我使用AsyncTask完成了我的工作，但是当我在一个活动（tab.java）和Default标签视图（Feed.java）中有标签时出现了问题，即第一个标签显示为默认值。两个类文件都有自己的XML。
我正在使用Async task＆amp; amp;来自Server Response的（tab.java）列表。在（Tab.java）我需要调用另一个服务器响应以显示在该页面上。
每次我从（tab.java）serverUrl得到响应时，我的应用程序都会崩溃。
如何进行这种操作？
谢谢。
我的代码：
tab.java：
public class Login_Header extends TabActivity
{
Button Find;
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState)
{
//To show Custom Title as image
requestWindowFeature(Window.FEATURE_CUSTOM_TITLE);
//getWindow().requestFeature(Window.FEATURE_ACTION_BAR);
setContentView(R.layout.login_header_bar);
super.onCreate(savedInstanceState);
getWindow().setFeatureInt(Window.FEATURE_CUSTOM_TITLE, R.layout.custom_title_about_tab);
// Font size has been changed through Styles.xml for tab
TabHost tabHost = getTabHost();
Intent feeds = new Intent(this,Feeds.class);
tabHost.addTab(tabHost.newTabSpec("Tab1")
.setIndicator("Feeds")
.setContent(feeds));
Intent challenges = new Intent(this,Challenges.class);
tabHost.addTab(tabHost.newTabSpec("Tab2")
.setIndicator("Challenges")
.setContent(challenges));
Intent friends = new Intent(this,Friends.class);
tabHost.addTab(tabHost.newTabSpec("Tab3")
.setIndicator("Friends")
.setContent(friends));
Intent group = new Intent(this,Groups.class);
tabHost.addTab(tabHost.newTabSpec("Tab4")
.setIndicator("Groups")
.setContent(group));
Intent details = new Intent(this,Details.class);
tabHost.addTab(tabHost.newTabSpec("Tab5")
.setIndicator("Details")
.setContent(details));
tabHost.setCurrentTab(0);
Find.setOnClickListener(new OnClickListener()
{
@Override
public void onClick(View v)
{
// TODO Auto-generated method stub
Intent find = new Intent(Login_Header.this,Find.class);
startActivity(find);
}
});
//To call async task
callNotificationCount();
}
private void callNotificationCount()
{
new NotificationCount_Async().execute("");
}
private class NotificationCount_Async extends AsyncTask<String, Void, String>
{
@Override
protected String doInBackground(String... params)
{
try
{
URL url=new URL(getString(R.string.WebServiceURL)+"/notifications/notificationcount");
HttpPost httppost = new HttpPost(url.toString());
HttpResponse responsePOST = LoginPage.httpClient.execute(httppost);
HttpEntity resEntity = responsePOST.getEntity();
InputStream instream = resEntity.getContent();
String result = convertStreamToString(instream);
Log.i("User Feed",result);
return result;
}
catch(Exception ex)
{
Log.e("error", "error", ex);
return null;
}
}
@Override
protected void onPostExecute(String result)
{
try {
JSONObject json = new JSONObject(result);
//Below code is for user count
JSONObject userNotificationjson = json.getJSONObject("user_notification");
if(json.has("user_notification"))
{
String userCount = userNotificationjson.getString("count");
int Count = Integer.parseInt(userCount);
if(Count > 0)
{
LinearLayout llUserCount = (LinearLayout)findViewById(R.id.llUserCount);
TextView userCountTextView =(TextView)findViewById(R.id.txtUserCount);
llUserCount.setVisibility(View.VISIBLE);
userCountTextView.setText(userCount);
}
}
}
private String convertStreamToString(InputStream is)
{
//code
}
`
我的默认标签Feed活动。
public class Feeds extends Activity
{
SessionManager session;
String custom_phpsess_id,logged_in_id_User,returnString;
// Declare Variables
JSONObject jsonobject;
JSONArray jsonarray;
ListView listview;
ListViewAdapter adapter;
ProgressDialog mProgressDialog;
ArrayList<HashMap<String, String>> arraylist;
static String FIRST_NAME = "firstname";
static String LAST_NAME = "lastname";
static String ACTION = "action";
// static String ACTIVITY_NAME = "activity_name";
static String IMAGE_URL = "image";
static String USER_ID = "user_id";
static String ACTIVITY_NAME = "activityname";
String strUrl = =new URL(getString(R.string.WebServiceURL)+"/users/userfeeds";
ListView mListView;
String id_User;
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
// Get the view from feeds.xml
setContentView(R.layout.feeds);
session = new SessionManager(getApplicationContext());
//To get values from session
HashMap<String, String> User = session.getUserDetails();
logged_in_id_User = User.get(SessionManager.KEY_ID);
custom_phpsess_id = User.get(SessionManager.KEY_USE);
// Creating a new non-ui thread task to download json data
// Execute DownloadJSON AsyncTask
Log.i("On Create", "Main On Create");
new DownloadJSON().execute();
}
// DownloadJSON AsyncTask
