从异步任务返回对象时出现java问题
我有一个扩展AsyncTask的类(RestClient.java): 包裹组织。stocktwits。助手
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.DefaultHttpClient;
import org.json.JSONException;
import org.json.JSONObject;
import 安卓.os.AsyncTask;
import 安卓.util.Log;
public class RestClient extends AsyncTask<String, Void, JSONObject>{
public JSONObject jsonObj = null;
private static String convertStreamToString(InputStream is) {
/*
* To convert the InputStream to String we use the BufferedReader.readLine()
* method. We iterate until the BufferedReader return null which means
* there's no more data to read. Each line will appended to a StringBuilder
* and returned as String.
*/
BufferedReader reader = new BufferedReader(new InputStreamReader(is));
StringBuilder sb = new StringBuilder();
String line = null;
try {
while ((line = reader.readLine()) != null) {
sb.append(line + "\n");
}
} catch (IOException e) {
e.printStackTrace();
} finally {
try {
is.close();
} catch (IOException e) {
e.printStackTrace();
}
}
return sb.toString();
}
/* This is a test function which will connects to a given
* rest service and prints it's response to Android Log with
* labels "Praeda".
*/
public static JSONObject connect(String url)
{
HttpClient httpclient = new DefaultHttpClient();
// Prepare a request object
HttpGet httpget = new HttpGet(url);
// Execute the request
HttpResponse response;
try {
response = httpclient.execute(httpget);
// Examine the response status
Log.i("Praeda",response.getStatusLine().toString());
// Get hold of the response entity
HttpEntity entity = response.getEntity();
if (entity != null) {
// A Simple JSON Response Read
InputStream instream = entity.getContent();
String result= convertStreamToString(instream);
// A Simple JSONObject Creation
JSONObject json=new JSONObject(result);
// Closing the input stream will trigger connection release
instream.close();
return json;
}
} catch (ClientProtocolException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (JSONException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return null;
}
@Override
protected JSONObject doInBackground(String... urls) {
return connect(urls[0]);
}
@Override
protected void onPostExecute(JSONObject json ) {
this.jsonObj = json;
}
public void setJSONObject(JSONObject jsonFromUI){
this.jsonObj = jsonFromUI;
}
public JSONObject getJSONObject(){
return this.jsonObj;
}
}
我正在尝试在我的主类(Main.java)上执行AsyncTask:
RestClient rc = new RestClient();
JSONObject json = new JSONObject();
rc.setJSONObject(json);
rc.execute(buildQuery());
json = rc.getJSONObject();
//do some stuff with the json object
try { JSONObject query = json.getJSONObject("query");
//...
}
json为null,因为它是在onPostExecute()之前调用的。如何获取JSON
更新: 我需要在onPostExecute()中运行这个try块:
try {
JSONObject query = json.getJSONObject("query");
JSONObject results = query.getJSONObject("results");
if (query.getString("count").equals("1")) { // YQL JSON doesn't
// return an array for
// single quotes
JSONObject quote = results.getJSONObject("quote");
Quote myQuote = new Quote();
myQuote.setName(quote.getString("Name"));
myQuote.setSymbol(quote.getString("Symbol"));
myQuote.setLastTradePriceOnly(quote
.getString("LastTradePriceOnly"));
myQuote.setChange(quote.getString("Change"));
myQuote.setOpen(quote.getString("Open"));
myQuote.setMarketCapitalization(quote
.getString("MarketCapitalization"));
myQuote.setDaysHigh(quote.getString("DaysHigh"));
myQuote.setYearHigh(quote.getString("YearHigh"));
myQuote.setDaysLow(quote.getString("DaysLow"));
myQuote.setYearLow(quote.getString("YearLow"));
myQuote.setVolume(quote.getString("Volume"));
myQuote.setAverageDailyVolume(quote
.getString("AverageDailyVolume"));
myQuote.setPeRatio(quote.getString("PERatio"));
myQuote.setDividendYield(quote.getString("DividendYield"));
myQuote.setPercentChange(quote.getString("PercentChange"));
quotesAdapter.add(myQuote);}
# 1 楼答案
我被doInBackground在onPostExecute中消耗的结果弄错了
doInBackground(参数…),援引 立即打开背景线程 在PreExecute()完成后 执行。此步骤用于 执行背景计算 可能需要很长时间。参数 异步任务的 到这一步测试结果 计算必须由该 步骤,并将传递回 最后一步。这一步也可以使用 出版进度(进度…)到 发布一个或多个单位的 进步这些值已发布 在UI线程上,在 onProgressUpdate(进度…)迈步
# 2 楼答案
嘿,你可以使用侦听器来解决这个问题。 为了使用这个,我稍微修改了代码
在这样的呼叫类中使用
别忘了实现侦听器