我尝试在我的 fragment 中实现 ListView 后出现错误。请检查我的代码，除了使用 ListView lv = getListView(); 之外，我正在尝试为我的 ListView 膨胀 xml 布局； .我知道该方法有效，但我不希望那样。请帮助我更正我的代码。
洛卡特:
11-07 10:54:36.828: E/AndroidRuntime(2947): FATAL EXCEPTION: main
11-07 10:54:36.828: E/AndroidRuntime(2947): java.lang.NullPointerException
11-07 10:54:36.828: E/AndroidRuntime(2947): at testing.app.FreeFragment$loadListView.onPostExecute(FreeFragment.java:132)
11-07 10:54:36.828: E/AndroidRuntime(2947): at testing.app.FreeFragment$loadListView.onPostExecute(FreeFragment.java:1)
11-07 10:54:36.828: E/AndroidRuntime(2947): at android.os.AsyncTask.finish(AsyncTask.java:417)
11-07 10:54:36.828: E/AndroidRuntime(2947): at android.os.AsyncTask.access$300(AsyncTask.java:127)
11-07 10:54:36.828: E/AndroidRuntime(2947): at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:429)
11-07 10:54:36.828: E/AndroidRuntime(2947): at android.os.Handler.dispatchMessage(Handler.java:99)
11-07 10:54:36.828: E/AndroidRuntime(2947): at android.os.Looper.loop(Looper.java:130)
11-07 10:54:36.828: E/AndroidRuntime(2947): at android.app.ActivityThread.main(ActivityThread.java:3691)
11-07 10:54:36.828: E/AndroidRuntime(2947): at java.lang.reflect.Method.invokeNative(Native Method)
11-07 10:54:36.828: E/AndroidRuntime(2947): at java.lang.reflect.Method.invoke(Method.java:507)
11-07 10:54:36.828: E/AndroidRuntime(2947): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:907)
11-07 10:54:36.828: E/AndroidRuntime(2947): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:665)
11-07 10:54:36.828: E/AndroidRuntime(2947): at dalvik.system.NativeStart.main(Native Method)
主要 Activity .java
public class MainActivity extends SherlockFragmentActivity {
Tab tab;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
AppRater.app_launched(this);
if (!isNetworkAvailable()) {
AlertDialog.Builder builder = new AlertDialog.Builder(this);
builder.setMessage("Internet Connection Required")
.setCancelable(false)
.setPositiveButton("Exit",
new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog,
int id) {
finish();
}
});
AlertDialog alert = builder.create();
alert.show();
} else {
ActionBar actionBar = getSupportActionBar();
actionBar.setDisplayShowHomeEnabled(false);
actionBar.setDisplayShowTitleEnabled(false);
actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);
tab = actionBar.newTab().setTabListener(new FreeFragment())
.setIcon(R.drawable.free);
actionBar.addTab(tab);
tab = actionBar.newTab().setTabListener(new BuyFragment())
.setIcon(R.drawable.buy);
actionBar.addTab(tab);
tab = actionBar.newTab().setTabListener(new ReaderFragment())
.setIcon(R.drawable.reader);
actionBar.addTab(tab);
}
}
private boolean isNetworkAvailable() {
ConnectivityManager connectivityManager = (ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE);
NetworkInfo activeNetworkInfo = connectivityManager
.getActiveNetworkInfo();
return activeNetworkInfo != null;
}
}
自由 fragment .java
public class FreeFragment extends Fragment implements
ActionBar.TabListener {
static final String URL = "https://myxml.xml";
static final String KEY_SONG = "song";
static final String KEY_ID = "id";
static final String KEY_TITLE = "title";
static final String KEY_CAT_ARTIST = "artistcat";
static final String KEY_DURATION = "duration";
static final String KEY_THUMB_URL = "thumb_url";
static final String KEY_BIG_URL = "big_url";
static final String KEY_CAT_URL = "cat_url";
static final String KEY_DESC = "cat_desc";
ArrayList<HashMap<String, String>> menuItems;
ListAdapter adapter;
private Fragment mFragment;
ListView lv;
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View v = inflater.inflate(R.id.listview); //<--- what do i inflate here?
