AsyncTask未按預期執行

Question

我的logcat在doInBackground（）中顯示問題。這可能是UI的主線程存在於doInBackground線程內而不是onPostExecute方法的問題，但我無法使其工作。有什麼建議麼？

非常感謝

AllProductsActivity.java：

package com.example.androidhive; 

import java.util.ArrayList; 
import java.util.HashMap; 
import java.util.List; 

import org.apache.http.NameValuePair; 
import org.json.JSONArray; 
import org.json.JSONException; 
import org.json.JSONObject; 

import android.app.ListActivity; 
import android.app.ProgressDialog; 
import android.content.Intent; 
import android.os.AsyncTask; 
import android.os.Bundle; 
import android.util.Log; 
import android.view.View; 
import android.widget.AdapterView; 
import android.widget.AdapterView.OnItemClickListener; 
import android.widget.ListAdapter; 
import android.widget.ListView; 
import android.widget.SimpleAdapter; 
import android.widget.TextView; 

public class AllProductsActivity extends ListActivity { 

    // Progress Dialog 
    private ProgressDialog pDialog; 

    // Creating JSON Parser object 
    JSONParser jParser = new JSONParser(); 

    ArrayList<HashMap<String, String>> productsList; 

    // url to get all products list 
    private static String url_all_products = "192.168.1.68/android_connect/get_all_products.php"; 

    // JSON Node names 
    private static final String TAG_SUCCESS = "success"; 
    private static final String TAG_PRODUCTS = "products"; 
    private static final String TAG_PID = "pid"; 
    private static final String TAG_NAME = "name"; 

    // products JSONArray 
    JSONArray products = null; 

    @Override 
    public void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.all_products); 

     // Hashmap for ListView 
     productsList = new ArrayList<HashMap<String, String>>(); 

     // Loading products in Background Thread 
     new LoadAllProducts().execute(); 

     // Get listview 
     ListView lv = getListView(); 

     // on seleting single product 
     // launching Edit Product Screen 
     lv.setOnItemClickListener(new OnItemClickListener() { 

      @Override 
      public void onItemClick(AdapterView<?> parent, View view, 
            int position, long id) { 
       // getting values from selected ListItem 
       String pid = ((TextView) view.findViewById(R.id.pid)).getText() 
         .toString(); 

       // Starting new intent 
       Intent in = new Intent(getApplicationContext(), 
         EditProductActivity.class); 
       // sending pid to next activity 
       in.putExtra(TAG_PID, pid); 

       // starting new activity and expecting some response back 
       startActivityForResult(in, 100); 
      } 
     }); 

    } 

    // Response from Edit Product Activity 
    @Override 
    protected void onActivityResult(int requestCode, int resultCode, Intent data) { 
     super.onActivityResult(requestCode, resultCode, data); 
     // if result code 100 
     if (resultCode == 100) { 
      // if result code 100 is received 
      // means user edited/deleted product 
      // reload this screen again 
      Intent intent = getIntent(); 
      finish(); 
      startActivity(intent); 
     } 

    } 

    /** 
    * Background Async Task to Load all product by making HTTP Request 
    * */ 
    class LoadAllProducts extends AsyncTask<String, String, String> { 

     /** 
     * Before starting background thread Show Progress Dialog 
     * */ 
     @Override 
     protected void onPreExecute() { 
      super.onPreExecute(); 
      pDialog = new ProgressDialog(AllProductsActivity.this); 
      pDialog.setMessage("Loading products. Please wait..."); 
      pDialog.setIndeterminate(false); 
      pDialog.setCancelable(false); 
      pDialog.show(); 
     } 

     /** 
     * getting All products from url 
     * */ 
     protected String doInBackground(String... args) { 
      // Building Parameters 
      List<NameValuePair> params = new ArrayList<NameValuePair>(); 

      // getting JSON string from URL 
      JSONObject json = jParser.makeHttpRequest(url_all_products, "GET", params); 

      // Check your log cat for JSON reponse 
      Log.d("All Products: ", json.toString()); 

      try { 
       // Checking for SUCCESS TAG 
       int success = json.getInt(TAG_SUCCESS); 

       if (success == 1) { 
        // products found 
        // Getting Array of Products 
        products = json.getJSONArray(TAG_PRODUCTS); 

        // looping through All Products 
        for (int i = 0; i < products.length(); i++) { 
         JSONObject c = products.getJSONObject(i); 

         // Storing each json item in variable 
         String id = c.getString(TAG_PID); 
         String name = c.getString(TAG_NAME); 

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

         // adding each child node to HashMap key => value 
         map.put(TAG_PID, id); 
         map.put(TAG_NAME, name); 

