我正在尝试将我的代码转换为使用片段。我对 Android 还是很陌生，我最初是通过制作很多类开始的，只是使用意图从一个 Activity 更改为另一个 Activity。我正在学习我的一个类，该类从服务器读取 JSON 数组并将表显示为列表并尝试将其转换为片段。为此，我遵循了此处提供的教程：
https://www.youtube.com/watch?v=TGXenxtDEGQ
它说我应该将我的 onCreate 更改为 onStart 并包含我已经完成的 onCreateView。我还将“ClassName.this”更改为它出现的“getActivity()”。该代码在尝试将其转换为片段之前运行良好，但现在我正在尝试使用片段时遇到问题。我认为这与 AsyncTask 有关。
在下面的代码块中，jParser 是我创建的 JSONParser 类的一个实例，它处理解析 JSON 数据。我还检查以确保我传递给该方法的 URL 返回有效的 JSON 以进行解析。这个类和我上面调用的方法作为一项活动工作得很好；当我在片段中操作时，我不能简单地做同样的事情吗？
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// TODO Auto-generated method stub
View view = inflater.inflate(R.layout.read_options, container, false);
return view;
}
@Override
public void onStart() {
super.onStart();
// TODO Auto-generated method stub
optionsList = new ArrayList<HashMap<String, String>>();
new LoadOptions().execute();
ListView lv = getListView();
...
(Code to launch new activity when an item in list is pressed)
...
}
class LoadOptions extends AsyncTask<String, String, String>{
@Override
protected void onPreExecute() {
super.onPreExecute();
pDialog = new ProgressDialog(getActivity());
pDialog.setMessage("Loading options. Please wait...");
pDialog.setIndeterminate(false);
pDialog.setCancelable(false);
pDialog.show();
}
protected String doInBackground(String... args){
List<NameValuePair> params = new ArrayList<NameValuePair>();
JSONObject json = jParser.makeHttpRequest(url_options, "GET", params);
Log.d("All Options: ", json.toString());
try{
int success = json.getInt(TAG_SUCCESS);
if (success == 1){
// Options Found, Iterate Through
options = json.getJSONArray(TAG_OPTIONS);
for(int i = 0; i < options.length(); i++){
JSONObject c = options.getJSONObject(i);
String id = c.getString(TAG_OPTIONID);
String duration = c.getString(TAG_DURATION);
String reward = c.getString(TAG_REWARD);
HashMap<String, String> map = new HashMap<String, String>();
map.put(TAG_OPTIONID, id);
map.put(TAG_DURATION, duration);
map.put(TAG_REWARD, reward);
optionsList.add(map);
}
} else {
// Options are not available or server is down.
// Dismiss the loading dialog and display an alert onPostExecute
pDialog.dismiss();
}
} catch (JSONException e) {
e.printStackTrace();
}
return null;
}
protected void onPostExecute(String file_url){
pDialog.dismiss();
getActivity().runOnUiThread(new Runnable() {
public void run() {
ListAdapter adapter = new SimpleAdapter(
getActivity(), optionsList, R.layout.list_options, new String[]
{TAG_OPTIONID, TAG_DURATION, TAG_REWARD},
new int[] {R.id.tvOption, R.id.tvDuration, R.id.tvReward});
setListAdapter(adapter);
// Check for whether or not there are options available and display alert
List<NameValuePair> params = new ArrayList<NameValuePair>();
JSONObject json = jParser.makeHttpRequest(url_options, "GET", params);
int success = 0;
try {
success = json.getInt(TAG_SUCCESS);
} catch (JSONException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
if (success == 0){
AlertDialog.Builder alertDialog = new AlertDialog.Builder(getActivity());
alertDialog.setTitle("No Options Available!");
alertDialog.setMessage("No options currently available. You will receive a " +
"notification when there are options available. Click 'Okay' to return to main screen");
alertDialog.setCancelable(false);
alertDialog.setPositiveButton("Okay", new DialogInterface.OnClickListener(){
public void onClick(DialogInterface dialog, int id){
Intent i = new Intent(getActivity().getApplicationContext(), MainActivity.class);
i.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
startActivity(i);
}
});
alertDialog.show();
}
}
});
}
错误日志如下：
03-03 23:30:50.812: W/System.err(28019): java.net.SocketException: Permission denied
