问题描述
我有两个片段在我tabhost(viewpager)和i解析JSON和我可以显示jsons在列表视图项目的每个片段,不同的仅仅是JSON的,现在我写setMenuVisibility方法现在,我可以当我want.for例如,如果我这就去第二个片段,第二类的AsyncTask乳宁加载的AsyncTask类,但是当我回到第一个活动(meybe又来了第二个片段)我有nullpoinexception。这是我的code,如果有人知道的解决方案,请帮助我
谢谢
这是我的Mainactivity.java类code
i have two fragment in my tabhost(viewpager)and i parsed json and i can show jsons's items in listview each fragment,the different is only json's url.first time both Asynctask class run same time but now i wrote setMenuVisibility method and now i can to load Asynctask class when i want.for example if i 'll go second fragment, second Asynctask class runing,but when i go back first activity (meybe again go second fragment) i have nullpoinexception. this is a my code if anyone knows solution please help methanksthis is a my Mainactivity.java class code
public class MainActivity extends FragmentActivity implements
TabHost.OnTabChangeListener, ViewPager.OnPageChangeListener {
private TabHost mTabHost;
private ViewPager mViewPager;
private HashMap<String, TabInfo> mapTabInfo = new HashMap<String, MainActivity.TabInfo>();
private PagerAdapter mPagerAdapter;
private HorizontalScrollView horizontalScrollView;
private ImageButton menubutton;
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
requestWindowFeature(Window.FEATURE_NO_TITLE);
setContentView(R.layout.activity_main);
menubutton = (ImageButton) findViewById(R.id.menubutton);
menubutton.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View arg0) {
Toast.makeText(getApplicationContext(), "Helo",
Toast.LENGTH_SHORT).show();
}
});
this.initialiseTabHost(savedInstanceState);
if (savedInstanceState != null) {
mTabHost.setCurrentTabByTag(savedInstanceState.getString("tab"));
}
this.intialiseViewPager();
}
protected void onSaveInstanceState(Bundle outState) {
outState.putString("tab", mTabHost.getCurrentTabTag());
super.onSaveInstanceState(outState);
}
private void intialiseViewPager() {
List<Fragment> fragments = new Vector<Fragment>();
fragments.add(Fragment.instantiate(this, Pirveli.class.getName()));
fragments.add(Fragment.instantiate(this, Meore.class.getName()));
this.mPagerAdapter = new PagerAdapter(
super.getSupportFragmentManager(), fragments);
//
this.mViewPager = (ViewPager) super.findViewById(R.id.viewpager);
this.horizontalScrollView = (HorizontalScrollView) super
.findViewById(R.id.horizontalScrollView);
this.mViewPager.setAdapter(this.mPagerAdapter);
this.mViewPager.setOnPageChangeListener(this);
}
public void centerTabItem(int position) {
mTabHost.setCurrentTab(position);
final TabWidget tabWidget = mTabHost.getTabWidget();
final int screenWidth = getWindowManager().getDefaultDisplay()
.getWidth();
final int leftX = tabWidget.getChildAt(position).getLeft();
int newX = 0;
newX = leftX + (tabWidget.getChildAt(position).getWidth() / 2)
- (screenWidth / 2);
if (newX < 0) {
newX = 0;
}
horizontalScrollView.scrollTo(newX, 0);
}
private void initialiseTabHost(Bundle args) {
mTabHost = (TabHost) findViewById(android.R.id.tabhost);
mTabHost.setup();
TabInfo tabInfo = null;
MainActivity.AddTab(
this,
this.mTabHost,
this.mTabHost.newTabSpec("All Channels").setIndicator(
"All Channels"), (tabInfo = new TabInfo("All Channels",
Pirveli.class, args)));
this.mapTabInfo.put(tabInfo.tag, tabInfo);
MainActivity.AddTab(
this,
this.mTabHost,
this.mTabHost.newTabSpec("Commersant").setIndicator(
"Commersant"), (tabInfo = new TabInfo("Commersant",
Meore.class, args)));
mTabHost.setOnTabChangedListener(this);
}
private static void AddTab(MainActivity activity, TabHost tabHost,