private class DownloadJSON extends AsyncTask<Void, Void, Void>
{
@Override
protected void onPreExecute()
{
Log.i("On DownloadJSON", "onPreExecute");
super.onPreExecute();
// Create a progressdialog
mProgressDialog = new ProgressDialog(Feeds.this);
// Set progressdialog title
mProgressDialog.setTitle("");
// Set progressdialog message
mProgressDialog.setMessage("Loading...");
mProgressDialog.setIndeterminate(false);
// Show progressdialog
mProgressDialog.show();
}
@Override
protected Void doInBackground(Void... params)
{
Log.i("On doInBackground", "doInBackground");
// Create the array
arraylist = new ArrayList<HashMap<String, String>>();
// Retrive JSON Objects from the given website URL in JSONfunctions.class
jsonobject = JSONfunctions
.getJSONfromURL(strUrl);
Log.i("On doInBackground-jsonObject", jsonobject.toString());
try
{
// Locate the array name
jsonarray = jsonobject.getJSONArray("userdata");
Log.i("On doInBackground-jsonarray", jsonarray.toString());
for (int i = 0; i < jsonarray.length(); i++)
{
HashMap<String, String> map = new HashMap<String, String>();
jsonobject = jsonarray.getJSONObject(i);
// Retrive JSON Objects
if(jsonobject.getString("actions").equals("Completed"))
{
map.put("firstname", jsonobject.getString("first_name"));
map.put("lastname", jsonobject.getString("last_name"));
map.put("action", jsonobject.getString("actions"));
map.put("image", jsonobject.getString("file_name"));
map.put("user_id", jsonobject.getString("id_user"));
map.put("activityname", jsonobject.getString("activity_name"));
Log.i("On doInBackground-Map", map.toString());
// Set the JSON Objects into the array
arraylist.add(map);
}
}
}
catch (JSONException e)
{
Log.i("On doInBackground-JSONException", e.toString());
Log.e("Error", e.getMessage());
e.printStackTrace();
}
return null;
}
@Override
protected void onPostExecute(Void args)
{
Log.i("On onPostExecute", "ON post exe");
// Locate the listview in listview_main.xml
listview = (ListView)findViewById(R.id.listview);
Log.i("On onPostExecute-onPostExecute-arraylist", arraylist.toString());
// Pass the results into ListViewAdapter.java
adapter = new ListViewAdapter(Feeds.this, arraylist);
Log.i("On onPostExecute-onPostExecute-Adapter", adapter.toString());
// Binds the Adapter to the ListView
listview.setAdapter(adapter);
// Close the progressdialog
mProgressDialog.dismiss();
}
}
}
Logcat：
06-24 11:44:11.412: W/SingleClientConnManager(422): Invalid use of SingleClientConnManager: connection still allocated.
06-24 11:44:11.412: W/SingleClientConnManager(422): Make sure to release the connection before allocating another one.
06-24 11:44:11.531: E/log_tag(422): Error in http connection java.net.SocketException: Socket closed
06-24 11:44:11.551: E/log_tag(422): Error converting result java.lang.NullPointerException
06-24 11:44:11.571: E/log_tag(422): Error parsing data org.json.JSONException: End of input at character 0 of
06-24 11:44:11.911: W/dalvikvm(422): threadid=10: thread exiting with uncaught exception (group=0x40014760)
06-24 11:44:12.701: E/AndroidRuntime(422): FATAL EXCEPTION: AsyncTask #2
06-24 11:44:12.701: E/AndroidRuntime(422): java.lang.RuntimeException: An error occured while executing doInBackground()
06-24 11:44:12.701: E/AndroidRuntime(422): at android.os.AsyncTask$3.done(AsyncTask.java:266)
06-24 11:44:12.701: E/AndroidRuntime(422): at java.util.concurrent.FutureTask$Sync.innerSetException(FutureTask.java:273)
06-24 11:44:12.701: E/AndroidRuntime(422): at java.util.concurrent.FutureTask.setException(FutureTask.java:124)
06-24 11:44:12.701: E/AndroidRuntime(422): at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:307)
06-24 11:44:12.701: E/AndroidRuntime(422): at java.util.concurrent.FutureTask.run(FutureTask.java:137)
06-24 11:44:12.701: E/AndroidRuntime(422): at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1081)
06-24 11:44:12.701: E/AndroidRuntime(422): at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:574)
06-24 11:44:12.701: E/AndroidRuntime(422): at java.lang.Thread.run(Thread.java:1020)
06-24 11:44:12.701: E/AndroidRuntime(422): Caused by: java.lang.NullPointerException
06-24 11:44:12.701: E/AndroidRuntime(422): at com.si.gtc.Feeds$DownloadJSON.doInBackground(Feeds.java:97)
06-24 11:44:12.701: E/AndroidRuntime(422): at com.si.gtc.Feeds$DownloadJSON.doInBackground(Feeds.java:1)
