我遇到了通过json从MySQL获取数据的问题。我已经尝试了很多，但无法解决我面临的问题。我正在尝试显示从数据库中获取的列表，并通过ListView中的json进行解析。下面是代码。请帮帮我！
GetAll.java
package com.example.energy;
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 GetAll 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 = "http://10.0.2.2/android/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.activity_main);
// 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(),
MainActivity.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(GetAll.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(),
MainActivity.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(
GetAll.this, productsList,
R.layout.listitem, new String[] { TAG_PID,
TAG_NAME},
new int[] { R.id.pid, R.id.name });
// updating listview
setListAdapter(adapter);
}
});
}
}
}
JSONParser.java
package com.example.energy;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.UnsupportedEncodingException;
import java.util.List;
import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.NameValuePair;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.entity.UrlEncodedFormEntity;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.client.utils.URLEncodedUtils;
import org.apache.http.impl.client.DefaultHttpClient;
import org.json.JSONException;
import org.json.JSONObject;
import android.util.Log;
public class JSONParser {
static InputStream is = null;
static JSONObject jObj = null;
static String json = "";
// constructor
public JSONParser() {
}
// function get json from url
// by making HTTP POST or GET mehtod
public JSONObject makeHttpRequest(String url, String method,
List<NameValuePair> params) {
// Making HTTP request
try {
// check for request method
if(method == "POST"){
// request method is POST
// defaultHttpClient
DefaultHttpClient httpClient = new DefaultHttpClient();
HttpPost httpPost = new HttpPost(url);
httpPost.setEntity(new UrlEncodedFormEntity(params));
HttpResponse httpResponse = httpClient.execute(httpPost);
HttpEntity httpEntity = httpResponse.getEntity();
is = httpEntity.getContent();
}else if(method == "GET"){
// request method is GET
DefaultHttpClient httpClient = new DefaultHttpClient();
String paramString = URLEncodedUtils.format(params, "utf-8");
url += "?" + paramString;
HttpGet httpGet = new HttpGet(url);
HttpResponse httpResponse = httpClient.execute(httpGet);
HttpEntity httpEntity = httpResponse.getEntity();
is = httpEntity.getContent();
}
} catch (UnsupportedEncodingException e) {
e.printStackTrace();
} catch (ClientProtocolException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
try {
BufferedReader reader = new BufferedReader(new InputStreamReader(
is, "iso-8859-1"), 8);
StringBuilder sb = new StringBuilder();
String line = null;
while ((line = reader.readLine()) != null) {
sb.append(line + "\n");
}
is.close();
json = sb.toString();
} catch (Exception e) {
Log.e("Buffer Error", "Error converting result " + e.toString());
}
// try parse the string to a JSON object
try {
jObj = new JSONObject(json);
} catch (JSONException e) {
Log.e("JSON Parser", "Error parsing data " + e.toString());
}
// return JSON String
return jObj;
}
}
get_all_products.php
<?php
$response=array();
require_once('/db_connect.php');
$db= new DB_CONNECT();
$db->construct();
$db->connect();
$result=mysql_query("Select * from files") or die (mysql_error());
if(mysql_num_rows($result)>0)
{
$response["products"]=array();
while($row=mysql_fetch_array($result))
{
$product = array();
$product["pid"] = $row["id"];
$product["name"] = $row["name"];
// $product["price"] = $row["price"];
// $product["created_at"] = $row["created_at"];
// $product["updated_at"] = $row["updated_at"];
array_push($response["products"], $product);
}
$response["success"] = 1;
// echoing JSON response
echo json_encode($response);
} else {
// no products found
$response["success"] = 0;
$response["message"] = "No products found";
// echo no users JSON
echo json_encode($response);
}
?>
在堆栈跟踪上显示错误
03-11 06:59:32.493: E/AndroidRuntime(1488): FATAL EXCEPTION: AsyncTask #1
03-11 06:59:32.493: E/AndroidRuntime(1488): Process: com.example.energy, PID: 1488
03-11 06:59:32.493: E/AndroidRuntime(1488): java.lang.RuntimeException: An error occured while executing doInBackground()
03-11 06:59:32.493: E/AndroidRuntime(1488): at android.os.AsyncTask$3.done(AsyncTask.java:300)
03-11 06:59:32.493: E/AndroidRuntime(1488): at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:355)
03-11 06:59:32.493: E/AndroidRuntime(1488): at java.util.concurrent.FutureTask.setException(FutureTask.java:222)
03-11 06:59:32.493: E/AndroidRuntime(1488): at java.util.concurrent.FutureTask.run(FutureTask.java:242)
03-11 06:59:32.493: E/AndroidRuntime(1488): at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:231)
03-11 06:59:32.493: E/AndroidRuntime(1488): at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112)
03-11 06:59:32.493: E/AndroidRuntime(1488): at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587)
03-11 06:59:32.493: E/AndroidRuntime(1488): at java.lang.Thread.run(Thread.java:841)
03-11 06:59:32.493: E/AndroidRuntime(1488): Caused by: java.lang.NullPointerException
03-11 06:59:32.493: E/AndroidRuntime(1488): at com.example.energy.GetAll$LoadAllProducts.doInBackground(GetAll.java:131)
03-11 06:59:32.493: E/AndroidRuntime(1488): at com.example.energy.GetAll$LoadAllProducts.doInBackground(GetAll.java:1)
03-11 06:59:32.493: E/AndroidRuntime(1488): at android.os.AsyncTask$2.call(AsyncTask.java:288)
03-11 06:59:32.493: E/AndroidRuntime(1488): at java.util.concurrent.FutureTask.run(FutureTask.java:237)
03-11 06:59:32.493: E/AndroidRuntime(1488): ... 4 more
03-11 06:59:33.803: I/Choreographer(1488): Skipped 61 frames! The application may be doing too much work on its main thread.