TabHost.TabSpec tabSpec, TabInfo tabInfo) {
tabSpec.setContent(activity.new TabFactory(activity));
tabHost.addTab(tabSpec);
}
public void onTabChanged(String tag) {
int pos = this.mTabHost.getCurrentTab();
this.mViewPager.setCurrentItem(pos);
}
@Override
public void onPageScrolled(int position, float positionOffset,
int positionOffsetPixels) {
}
@Override
public void onPageSelected(int position) {
centerTabItem(position);
}
@Override
public void onPageScrollStateChanged(int state) {
}
private class TabInfo {
private String tag;
private Class<?> clss;
private Bundle args;
private Fragment fragment;
TabInfo(String tag, Class<?> clazz, Bundle args) {
this.tag = tag;
this.clss = clazz;
this.args = args;
}
}
class TabFactory implements TabContentFactory {
private final Context mContext;
public TabFactory(Context context) {
mContext = context;
}
public View createTabContent(String tag) {
View v = new View(mContext);
v.setMinimumWidth(0);
v.setMinimumHeight(0);
return v;
}
}
}
这是我的第一个片段code
this is a my first fragment code
public class Pirveli extends Fragment {
private String URL = "***********************";
public static String KEY_title = "title";
public static String KEY_description = "description";
public static String KEY_image = "image";
public static String KEY_journal = "journal";
public static String KEY_JournalID = "JournalID";
public static String KEY_pubDate = "pubDate";
public static String KEY_statID = "statID";
public JSONArray jsonarray;
public ListView list;
public JSONParser jsonparser;
static DealBoxAdapter adapter;
ProgressDialog pDialog, pDialog1;
ArrayList<HashMap<String, String>> itemList = new ArrayList<HashMap<String, String>>();
private int screenSize;
private LoadDataAllChanelsToServer loader;
public static String dateTime;
public TextView journal, tittle, description, smalllink, DateTime,
smallstatID;
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.send_items, container, false);
list = (ListView) rootView.findViewById(R.id.pirvelilistview);
// pd = new TransparentProgressDialog(getActivity(), R.drawable.loader);
screenSize = getResources().getConfiguration().screenLayout
& Configuration.SCREENLAYOUT_SIZE_MASK;
loader = new LoadDataAllChanelsToServer();
loader.execute();
return rootView;
}
private class LoadDataAllChanelsToServer extends
AsyncTask<String, Integer, String> {
@Override
protected void onPreExecute() {
pDialog = new ProgressDialog(getActivity());
pDialog.setMessage("Authenticating user...");
pDialog.show();
// pd.show();
}
@Override
protected String doInBackground(String... urls) {
jsonparser = new JSONParser();
JSONObject jsonobject = jsonparser.getJSONfromURL(URL);
try {
jsonarray = jsonobject.getJSONArray("data");
for (int i = 0; i < jsonarray.length(); i++) {
jsonobject = jsonarray.getJSONObject(i);
HashMap<String, String> map = new HashMap<String, String>();
map.put("journal", jsonobject.getString(KEY_journal));
map.put("image", jsonobject.getString(KEY_image));
map.put("title", jsonobject.getString(KEY_title));
map.put("description",
jsonobject.getString(KEY_description));
map.put("JournalID", jsonobject.getString(KEY_JournalID));
map.put("pubDate", jsonobject.getString(KEY_pubDate));
map.put("statID", jsonobject.getString(KEY_statID));
itemList.add(map);
dateTime = itemList.get(itemList.size() - 1).get(
KEY_pubDate);
}
} catch (JSONException e) {
Log.e("Error", e.getMessage());
e.printStackTrace();
}
return itemList.toString();
}
@Override
protected void onPostExecute(String result) {
try {
if (pDialog != null) {
pDialog.dismiss();
}
} catch (Exception e) {
