AsyncTask doInBackground() 方法中的空指针异常
NullPointer Exception in AsyncTask's doInBackground() method
我正在尝试将从 Facebook api 获得的用户详细信息存储到数据库中，使用 php.I 使用 JSONParser class 来执行 POST which returns a JSON object.When 我从另一个 class 中的 AsyncTask 调用 JSONParser class 中的 makeHttpRequest 方法，我得到一个空指针 exception.I 检查我传递的任何参数是否为空，但它们不是也无法理解为什么我无法得到响应。我试图从 SO 中提出的类似问题中找到答案, 但它进入 vain.Kindly 帮助 me.Thanks
这是 class 中的 AsyncTask，它试图在 JSONparser class:
中调用 makeHTTPRequest 方法
private class CreateUser extends AsyncTask<String, String, String> {
@Override
protected void onPreExecute() {
super.onPreExecute();
// Log.d("email", email);
pDialog = new ProgressDialog(FbProfileActivity.this);
pDialog.setMessage("Creating User...");
pDialog.setIndeterminate(false);
pDialog.setCancelable(true);
pDialog.show();
}
@Override
protected String doInBackground(String... args) {
// TODO Auto-generated method stub
// Check for success tag
int success;
try {
// Building Parameters
// Log.d("param_username", username);
List<NameValuePair> params = new ArrayList<NameValuePair>();
params.add(new BasicNameValuePair("username", username));
// params.add(new BasicNameValuePair("age", age));
params.add(new BasicNameValuePair("gender",gender));
params.add(new BasicNameValuePair("email", email));
// params.add(new BasicNameValuePair("location", location));
Log.d("params","params" + params);
Log.d("JsonParser's URL", "params" +REGISTER_URL );
Log.d("request!", "starting",new Exception()); //Posting user data to script
JSONObject json = jsonParser.makeHttpRequest(REGISTER_URL, "POST", params);
// full json response
// Log.d("Registering attempt", json.toString());
// json success element
success = json.getInt(TAG_SUCCESS);
if (success == 1) {
Log.d("User Created", json.toString());
finish();
return json.getString(TAG_MESSAGE);
}else{
Log.d("Registering Failure!", json.getString(TAG_MESSAGE));
return json.getString(TAG_MESSAGE);
}
} catch (JSONException e) {
e.printStackTrace();
}
return null;
}
protected void onPostExecute(String file_url) {
// dismiss the dialog once product deleted
pDialog.dismiss();
if (file_url != null){
Toast.makeText(FbProfileActivity.this, file_url, Toast.LENGTH_LONG).show();
}
}
}
这是我得到空指针异常的行：
JSONObject json = jsonParser.makeHttpRequest(REGISTER_URL, "POST", params);
这是来自 JSONParser class 的 makeHttpRequest 方法：
public JSONObject makeHttpRequest(String url, String method,
List<NameValuePair> params) {
Log.d(TAG,"makeHttpRequest() is called");
// 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;
}
堆栈跟踪：
02-06 19:28:13.720: D/request!(2247): starting
02-06 19:28:13.720: D/request!(2247): java.lang.Exception
02-06 19:28:13.720: D/request!(2247): at com.example.letschatindia.FbProfileActivity$CreateUser.doInBackground(FbProfileActivity.java:448)
02-06 19:28:13.720: D/request!(2247): at com.example.letschatindia.FbProfileActivity$CreateUser.doInBackground(FbProfileActivity.java:1)
02-06 19:28:13.720: D/request!(2247): at android.os.AsyncTask.call(AsyncTask.java:288)
02-06 19:28:13.720: D/request!(2247): at java.util.concurrent.FutureTask.run(FutureTask.java:237)
02-06 19:28:13.720: D/request!(2247): at android.os.AsyncTask$SerialExecutor.run(AsyncTask.java:231)
02-06 19:28:13.720: D/request!(2247): at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112)
02-06 19:28:13.720: D/request!(2247): at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587)
02-06 19:28:13.720: D/request!(2247): at java.lang.Thread.run(Thread.java:841)
02-06 19:28:13.721: W/dalvikvm(2247): threadid=19: thread exiting with uncaught exception (group=0x4165fd40)