06-24 11:44:12.701: E/AndroidRuntime(422): at android.os.AsyncTask$2.call(AsyncTask.java:252)
06-24 11:44:12.701: E/AndroidRuntime(422): at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:305)
06-24 11:44:12.701: E/AndroidRuntime(422): ... 4 more
06-24 11:44:13.661: E/WindowManager(422): Activity com.si.gtc.Login_Header has leaked window com.android.internal.policy.impl.PhoneWindow$DecorView@40feb498 that was originally added here
06-24 11:44:13.661: E/WindowManager(422): android.view.WindowLeaked: Activity com.si.gtc.Login_Header has leaked window com.android.internal.policy.impl.PhoneWindow$DecorView@40feb498 that was originally added here
06-24 11:44:13.661: E/WindowManager(422): at android.view.ViewRoot.<init>(ViewRoot.java:285)
06-24 11:44:13.661: E/WindowManager(422): at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:152)
06-24 11:44:13.661: E/WindowManager(422): at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:95)
06-24 11:44:13.661: E/WindowManager(422): at android.view.Window$LocalWindowManager.addView(Window.java:526)
06-24 11:44:13.661: E/WindowManager(422): at android.app.Dialog.show(Dialog.java:269)
06-24 11:44:13.661: E/WindowManager(422): at com.si.gtc.Feeds$DownloadJSON.onPreExecute(Feeds.java:85)
06-24 11:44:13.661: E/WindowManager(422): at android.os.AsyncTask.executeOnExecutor(AsyncTask.java:549)
06-24 11:44:13.661: E/WindowManager(422): at android.os.AsyncTask.execute(AsyncTask.java:499)
06-24 11:44:13.661: E/WindowManager(422): at com.si.gtc.Feeds.onCreate(Feeds.java:66)
06-24 11:44:13.661: E/WindowManager(422): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1048)
06-24 11:44:13.661: E/WindowManager(422): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1712)
06-24 11:44:13.661: E/WindowManager(422): at android.app.ActivityThread.startActivityNow(ActivityThread.java:1589)
06-24 11:44:13.661: E/WindowManager(422): at android.app.LocalActivityManager.moveToState(LocalActivityManager.java:130)
06-24 11:44:13.661: E/WindowManager(422): at android.app.LocalActivityManager.startActivity(LocalActivityManager.java:342)
06-24 11:44:13.661: E/WindowManager(422): at android.widget.TabHost$IntentContentStrategy.getContentView(TabHost.java:676)
06-24 11:44:13.661: E/WindowManager(422): at android.widget.TabHost.setCurrentTab(TabHost.java:345)
06-24 11:44:13.661: E/WindowManager(422): at android.widget.TabHost.addTab(TabHost.java:235)
06-24 11:44:13.661: E/WindowManager(422): at com.si.gtc.Login_Header.onCreate(Login_Header.java:104)
06-24 11:44:13.661: E/WindowManager(422): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1048)
06-24 11:44:13.661: E/WindowManager(422): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1712)
06-24 11:44:13.661: E/WindowManager(422): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1764)
06-24 11:44:13.661: E/WindowManager(422): at android.app.ActivityThread.access$1500(ActivityThread.java:122)
06-24 11:44:13.661: E/WindowManager(422): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1002)
06-24 11:44:13.661: E/WindowManager(422): at android.os.Handler.dispatchMessage(Handler.java:99)
06-24 11:44:13.661: E/WindowManager(422): at android.os.Looper.loop(Looper.java:132)
06-24 11:44:13.661: E/WindowManager(422): at android.app.ActivityThread.main(ActivityThread.java:4025)
06-24 11:44:13.661: E/WindowManager(422): at java.lang.reflect.Method.invokeNative(Native Method)
06-24 11:44:13.661: E/WindowManager(422): at java.lang.reflect.Method.invoke(Method.java:491)
06-24 11:44:13.661: E/WindowManager(422): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:841)
06-24 11:44:13.661: E/WindowManager(422): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:599)
06-24 11:44:13.661: E/WindowManager(422): at dalvik.system.NativeStart.main(Native Method)
答案 0 :(得分：0)
在AsyncTask的doInBackground方法中，记得关闭InputStream，如下所示：
try
{
URL url=new URL(getString(R.string.WebServiceURL)+"/notifications/notificationcount");
HttpPost httppost = new HttpPost(url.toString());
HttpResponse responsePOST = LoginPage.httpClient.execute(httppost);
HttpEntity resEntity = responsePOST.getEntity();
InputStream instream = resEntity.getContent();
String result = convertStreamToString(instream);
Log.i("User Feed",result);
return result;
}
catch(Exception ex)
{
Log.e("error", "error", ex);
return null;
}
finally{
instream.close();
}
您还可以查看this问题和相关答案，也许它可以帮助您。