java - json 请求的 AsycTask 问题

Question

    package com.example.hstnc_activity;

import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.Reader;
import java.net.URL;

import android.annotation.SuppressLint;
import android.app.Activity;
import android.app.ListActivity;
import android.content.Intent;
import android.os.AsyncTask;
import android.os.Build;
import android.os.Bundle;
import android.support.v4.app.NavUtils;
import android.util.JsonReader;
import android.view.MenuItem;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;

import android.widget.ArrayAdapter;
import android.widget.ListAdapter;
import android.widget.ListView;
import android.widget.SimpleAdapter;


public class DisplayServiceActivity extends ListActivity {
    private ListView listOfServices;

    //JSONArrays?
    JSONArray directory = null; 

    //JSON Node names
    private static String TAG_ID = "id";
    private static String TAG_NAME= "name";
    private static String TAG_DIRECTORY = "Categories";
    private final static String url;    
    JSONObject json;
    jsonParser jParser = new jsonParser();

    @SuppressLint("NewApi")
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        new Request().onPostExecute(url);

        listOfServices =getListView(); //get builtin listView


        ArrayList<HashMap<String, String>> directoryList = new ArrayList<HashMap<String, String>>();

        // Intent intent = getIntent();
        //String url = intent.getStringExtra("SERVICES_DIRECTORY");


        try{
            //getting Array
            directory = json.getJSONArray(TAG_DIRECTORY);

            for(int i= 0; i<directory.length(); i++){
                JSONObject addItem =directory.getJSONObject(i);

                //store each item in variable 
                String id = addItem.getString(TAG_ID);
                String name= addItem.getString(TAG_NAME);

                //create new HashMap
                HashMap<String,String> map = new HashMap<String, String>();

                //add each child node to HashMap key
                map.put(TAG_ID, id);
                map.put(TAG_NAME, name);

                //adding HashList to ArrarList
                directoryList.add(map);
            }

        } catch (JSONException e){
            e.printStackTrace();
        }

        ListAdapter adapter = new SimpleAdapter(this,
                directoryList, 
                R.layout.list_item, 
                new String[] { TAG_ID,TAG_NAME }, 
                new int[] { android.R.id.text1,android.R.id.text2 });

        setListAdapter(adapter);
        setContentView(R.layout.service);
        // Make sure we're running on Honeycomb or higher to use ActionBar APIs
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB) {
            // Show the Up button in the action bar.
            getActionBar().setDisplayHomeAsUpEnabled(true);
        }
    }// end of onCreate Method
    @SuppressWarnings("unused")
    public class Request extends AsyncTask<Void, Void, Void> {
        protected Void doInBackground(Void... params) {
            json = jParser.getJSONfromURL(url);
            return null;
        }
         protected void onPostExecute(String url) {
             json = jParser.getJSONfromURL(url);
         }

    }


    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        switch (item.getItemId()) {
        case android.R.id.home:
            NavUtils.navigateUpFromSameTask(this);
            return true;
        }
        return super.onOptionsItemSelected(item);
    }
}

我正在尝试在 Android 中执行 JSON 请求并获取信息并将其放入 ListView 中。当我调试时，我不断收到“HTTP 连接错误 android.os.NetworkOnMainThreadException”错误。运行 apk 时，当我打开此 Activity 时，它只是强制关闭。此 Activity 是通过另一个屏幕上的按钮启动的。

Answer 1

为什么这个 json = jParser.getJSONfromURL(url) 出现在 onPostExecute() 中？我假设您只是忘记删除它，因为您在 doInBackground() 中也有它应该在的位置

将其移出那里，因为 onPostExecute() 在 UI 线程 上运行，您将收到 NetworkOnMainThreadException

我没有注意到 UI 上运行的任何网络操作，但如果有，则将其移至 doInBackground()

此外，您不应直接调用 onPostExecute() 或任何其他 AsyncTask 方法。你需要用类似的东西来做到这一点

Request = new Request();  // can send parameters to constructor if needed
request.execute();   // execute doInBackground()-- you can pass your url param in here for doInBackground to receive but you have to change the class declaration so that the first param takes a url

AsyncTask Docs