我正在关注andorid开发指南，并且在尝试注册帐户时似乎越来越错误，我知道问题和位置（第197行）但我似乎无法解决问题 请在下面找到logcat和我的注册码的副本，如果您需要更多信息，请发表评论，我会尽力帮助。
04-24 21:24:32.735: E/AndroidRuntime(30368): FATAL EXCEPTION: main
04-24 21:24:32.735: E/AndroidRuntime(30368): java.lang.NullPointerException
04-24 21:24:32.735: E/AndroidRuntime(30368): at com.loggedin.Register$ProcessRegister.onPostExecute(Register.java:197)
04-24 21:24:32.735: E/AndroidRuntime(30368): at com.loggedin.Register$ProcessRegister.onPostExecute(Register.java:1)
04-24 21:24:32.735: E/AndroidRuntime(30368): at android.os.AsyncTask.finish(AsyncTask.java:631)
04-24 21:24:32.735: E/AndroidRuntime(30368): at android.os.AsyncTask.access$600(AsyncTask.java:177)
04-24 21:24:32.735: E/AndroidRuntime(30368): at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:644)
04-24 21:24:32.735: E/AndroidRuntime(30368): at android.os.Handler.dispatchMessage(Handler.java:99)
04-24 21:24:32.735: E/AndroidRuntime(30368): at android.os.Looper.loop(Looper.java:176)
04-24 21:24:32.735: E/AndroidRuntime(30368): at android.app.ActivityThread.main(ActivityThread.java:5419)
04-24 21:24:32.735: E/AndroidRuntime(30368): at java.lang.reflect.Method.invokeNative(Native Method)
04-24 21:24:32.735: E/AndroidRuntime(30368): at java.lang.reflect.Method.invoke(Method.java:525)
04-24 21:24:32.735: E/AndroidRuntime(30368): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1046)
04-24 21:24:32.735: E/AndroidRuntime(30368): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:862)
04-24 21:24:32.735: E/AndroidRuntime(30368): at dalvik.system.NativeStart.main(Native Method)
04-24 21:25:05.435: I/Process(30368): Sending signal. PID: 30368 SIG: 9
注册java
import android.app.Activity;
import android.app.ProgressDialog;
import android.content.Context;
import android.content.Intent;
import android.net.ConnectivityManager;
import android.net.NetworkInfo;
import android.os.AsyncTask;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;
import com.loggedin.internal.DatabaseHandler;
import com.loggedin.internal.UserFunctions;
import org.json.JSONException;
import org.json.JSONObject;
import java.io.IOException;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
public class Register extends Activity {
/**
* JSON Response node names.
**/
private static String KEY_SUCCESS = "success";
private static String KEY_UID = "id";
private static String KEY_FIRSTNAME = "FirstName";
private static String KEY_LASTNAME = "LastName";
private static String KEY_USERNAME = "Username";
private static String KEY_EMAIL = "email";
private static String KEY_DOB = "DOB";
private static String KEY_CREATED_AT = "created_at";
private static String KEY_ERROR = "error";
/**
* Defining layout items.
**/
EditText inputFirstName;
EditText inputLastName;
EditText inputUsername;
EditText inputEmail;
EditText inputDOB;
EditText inputPassword;
Button registerbtn;
TextView register_error;
/**
* Called when the activity is first created.
*/
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_register);
/**
* Defining all layout items
**/
inputFirstName = (EditText) findViewById(R.id.FirstName);
inputLastName = (EditText) findViewById(R.id.LastName);
inputUsername = (EditText) findViewById(R.id.Username);
inputEmail = (EditText) findViewById(R.id.email);
inputDOB = (EditText) findViewById(R.id.DOB);
inputPassword = (EditText) findViewById(R.id.Password);
registerbtn = (Button) findViewById(R.id.registerbtn);
register_error = (TextView) findViewById(R.id.register_error);
/**
* Button which Switches back to the login screen on clicked
**/
Button login = (Button) findViewById(R.id.bktologinbtn);
login.setOnClickListener(new View.OnClickListener() {
public void onClick(View view) {
Intent myIntent = new Intent(view.getContext(), Login.class);
startActivityForResult(myIntent, 0);
finish();
}
});
/**
* Register Button click event.
* A Toast is set to alert when the fields are empty.
* Another toast is set to alert Username must be 5 characters.
**/
registerbtn.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
if ( ( !inputUsername.getText().toString().equals("")) && ( !inputPassword.getText().toString().equals("")) && ( !inputFirstName.getText().toString().equals("")) && ( !inputLastName.getText().toString().equals("")) && ( !inputDOB.getText().toString().equals("")) && ( !inputEmail.getText().toString().equals("")) )
{
if ( inputUsername.getText().toString().length() > 5 ){
InternetAsync(view);
}
else
{
Toast.makeText(getApplicationContext(),
"Username should be minimum 5 characters", Toast.LENGTH_SHORT).show();
}
}
else
{
Toast.makeText(getApplicationContext(),
"One or more fields are empty", Toast.LENGTH_SHORT).show();
}
}
});
}
/**
* Async Task to check whether internet connection is working
**/
private class InternetCheck extends AsyncTask<String, Boolean, Boolean> {
private ProgressDialog nDialog;
@Override
protected void onPreExecute(){
super.onPreExecute();
nDialog = new ProgressDialog(Register.this);
nDialog.setMessage("Loading..");
nDialog.setTitle("Checking Network");
nDialog.setIndeterminate(false);
nDialog.setCancelable(true);
nDialog.show();
}
@Override
protected Boolean doInBackground(String... args){
/**
* Gets current device state and checks for working internet connection by trying Google.
