我正在尝试将json数据加载到我的Android设备中，但是有一个条件。
1.）如果有互联网，则通过特定网址从互联网下载数据。
2.）如果没有互联网，则使用名称为tch.txt的资产文件夹中的本地数据。
我这是检查互联网并执行所需的课程。
我的代码在有互联网的情况下可以正常获取数据，但它会让我出现以下错误
M <- cbind(c(t(A)), c(t(B)))
fnc <- function(){
n <- nrow(A)
ind <- sample(n) + (1:n-1)*n
M[ind, ]
}
set.seed(0)
do.call(cbind, lapply(1:5, function(i)fnc()))
# [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10]
# [1,] 1 4 9 1 1 4 9 1 4 2
# [2,] 7 4 3 3 4 5 7 4 4 5
# [3,] 2 7 1 3 1 3 9 2 9 2
我在想我的listviewadapter类也存在一些问题，但无法弄明白。我附加了我的JsonLoader类和ListviewAdapterClass。
JsonLoadSubFirstFirst.java
07-13 16:24:03.800 14691-14691/scientist.jobless.foodmana I/dalvikvm-heap﹕ Grow heap (frag case) to 11.560MB for 692236-byte allocation
07-13 16:24:03.828 14691-14691/scientist.jobless.foodmana I/dalvikvm-heap﹕ Grow heap (frag case) to 12.259MB for 692236-byte allocation
07-13 16:24:03.904 14691-14691/scientist.jobless.foodmana W/EGL_genymotion﹕ eglSurfaceAttrib not implemented
07-13 16:24:03.988 14691-14697/scientist.jobless.foodmana I/jdwp﹕ Ignoring second debugger -- accepting and dropping
07-13 16:24:06.792 14691-14691/scientist.jobless.foodmana W/EGL_genymotion﹕ eglSurfaceAttrib not implemented
07-13 16:24:06.840 14691-14691/scientist.jobless.foodmana W/EGL_genymotion﹕ eglSurfaceAttrib not implemented
07-13 16:24:07.764 14691-14691/scientist.jobless.foodmana I/dalvikvm﹕ Could not find method android.content.res.TypedArray.getChangingConfigurations, referenced from method android.support.v7.internal.widget.TintTypedArray.getChangingConfigurations
07-13 16:24:07.764 14691-14691/scientist.jobless.foodmana W/dalvikvm﹕ VFY: unable to resolve virtual method 491: Landroid/content/res/TypedArray;.getChangingConfigurations ()I
07-13 16:24:07.764 14691-14691/scientist.jobless.foodmana I/dalvikvm﹕ Could not find method android.content.res.TypedArray.getType, referenced from method android.support.v7.internal.widget.TintTypedArray.getType
07-13 16:24:07.764 14691-14691/scientist.jobless.foodmana W/dalvikvm﹕ VFY: unable to resolve virtual method 513: Landroid/content/res/TypedArray;.getType (I)I
07-13 16:24:07.780 14691-14742/scientist.jobless.foodmana W/System.err﹕ org.json.JSONException: No value for Name
07-13 16:24:07.780 14691-14742/scientist.jobless.foodmana W/System.err﹕ at org.json.JSONObject.get(JSONObject.java:354)
07-13 16:24:07.780 14691-14742/scientist.jobless.foodmana W/System.err﹕ at org.json.JSONObject.getString(JSONObject.java:510)
07-13 16:24:07.780 14691-14742/scientist.jobless.foodmana W/System.err﹕ at scientist.jobless.foodmana.JsonLoadSubFirstFirst$LocalDownloadJSON.doInBackground(JsonLoadSubFirstFirst.java:141)
07-13 16:24:07.780 14691-14742/scientist.jobless.foodmana W/System.err﹕ at scientist.jobless.foodmana.JsonLoadSubFirstFirst$LocalDownloadJSON.doInBackground(JsonLoadSubFirstFirst.java:80)
07-13 16:24:07.780 14691-14742/scientist.jobless.foodmana W/System.err﹕ at android.os.AsyncTask$2.call(AsyncTask.java:287)
07-13 16:24:07.780 14691-14742/scientist.jobless.foodmana W/System.err﹕ at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:305)
07-13 16:24:07.780 14691-14742/scientist.jobless.foodmana W/System.err﹕ at java.util.concurrent.FutureTask.run(FutureTask.java:137)
07-13 16:24:07.780 14691-14742/scientist.jobless.foodmana W/System.err﹕ at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:230)
07-13 16:24:07.780 14691-14742/scientist.jobless.foodmana W/System.err﹕ at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1076)
07-13 16:24:07.780 14691-14742/scientist.jobless.foodmana W/System.err﹕ at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:569)
