我是android开发的初学者，在下面的代码中得到错误。我正在调用http请求的asyn方法。它给我java.lang.RuntimeException错误执行doInBackground（）
private class PostAlert extends AsyncTask<String, Integer, JSONArray>{
private ProgressDialog progressDialog;
@Override
protected JSONArray doInBackground(String... params) {
// TODO Auto-generated method stub
JSONArray menuitemArr = null;
String url=params[0];
System.out.println("fsfsddddf"+params[0]);
ControlDashboard obj = new ControlDashboard();
try{
JSONObject aobj = obj.getJSONFromUrl(url);
JSONObject array = aobj.getJSONObject("alert_list");
menuitemArr = array.getJSONArray("array");
}
catch (JSONException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return menuitemArr;
}
@Override
protected void onPostExecute(JSONArray menuitemArr) {
// TODO Auto-generated method stub
super.onPostExecute(menuitemArr);
if (menuitemArr.length() == 0) {
startActivity(new Intent("com.example.mysampleapp.ABOUT"));
//Toast.makeText(Alert.this, "No Alerts", Toast.LENGTH_LONG).show();
}else{
name = new String[menuitemArr.length()];
alert = new String[menuitemArr.length()];
date = new String[menuitemArr.length()];
for (int i = 0; i < menuitemArr.length(); i++) {
// printing the values to the logcat
try {
name[i] = menuitemArr.getJSONObject(i).getString("name").toString();
alert[i] = menuitemArr.getJSONObject(i).getString("message").toString();
date[i] = menuitemArr.getJSONObject(i).getString("date").toString();
} catch (JSONException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
ListView list = (ListView) findViewById(R.id.listView3);
ArrayList<HashMap<String, String>> mylistData = new ArrayList<HashMap<String, String>>();
String[] columnTags = new String[] {"col1", "col2", "col3"};
int[] columnIds = new int[] {R.id.alert1, R.id.alert2, R.id.alert3};
for(int i=0; i<name.length; i++)
{
HashMap<String,String> map = new HashMap<String, String>();
map.put("col1", name[i]);
map.put("col2", alert[i]);
map.put("col3", date[i]);
mylistData.add(map);
}
SimpleAdapter arrayAdapter = new SimpleAdapter(Alert.this, mylistData, R.layout.alert_view,columnTags,columnIds);
list.setAdapter(arrayAdapter);
}
}
@Override
protected void onPreExecute() {
// TODO Auto-generated method stub
super.onPreExecute();
progressDialog = new ProgressDialog(Alert.this);
progressDialog.setProgressStyle(ProgressDialog.STYLE_SPINNER);
progressDialog.setMessage("please wait...");
progressDialog.setCancelable(false);
progressDialog.setIndeterminate(false);
progressDialog.setMax(100);
progressDialog.setProgress(0);
progressDialog.show();
}
@Override
protected void onProgressUpdate(Integer... values) {
// TODO Auto-generated method stub
super.onProgressUpdate(values);
//progressDialog.dismiss();
}
}
运行我的Android应用程序时出错。
12-17 13:22:48.035: W/dalvikvm(1160): threadid=8: thread exiting with uncaught exception (group=0x4001d800)
12-17 13:22:48.045: E/AndroidRuntime(1160): FATAL EXCEPTION: AsyncTask #2
12-17 13:22:48.045: E/AndroidRuntime(1160): java.lang.RuntimeException: An error occured while executing doInBackground()
12-17 13:22:48.045: E/AndroidRuntime(1160): at android.os.AsyncTask$3.done(AsyncTask.java:200)
12-17 13:22:48.045: E/AndroidRuntime(1160): at java.util.concurrent.FutureTask$Sync.innerSetException(FutureTask.java:273)
12-17 13:22:48.045: E/AndroidRuntime(1160): at java.util.concurrent.FutureTask.setException(FutureTask.java:124)
12-17 13:22:48.045: E/AndroidRuntime(1160): at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:307)
12-17 13:22:48.045: E/AndroidRuntime(1160): at java.util.concurrent.FutureTask.run(FutureTask.java:137)
json请求类：
public class ControlDashboard extends Activity {
public static DefaultHttpClient httpClient;
static InputStream is = null;
static JSONObject jObj = null;
static String json = "";
public JSONObject getJSONFromUrl(String url) {
// Making HTTP request
try {
// defaultHttpClient
httpClient = new DefaultHttpClient();
HttpPost httpPost = new HttpPost(url);
HttpResponse httpResponse = httpClient.execute(httpPost);
HttpEntity httpEntity = httpResponse.getEntity();
