ArrayList.add 不适用于 AsyncTask
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【中文标题】ArrayList.add 不适用于 AsyncTask【英文标题】：ArrayList.add not working with AsyncTask 【发布时间】：2018-12-09 07:14:53 【问题描述】：我正在使用片段视图在我的 android 应用程序中显示 ListView。当我手动输入ArrayList 时，它工作得很好。但现在我想将 JSON 数组添加到 AsyncTask 类中的 ArryList 并将 ArrayList 添加到适配器。
所以我得到了 JSON 数组并将其放入 ArrayList。这个过程在AsyncTask 类中进行。
我在 Fragment 的 onCreateView() 方法中执行 AsyncTask 类。然后我将ArrayList 设置为适配器。但是问题就在那里..
执行AsyncTask 类后，完美获取我的JSON 数组并添加到ArrayList。但是当我尝试将我的ArrayList 添加到适配器时。然后我的ArryaList 为空。
这是我的带有AsyncTask 部分的片段类
public class FragmentCategory extends Fragment
private ListView lvCategory;
private CategoryAdapter categotyAdapter;
private List<Category> mCategoryLst;
View view;
@Nullable
@Override
public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState)
view = inflater.inflate(R.layout.fragment_category , container, false);
lvCategory = (ListView) view.findViewById(R.id.listview_category);
mCategoryLst = new ArrayList<>();
/*mCategoryLst.add(new Category(1, "hghjj" ,null));
mCategoryLst.add(new Category(2,"Abcd", null));
mCategoryLst.add(new Category(3,"Aeec", null));*/
new FetchDataTask().execute();
if(mCategoryLst!=null && mCategoryLst.size()>0)
categotyAdapter = new CategoryAdapter(getContext(), mCategoryLst);
lvCategory.setAdapter(categotyAdapter);
return view;
@Override
public void onCreate(@Nullable Bundle savedInstanceState)
super.onCreate(savedInstanceState);
//new FetchDataTask().execute();
public class FetchDataTask extends AsyncTask<String,String,Void>
private ProgressDialog progressDialog = new ProgressDialog(getActivity());
private String mUrlCategory;
@Override
protected void onPreExecute()
progressDialog.setMessage("Downloading your data...");
progressDialog.show();
progressDialog.setOnCancelListener(new DialogInterface.OnCancelListener()
public void onCancel(DialogInterface arg0)
FetchDataTask.this.cancel(true);
);
@Override
protected Void doInBackground(String... strings)
HttpURLConnection urlConnection = null;
BufferedReader reader = null;
Uri bUri = Uri.parse(getString(R.string.url_category));
URL url;
try
url = new URL(bUri.toString());
urlConnection = (HttpURLConnection)url.openConnection();
urlConnection.setRequestMethod("GET");
urlConnection.connect();
InputStream inputStream = urlConnection.getInputStream();
StringBuffer buffer = new StringBuffer();
if(inputStream==null)
return null;
reader = new BufferedReader(new InputStreamReader(inputStream));
String line;
while ((line = reader.readLine()) != null)
buffer.append(line + "\n");
if(buffer.length() == 0)
return null;
mUrlCategory = buffer.toString();
catch (MalformedURLException e)
e.printStackTrace();
catch (IOException e)
e.printStackTrace();
/*catch (JSONException e)
e.printStackTrace();
*/finally
if (urlConnection != null)
urlConnection.disconnect();
if (reader != null)
try
reader.close();
catch (final IOException e)
Log.e("MainActivity", "Error closing stream", e);
return null;
@Override
protected void onPostExecute(Void aVoid)
try
if (progressDialog.isShowing())
progressDialog.dismiss();
JSONArray jArray = new JSONArray(mUrlCategory);
for (int i = 0; i < jArray.length(); i++)
JSONObject jObject = jArray.getJSONObject(i);
int id = Integer.parseInt(jObject.getString("id"));
String name = jObject.getString("categoryName");
String imageUrl = jObject.getString("iconPath");
mCategoryLst.add(new Category(id, name ,null));
catch (JSONException e)
Log.e("JSONException", "Error: " + e.toString());
// catch (Exception e)
这是我的类别类
这个用于创建ArrayList
public class Category
private int categoryId;
private String categoryName;
private String imgUrl;
public Category()
public Category(int id,String name, String img)
this.categoryId=id;
this.categoryName=name;
this.imgUrl=img;
//Gettert
public int getCategoryId()
return categoryId;
public String getCategoryName()
return categoryName;
public String getImgUrl()
return imgUrl;
//Settert
public void setCategoryId(int categoryId)
this.categoryId = categoryId;
public void setCategoryName(String categoryName)
this.categoryName = categoryName;
public void setImgUrl(String imgUrl)
this.imgUrl = imgUrl;
这是我的适配器类
public class CategoryAdapter extends BaseAdapter
private Context mContext;
private List<Category> mCategoryList;
//Constructor
public CategoryAdapter(Context mContext, List<Category> mCategoryList)
this.mContext = mContext;
this.mCategoryList = mCategoryList;
@Override
public int getCount()
return mCategoryList.size();
@Override
public Object getItem(int position)
return mCategoryList.get(position);
@Override
public long getItemId(int position)
return position;
@Override
public View getView(int position, View convertView, ViewGroup parent)
View v = View.inflate(mContext, R.layout.item_category, null);
TextView tvCategoryName = (TextView) v.findViewById(R.id.category_name);
ImageView ivCategoryImg = (ImageView) v.findViewById(R.id.img_category);
//Set Value
tvCategoryName.setText(mCategoryList.get(position).getCategoryName());
//ivCategoryImg.setImageResource();
//Set ID
v.setTag(mCategoryList.get(position).getCategoryId());
return v;
【问题讨论】：
在你的onPostExecute 方法中添加这一行 categotyAdapter = new CategoryAdapter(getContext(), mCategoryLst); lvCategory.setAdapter(categotyAdapter); 它将起作用
在mCategoryLst 中添加数据后更好地使用categotyAdapter.notifyDataSetChanged(); onPostExecute onPostExecute asynctask 方法
@Nilesh 谢谢你..它的工作...
