我的应用程序尝试从 mysql 数据库中检索数据时遇到问题。当我运行应用程序时，我收到一条我在 php 代码中创建的消息，上面写着“找不到学生”。这是java代码：
public class StudentEditAccount extends Activity {
EditText txtsid;
EditText txtfirstname;
EditText txtlastname;
EditText txtcoursecode;
EditText txtphonenumber;
EditText txtemail;
Button btnSave;
Button btnDelete;
String sid;
// Progress Dialog
private ProgressDialog pDialog;
// JSON parser class
JSONParser jsonParser = new JSONParser();
// single student url
private static final String url_product_detials = "http://10.0.2.2/example/get_product_details.php";
// url to update student
private static final String url_update_product = "http://10.0.2.2/example/update_product.php";
// url to delete student
private static final String url_delete_product = "http://10.0.2.2/example/delete_product.php";
// JSON Node names
private static final String TAG_SUCCESS = "success";
private static final String TAG_STUDENTS = "students";
private static final String TAG_SID = "sid";
private static final String TAG_FIRSTNAME = "firstname";
private static final String TAG_LASTNAME = "lastname";
private static final String TAG_COURSECODE = "coursecode";
private static final String TAG_PHONENUMBER = "phonenumber";
private static final String TAG_EMAIL = "email";
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.studenteditaccount);
// save button
btnSave = (Button) findViewById(R.id.btnSave);
btnDelete = (Button) findViewById(R.id.btnDelete);
// getting student details from intent
Intent i = getIntent();
// getting student id (id) from intent
sid = i.getStringExtra(TAG_SID);
// Getting complete student details in background thread
new GetStudentAccountDetails().execute();
// save button click event
btnSave.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
// starting background task to update student
new SaveStudentAccountDetails().execute();
}
});
// Delete button click event
btnDelete.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
// deleting student in background thread
new DeleteStudentAccount().execute();
}
});
}
/**
* Background Async Task to Get complete student details
* */
class GetStudentAccountDetails extends AsyncTask<String, String, String> {
/**
* Before starting background thread Show Progress Dialog
* */
@Override
protected void onPreExecute() {
super.onPreExecute();
pDialog = new ProgressDialog(StudentEditAccount.this);
pDialog.setMessage("Loading account details. Please wait...");
pDialog.setIndeterminate(false);
pDialog.setCancelable(true);
pDialog.show();
}
/**
* Getting student details in background thread
* */
protected String doInBackground(String... params) {
// updating UI from Background Thread
runOnUiThread(new Runnable() {
public void run() {
// Check for success tag
int success;
try {
// Building Parameters
List<NameValuePair> params = new ArrayList<NameValuePair>();
params.add(new BasicNameValuePair("sid", sid));
// getting student details by making HTTP request
// Note that student details url will use GET request
JSONObject json = jsonParser.makeHttpRequest(
url_product_detials, "GET", params);
// check your log for json response
Log.d("Single student Details", json.toString());
// json success tag
success = json.getInt(TAG_SUCCESS);
if (success == 1) {
// successfully received student details
JSONArray studentsObj = json
.getJSONArray(TAG_STUDENTS); // JSON Array
// get first student object from JSON Array
JSONObject students = studentsObj.getJSONObject(0);
// student with this sid found
// Edit Text
txtfirstname = (EditText) findViewById(R.id.inputfname);
txtlastname = (EditText) findViewById(R.id.inputlname);
txtcoursecode = (EditText) findViewById(R.id.inputcoursecode);
txtphonenumber = (EditText) findViewById(R.id.inputphonenumber);
txtemail = (EditText) findViewById(R.id.inputemail);
// display student data in EditText
txtfirstname.setText(students.getString(TAG_FIRSTNAME));
txtlastname.setText(students.getString(TAG_LASTNAME));
txtcoursecode.setText(students.getString(TAG_COURSECODE));
txtphonenumber.setText(students.getString(TAG_PHONENUMBER));
txtemail.setText(students.getString(TAG_EMAIL));
}else{
// student with sid not found
}
} catch (JSONException e) {
e.printStackTrace();
}
}
});
return null;
}
/**
* After completing background task Dismiss the progress dialog
* **/
protected void onPostExecute(String file_url) {
// dismiss the dialog once got all details
pDialog.dismiss();
}
}
/**
* Background Async Task to Save student Details
* */
class SaveStudentAccountDetails extends AsyncTask<String, String, String> {
/**
* Before starting background thread Show Progress Dialog
* */
@Override
protected void onPreExecute() {
super.onPreExecute();
pDialog = new ProgressDialog(StudentEditAccount.this);