is = httpEntity.getContent();
} catch (UnsupportedEncodingException e) {
e.printStackTrace();
} catch (ClientProtocolException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
try {
BufferedReader reader = new BufferedReader(new InputStreamReader(
is, "iso-8859-1"), 8);
StringBuilder sb = new StringBuilder();
String line = null;
while ((line = reader.readLine()) != null) {
sb.append(line + "\n");
}
is.close();
json = sb.toString();
} catch (Exception e) {
Log.e("Buffer Error", "Error converting result " + e.toString());
}
// try parse the string to a JSON object
try {
jObj = new JSONObject(json);
} catch (JSONException e) {
jObj = null;
Log.e("JSON Parser", "Error parsing data " + e.toString());
}
// return JSON String
return jObj;
}
}
答案 0 :(得分：3)
startActivity(new Intent("com.example.mysampleapp.ABOUT"));
或
ListView list = (ListView) findViewById(R.id.listView3);
这里你试图从背景线程中访问UI元素，这意味着从AsyncTask doInBackground这是不可能的
解决方案移动onPostExecute中所有与ui相关的代码，以便在doInBackground完成后更新ui
您可以在此处看到我们如何在onPostExecute执行完成后doInBackground更新用户界面
编辑：或只使用此PostAlert AsyncTask类：
private class PostAlert extends AsyncTask<String, Integer, JSONArray>{
private ProgressDialog progressDialog;
@Override
protected JSONArray doInBackground(String... params) {
// TODO Auto-generated method stub
JSONArray menuitemArr=null;
String url=params[0];
System.out.println("fsfsddddf"+url);
// System.out.println("fsfsddddfobj"+obj);
try{
JSONObject aobj = obj.getJSONFromUrl(url);
System.out.println("fsfsf"+aobj);
JSONObject array = aobj.getJSONObject("alert_list");
menuitemArr = array.getJSONArray("array");
catch (JSONException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return menuitemArr;
}
@Override
protected void onPostExecute(JSONArray menuitemArr) {
// TODO Auto-generated method stub
if (menuitemArr.length() == 0) {
startActivity(new Intent("com.example.mysampleapp.ABOUT"));
//Toast.makeText(Alert.this, "No Alerts", Toast.LENGTH_LONG).show();
}else{
name = new String[menuitemArr.length()];
System.out.println("name"+name);
alert = new String[menuitemArr.length()];
date = new String[menuitemArr.length()];
for (int i = 0; i < menuitemArr.length(); i++) {
// printing the values to the logcat
name[i] = menuitemArr.getJSONObject(i).getString("name").toString();
alert[i] = menuitemArr.getJSONObject(i).getString("message").toString();
date[i] = menuitemArr.getJSONObject(i).getString("date").toString();
}
ListView list = (ListView) findViewById(R.id.listView3);
ArrayList<HashMap<String, String>> mylistData = new ArrayList<HashMap<String, String>>();
String[] columnTags = new String[] {"col1", "col2", "col3"};
int[] columnIds = new int[] {R.id.alert1, R.id.alert2, R.id.alert3};
for(int i=0; i<name.length; i++)
{
HashMap<String,String> map = new HashMap<String, String>();
map.put("col1", name[i]);
map.put("col2", alert[i]);
map.put("col3", date[i]);
mylistData.add(map);
}
SimpleAdapter arrayAdapter = new SimpleAdapter(Alert.this, mylistData, R.layout.alert_view,columnTags,columnIds);
list.setAdapter(arrayAdapter);
}
}
super.onPostExecute(result);
}
@Override
protected void onPreExecute() {
// TODO Auto-generated method stub
progressDialog = new ProgressDialog(Alert.this);
progressDialog.setProgressStyle(ProgressDialog.STYLE_SPINNER);
progressDialog.setMessage("please wait...");
progressDialog.setCancelable(false);
progressDialog.setIndeterminate(false);
progressDialog.setMax(100);
progressDialog.setProgress(0);
progressDialog.show();
System.out.println("fsgsgsg");
}
@Override
protected void onProgressUpdate(Integer... values) {
// TODO Auto-generated method stub
progressDialog.setProgress(values[0]);
}
}
}
http://developer.android.com/reference/android/os/AsyncTask.html
答案 1 :(得分：1)
您正在后台设置ListAdapter，因为它是UI线程任务，所以不应该这样做。将doInBackground()中的整个代码更改为onPostExecute()，getJsonFromUrl(url)除外。你可以从doInBackground()返回jsonobject，你可以在onPostExecute()作为结果参数。您仍然可以在onPostExecute()中获得运行时错误，然后在
listview.setAdapter()
runOnUIThread(new Runnable(){
public void run()
{
}
});
我希望它清楚，它会对你有用。