07-13 16:24:07.780 14691-14742/scientist.jobless.foodmana W/System.err﹕ at java.lang.Thread.run(Thread.java:856)
07-13 16:24:07.804 14691-14691/scientist.jobless.foodmana W/EGL_genymotion﹕ eglSurfaceAttrib not implemented
07-13 16:24:07.812 14691-14691/scientist.jobless.foodmana W/EGL_genymotion﹕ eglSurfaceAttrib not implemented
07-13 16:24:07.816 14691-14691/scientist.jobless.foodmana I/MemoryCache﹕ MemoryCache will use up to 16.0MB
07-13 16:24:07.816 14691-14691/scientist.jobless.foodmana W/dalvikvm﹕ threadid=1: thread exiting with uncaught exception (group=0xa6266288)
07-13 16:24:07.816 14691-14691/scientist.jobless.foodmana E/AndroidRuntime﹕ FATAL EXCEPTION: main
java.lang.NullPointerException
at scientist.jobless.foodmana.ListViewAdapter.getCount(ListViewAdapter.java:39)
at android.widget.ListView.setAdapter(ListView.java:460)
at scientist.jobless.foodmana.JsonLoadSubFirstFirst$LocalDownloadJSON.onPostExecute(JsonLoadSubFirstFirst.java:176)
at scientist.jobless.foodmana.JsonLoadSubFirstFirst$LocalDownloadJSON.onPostExecute(JsonLoadSubFirstFirst.java:80)
at android.os.AsyncTask.finish(AsyncTask.java:631)
at android.os.AsyncTask.access$600(AsyncTask.java:177)
at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:644)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:137)
at android.app.ActivityThread.main(ActivityThread.java:4745)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:511)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
at dalvik.system.NativeStart.main(Native Method)
ListViewAdapter.java
public class JsonLoadSubFirstFirst extends ActionBarActivity {
// Declare Variables
//firstactivity seems like to be main, lets see
ProgressDialog pd;
JSONObject jsonobject;
JSONObject jsonobject2;
String myjsonstring;
JSONArray jsonarray;
ListView listview;
ListViewAdapter adapter;
ProgressDialog mProgressDialog;
ArrayList<HashMap<String, String>> arraylist;
ArrayList<HashMap<String, String>> localarraylist;
static String RANK = "rank";
static String COUNTRY = "country";
static String POPULATION = "population";
static String FLAG = "flag";
static final String NAME = "Name";
static final String TIME = "Time";
static final String VENUE = "Serves";
static final String ingredients = "ingredients";
static final String PRIZE_MONEY2 = "prize2";
static final String REGISTRATION_FEE = "date";
static final String DESCRIPTION = "Description";
private boolean isNetworkAvailable() {
ConnectivityManager connectivityManager
= (ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE);
NetworkInfo activeNetworkInfo = connectivityManager.getActiveNetworkInfo();
return activeNetworkInfo != null && activeNetworkInfo.isConnected();
}
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
// Get the view from listview_main.xml
setContentView(R.layout.listview_main);
// Execute DownloadJSON AsyncTask
if(isNetworkAvailable())
new DownloadJSON(this).execute();
else
//setContentView(R.layout.nonet);
new LocalDownloadJSON().execute();
}
private class LocalDownloadJSON extends AsyncTask<Void, Void, Void> {
@Override
protected void onPreExecute() {
super.onPreExecute();
pd = new ProgressDialog(JsonLoadSubFirstFirst.this);
pd.setMessage("Loading...");
pd.setProgressStyle(ProgressDialog.STYLE_SPINNER);
pd.setIndeterminate(true);
pd.setCancelable(false);
pd.show();
}
@Override
protected Void doInBackground(Void... params) {
// Create an array
localarraylist = new ArrayList<HashMap<String, String>>();
// Retrieve JSON Objects from the given URL address
StringBuffer sb = new StringBuffer();
BufferedReader br = null;
try {
br = new BufferedReader(new InputStreamReader(getAssets().open("tch.txt")));
String temp;