02-06 19:28:13.723: E/AndroidRuntime(2247): FATAL EXCEPTION: AsyncTask #5
02-06 19:28:13.723: E/AndroidRuntime(2247): Process: com.example.letschatindia, PID: 2247
02-06 19:28:13.723: E/AndroidRuntime(2247): java.lang.RuntimeException: An error occured while executing doInBackground()
02-06 19:28:13.723: E/AndroidRuntime(2247): at android.os.AsyncTask.done(AsyncTask.java:300)
02-06 19:28:13.723: E/AndroidRuntime(2247): at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:355)
02-06 19:28:13.723: E/AndroidRuntime(2247): at java.util.concurrent.FutureTask.setException(FutureTask.java:222)
02-06 19:28:13.723: E/AndroidRuntime(2247): at java.util.concurrent.FutureTask.run(FutureTask.java:242)
02-06 19:28:13.723: E/AndroidRuntime(2247): at android.os.AsyncTask$SerialExecutor.run(AsyncTask.java:231)
02-06 19:28:13.723: E/AndroidRuntime(2247): at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112)
02-06 19:28:13.723: E/AndroidRuntime(2247): at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587)
02-06 19:28:13.723: E/AndroidRuntime(2247): at java.lang.Thread.run(Thread.java:841)
02-06 19:28:13.723: E/AndroidRuntime(2247): Caused by: java.lang.NullPointerException
02-06 19:28:13.723: E/AndroidRuntime(2247): at com.example.letschatindia.FbProfileActivity$CreateUser.doInBackground(FbProfileActivity.java:449)
02-06 19:28:13.723: E/AndroidRuntime(2247): at com.example.letschatindia.FbProfileActivity$CreateUser.doInBackground(FbProfileActivity.java:1)
02-06 19:28:13.723: E/AndroidRuntime(2247): at android.os.AsyncTask.call(AsyncTask.java:288)
02-06 19:28:13.723: E/AndroidRuntime(2247): at java.util.concurrent.FutureTask.run(FutureTask.java:237)
您的 jsonParser 为空。我看不到你在哪里实例化它，所以检查你的代码以避免在创建对象之前使用它。
我认为 jsonParser 是空的，在使用它之前必须实例化它。
我正在尝试将从 Facebook api 获得的用户详细信息存储到数据库中，使用 php.I 使用 JSONParser class 来执行 POST which returns a JSON object.When 我从另一个 class 中的 AsyncTask 调用 JSONParser class 中的 makeHttpRequest 方法，我得到一个空指针 exception.I 检查我传递的任何参数是否为空，但它们不是也无法理解为什么我无法得到响应。我试图从 SO 中提出的类似问题中找到答案, 但它进入 vain.Kindly 帮助 me.Thanks
这是 class 中的 AsyncTask，它试图在 JSONparser class:
中调用 makeHTTPRequest 方法private class CreateUser extends AsyncTask<String, String, String> {
@Override
protected void onPreExecute() {
super.onPreExecute();
// Log.d("email", email);
pDialog = new ProgressDialog(FbProfileActivity.this);
pDialog.setMessage("Creating User...");
pDialog.setIndeterminate(false);
pDialog.setCancelable(true);
pDialog.show();
}
@Override
protected String doInBackground(String... args) {
// TODO Auto-generated method stub
// Check for success tag
int success;
try {
// Building Parameters
// Log.d("param_username", username);
List<NameValuePair> params = new ArrayList<NameValuePair>();
params.add(new BasicNameValuePair("username", username));
// params.add(new BasicNameValuePair("age", age));
params.add(new BasicNameValuePair("gender",gender));
params.add(new BasicNameValuePair("email", email));
// params.add(new BasicNameValuePair("location", location));
Log.d("params","params" + params);
Log.d("JsonParser's URL", "params" +REGISTER_URL );
Log.d("request!", "starting",new Exception()); //Posting user data to script
JSONObject json = jsonParser.makeHttpRequest(REGISTER_URL, "POST", params);
// full json response
// Log.d("Registering attempt", json.toString());
// json success element
success = json.getInt(TAG_SUCCESS);
if (success == 1) {
Log.d("User Created", json.toString());
finish();
return json.getString(TAG_MESSAGE);
}else{