03-03 23:30:50.863: W/System.err(28019): at org.apache.harmony.luni.platform.OSNetworkSystem.socket(Native Method)
03-03 23:30:50.863: W/System.err(28019): at dalvik.system.BlockGuard$WrappedNetworkSystem.socket(BlockGuard.java:335)
03-03 23:30:50.863: W/System.err(28019): at org.apache.harmony.luni.net.PlainSocketImpl.create(PlainSocketImpl.java:216)
03-03 23:30:50.863: W/System.err(28019): at java.net.Socket.checkOpenAndCreate(Socket.java:821)
03-03 23:30:50.863: W/System.err(28019): at java.net.Socket.connect(Socket.java:967)
03-03 23:30:50.863: W/System.err(28019): at org.apache.http.conn.scheme.PlainSocketFactory.connectSocket(PlainSocketFactory.java:119)
03-03 23:30:50.863: W/System.err(28019): at org.apache.http.impl.conn.DefaultClientConnectionOperator.openConnection(DefaultClientConnectionOperator.java:156)
03-03 23:30:50.863: W/System.err(28019): at org.apache.http.impl.conn.AbstractPoolEntry.open(AbstractPoolEntry.java:164)
03-03 23:30:50.867: W/System.err(28019): at org.apache.http.impl.conn.AbstractPooledConnAdapter.open(AbstractPooledConnAdapter.java:119)
03-03 23:30:50.867: W/System.err(28019): at org.apache.http.impl.client.DefaultRequestDirector.execute(DefaultRequestDirector.java:359)
03-03 23:30:50.867: W/System.err(28019): at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:555)
03-03 23:30:50.867: W/System.err(28019): at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:487)
03-03 23:30:50.867: W/System.err(28019): at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:465)
03-03 23:30:50.867: W/System.err(28019): at com.example.abtest.JSONParser.makeHttpRequest(JSONParser.java:62)
03-03 23:30:50.867: W/System.err(28019): at com.example.abtest.ReadOptionsFragment$LoadOptions.doInBackground(ReadOptionsFragment.java:111)
03-03 23:30:50.867: W/System.err(28019): at com.example.abtest.ReadOptionsFragment$LoadOptions.doInBackground(ReadOptionsFragment.java:1)
03-03 23:30:50.867: W/System.err(28019): at android.os.AsyncTask$2.call(AsyncTask.java:185)
03-03 23:30:50.867: W/System.err(28019): at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:306)
03-03 23:30:50.867: W/System.err(28019): at java.util.concurrent.FutureTask.run(FutureTask.java:138)
03-03 23:30:50.871: W/System.err(28019): at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1088)
03-03 23:30:50.871: W/System.err(28019): at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:581)
03-03 23:30:50.871: W/System.err(28019): at java.lang.Thread.run(Thread.java:1019)
03-03 23:30:50.871: E/Buffer Error(28019): Error converting result java.lang.NullPointerException
03-03 23:30:50.871: E/JSON Parser(28019): Error parsing data org.json.JSONException: End of input at character 0 of
03-03 23:30:50.882: W/dalvikvm(28019): threadid=10: thread exiting with uncaught exception (group=0x4001e578)
03-03 23:30:50.882: E/AndroidRuntime(28019): FATAL EXCEPTION: AsyncTask #1
03-03 23:30:50.882: E/AndroidRuntime(28019): java.lang.RuntimeException: An error occured while executing doInBackground()
03-03 23:30:50.882: E/AndroidRuntime(28019): at android.os.AsyncTask$3.done(AsyncTask.java:200)
03-03 23:30:50.882: E/AndroidRuntime(28019): at java.util.concurrent.FutureTask$Sync.innerSetException(FutureTask.java:274)
03-03 23:30:50.882: E/AndroidRuntime(28019): at java.util.concurrent.FutureTask.setException(FutureTask.java:125)
03-03 23:30:50.882: E/AndroidRuntime(28019): at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:308)
03-03 23:30:50.882: E/AndroidRuntime(28019): at java.util.concurrent.FutureTask.run(FutureTask.java:138)
03-03 23:30:50.882: E/AndroidRuntime(28019): at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1088)