while ((temp = br.readLine()) != null)
sb.append(temp);
}
catch (IOException e)
{
e.printStackTrace();
}
finally
{
try
{
br.close();
}
catch (IOException e)
{
e.printStackTrace();
}
}
myjsonstring = sb.toString();
try{
JSONObject jsonObj = new JSONObject(myjsonstring);
JSONArray Attendance = jsonObj.getJSONArray("events");
for (int i = 0; i < Attendance.length(); i++)
{
JSONObject a = Attendance.getJSONObject(i);
String Name = a.getString("Name");
String time = a.getString("time");
String ingredients = a.getString("ingredients");
String Serves = a.getString("Serves");
String descr = a.getString("descr");
HashMap<String, String> contact = new HashMap<String, String>();
// adding each child node to HashMap key => value
contact.put("event", Name);
contact.put("fee", time);
contact.put("prize1", ingredients);
contact.put("prize2", Serves);
contact.put("descr", descr);
// adding contact to contact list
localarraylist.add(contact);
}
} catch (JSONException e) {
e.printStackTrace();
}
return null;
}
@Override
protected void onPostExecute(Void args) {
// Locate the listview in listview_main.xml
//setContentView(R.layout.listview_main);
listview = (ListView) findViewById(R.id.listview);
// Pass the results into ListViewAdapter.java
adapter = new ListViewAdapter(JsonLoadSubFirstFirst.this, arraylist);
// Set the adapter to the ListView
listview.setAdapter(adapter);
// Close the progressdialog
// mProgressDialog.dismiss();
// textView.setVisibility(View.VISIBLE);
pd.dismiss();
super.onPostExecute(args);
}
}
private class DownloadJSON extends AsyncTask<Void, Void, Void> {
private final ProgressDialog progressDialog;
public DownloadJSON(Context ctx) {
progressDialog = MyCustomProgressDialog.ctor(ctx);
}
@Override
protected void onPreExecute() {
super.onPreExecute();
progressDialog.show();
}
@Override
protected Void doInBackground(Void... params) {
// Create an array
arraylist = new ArrayList<HashMap<String, String>>();
// Retrieve JSON Objects from the given URL address
jsonobject = JSONfunctions.getJSONfromURL("https://lit-hamlet-6856.herokuapp.com/eventsList/TECHNICAL");
try {
// Locate the array name in JSON
jsonarray = jsonobject.getJSONArray("events");
for (int i = 0; i < jsonarray.length(); i++) {
HashMap<String, String> map = new HashMap<String, String>();
jsonobject = jsonarray.getJSONObject(i);
// Retrive JSON Objects
map.put("Name", jsonobject.getString("Name"));
map.put("Time", jsonobject.getString("Time"));
map.put("Serves", jsonobject.getString("Serves"));
map.put("ingredients", jsonobject.getString("ingredients"));
map.put("Description",jsonobject.getString("Description"));
// Set the JSON Objects into the array
arraylist.add(map);
}
} catch (JSONException e) {
Log.e("Error", e.getMessage());
e.printStackTrace();
}
return null;
}
@Override
protected void onPostExecute(Void args) {
// Locate the listview in listview_main.xml
//setContentView(R.layout.listview_main);
listview = (ListView) findViewById(R.id.listview);
// Pass the results into ListViewAdapter.java
adapter = new ListViewAdapter(JsonLoadSubFirstFirst.this, arraylist);
// Set the adapter to the ListView
listview.setAdapter(adapter);
// Close the progressdialog
// mProgressDialog.dismiss();
super.onPostExecute(args);
// textView.setVisibility(View.VISIBLE);
progressDialog.hide();
super.onPostExecute(args);
}
}
}
有谁能告诉我代码中有什么问题:-)？
答案 0 :(得分：1)
在LocalDownloadJSON课程中，您要将项目添加到localarraylist，然后在适配器构造函数中使用arraylist，这就是您总是获得空数据（blanc屏幕）的原因。< / p>
只需改变：
adapter = new ListViewAdapter(JsonLoadSubFirstFirst.this, arraylist);
到
adapter = new ListViewAdapter(JsonLoadSubFirstFirst.this, localarraylist);
onPostExecute()方法中的。