         // adding HashList to ArrayList 
         productsList.add(map); 
        } 
       } else { 
        // no products found 
        // Launch Add New product Activity 
        Intent i = new Intent(getApplicationContext(), 
          NewProductActivity.class); 
        // Closing all previous activities 
        i.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP); 
        startActivity(i); 
       } 
      } catch (JSONException e) { 
       e.printStackTrace(); 
      } 

      return null; 
     } 

     /** 
     * After completing background task Dismiss the progress dialog 
     * **/ 
     protected void onPostExecute(String file_url) { 
      // dismiss the dialog after getting all products 
      pDialog.dismiss(); 
      // updating UI from Background Thread 
      runOnUiThread(new Runnable() { 
       public void run() { 
        /** 
        * Updating parsed JSON data into ListView 
        * */ 
        ListAdapter adapter = new SimpleAdapter(
          AllProductsActivity.this, productsList, 
          R.layout.list_item, new String[] { TAG_PID, 
          TAG_NAME}, 
          new int[] { R.id.pid, R.id.name }); 
        // updating listview 
        setListAdapter(adapter); 
       } 
      }); 

     } 

    } 
} 

的logcat：

09-23 04:16:12.898 8201-8274/com.example.androidhive E/AndroidRuntime﹕ FATAL EXCEPTION: AsyncTask #1 
    Process: com.example.androidhive, PID: 8201 
    java.lang.RuntimeException: An error occured while executing doInBackground() 
      at android.os.AsyncTask$3.done(AsyncTask.java:300) 
      at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:355) 
      at java.util.concurrent.FutureTask.setException(FutureTask.java:222) 
      at java.util.concurrent.FutureTask.run(FutureTask.java:242) 
      at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:231) 
      at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112) 
      at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587) 
      at java.lang.Thread.run(Thread.java:841) 
    Caused by: java.lang.IllegalStateException: Target host must not be null, or set in parameters. scheme=null, host=null, path=192.168.1.68/android_connect/get_all_products.php 
      at org.apache.http.impl.client.DefaultRequestDirector.determineRoute(DefaultRequestDirector.java:591) 
      at org.apache.http.impl.client.DefaultRequestDirector.execute(DefaultRequestDirector.java:293) 
      at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:555) 
      at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:487) 
      at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:465) 
      at com.example.androidhive.JSONParser.makeHttpRequest(JSONParser.java:62) 
      at com.example.androidhive.AllProductsActivity$LoadAllProducts.doInBackground(AllProductsActivity.java:128) 
      at com.example.androidhive.AllProductsActivity$LoadAllProducts.doInBackground(AllProductsActivity.java:105) 
      at android.os.AsyncTask$2.call(AsyncTask.java:288) 
      at java.util.concurrent.FutureTask.run(FutureTask.java:237) 
            at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:231) 
            at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112) 
            at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587) 
            at java.lang.Thread.run(Thread.java:841) 
09-23 04:16:13.018 8201-8201/com.example.androidhive E/WindowManager﹕ android.view.WindowLeaked: Activity com.example.androidhive.AllProductsActivity has leaked window com.android.internal.policy.impl.PhoneWindow$DecorView{423ea0f0 V.E..... R......D 0,0-959,192} that was originally added here 
      at android.view.ViewRootImpl.<init>(ViewRootImpl.java:346) 
      at android.view.WindowManagerGlobal.addView(WindowManagerGlobal.java:248) 
      at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:69) 
      at android.app.Dialog.show(Dialog.java:286) 
      at com.example.androidhive.AllProductsActivity$LoadAllProducts.onPreExecute(AllProductsActivity.java:117) 
      at android.os.AsyncTask.executeOnExecutor(AsyncTask.java:587) 
      at android.os.AsyncTask.execute(AsyncTask.java:535) 
      at com.example.androidhive.AllProductsActivity.onCreate(AllProductsActivity.java:57) 
      at android.app.Activity.performCreate(Activity.java:5231) 
      at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087) 
      at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2148) 
      at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2233) 
      at android.app.ActivityThread.access$800(ActivityThread.java:135) 
      at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196) 
      at android.os.Handler.dispatchMessage(Handler.java:102) 
      at android.os.Looper.loop(Looper.java:136) 
      at android.app.ActivityThread.main(ActivityThread.java:5001) 
      at java.lang.reflect.Method.invokeNative(Native Method) 
      at java.lang.reflect.Method.invoke(Method.java:515) 
      at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785) 
      at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601) 
      at dalvik.system.NativeStart.main(Native Method) 

Answer 1

其實正確的aswer是：JSON查詢首先返回的錯誤，那麼查詢，以便當應用程序試圖加載從查詢的信息中，JSON轉換解析錯誤首先因此失敗，因爲它不是有效的JSON查詢。只要將這些錯誤隱藏在php文件中，一切就會順利進行。

Answer 2

HTTP協議中缺少稱爲URL。在簡單的HTTP的情況下，你能解決這樣的：

private static String url_all_products = "http://192.168.1.68/android_connect/get_all_products.php";