大家好日子。
我正在创建一个社交Android应用程序，用于为熟练技术人员发布服务。在我们的大学里才华横溢。我使用Android的传统语言：Java和XML。
但是每当我在CreateOfferActivity中调用createOffer方法时，应用程序崩溃而不会产生任何异常，只需重新启动即可。
这里是CreateOfferActivity的代码：
package com.italent.italent;
import android.app.ProgressDialog;
import android.content.Context;
import android.content.Intent;
import android.content.SharedPreferences;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.util.Log;
import android.view.View;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Spinner;
import android.widget.Toast;
import com.android.volley.Request;
import com.android.volley.Response;
import com.android.volley.VolleyError;
import com.android.volley.toolbox.StringRequest;
import org.json.JSONException;
import org.json.JSONObject;
import java.text.DateFormat;
import java.util.Date;
import java.util.HashMap;
import java.util.Map;
public class CreateOfferActivity extends AppCompatActivity {
private EditText offerTitle;
private EditText offerDesc;
private EditText offerMinPrice;
private EditText offerMaxPrice;
private Spinner offerCategory;
private Button crtOffer;
String offCategory;
String imagePath;
public double minPrice;
public double maxPrice;
private static final String TAG = "CreateOfferActivity";
private static final String URL_FOR_CREATING_OFFER = "https://*****/create_offer.php";
ProgressDialog progressDialog;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_create_offer);
offerTitle = (EditText) findViewById(R.id.etOfferTitle);
offerDesc = (EditText) findViewById(R.id.etOfferDesc);
offerMinPrice = (EditText) findViewById(R.id.etMinPrice);
offerMaxPrice = (EditText) findViewById(R.id.etMaxPrice);
offerCategory = (Spinner) findViewById(R.id.spCategories);
crtOffer = (Button) findViewById(R.id.bCreateOffer);
ArrayAdapter<CharSequence> arrAdapter = ArrayAdapter.createFromResource(this,
R.array.category_Array, android.R.layout.simple_spinner_item);
// Specify the layout to use when the list of choices appears
arrAdapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
// Apply the adapter to the spinner
offerCategory.setAdapter(arrAdapter);
//Create Offer button onClick listener
crtOffer.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
submitOfferForm();
Toast.makeText(CreateOfferActivity.this, "It works...", Toast.LENGTH_LONG).show();
}
});
}
private void submitOfferForm() {
String offTitle = offerTitle.getText().toString();
String offDesc = offerDesc.getText().toString();
//////////Replace image path later with a valid one
imagePath = "Some Image Path";
offCategory = offerCategory.getSelectedItem().toString();
//getting sharedPreferences file named userInfo to retrieve MemberName, Username and branch
SharedPreferences sharedPreferences = getSharedPreferences("userInfo", Context.MODE_PRIVATE);
String ofMName = sharedPreferences.getString("MemberName:", "");
String ofUName = sharedPreferences.getString("UserName:", "");
String ofBranch = sharedPreferences.getString("Branch:", "");
String mnPri = " " + minPrice;
String mxPri = " " + maxPrice;
createOffer(ofMName, ofUName, offTitle, offDesc, ofBranch, mnPri, mxPri, imagePath, offCategory);
}
private void createOffer(final String oMName, final String oUName, final String oTitle, final String oText,
final String oBranch,final String oMinPri, final String oMaxPri, final String oImage, final String oCategory) {
// Tag used to cancel the request
String cancel_req_tag = "offer";
progressDialog.setMessage("Adding your offer...");
showDialog();
StringRequest strReq = new StringRequest(Request.Method.POST,
URL_FOR_CREATING_OFFER, new Response.Listener<String>() {
@Override
public void onResponse(String response) {
Log.d(TAG, "Offer Response: " + response.toString());
hideDialog();
try {
JSONObject jObj = new JSONObject(response);
boolean error = jObj.getBoolean("error");
if (!error) { // error is set to false, meaning no error
//String user = jObj.getJSONObject("offer").getString("name");
Toast.makeText(CreateOfferActivity.this, "Your Offer has been created!", Toast.LENGTH_SHORT).show();
// Launch Home activity
Intent HomeIntent = new Intent(CreateOfferActivity.this, HomeActivity.class);
startActivity(HomeIntent);
finish();
} else {
String errorMsg = jObj.getString("error_msg");
Toast.makeText(CreateOfferActivity.this, errorMsg, Toast.LENGTH_LONG).show();
}
} catch (JSONException e) {
e.printStackTrace();
}
}
}, new Response.ErrorListener() {
@Override
public void onErrorResponse(VolleyError error) {
