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从 AsyncTask 返回对象时出现问题

发布于 2024-09-19 02:01:32 字数 5612 浏览 3 评论 0原文

我有一个扩展 AsyncTask 的类（RestClient.java）： 包 org.stocktwits.helper;

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 android.os.AsyncTask;
import android.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;
    }

}

我试图在我的主类 (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。我如何获取我的 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);}
原文

I have a class (RestClient.java) that extends AsyncTask:
package org.stocktwits.helper;

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 android.os.AsyncTask;
import android.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;
    }

}

I am trying to execute the AsyncTask on my Main class (Main.java):

    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 is null because it is called before onPostExecute(). How can I get my JSON?

UPDATE:
I need to run this try block in onPostExecute():

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);}

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评论（4）

沙沙粒小 2024-09-26 02:01:32

嘿，你可以使用监听器来解决这个问题。
我稍微更改了代码以使用它。

package com.insidetip.uob.data;
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 android.app.ProgressDialog;
import android.content.Context;
import android.os.AsyncTask;
import android.util.Log;

public class JSONClient extends AsyncTask<String, Void, JSONObject>{
    ProgressDialog progressDialog ;
    GetJSONListener getJSONListener;
    Context curContext;
    public JSONClient(Context context, GetJSONListener listener){
        this.getJSONListener = listener;
        curContext = context;
    }
    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();
    }


    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
    public void onPreExecute() {
        progressDialog = new ProgressDialog(curContext);
        progressDialog.setMessage("Loading..Please wait..");
        progressDialog.setCancelable(false);
        progressDialog.setIndeterminate(true);
        progressDialog.show();

    }

    @Override
    protected JSONObject doInBackground(String... urls) {
        return connect(urls[0]);
    }

    @Override
    protected void onPostExecute(JSONObject json ) {
        getJSONListener.onRemoteCallComplete(json);
        progressDialog.dismiss();
    }
}

像这样在调用类中使用。

    JSONClient client = new JSONClient(context, listener);
    client.execute(URL);

不要忘记实现监听器

public interface GetJSONListener {
    public void onRemoteCallComplete(JSONObject jsonFromNet);
}

Hey You can use listeners to fix this problem.
I've changed the code slightly to use this.

package com.insidetip.uob.data;
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 android.app.ProgressDialog;
import android.content.Context;
import android.os.AsyncTask;
import android.util.Log;

public class JSONClient extends AsyncTask<String, Void, JSONObject>{
    ProgressDialog progressDialog ;
    GetJSONListener getJSONListener;
    Context curContext;
    public JSONClient(Context context, GetJSONListener listener){
        this.getJSONListener = listener;
        curContext = context;
    }
    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();
    }


    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
    public void onPreExecute() {
        progressDialog = new ProgressDialog(curContext);
        progressDialog.setMessage("Loading..Please wait..");
        progressDialog.setCancelable(false);
        progressDialog.setIndeterminate(true);
        progressDialog.show();

    }

    @Override
    protected JSONObject doInBackground(String... urls) {
        return connect(urls[0]);
    }

    @Override
    protected void onPostExecute(JSONObject json ) {
        getJSONListener.onRemoteCallComplete(json);
        progressDialog.dismiss();
    }
}

Use in the calling class like this.

    JSONClient client = new JSONClient(context, listener);
    client.execute(URL);

Dont forget to implement the listener

public interface GetJSONListener {
    public void onRemoteCallComplete(JSONObject jsonFromNet);
}
回复 原文
你没皮卡萌 2024-09-26 02:01:32

我错误地认为 doInBackground 的结果可以在 onPostExecute doInBackground(Params...) 中消耗

，调用于
立即启动后台线程
PreExecute() 完成后
执行。此步骤用于
执行后台计算
可能需要很长时间。参数
异步任务的传递
到这一步。 结果
计算必须由此返回
步骤并将被传递回
最后一步。这一步也可以用
发布进度（进度...）到
出版一个或多个单元
进步。这些值已发布
在 UI 线程上，在
onProgressUpdate(进度...) 步骤。

@Override

protected void onPostExecute(JSONObject json ) {
// DO stuff here ( it's UI thread )
 mJsonFromTheActivity = json;
}

I'm be mistaken by result of doInBackground can be consumed in onPostExecute

doInBackground(Params...), invoked on
the background thread immediately
after on PreExecute() finishes
executing. This step is used to
perform background computation that
can take a long time. The parameters
of the asynchronous task are passed
to this step. The result of the
computation must be returned by this
step and will be passed back to the
last step. This step can also use
publishProgress(Progress...) to
publish one or more units of
progress. These values are published
on the UI thread, in the
onProgressUpdate(Progress...) step.

@Override

protected void onPostExecute(JSONObject json ) {
// DO stuff here ( it's UI thread )
 mJsonFromTheActivity = json;
}
回复 原文
奢望 2024-09-26 02:01:32

execute() 始终返回 AsyncTask 本身。从 doInBackground() 返回的对象将在 onPostExecute() 中交给您。

execute() always returns the AsyncTask itself. The object you return from doInBackground() is handed to you in onPostExecute().

回复 原文
浊酒尽余欢 2024-09-26 02:01:32

如果您将 asynctask 作为活动的嵌套内部类，则可以将活动变量之一设置为 asynctask 的结果

If you have your asynctask as a nested inner class of your activity, you can set one of your activities variables to the result of your asynctask

回复 原文
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