我正在创建一个酒店目录。当我点击酒店的列表项时，它显示列表，但是当我点击单个列表时，它崩溃并在方法doinbackground中的此文件中给出空指针异常。
在这个文件中我试图从数据库中获取每个酒店的数据。我在一个活动中输入酒店数据，它将保存到数据库并以list的形式显示。但是我点击每个列表项即ie hotel它应该显示酒店的详细信息，如位置和电话号码等。这是我的 EditProductActivity.java 代码：
import java.util.ArrayList;
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;
public class EditProductActivity extends Activity {
EditText txtName;
EditText txtPhone;
EditText txtMobile;
EditText txtDesc;
EditText txtCreatedAt;
Button btnSave;
Button btnDelete;
String pid;
// Progress Dialog
private ProgressDialog pDialog;
// JSON parser class
JSONParser jsonParser = new JSONParser();
// single product url
private static final String url_product_detials = "http://10.0.2.2/android_hive/get_product_details1.php";
// url to update product
private static final String url_update_product = "http://10.0.2.2/android_hive/update_product1.php";
// url to delete product
private static final String url_delete_product = "http://10.0.2.2/android_hive/delete_product1.php";
// JSON Node names
private static final String TAG_SUCCESS = "success";
private static final String TAG_PRODUCT = "product";
private static final String TAG_PID = "pid";
private static final String TAG_NAME = "name";
private static final String TAG_PRICE = "phone";
private static final String TAG_MOBILE = "mobile";
private static final String TAG_DESCRIPTION = "location";
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.edit_product);
// save button
btnSave = (Button) findViewById(R.id.btnSave);
btnDelete = (Button) findViewById(R.id.btnDelete);
// getting product details from intent
Intent i = getIntent();
// getting product id (pid) from intent
pid = i.getStringExtra(TAG_PID);
// Getting complete product details in background thread
new GetProductDetails().execute();
// save button click event
btnSave.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View arg0) {
// starting background task to update product
new SaveProductDetails().execute();
}
});
// Delete button click event
btnDelete.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View arg0) {
// deleting product in background thread
new DeleteProduct().execute();
}
});
}
/**
* Background Async Task to Get complete product details
* */
class GetProductDetails extends AsyncTask<String, String, String> {
/**
* Before starting background thread Show Progress Dialog
* */
@Override
protected void onPreExecute() {
super.onPreExecute();
pDialog = new ProgressDialog(EditProductActivity.this);
pDialog.setMessage("Loading hotel details. Please wait...");
pDialog.setIndeterminate(false);
pDialog.setCancelable(true);
pDialog.show();
}
/**
* Getting product 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("pid", pid));
// getting product details by making HTTP request
// Note that product details url will use GET request
JSONObject json = jsonParser.makeHttpRequest(
url_product_detials, "GET", params);
// check your log for json response
Log.d("Single Product Details", json.toString());
// json success tag
success = json.getInt(TAG_SUCCESS);
if (success == 1) {
// successfully received product details
JSONArray productObj = json
.getJSONArray(TAG_PRODUCT); // JSON Array
// get first product object from JSON Array
JSONObject product = productObj.getJSONObject(0);
// hotel with this pid found
// Edit Text
txtName = (EditText) findViewById(R.id.inputName);
txtPhone = (EditText) findViewById(R.id.inputPrice);
txtMobile = (EditText) findViewById(R.id.inputMobile);
txtDesc = (EditText) findViewById(R.id.inputDesc);
// display product data in EditText
txtName.setText(product.getString(TAG_NAME));
txtPhone.setText(product.getString(TAG_PRICE));
txtMobile.setText(product.getString(TAG_MOBILE));
txtDesc.setText(product.getString(TAG_DESCRIPTION));
}else{
// product with pid 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 product Details
* */
class SaveProductDetails extends AsyncTask<String, String, String> {
/**
* Before starting background thread Show Progress Dialog
* */
@Override
protected void onPreExecute() {
super.onPreExecute();
pDialog = new ProgressDialog(EditProductActivity.this);
pDialog.setMessage("Saving product ...");
pDialog.setIndeterminate(false);
pDialog.setCancelable(true);
pDialog.show();
}
/**
* Saving product
* */
protected String doInBackground(String... args) {
// getting updated data from EditTexts
String name = txtName.getText().toString();
String phone = txtPhone.getText().toString();
String mobile = txtMobile.getText().toString();
String location = txtDesc.getText().toString();
// Building Parameters
List<NameValuePair> params = new ArrayList<NameValuePair>();
params.add(new BasicNameValuePair(TAG_PID, pid));
