JSON解析的数据。
这是粗略的代码
public class MyFragment extends Fragment {
public MyFragment() {
// Empty constructor required for fragment subclasses
}
//initialize some variables here....
PullToRefreshListView list;
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,Bundle savedInstanceState) {
final View rootView = inflater.inflate(//my layout xml, container, false);
aq = new AQuery(getActivity(),rootView);
list = (PullToRefreshListView) rootView.findViewById(R.id.list);
asyncJson(); // this method fetches,parses json and sets adapter to the listview
return rootView;
}
}
asyncJson（）方法是这样的。
public void asyncJson(){
aq.ajax(url, JSONArray.class, expire, new AjaxCallback<JSONArray>() {
@Override
public void callback(String url, JSONArray json, AjaxStatus status) {
try{
// fetch and parse json store data in array<List>
}
if(adapter == null){
adapter = new MyAdapter(getView().getContext(),//array<list> variables);
list.setAdapter(adapter);
}
else if(adapter != null){
adapter.notifyDataSetChanged();
}
}
});
}
Logcat在list.setAdapter(adapter);这一行给出了空指针异常。我没有语法错误。
这是因为我传递给适配器的上下文我尝试了getActivity（），但这也不起作用
列表是null还是适配器？ ：0
我做错了什么？
谢谢！的 Logcat Image
app项目文件：https://www.dropbox.com/s/9sa1l8wm4rnmnew/stackoverflow.zip
答案 0 :(得分：0)
主要是你的Context给你NullPointerException。
尝试通过构造函数将Context传递给您的片段，并在适配器中使用它。
private Context ctx;
public MyFragment(Context ctx) {
this.ctx = ctx;
}
并像这样初始化适配器：
adapter = new MyAdapter(ctx, array<list> variables);
答案 1 :(得分：0)
我猜你正在使用这个库...
https://github.com/chrisbanes/Android-PullToRefresh
下载它，您需要导入以下内容并将其添加为我们项目的依赖项。
PullToRefreshListFragment 文库
我修改了您从评论链接下载的项目。你可以从这里下载：
我也要编写代码，所以我们不依赖于这个答案的链接;）。所以我们只有一个类调用MainActivity，它扩展自FragmentActivity。
public class MainActivity extends FragmentActivity implements PullToRefreshBase.OnRefreshListener<ListView> {
FragmentManager fm = getSupportFragmentManager();
private PullToRefreshListFragment mPullRefreshListFragment;
private PullToRefreshListView mPullRefreshListView;
private ListView mActualListView;
private String[] mStrings = {"Abbaye de Belloc", "Abbaye du Mont des Cats", "Abertam", "Abondance", "Ackawi",
"Acorn", "Adelost", "Affidelice au Chablis", "Afuega'l Pitu", "Airag", "Airedale", "Aisy Cendre",
"Allgauer Emmentaler", "Abbaye de Belloc", "Abbaye du Mont des Cats", "Abertam", "Abondance", "Ackawi",
"Acorn", "Adelost", "Affidelice au Chablis", "Afuega'l Pitu", "Airag", "Airedale", "Aisy Cendre",
"Allgauer Emmentaler"};
private LinkedList<String> mListItems;
private ArrayAdapter<String> mAdapter;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
// sliding menu implementation
/*final SlidingMenu menu = new SlidingMenu(this);
menu.setMode(SlidingMenu.LEFT);
menu.setTouchModeAbove(SlidingMenu.TOUCHMODE_FULLSCREEN);
menu.setShadowWidthRes(R.dimen.shadow_width);
menu.setShadowDrawable(R.drawable.shadow);
menu.setBehindOffsetRes(R.dimen.slidingmenu_offset);
menu.setFadeDegree(0.35f);
menu.attachToActivity(this, SlidingMenu.SLIDING_CONTENT);
menu.setMenu(R.layout.menu);*/
// event handlers come after slidingmenu
mPullRefreshListFragment = (PullToRefreshListFragment) getSupportFragmentManager().findFragmentById(R.id.frag_ptr_list);
//aq = new AQuery(getActivity(),mPullToRefreshListFragment.getView());
/*mPullRefreshListView.setOnScrollListener(new EndlessScrollListener();*/
mPullRefreshListView = mPullRefreshListFragment.getPullToRefreshListView();
// Set a listener to be invoked when the list should be refreshed.
mPullRefreshListView.setOnRefreshListener(this);
// You can also just use mPullRefreshListFragment.getListView()
mActualListView = mPullRefreshListView.getRefreshableView();
mListItems = new LinkedList<String>();
mListItems.addAll(Arrays.asList(mStrings));
mAdapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, mListItems);
View headerView = getLayoutInflater().inflate(R.layout.list_header, null);
mActualListView.addHeaderView(headerView);
mActualListView.setAdapter(mAdapter);
mPullRefreshListFragment.setListShown(true);
/*asyncJson(1,expire);*/
}
public void asyncJson(int page, final long expire) {
// GET JSON FROM THE WEB AND PARSE IT
// ALSO STORE DATA IN ARRAY LIST VARIABLES
if (expire == -1) {
mPullRefreshListView.onRefreshComplete();
}
//if(pg == 1 && expire !=-1){
//If you wanna add a header at this point, do it like this
View headerView = getLayoutInflater().inflate(R.layout.list_header, null);
mActualListView.addHeaderView(headerView);
// DO SOMETHING
//}
//Just notify the changes because the adapter do exist
mAdapter.notifyDataSetChanged();
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
@Override
public void onRefresh(PullToRefreshBase<ListView> refreshView) {
// Do work to refresh the list here.
new GetDataTask().execute();
}
private class GetDataTask extends AsyncTask<Void, Void, String[]> {
@Override
protected String[] doInBackground(Void... params) {
// Simulates a background job.
try {
Thread.sleep(4000);
} catch (InterruptedException e) {
}
return mStrings;
}
@Override
protected void onPostExecute(String[] result) {
mListItems.addFirst("Added after refresh...");
mAdapter.notifyDataSetChanged();
// Call onRefreshComplete when the list has been refreshed.
mPullRefreshListView.onRefreshComplete();
super.onPostExecute(result);
}
}
}
这是我们的布局：
activity_main.xml中
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context=".MainActivity" >
<fragment
android:id="@+id/frag_ptr_list"
android:name="com.handmark.pulltorefresh.extras.listfragment.PullToRefreshListFragment"
android:layout_width="match_parent"
android:layout_height="match_parent" />
</RelativeLayout>
list_row.xml
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent">
<TextView
android:id="@+id/text"
android:layout_width="wrap_content"
android:layout_height="wrap_content"/>
</RelativeLayout>
list_header.xml
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="#4a2">
<TextView
android:id="@+id/text"
android:gravity="center"
android:text="My Header"
android:textColor="#fff"
android:layout_width="match_parent"
android:layout_height="40dp"/>
</RelativeLayout>