03-03 23:30:50.882: E/AndroidRuntime(28019): at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:581)
03-03 23:30:50.882: E/AndroidRuntime(28019): at java.lang.Thread.run(Thread.java:1019)
03-03 23:30:50.882: E/AndroidRuntime(28019): Caused by: java.lang.NullPointerException
03-03 23:30:50.882: E/AndroidRuntime(28019): at com.example.abtest.ReadOptionsFragment$LoadOptions.doInBackground(ReadOptionsFragment.java:112)
03-03 23:30:50.882: E/AndroidRuntime(28019): at com.example.abtest.ReadOptionsFragment$LoadOptions.doInBackground(ReadOptionsFragment.java:1)
03-03 23:30:50.882: E/AndroidRuntime(28019): at android.os.AsyncTask$2.call(AsyncTask.java:185)
03-03 23:30:50.882: E/AndroidRuntime(28019): at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:306)
03-03 23:30:50.882: E/AndroidRuntime(28019): ... 4 more
03-03 23:30:56.742: E/WindowManager(28019): Activity com.example.abtest.MainActivity has leaked window com.android.internal.policy.impl.PhoneWindow$DecorView@4055c690 that was originally added here
03-03 23:30:56.742: E/WindowManager(28019): android.view.WindowLeaked: Activity com.example.abtest.MainActivity has leaked window com.android.internal.policy.impl.PhoneWindow$DecorView@4055c690 that was originally added here
03-03 23:30:56.742: E/WindowManager(28019): at android.view.ViewRoot.<init>(ViewRoot.java:263)
03-03 23:30:56.742: E/WindowManager(28019): at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:171)
03-03 23:30:56.742: E/WindowManager(28019): at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:114)
03-03 23:30:56.742: E/WindowManager(28019): at android.view.Window$LocalWindowManager.addView(Window.java:424)
03-03 23:30:56.742: E/WindowManager(28019): at android.app.Dialog.show(Dialog.java:242)
03-03 23:30:56.742: E/WindowManager(28019): at com.example.abtest.ReadOptionsFragment$LoadOptions.onPreExecute(ReadOptionsFragment.java:104)
03-03 23:30:56.742: E/WindowManager(28019): at android.os.AsyncTask.execute(AsyncTask.java:391)
03-03 23:30:56.742: E/WindowManager(28019): at com.example.abtest.ReadOptionsFragment.onStart(ReadOptionsFragment.java:62)
03-03 23:30:56.742: E/WindowManager(28019): at android.support.v4.app.Fragment.performStart(Fragment.java:1332)
03-03 23:30:56.742: E/WindowManager(28019): at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:906)
03-03 23:30:56.742: E/WindowManager(28019): at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1080)
03-03 23:30:56.742: E/WindowManager(28019): at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:622)
03-03 23:30:56.742: E/WindowManager(28019): at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1416)
03-03 23:30:56.742: E/WindowManager(28019): at android.support.v4.app.FragmentManagerImpl$1.run(FragmentManager.java:420)
03-03 23:30:56.742: E/WindowManager(28019): at android.os.Handler.handleCallback(Handler.java:587)
03-03 23:30:56.742: E/WindowManager(28019): at android.os.Handler.dispatchMessage(Handler.java:92)
03-03 23:30:56.742: E/WindowManager(28019): at android.os.Looper.loop(Looper.java:130)
03-03 23:30:56.742: E/WindowManager(28019): at android.app.ActivityThread.main(ActivityThread.java:3687)
03-03 23:30:56.742: E/WindowManager(28019): at java.lang.reflect.Method.invokeNative(Native Method)
03-03 23:30:56.742: E/WindowManager(28019): at java.lang.reflect.Method.invoke(Method.java:507)
03-03 23:30:56.742: E/WindowManager(28019): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:842)
03-03 23:30:56.742: E/WindowManager(28019): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:600)
03-03 23:30:56.742: E/WindowManager(28019): at dalvik.system.NativeStart.main(Native Method)
谢谢 - 非常感谢任何朝着正确方向的帮助或轻推！