Log.e(TAG, "Error in creating offer: " + error.getMessage());
Toast.makeText(CreateOfferActivity.this,
error.getMessage(), Toast.LENGTH_LONG).show();
hideDialog();
}
}) {
@Override
protected Map<String, String> getParams() {
// Posting params to create offer url
Map<String, String> params = new HashMap<String, String>();
params.put("offerMemberName", oMName);
params.put("offerUserName", oUName);
params.put("offerTitle", oTitle);
params.put("OfferText", oText);
params.put("OfferBranch", oBranch);
params.put("OfferDateTime", DateFormat.getDateTimeInstance().format(new Date()));
params.put("OfferMinPrice", "" + oMinPri);
params.put("OfferMaxPrice", "" + oMaxPri);
params.put("OfferCategory", oCategory);
params.put("OfferImage", oImage);
return params;
}
};
// Adding request to request queue
AppSingleton.getInstance(getApplicationContext()).addToRequestQueue(strReq, cancel_req_tag);
}
private void showDialog() {
if (!progressDialog.isShowing())
progressDialog.show();
}
private void hideDialog() {
if (progressDialog.isShowing())
progressDialog.dismiss();
}
}
以及create_offer.php的代码
<?php
require_once 'update_user_info.php';
$db = new update_user_info();
// json response array
$response = array("error" => FALSE);
if (isset($_POST['offerTitle']) && isset($_POST['offerMname']) && isset($_POST['offerBranch']) && isset($_POST['offerText']) && isset($_POST['offerImageURL']) &&
isset($_POST['offerDateTime']) && isset($_POST['offerMinPrice']) && isset($_POST['offerMaxPrice']) && isset($_POST['offerCategory']) && isset($_POST['offerUname'])) {
// receiving the post params
$ofTitle = $_POST['offerTitle'];
$ofMName = $_POST['offerMname'];
$ofBranch = $_POST['offerBranch'];
$ofText = $_POST['offerText'];
$ofImageURL = $_POST['offerImageURL'];
$ofDateTime = $_POST['offerDateTime'];
$ofMinPri = $_POST['offerMinPrice'];
$ofMaxPri = $_POST['offerMaxPrice'];
$ofCategory = $_POST['offerCategory'];
$ofUName = $_POST['offerUname'];
// check if user is already existed with the same email
if (!($db->checkExistingUserThruUname($ofUName))) {
// user doesn't exist
$response["error"] = TRUE;
$response["error_msg"] = "Visitors cannot post an offer. Please register first.";
echo json_encode($response);
} else {
// create a new offer
$user = $db->storeOfferInfo($ofTitle, $ofMName, $ofBranch, $ofText, $ofImageURL, $ofDateTime, $ofMinPri, $ofMaxPri, $ofCategory, $ofUName);
if ($offer) {
// offer stored successfully
$response["error"] = FALSE;
$response["offer"]["offTitle"] = $offer["offTitle"];
$response["offer"]["offMname"] = $offer["offMname"];
$response["offer"]["offBranch"] = $offer["offBranch"];
$response["offer"]["offText"] = $offer["offText"];
$response["offer"]["offImageURL"] = $offer["offImageURL"];
$response["offer"]["offDateTime"] = $offer["offDateTime"];
$response["offer"]["offMinPrice"] = $offer["offMinPrice"];
$response["offer"]["offMaxPrice"] = $offer["offMaxPrice"];
$response["offer"]["offCategory"] = $offer["offCategory"];
$response["offer"]["offUname"] = $offer["offUname"];
echo json_encode($response);
} else {
// offer failed to store
$response["error"] = TRUE;
$response["error_msg"] = "Unknown error occurred in offer creation!";
echo json_encode($response);
}
}
} else {
$response["error"] = TRUE;
$response["error_msg"] = "A required field is missing!";
echo json_encode($response);
}
?>
这是Logcat：
04-22 03:24:38.950 27998-27998/com.italent.italent E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.italent.italent, PID: 27998
java.lang.NullPointerException: Attempt to invoke virtual method 'void android.app.ProgressDialog.setMessage(java.lang.CharSequence)' on a null object reference
at com.italent.italent.CreateOfferActivity.createOffer(CreateOfferActivity.java:122)
at com.italent.italent.CreateOfferActivity.submitOfferForm(CreateOfferActivity.java:113)
at com.italent.italent.CreateOfferActivity.access$000(CreateOfferActivity.java:30)
at com.italent.italent.CreateOfferActivity$1.onClick(CreateOfferActivity.java:86)
at android.view.View.performClick(View.java:5697)
at android.widget.TextView.performClick(TextView.java:10826)
at android.view.View$PerformClick.run(View.java:22526)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:158)
at android.app.ActivityThread.main(ActivityThread.java:7225)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120)
P.S。我使用几乎完全相同的java代码，PHP代码和数据库进行注册，它工作正常，但我无法找到它为什么不能使用这个类。
我感谢任何指导或帮助。谢谢！
答案 0 :(得分：1)
progressDialog变量未初始化。在您的活动onCreate()
ProgressDialog progressDialog = new ProgressDialog(this);