Question

这是我的代码。这只是整个应用程序的一小部分。它发出HTTP请求并从septa获取列车数据。代码是正确的，因为它在java项目中工作。请注意，当我尝试在单独的java类中执行简单的http请求部分并将其作为java文件运行时。在运行中，它给了我一个致命错误：java.lang.String的无效布局值。我试着在这个论坛上查看帖子。什么都行不通。不知道为什么会这样。代码在以前工作了！

package com.cs275.septaassignment;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.URL;
import java.net.HttpURLConnection;

import android.app.Activity;
import android.os.Bundle;
import android.os.AsyncTask;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import android.widget.TextView;

import com.google.gson.*;

import java.util.ArrayList;

public class TrainInfo extends Activity
{
protected static String startStation;
protected static String endStation;

private ListView listView;//ListView for the output
private ArrayAdapter<String> adapter;//Adapter to interact with the ListView


protected void onCreate(Bundle savedInstanceState)
{
    super.onCreate(savedInstanceState);
    setContentView(R.layout.train_infolayout);

    startStation = this.getIntent().getExtras().getString("fromStation");
    endStation = this.getIntent().getExtras().getString("toStation");

    ArrayList<String> trainInfo = new ArrayList<String>();

    adapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, trainInfo);//initializing the ArrayAdapter

    listView = (ListView)findViewById(R.id.train_listView);
    listView.setAdapter(adapter);//Linking the adapter      
    adapter.setNotifyOnChange(true);//This ensures that the changes in data so the UI components can refresh themselves     

    TrainData trainSchedule = new TrainData();
    trainSchedule.execute();
}
public class TrainData extends AsyncTask<Void,Void,Void>
{
    ArrayList<String> nextTrains;

    protected void onPostExecute(Void arg0)//This method is called after the background process is complete 
    {
        adapter.clear();
        for(int i = 0;i<nextTrains.size();i++)
        {
            System.out.println(nextTrains.get(i));
            adapter.add(nextTrains.get(i));
        }
        adapter.add("Hello World");
        TextView updateMessage = (TextView) findViewById(R.id.train_list_info);
        updateMessage.setText("Here are the available trains for your trip from " + startStation + " to " + endStation);
        adapter.notifyDataSetChanged();//This send the signal that the data is changes and allows the UI components like the ListView to get updated.           

    }
    @Override
    protected Void doInBackground(Void... params) 
    {
        // TODO Auto-generated method stub
        try
        {
            String sURL = "http://www3.septa.org/hackathon/NextToArrive/"+ startStation + "/" + endStation + "/10"; 
            System.out.println(sURL);
            URL url = new URL(sURL);
            HttpURLConnection request = (HttpURLConnection) url.openConnection();
            request.connect();

            JsonParser jp = new JsonParser();//Json parsing tool
            JsonElement root = jp.parse(new InputStreamReader((InputStream) request.getContent()));//Getting content in Json
            System.out.println("root:\n" + root);
            JsonArray rootArray = root.getAsJsonArray();

            nextTrains = new ArrayList<String>();
            if(rootArray.size() > 0)
            {
                for(int i = 0;i<rootArray.size();i++)
                {
                    JsonObject train = rootArray.get(i).getAsJsonObject();
                    String departureTime = train.get("orig_departure_time").getAsString();
                    String arrivalTime = train.get("orig_arrival_time").getAsString();
                    String delayTime = train.get("orig_delay").getAsString();
                    String trainNumber = train.get("orig_train").getAsString();

                    String result = "Train " + trainNumber + "\nDeparts from " + startStation + ": " + departureTime
                                    + "\nArrives at " + endStation + ": " + arrivalTime;
                    if(!delayTime.equals("On Time"))
                        result = result + "\nDelayed: " + delayTime;
                    nextTrains.add(result);
                }
            }else
            {
                nextTrains.add("No trains available from " + startStation + " to " + endStation);
            }


            }catch(Exception e)
            {
                System.out.println("Unable to make http request!");
            }
        return null;
    }
    public void retrieveData()
    {

        }
}

}

Answer 1

您应该通过将AsyncTask定义为<Intent, Void, Void>来避免可能的线程问题，并调用其执行方法，例如trainSchedule.execute(getIntent());将doInBackground(Void... params)更改为doInBackground(Intent... params)并从之前获取该意图的额外内容您使用

设置URL

String start = params[0].getExtras().getString("fromStation");
String end = params[0].getExtras().getString("toStation");

Answer 2

使用URLEncoder encode方法对您的网址进行编码，这会将空格更改为%20以及其他必要的编码

更新

正如所指出的，上面的方法实际上会将空格编码为+，这在这种情况下并不好，因为服务器不能很好地处理它们。您也可以尝试Uri.encode，看起来它应该像你想要的那样将空格编码为％20。

进一步更新

根据this answer，您必须在使用URLEncoder之后自行对空格进行编码，如下所示：URLEncoder.encode(sURL, "UTF-8").replace("+", "%20")

Answer 3

将其作为java文件运行。在运行中它给我一个致命错误：java.lang.String的值无效布局值为

将其作为Android应用程序运行，而不是作为通用Java应用程序运行。

Android没有得到Json的结果

3 个答案:

更新

进一步更新