lv = (ListView) v.findViewById(R.id.list);
if (!isNetworkAvailable()) {
AlertDialog.Builder builder = new AlertDialog.Builder(getActivity());
builder.setMessage("Internet Connection Required")
.setCancelable(false)
.setPositiveButton("Exit",
new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog,
int id) {
FileCache loader = new FileCache(null);
loader.clear();
getActivity().finish();
}
});
AlertDialog alert = builder.create();
alert.show();
} else {
new loadListView().execute();
}
return v;
}
private boolean isNetworkAvailable() {
ConnectivityManager connectivityManager = (ConnectivityManager) getActivity()
.getSystemService(Context.CONNECTIVITY_SERVICE);
NetworkInfo activeNetworkInfo = connectivityManager
.getActiveNetworkInfo();
return activeNetworkInfo != null;
}
public class loadListView extends AsyncTask<Integer, String, String> {
@Override
protected void onPreExecute() {
super.onPreExecute();
}
@Override
protected String doInBackground(Integer... args) {
// updating UI from Background Thread
menuItems = new ArrayList<HashMap<String, String>>();
XMLParser parser = new XMLParser();
String xml = parser.getXmlFromUrl(URL); // getting XML
Document doc = parser.getDomElement(xml); // getting DOM element
NodeList nl = doc.getElementsByTagName(KEY_SONG);
// looping through all item nodes <item>
for (int i = 0; i < nl.getLength(); i++) {
// creating new HashMap
HashMap<String, String> map = new HashMap<String, String>();
Element e = (Element) nl.item(i);
// adding each child node to HashMap key => value
map.put(KEY_ID, parser.getValue(e, KEY_ID));
map.put(KEY_TITLE, parser.getValue(e, KEY_TITLE));
map.put(KEY_CAT_ARTIST, parser.getValue(e, KEY_CAT_ARTIST));
map.put(KEY_DURATION, parser.getValue(e, KEY_DURATION));
map.put(KEY_THUMB_URL, parser.getValue(e, KEY_THUMB_URL));
map.put(KEY_BIG_URL, parser.getValue(e, KEY_BIG_URL));
map.put(KEY_CAT_URL, parser.getValue(e, KEY_CAT_URL));
map.put(KEY_DESC, parser.getValue(e, KEY_DESC));
// adding HashList to ArrayList
menuItems.add(map);
}
return null;
}
@Override
protected void onPostExecute(String args) {
if (getActivity() != null) {
adapter = new MainPageLazyAdapter(getActivity(), menuItems);
lv = (ListView)getActivity().findViewById(R.id.list);
//setListAdapter(adapter);
lv.setAdapter(adapter);
}
}
}
@Override
public void onTabSelected(Tab tab, FragmentTransaction ft) {
mFragment = new FreeFragment();
ft.add(android.R.id.content, mFragment);
ft.attach(mFragment);
}
@Override
public void onTabUnselected(Tab tab, FragmentTransaction ft) {
ft.remove(mFragment);
}
@Override
public void onTabReselected(Tab tab, FragmentTransaction ft) {
}
}
ListView .xml
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:ads="http://schemas.android.com/apk/lib/com.google.ads"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent">
<com.google.ads.AdView android:id="@+id/adView"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_centerHorizontal="true"
ads:adUnitId="mycode"
ads:adSize="BANNER"
ads:loadAdOnCreate="true"
/>
<ListView
xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/list"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:layout_below="@+id/adView"
android:cacheColorHint="#00000000" >
</ListView>
</RelativeLayout>
最佳答案
当然 ListView 是空的。
这个:
@Override
protected void onPostExecute(String args) {
if (getActivity() != null) {
adapter = new MainPageLazyAdapter(getActivity(), menuItems);
lv.setAdapter(adapter);
lv = (ListView)getActivity().findViewById(R.id.list);
}
}
需要这样:
@Override
protected void onPostExecute(String args) {
if (getActivity() != null) {
adapter = new MainPageLazyAdapter(getActivity(), menuItems);
lv = (ListView)getActivity().findViewById(R.id.list);
lv.setAdapter(adapter);
}
}
在初始化 ListView 之前，您不能在 ListView 上设置适配器。
更重要的是，您做错了:您使用的是 SherlockListFragment，它本身扩展了 ListFragment，您可以认为它类似于 >ListActivity - 它只是为您设置listview 提供了一些便利。您只需在 postExecute 中调用 setListAdapter。您不需要自己扩充任何 ListView ；这就是 ListFragment 的全部要点。
编辑:
因为，正如您所指出的，您希望在 Fragment 中拥有的不仅仅是一个 ListView，所以不要使用 SherlockListFragment。相反，扩展一个普通的旧 fragment 。然后在 onCreateView 内部，执行此操作:
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View v = inflater.inflate(R.layout.listview);
lv = v.findViewById(R.id.list);
return v;
}
现在您有对该 ListView 的引用作为字段。现在，在您的 onPostExecute 中，您可以执行 lv.setAdapter(adapter);
关于使用 XML 的 Android fragment ListView ，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/13262537/