【参考方案1】：
categotyAdapter = new CategoryAdapter(getActivity(), mCategoryLst);
lvCategory.setAdapter(categotyAdapter);
【讨论】：
虽然此代码 sn-p 可能是解决方案，但 including an explanation 确实有助于提高您的帖子质量。请记住，您是在为将来的读者回答问题，而这些人可能不知道您提出代码建议的原因。【参考方案2】：根据您的代码，我所看到的，对 AysncTask 类的 Fragment OnCreateView() 和 OnPostExecution 进行如下代码的更改。
public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState)
view = inflater.inflate(R.layout.fragment_category , container, false);
lvCategory = (ListView) view.findViewById(R.id.listview_category);
mCategoryLst = new ArrayList<>();
/*mCategoryLst.add(new Category(1, "hghjj" ,null));
mCategoryLst.add(new Category(2,"Abcd", null));
mCategoryLst.add(new Category(3,"Aeec", null));*/
new FetchDataTask().execute();
categotyAdapter = new CategoryAdapter(getContext(), mCategoryLst);
lvCategory.setAdapter(categotyAdapter);
return view;
在 OpPostExecution 中
protected void onPostExecute(Void aVoid)
try
if (progressDialog.isShowing())
progressDialog.dismiss();
JSONArray jArray = new JSONArray(mUrlCategory);
for (int i = 0; i < jArray.length(); i++)
JSONObject jObject = jArray.getJSONObject(i);
int id = Integer.parseInt(jObject.getString("id"));
String name = jObject.getString("categoryName");
String imageUrl = jObject.getString("iconPath");
mCategoryLst.add(new Category(id, name ,null));
categotyAdapter.notifyDataSetChanged();
catch (JSONException e)
Log.e("JSONException", "Error: " + e.toString());
// catch (Exception e)
【讨论】：
这对我不起作用。但谢谢。你的回答帮助我解决了这个问题【参考方案3】：问题已解决
我像这样更改我的onPostExecute() 方法...
@Override
protected void onPostExecute(Void aVoid)
try
if (progressDialog.isShowing())
progressDialog.dismiss();
JSONObject jsonObject = new JSONObject(mUrlCategory);
Log.v("Response", jsonObject.toString());
JSONArray categoryArray = jsonObject.getJSONArray("itemcategory");
for (int i = 0; i < categoryArray.length(); i++)
JSONObject jCategory = (JSONObject) categoryArray.get(i);
int id = Integer.parseInt(jCategory.getString("id"));
String name = jCategory.getString("categoryName");
String imageUrl = jCategory.getString("iconPath");
mCategoryLst.add(new Category(id, name, null));
if (mCategoryLst != null && mCategoryLst.size() > 0)
categotyAdapter = new CategoryAdapter(getContext(), mCategoryLst);
lvCategory.setAdapter(categotyAdapter);
categotyAdapter.notifyDataSetChanged();
catch (JSONException e)
Log.e("JSONException", "Error: " + e.toString());
// catch (Exception e)
当我放这部分时
if (mCategoryLst != null && mCategoryLst.size() > 0)
categotyAdapter = new CategoryAdapter(getContext(), mCategoryLst);
lvCategory.setAdapter(categotyAdapter);
OnCreateView() 应用程序不工作。所以我把它放在onPostExecute()。然后它完美地工作。谢谢大家
【讨论】：
【参考方案4】：当你有数据时，你需要在你的适配器上调用notifyDataSetChanged()：
for (int i = 0; i < jArray.length(); i++)
JSONObject jObject = jArray.getJSONObject(i);
int id = Integer.parseInt(jObject.getString("id"));
String name = jObject.getString("categoryName");
String imageUrl = jObject.getString("iconPath");
mCategoryLst.add(new Category(id, name, null));
categotyAdapter.notifyDataSetChanged();
【讨论】：
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