**/
ConnectivityManager cm = (ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE);
NetworkInfo netInfo = cm.getActiveNetworkInfo();
if (netInfo != null && netInfo.isConnected()) {
try {
URL url = new URL("http://www.google.com");
HttpURLConnection urlc = (HttpURLConnection) url.openConnection();
urlc.setConnectTimeout(3000);
urlc.connect();
if (urlc.getResponseCode() == 200) {
return true;
}
} catch (MalformedURLException e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
return false;
}
@Override
protected void onPostExecute(Boolean th){
if(th == true){
nDialog.dismiss();
new ProcessRegister().execute();
}
else{
nDialog.dismiss();
register_error.setText("Error in Network Connection");
}
}
}
private class ProcessRegister extends AsyncTask <String, String, JSONObject>{
/**
* Defining Process dialog
**/
private ProgressDialog pDialog;
String email,Password,FirstName,LastName,DOB,Username;
@Override
protected void onPreExecute() {
super.onPreExecute();
inputUsername = (EditText) findViewById(R.id.Username);
inputPassword = (EditText) findViewById(R.id.Password);
FirstName = inputFirstName.getText().toString();
LastName = inputLastName.getText().toString();
email = inputEmail.getText().toString();
DOB = inputDOB.getText().toString();
Username= inputUsername.getText().toString();
Password = inputPassword.getText().toString();
pDialog = new ProgressDialog(Register.this);
pDialog.setTitle("Contacting Servers");
pDialog.setMessage("Registering ...");
pDialog.setIndeterminate(false);
pDialog.setCancelable(true);
pDialog.show();
}
@Override
protected JSONObject doInBackground(String... args) {
UserFunctions userFunction = new UserFunctions();
JSONObject json = userFunction.registerUser(FirstName, LastName, DOB, email, Username, Password);
return json;
}
@Override
protected void onPostExecute(JSONObject json) {
/**
* Checks for success message.
**/
if (json ==null){
}
try {
if (json.getString(KEY_SUCCESS) != null) {
register_error.setText("");
String res = json.getString(KEY_SUCCESS);
String red = json.getString(KEY_ERROR);
if(Integer.parseInt(res) == 1){
pDialog.setTitle("Getting Data");
pDialog.setMessage("Loading Info");
register_error.setText("Successfully Registered");
DatabaseHandler db = new DatabaseHandler(getApplicationContext());
JSONObject json_user = json.getJSONObject("user");
/**
* Removes all the previous data in the SQlite database
**/
UserFunctions logout = new UserFunctions();
logout.logoutUser(getApplicationContext());
db.addUser(json_user.getString(KEY_FIRSTNAME),json_user.getString(KEY_LASTNAME),json_user.getString(KEY_EMAIL),json_user.getString(KEY_USERNAME),json_user.getString(KEY_UID),json_user.getString(KEY_CREATED_AT));
/**
* Stores registered data in SQlite Database
* Launch Registered screen
**/
Intent registered = new Intent(getApplicationContext(), Registered.class);
/**
* Close all views before launching Registered screen
**/
registered.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
pDialog.dismiss();
startActivity(registered);
finish();
}
else if (Integer.parseInt(red) ==2){
pDialog.dismiss();
register_error.setText("User already exists");
}
else if (Integer.parseInt(red) ==3){
pDialog.dismiss();
register_error.setText("Invalid Email id");
}
}
else{
pDialog.dismiss();
register_error.setText("Error occured in registration");
}
} catch (JSONException e) {
e.printStackTrace();
}
}
}
public void InternetAsync(View view){
new InternetCheck().execute();
}
}
答案 0 :(得分：1)
我可以看到三种可能性：
if (json ==null){
}
这没有做任何事情，json可以为null和
json.getString(KEY_SUCCESS)
可能是罪魁祸首。
另一种可能是 pDialog 或 register_error 。确保在引用之前检查每个资源，你可以看到每个人猜测它是哪一个。
事实上，NPE是最常见的异常之一，所以请确保在使用之前验证数据，这样可以避免一些麻烦。
解决方案：
if (json ==null){
return; //You can potentially Log the error too, if it helps.
}
OR
if(json != null) {
try{
if (json.getString(KEY_SUCCESS) != null) {
//...
}
另外，添加以下检查：
if(pDialog != null) {
//Manipulate the element to do what you want.
}
和
if(register_error != null) {
//Manipulate the element to do what you want.
}
答案 1 :(得分：0)
似乎json对象为null。你应该以正确的方式处理它。现在你只是忽略它。这里：
/**
* Checks for success message.
**/
if (json ==null){
return; // <-- just a sample, handle null in yuor way, don't ignore it
}