03-11 06:59:34.703: I/Choreographer(1488): Skipped 56 frames! The application may be doing too much work on its main thread.
03-11 06:59:35.983: I/Choreographer(1488): Skipped 138 frames! The application may be doing too much work on its main thread.
03-11 06:59:38.313: I/Choreographer(1488): Skipped 240 frames! The application may be doing too much work on its main thread.
03-11 06:59:38.783: I/Choreographer(1488): Skipped 33 frames! The application may be doing too much work on its main thread.
03-11 06:59:40.323: E/WindowManager(1488): android.view.WindowLeaked: Activity com.example.energy.GetAll has leaked window com.android.internal.policy.impl.PhoneWindow$DecorView{b1d86d70 V.E..... R.....ID 0,0-684,192} that was originally added here
03-11 06:59:40.323: E/WindowManager(1488): at android.view.ViewRootImpl.<init>(ViewRootImpl.java:346)
03-11 06:59:40.323: E/WindowManager(1488): at android.view.WindowManagerGlobal.addView(WindowManagerGlobal.java:248)
03-11 06:59:40.323: E/WindowManager(1488): at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:69)
03-11 06:59:40.323: E/WindowManager(1488): at android.app.Dialog.show(Dialog.java:286)
03-11 06:59:40.323: E/WindowManager(1488): at com.example.energy.GetAll$LoadAllProducts.onPreExecute(GetAll.java:118)
03-11 06:59:40.323: E/WindowManager(1488): at android.os.AsyncTask.executeOnExecutor(AsyncTask.java:587)
03-11 06:59:40.323: E/WindowManager(1488): at android.os.AsyncTask.execute(AsyncTask.java:535)
03-11 06:59:40.323: E/WindowManager(1488): at com.example.energy.GetAll.onCreate(GetAll.java:58)
03-11 06:59:40.323: E/WindowManager(1488): at android.app.Activity.performCreate(Activity.java:5231)
03-11 06:59:40.323: E/WindowManager(1488): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
03-11 06:59:40.323: E/WindowManager(1488): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2148)
03-11 06:59:40.323: E/WindowManager(1488): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2233)
03-11 06:59:40.323: E/WindowManager(1488): at android.app.ActivityThread.access$800(ActivityThread.java:135)
03-11 06:59:40.323: E/WindowManager(1488): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
03-11 06:59:40.323: E/WindowManager(1488): at android.os.Handler.dispatchMessage(Handler.java:102)
03-11 06:59:40.323: E/WindowManager(1488): at android.os.Looper.loop(Looper.java:136)
03-11 06:59:40.323: E/WindowManager(1488): at android.app.ActivityThread.main(ActivityThread.java:5001)
03-11 06:59:40.323: E/WindowManager(1488): at java.lang.reflect.Method.invokeNative(Native Method)
03-11 06:59:40.323: E/WindowManager(1488): at java.lang.reflect.Method.invoke(Method.java:515)
03-11 06:59:40.323: E/WindowManager(1488): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785)
03-11 06:59:40.323: E/WindowManager(1488): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601)
03-11 06:59:40.323: E/WindowManager(1488): at dalvik.system.NativeStart.main(Native Method)
03-11 06:59:40.333: I/Choreographer(1488): Skipped 50 frames! The application may be doing too much work on its main thread.
03-11 07:04:14.003: I/Process(1488): Sending signal. PID: 1488 SIG: 9
答案 0 :(得分：0)
这清楚地表明您的Json值返回null。因此，您需要调试整个项目。
die(json_encode($response));，如果回应它。params[]中使用AsyncTask。当您在任何地方调用继承的AsyncTask和Log时，请传递您的数据。因为，你的Log返回一个空指针，我认为你的Parser或你的Php脚本中有一个逻辑错误。
P.S ：这可能需要一段时间，但是一步一步地做，肯定会给你带来一些成熟的成果。