pDialog.setMessage("Saving account ...");
pDialog.setIndeterminate(false);
pDialog.setCancelable(true);
pDialog.show();
}
/**
* Saving student
* */
protected String doInBackground(String... args) {
// getting updated data from EditTexts
String sid = txtsid.getText().toString();
String firstname = txtfirstname.getText().toString();
String lastname = txtlastname.getText().toString();
String coursecode = txtcoursecode.getText().toString();
String phonenumber = txtphonenumber.getText().toString();
String email = txtemail.getText().toString();
// Building Parameters
List<NameValuePair> params = new ArrayList<NameValuePair>();
params.add(new BasicNameValuePair(TAG_SID, sid));
params.add(new BasicNameValuePair(TAG_FIRSTNAME, firstname));
params.add(new BasicNameValuePair(TAG_LASTNAME, lastname));
params.add(new BasicNameValuePair(TAG_COURSECODE, coursecode));
params.add(new BasicNameValuePair(TAG_PHONENUMBER, phonenumber));
params.add(new BasicNameValuePair(TAG_EMAIL, email));
// sending modified data through http request
// Notice that update student url accepts POST method
JSONObject json = jsonParser.makeHttpRequest(url_update_product,
"POST", params);
// check json success tag
try {
int success = json.getInt(TAG_SUCCESS);
if (success == 1) {
// successfully updated
Intent i = getIntent();
// send result code 100 to notify about student update
setResult(100, i);
finish();
} else {
// failed to update student
}
} catch (JSONException e) {
e.printStackTrace();
}
return null;
}
/**
* After completing background task Dismiss the progress dialog
* **/
protected void onPostExecute(String file_url) {
// dismiss the dialog once student updated
pDialog.dismiss();
}
}
/*****************************************************************
* Background Async Task to Delete Product
* */
class DeleteStudentAccount extends AsyncTask<String, String, String> {
/**
* Before starting background thread Show Progress Dialog
* */
@Override
protected void onPreExecute() {
super.onPreExecute();
pDialog = new ProgressDialog(StudentEditAccount.this);
pDialog.setMessage("Deleting Account...");
pDialog.setIndeterminate(false);
pDialog.setCancelable(true);
pDialog.show();
}
/**
* Deleting student
* */
protected String doInBackground(String... args) {
// Check for success tag
int success;
try {
// Building Parameters
List<NameValuePair> params = new ArrayList<NameValuePair>();
params.add(new BasicNameValuePair("sid", sid));
// getting student details by making HTTP request
JSONObject json = jsonParser.makeHttpRequest(
url_delete_product, "POST", params);
// check your log for json response
Log.d("Delete student", json.toString());
// json success tag
success = json.getInt(TAG_SUCCESS);
if (success == 1) {
// student successfully deleted
// notify previous activity by sending code 100
Intent i = getIntent();
// send result code 100 to notify about student deletion
setResult(100, i);
finish();
}
} catch (JSONException e) {
e.printStackTrace();
}
return null;
}
/**
* After completing background task Dismiss the progress dialog
* **/
protected void onPostExecute(String file_url) {
// dismiss the dialog once student deleted
pDialog.dismiss();
}
}
}
这是PHP代码：
<?php
// array for JSON response
$response = array();
// include db connect class
require_once __DIR__ . '/db_connect.php';
// connecting to db
$db = new DB_CONNECT();
// check for post data
if (isset($_GET["sid"])) {
$sid = $_GET['sid'];
// get a students from student table
$result = mysql_query("SELECT *FROM student WHERE sid = $sid");
if (!empty($result)) {
// check for empty result
if (mysql_num_rows($result) > 0) {
$result = mysql_fetch_array($result);
$students = array();
$students["sid"] = $result["sid"];
$students["firstname"] = $result["firstname"];
$students["lastname"] = $result["lastname"];
$students["coursecode"] = $result["coursecode"];
$students["phonenumber"] = $result["phonenumber"];
$students["email"] = $result["email"];
// success
$response["success"] = 1;
// user node
$response["students"] = array();
array_push($response["students"], $students);
// echoing JSON response
echo json_encode($response);
} else {
// no student found
$response["success"] = 0;
$response["message"] = "No student found";
// echo no users JSON
echo json_encode($response);
}
} else {
// no student found
$response["success"] = 0;
$response["message"] = "No student found";
// echo no users JSON
echo json_encode($response);
}
} else {
// required field is missing
$response["success"] = 0;
$response["message"] = "Required field(s) is missing";
// echoing JSON response
echo json_encode($response);
}
?>
我的问题是：每次我尝试从 Mysql 数据库中检索数据时，导致应用程序显示消息“未找到学生”的问题是什么？谢谢你。