params.add(new BasicNameValuePair(TAG_NAME, name));
params.add(new BasicNameValuePair(TAG_PRICE, phone));
params.add(new BasicNameValuePair(TAG_MOBILE, mobile));
params.add(new BasicNameValuePair(TAG_DESCRIPTION, location));
// sending modified data through http request
// Notice that update product 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 product update
setResult(100, i);
finish();
} else {
// failed to update product
}
} 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 product uupdated
pDialog.dismiss();
}
}
/*****************************************************************
* Background Async Task to Delete Product
* */
class DeleteProduct extends AsyncTask<String, String, String> {
/**
* Before starting background thread Show Progress Dialog
* */
@Override
protected void onPreExecute() {
super.onPreExecute();
pDialog = new ProgressDialog(EditProductActivity.this);
pDialog.setMessage("Deleting Product...");
pDialog.setIndeterminate(false);
pDialog.setCancelable(true);
pDialog.show();
}
/**
* Deleting product
* */
protected String doInBackground(String... args) {
// Check for success tag
int success;
try {
// Building Parameters
List<NameValuePair> params = new ArrayList<NameValuePair>();
params.add(new BasicNameValuePair("pid", pid));
// getting product details by making HTTP request
JSONObject json = jsonParser.makeHttpRequest(
url_delete_product, "POST", params);
// check your log for json response
Log.d("Delete Product", json.toString());
// json success tag
success = json.getInt(TAG_SUCCESS);
if (success == 1) {
// product successfully deleted
// notify previous activity by sending code 100
Intent i = getIntent();
// send result code 100 to notify about product 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 product deleted
pDialog.dismiss();
}
}
}
我使用数据库和WAMP服务器从php获取数据。实际上这个文件必须显示一个编辑屏幕，如果我想我可以进行更改或保存或使用按钮删除它。 我的PHP代码是：
<?php
/*
* Following code will get single product details
* A product is identified by product id (pid)
*/
// array for JSON response
$response = array();
// include db connect class
require_once __DIR__ . '/db_connect1.php';
// connecting to db
$db = new DB_CONNECT();
// check for post data
if (isset($_GET["pid"])) {
$pid = $_GET['pid'];
// get a product from products table
$result = mysql_query("SELECT *FROM info WHERE pid = $pid");
if (!empty($result)) {
// check for empty result
if (mysql_num_rows($result) > 0) {
$result = mysql_fetch_array($result);
$product = array();
$product["pid"] = $result["pid"];
$product["name"] = $result["name"];
$product["phone"] = $result["phone"];
$product["mobile"] = $result["mobile"];
$product["location"] = $result["location"];
$product["created_at"] = $result["created_at"];
$product["updated_at"] = $result["updated_at"];
// success
$response["success"] = 1;
// user node
$response["product"] = array();
array_push($response["product"], $product);
// echoing JSON response
echo json_encode($response);
} else {
// no product found
$response["success"] = 0;
$response["message"] = "No product found";
// echo no users JSON
echo json_encode($response);
}
} else {
// no product found
$response["success"] = 0;
$response["message"] = "No product found";
// echo no users JSON
echo json_encode($response);
}
} else {
// required field is missing
$response["success"] = 0;
$response["message"] = "Required field(s) is missing";
// echoing JSON response
echo json_encode($response);
}
?>
这是一个php代码，通过url.i链接到上面的java代码我使用json解析器作为辅助类来建立到数据库和服务器的http连接 请任何人都可以帮助我，并告诉我我的应用程序崩溃
答案 0 :(得分：0)
你的问题是：
txtName = (EditText) findViewById(R.id.inputName);
txtPhone = (EditText) findViewById(R.id.inputPrice);
txtMobile = (EditText) findViewById(R.id.inputMobile);
txtDesc = (EditText) findViewById(R.id.inputDesc);
// display product data in EditText
txtName.setText(product.getString(TAG_NAME));
txtPhone.setText(product.getString(TAG_PRICE));
txtMobile.setText(product.getString(TAG_MOBILE));
txtDesc.setText(product.getString(TAG_DESCRIPTION));
您需要将它们移至onPostExecute()您无法在doInBackground
所以看起来应该是这样的：
protected void onPostExecute(String file_url) {
// dismiss the dialog once got all details
pDialog.dismiss();
txtName = (EditText) findViewById(R.id.inputName);
txtPhone = (EditText) findViewById(R.id.inputPrice);
txtMobile = (EditText) findViewById(R.id.inputMobile);
txtDesc = (EditText) findViewById(R.id.inputDesc);
// display product data in EditText
txtName.setText(product.getString(TAG_NAME));
txtPhone.setText(product.getString(TAG_PRICE));
txtMobile.setText(product.getString(TAG_MOBILE));
txtDesc.setText(product.getString(TAG_DESCRIPTION));
}
您可能需要考虑将JSONObject product作为全局变量，以便可以在doInBackground和onPostExecute中访问它。