}
try {
adapter = new DealBoxAdapter(getActivity(), itemList,
screenSize);
adapter.notifyDataSetChanged();
list.setAdapter(adapter);
} catch (NullPointerException e) {
e.printStackTrace();
}
}
}
@Override
public void onDestroy() {
super.onDestroy();
try {
if (loader != null) {
loader.cancel(true);
loader = null;
}
} catch (Exception e) {
}
}
}
和第二个片段的code
}and second fragment's code
public class Meore extends Fragment {
private String URL = "*************************";
public static String KEY_title = "title";
public static String KEY_description = "description";
public static String KEY_image = "image";
public static String KEY_journal = "journal";
public static String KEY_JournalID = "JournalID";
public static String KEY_pubDate = "pubDate";
public static String KEY_statID = "statID";
public JSONArray jsonarray;
public ListView list;
public TransparentProgressDialog pd;
public JSONParser jsonparser;
static DealBoxAdapter adapter;
ProgressDialog pDialog, pDialog1;
ArrayList<HashMap<String, String>> itemList = new ArrayList<HashMap<String, String>>();
private int screenSize;
LoadDataAllChanelsToServer1 load;
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.recived_items, container,
false);
list = (ListView) rootView.findViewById(R.id.listView2);
pd = new TransparentProgressDialog(getActivity(), R.drawable.loader);
screenSize = getResources().getConfiguration().screenLayout
& Configuration.SCREENLAYOUT_SIZE_MASK;
load = new LoadDataAllChanelsToServer1();
return rootView;
}
private class LoadDataAllChanelsToServer1 extends
AsyncTask<String, Integer, String> {
@Override
protected void onPreExecute() {
pd.show();
}
@Override
protected String doInBackground(String... urls) {
jsonparser = new JSONParser();
JSONObject jsonobject = jsonparser.getJSONfromURL(URL);
try {
jsonarray = jsonobject.getJSONArray("data");
for (int i = 0; i < jsonarray.length(); i++) {
jsonobject = jsonarray.getJSONObject(i);
HashMap<String, String> map = new HashMap<String, String>();
map.put("journal", jsonobject.getString(KEY_journal));
map.put("image", jsonobject.getString(KEY_image));
map.put("title", jsonobject.getString(KEY_title));
map.put("description",
jsonobject.getString(KEY_description));
map.put("JournalID", jsonobject.getString(KEY_JournalID));
map.put("pubDate", jsonobject.getString(KEY_pubDate));
map.put("statID", jsonobject.getString(KEY_statID));
itemList.add(map);
}
} catch (JSONException e) {
Log.e("Error", e.getMessage());
e.printStackTrace();
}
return itemList.toString();
}
@Override
protected void onPostExecute(String result) {
try {
if (pd != null) {
pd.dismiss();
}
} catch (Exception e) {
}
try {
adapter = new DealBoxAdapter(getActivity(), itemList,
screenSize);
list.setAdapter(adapter);
} catch (NullPointerException e) {
e.printStackTrace();
}
}
}
@Override
public void setMenuVisibility(final boolean visible) {
super.setMenuVisibility(visible);
if (visible) {
load.execute();
}
}
@Override
public void onDestroy() {
super.onDestroy();
try {
if (load != null) {
load.cancel(true);
load = null;
}
} catch (Exception e) {
}
}
}
我logcat的错误是:java.lang.illegalStateException:无法执行任务:任务已经执行(在第二片段的setMenuVisibility法)
}my logcat error is : java.lang.illegalStateException: Cannot execute task:the task has already been executed (in second fragments's setMenuVisibility method)
推荐答案
试试这个code:
if (visible) {
new LoadDataAllChanelsToServer1().execute();
//load.execute();
}
而不是:
if (visible) {
load.execute();
}
这篇关于Android的两个片段的AsyncTask类nullpointexception的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持!