大家好，新年快乐，我正在尝试从 MySQL 数据库中获取数据并将其显示在我的 android 项目的 ListView 中。
这是主要活动的代码：
MainActivity.java
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import org.apache.http.NameValuePair;
import org.apache.http.message.BasicNameValuePair;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import android.app.Activity;
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.Button;
import android.widget.EditText;
import android.widget.ListView;
import android.widget.SimpleAdapter;
public class MainActivity extends Activity {
private ProgressDialog pDialog;
Button BTconnect;
EditText EDlogin;
EditText EDmdp;
private String login;
private String mdp;
private HDdb dbase;
private JSONParser jsonParser = new JSONParser();
public final static String EXTRA_MESSAGE="com.example.HDtesr.id";
private static String KEY_SUCCESS = "success";
private static String loginURL = "http://10.0.2.2/android_connect/identification.php";
private static final String TAG_CMDS = "commandes";
private static final String TAG_CLIENT = "client";
private static final String TAG_DEMANDE = "demande";
private static final String TAG_DATE = "date";
private static final String TAG_TIME = "time";
JSONArray cmds = null;
ArrayList<HashMap<String, String>> cmdsList;
private HashMap<String, String> map;
private ListView lv;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
BTconnect = (Button) findViewById(R.id.connect);
EDlogin = (EditText) findViewById(R.id.login);
EDmdp = (EditText) findViewById(R.id.mdp);
lv = (ListView) findViewById(R.id.list);
BTconnect.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
login = EDlogin.getText().toString();
mdp = EDmdp.getText().toString();
new Identify().execute();
}
});
}
class Identify extends AsyncTask<String, String, String> {
@Override
protected void onPreExecute() {
super.onPreExecute();
pDialog = new ProgressDialog(MainActivity.this);
pDialog.setMessage("Envoi en cours...");
pDialog.setIndeterminate(false);
pDialog.setCancelable(true);
pDialog.show();
}
protected String doInBackground(String... args) {
List<NameValuePair> params = new ArrayList<NameValuePair>();
params.add(new BasicNameValuePair("login", login));
params.add(new BasicNameValuePair("mdp", mdp));
JSONObject json = jsonParser.makeHttpRequest(loginURL,"POST", params);
// check log cat for response
Log.d("Create Response", json.toString());
// check for success tag
try {
int success = json.getInt(KEY_SUCCESS);
if(success == 1){
cmds = json.getJSONArray(TAG_CMDS);
for (int i = 0; i < cmds.length(); i++) {
JSONObject c = cmds.getJSONObject(i);
// Storing each json item in variable
String client = c.getString(TAG_CLIENT);
String demande = c.getString(TAG_DEMANDE);
String date = c.getString(TAG_DATE);
String time = c.getString(TAG_TIME);
map = new HashMap<String, String>();
// adding each child node to HashMap key => value
map.put(TAG_CLIENT, client);
// map.put(TAG_DEMANDE, demande);
map.put(TAG_DATE, date);
map.put(TAG_TIME, time);
cmdsList.add(map);
}
finish();
}else{
// Error in login
}
} catch (JSONException e) {
e.printStackTrace();
}
return null;
}
protected void onPostExecute(String file_url) {
// dismiss the dialog once done
pDialog.dismiss();
runOnUiThread(new Runnable() {
public void run() {
adapter = new SimpleAdapter(Commande.this, cmdsList,R.layout.menuitem,new String[] { TAG_DEMANDE,TAG_CLIENT,TAG_TIME},
new int[] { R.id.demande,R.id.client,R.id.time});
lv.setAdapter(adapter);
}
});
}
}
}
JSONParser.java
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() {
}
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;
}
}
LogCat 显示它收到了数据，然后显示 JAVA.NULLPOINTEREXCEPTION ！
01-01 14:51:31.541: E/AndroidRuntime(660): FATAL EXCEPTION: AsyncTask #1
01-01 14:51:31.541: E/AndroidRuntime(660): java.lang.RuntimeException: An error occured while executing doInBackground()
01-01 14:51:31.541: E/AndroidRuntime(660): at android.os.AsyncTask$3.done(AsyncTask.java:299)
01-01 14:51:31.541: E/AndroidRuntime(660): at java.util.concurrent.FutureTask$Sync.innerSetException(FutureTask.java:273)
01-01 14:51:31.541: E/AndroidRuntime(660): at java.util.concurrent.FutureTask.setException(FutureTask.java:124)
01-01 14:51:31.541: E/AndroidRuntime(660): at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:307)
01-01 14:51:31.541: E/AndroidRuntime(660): at java.util.concurrent.FutureTask.run(FutureTask.java:137)
01-01 14:51:31.541: E/AndroidRuntime(660): at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:230)
01-01 14:51:31.541: E/AndroidRuntime(660): at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1076)
01-01 14:51:31.541: E/AndroidRuntime(660): at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:569)
01-01 14:51:31.541: E/AndroidRuntime(660): at java.lang.Thread.run(Thread.java:856)
01-01 14:51:31.541: E/AndroidRuntime(660): Caused by: java.lang.NullPointerException
01-01 14:51:31.541: E/AndroidRuntime(660): at com.example.hd_test.MainActivity$Identify.doInBackground(MainActivity.java:95)
01-01 14:51:31.541: E/AndroidRuntime(660): at com.example.hd_test.MainActivity$Identify.doInBackground(MainActivity.java:1)
01-01 14:51:31.541: E/AndroidRuntime(660): at android.os.AsyncTask$2.call(AsyncTask.java:287)
01-01 14:51:31.541: E/AndroidRuntime(660): at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:305)
01-01 14:51:31.541: E/AndroidRuntime(660): ... 5 more