【发布时间】：2012-09-17 05:07:39
【问题描述】：
我的应用程序中现在至少有三个活动，它们使用 AsyncTask 将 JSON 结果返回到 ListView。我已经开始开发这个应用程序，但是一旦他掌握了基础知识，另一个人就会接管开发，所以我想尝试让事情尽可能易于使用。这意味着我正在尝试将尽可能多的可重复代码转换为可调用函数，因此每次需要查询 Web 服务时不需要复制/粘贴/重用 30-40 行代码，他们只需将参数传递给一个函数。
目前，我在一项通过 php 网络服务从 mysql 数据库中提取体育课程列表的活动中具有以下内容：
class LoadAllClasses extends AsyncTask<String, String, String> {
/**
* Before starting background thread Show Progress Dialog
* */
@Override
protected void onPreExecute() {
super.onPreExecute();
// pDialog = new ProgressDialog(Checkin.this);
// pDialog.setMessage("Loading products. Please wait...");
// pDialog.setIndeterminate(false);
// pDialog.setCancelable(false);
// pDialog.show();
}
/**
* getting All products from url
* */
@Override
protected String doInBackground(String... args) {
// Building Parameters
List<NameValuePair> params = new ArrayList<NameValuePair>();
params.add(new BasicNameValuePair("tag", getclasses_tag));
// getting JSON string from URL
JSONObject json = jParser.makeHttpRequest(SmashGyms.WEBSERVICE_URL,
"POST", params);
// Check your log cat for JSON response
Log.d("CheckinDialog", json.toString());
try {
// Checking for SUCCESS TAG
int success = json.getInt(TAG_SUCCESS);
if (success == 1) {
// classes found
// Getting Array of Classes
classes2 = json.getJSONArray(TAG_CLASSES);
// looping through All Classes
for (int i = 0; i < classes2.length(); i++) {
JSONObject c = classes2.getJSONObject(i);
// Storing each json item in variable
String id = c.getString(TAG_CLASSID);
String name = c.getString(TAG_CLASSNAME);
//String day = c.getString(TAG_DAY);
// creating new HashMap
HashMap<String, String> map = new HashMap<String, String>();
// adding each child node to HashMap key => value
map.put(TAG_CLASSID, id);
map.put(TAG_CLASSNAME, name);
//map.put(TAG_DAY, day);
// adding HashList to ArrayList
allclasseslist.add(map);
Log.d("map: ", map.toString());
}
}
} catch (JSONException e) {
e.printStackTrace();
}
return null;
}
/**
* After completing background task Dismiss the progress dialog
* **/
@Override
protected void onPostExecute(String file_url) {
// dismiss the dialog after getting all products
runOnUiThread(new Runnable() {
@Override
public void run() {
/**
* Updating parsed JSON data into ListView
* */
adapter = new SimpleAdapter(CheckinDialog.this,
allclasseslist, R.layout.checkin_item,
new String[] { TAG_CLASSID, TAG_CLASSNAME },
new int[] { R.id.pid, R.id.name });
setListAdapter(adapter);
}
});
//pDialog.dismiss();
// updating UI from Background Thread
}
}
我想把它移到我拥有的另一个类，称为“WebServiceTasks”，这样我就可以在活动的 OnCreate() 中调用类似的东西：
allclasseslist = new ArrayList<HashMap<String, String>>();
allclasseslist = new WebServiceTasks.LoadAllClasses().get();
adapter = new SimpleAdapter(CheckinDialog.this,
allclasseslist, R.layout.checkin_item,
new String[] { TAG_CLASSID, TAG_CLASSNAME },
new int[] { R.id.pid, R.id.name });
setListAdapter(adapter);
虽然我已经尝试过这个，但我得到了一些与定义 asyncTask 错误或其他不匹配的错误有关的错误。
这是我尝试放入“WebServiceTasks”类的内容：
public static class LoadAllClasses extends
AsyncTask<String, String, ArrayList<HashMap<String, String>>> {
JSONParser jParser = new JSONParser();
ArrayList<HashMap<String, String>> allclasseslist;
// JSON Node names
private static final String TAG_SUCCESS = "success";
private static final String TAG_CLASSES = "classes";
private static final String TAG_CLASSID = "id";
private static final String TAG_CLASSNAME = "class";
private static final String getclasses_tag = "getclasses";
JSONArray classes2 = null;
/**
* Before starting background thread Show Progress Dialog
* */
@Override
protected void onPreExecute() {
super.onPreExecute();
// pDialog = new ProgressDialog(Checkin.this);
// pDialog.setMessage("Loading products. Please wait...");
// pDialog.setIndeterminate(false);
// pDialog.setCancelable(false);
// pDialog.show();
}
/**
* getting All classes from url
* */
@Override
protected ArrayList<HashMap<String, String>> doInBackground(
String... args) {
// Building Parameters
List<NameValuePair> params = new ArrayList<NameValuePair>();
params.add(new BasicNameValuePair("tag", getclasses_tag));
// getting JSON string from URL
JSONObject json = jParser.makeHttpRequest(SmashGyms.WEBSERVICE_URL,
"POST", params);
// Check your log cat for JSON response
Log.d("CheckinDialog", json.toString());
try {
// Checking for SUCCESS TAG
int success = json.getInt(TAG_SUCCESS);
if (success == 1) {
// classes found
// Getting Array of Classes
classes2 = json.getJSONArray(TAG_CLASSES);
// looping through All Classes
for (int i = 0; i < classes2.length(); i++) {
JSONObject c = classes2.getJSONObject(i);
// Storing each json item in variable
String id = c.getString(TAG_CLASSID);
String name = c.getString(TAG_CLASSNAME);
//String day = c.getString(TAG_DAY);
// creating new HashMap
HashMap<String, String> map = new HashMap<String, String>();
// adding each child node to HashMap key => value
map.put(TAG_CLASSID, id);
map.put(TAG_CLASSNAME, name);
//map.put(TAG_DAY, day);
// adding HashList to ArrayList
allclasseslist.add(map);
Log.d("map: ", map.toString());
}
}
} catch (JSONException e) {
e.printStackTrace();
}
return allclasseslist;
}
/**
* After completing background task Dismiss the progress dialog
* **/
@Override
protected void onPostExecute(
ArrayList<HashMap<String, String>> allclasses) {
// dismiss the dialog after getting all products
//pDialog.dismiss();
// updating UI from Background Thread
}
}
这可能吗，如果可以，我做错了什么？
【问题讨论】：
-
看这个例子Seperate AsyncTwsk
-
感谢您的链接。我尝试按照您的代码进行操作，虽然我认为它可能有效，但我现在在“doinBackground”中的以下行中得到一个空指针异常： final HashMap
map = new HashMap ();跨度> -
无视，我忘了初始化arraylist。结合使用您的代码和 Lalit 的代码，我能够让它工作，将我的结果作为答案发布。谢谢你们俩。
标签： android arraylist android-asynctask