Log.d("Registering Failure!", json.getString(TAG_MESSAGE));
return json.getString(TAG_MESSAGE);
}
} catch (JSONException e) {
e.printStackTrace();
}
return null;
}
protected void onPostExecute(String file_url) {
// dismiss the dialog once product deleted
pDialog.dismiss();
if (file_url != null){
Toast.makeText(FbProfileActivity.this, file_url, Toast.LENGTH_LONG).show();
}
}
}
这是我得到空指针异常的行：
JSONObject json = jsonParser.makeHttpRequest(REGISTER_URL, "POST", params);
这是来自 JSONParser class 的 makeHttpRequest 方法：
public JSONObject makeHttpRequest(String url, String method,
List<NameValuePair> params) {
Log.d(TAG,"makeHttpRequest() is called");
// 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;
}
堆栈跟踪：
02-06 19:28:13.720: D/request!(2247): starting
02-06 19:28:13.720: D/request!(2247): java.lang.Exception
02-06 19:28:13.720: D/request!(2247): at com.example.letschatindia.FbProfileActivity$CreateUser.doInBackground(FbProfileActivity.java:448)
02-06 19:28:13.720: D/request!(2247): at com.example.letschatindia.FbProfileActivity$CreateUser.doInBackground(FbProfileActivity.java:1)
02-06 19:28:13.720: D/request!(2247): at android.os.AsyncTask.call(AsyncTask.java:288)
02-06 19:28:13.720: D/request!(2247): at java.util.concurrent.FutureTask.run(FutureTask.java:237)
02-06 19:28:13.720: D/request!(2247): at android.os.AsyncTask$SerialExecutor.run(AsyncTask.java:231)
02-06 19:28:13.720: D/request!(2247): at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112)
02-06 19:28:13.720: D/request!(2247): at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587)
02-06 19:28:13.720: D/request!(2247): at java.lang.Thread.run(Thread.java:841)
02-06 19:28:13.721: W/dalvikvm(2247): threadid=19: thread exiting with uncaught exception (group=0x4165fd40)
02-06 19:28:13.723: E/AndroidRuntime(2247): FATAL EXCEPTION: AsyncTask #5
02-06 19:28:13.723: E/AndroidRuntime(2247): Process: com.example.letschatindia, PID: 2247
02-06 19:28:13.723: E/AndroidRuntime(2247): java.lang.RuntimeException: An error occured while executing doInBackground()
02-06 19:28:13.723: E/AndroidRuntime(2247): at android.os.AsyncTask.done(AsyncTask.java:300)
02-06 19:28:13.723: E/AndroidRuntime(2247): at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:355)
02-06 19:28:13.723: E/AndroidRuntime(2247): at java.util.concurrent.FutureTask.setException(FutureTask.java:222)
02-06 19:28:13.723: E/AndroidRuntime(2247): at java.util.concurrent.FutureTask.run(FutureTask.java:242)
02-06 19:28:13.723: E/AndroidRuntime(2247): at android.os.AsyncTask$SerialExecutor.run(AsyncTask.java:231)
02-06 19:28:13.723: E/AndroidRuntime(2247): at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112)
02-06 19:28:13.723: E/AndroidRuntime(2247): at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587)
02-06 19:28:13.723: E/AndroidRuntime(2247): at java.lang.Thread.run(Thread.java:841)
02-06 19:28:13.723: E/AndroidRuntime(2247): Caused by: java.lang.NullPointerException
02-06 19:28:13.723: E/AndroidRuntime(2247): at com.example.letschatindia.FbProfileActivity$CreateUser.doInBackground(FbProfileActivity.java:449)
02-06 19:28:13.723: E/AndroidRuntime(2247): at com.example.letschatindia.FbProfileActivity$CreateUser.doInBackground(FbProfileActivity.java:1)
02-06 19:28:13.723: E/AndroidRuntime(2247): at android.os.AsyncTask.call(AsyncTask.java:288)
02-06 19:28:13.723: E/AndroidRuntime(2247): at java.util.concurrent.FutureTask.run(FutureTask.java:237)
您的 jsonParser 为空。我看不到你在哪里实例化它，所以检查你的代码以避免在创建对象之前使用它。
我认为 jsonParser 是空的，在使用它之前必须实例化它。