空对象引用错误：使用SQLite

时间：2015-05-12 01:35:13

标签： android sqlite android-volley

所以我试图改编本教程：http://www.androidhive.info/2012/01/android-login-and-registration-with-php-mysql-and-sqlite/

到我自己的项目。这是一个基本的寄存器＆amp;使用SQLite＆amp; amp;登录Android / Java通过PHP排到SQL服务器。 我可以把教程写成书面工作没问题。然而，在将它转移到我的项目时，我遇到了崩溃; 

05-12 01:18:05.763    1965-1965/com.disclosure_scots.disclosure_scots E/AndroidRuntime? FATAL EXCEPTION: main
Process: com.disclosure_scots.disclosure_scots, PID: 1965
java.lang.NullPointerException: Attempt to invoke virtual method 'void com.disclosure_scots.disclosure_scots.AppController.addToRequestQueue(com.android.volley.Request, java.lang.String)' on a null object reference
        at com.disclosure_scots.disclosure_scots.RegisterActivity.registerUser(RegisterActivity.java:194)
        at com.disclosure_scots.disclosure_scots.RegisterActivity.access$300(RegisterActivity.java:34)
        at com.disclosure_scots.disclosure_scots.RegisterActivity$1.onClick(RegisterActivity.java:90)
        at android.view.View.performClick(View.java:4780)
        at android.view.View$PerformClick.run(View.java:19866)
        at android.os.Handler.handleCallback(Handler.java:739)
        at android.os.Handler.dispatchMessage(Handler.java:95)
        at android.os.Looper.loop(Looper.java:135)
        at android.app.ActivityThread.main(ActivityThread.java:5257)
        at java.lang.reflect.Method.invoke(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:372)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)

它引用的RegisterActivity中的行也是; 

AppController.getInstance().addToRequestQueue(strReq, tag_string_req);
    }

所涉及的活动是;

RegisterActivity 

    package com.disclosure_scots.disclosure_scots;

import android.app.ProgressDialog;
import android.content.Intent;
import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.Menu;
import android.view.MenuItem;

import com.disclosure_scots.disclosure_scots.AppConfig;
import com.disclosure_scots.disclosure_scots.AppController;
import com.disclosure_scots.disclosure_scots.SQLiteHandler;
import com.disclosure_scots.disclosure_scots.SessionManager;

import org.json.JSONException;
import org.json.JSONObject;

import java.util.HashMap;
import java.util.Map;

import android.view.View;
import android.widget.Button;
import android.widget.CheckBox;
import android.widget.EditText;
import android.widget.Toast;

import com.android.volley.Request.Method;
import com.android.volley.Response;
import com.android.volley.VolleyError;
import com.android.volley.toolbox.StringRequest;


public class RegisterActivity extends ActionBarActivity {

    private static final String TAG = RegisterActivity.class.getSimpleName();
    private Button btnRegister;
    private EditText inputFullName;
    private EditText inputEmail;
    private EditText inputPassword;
    private EditText inputTel_No;
    private EditText inputHome_Add;
    private EditText inputPostcode;
    private CheckBox inputPostal;
    private ProgressDialog pDialog;
    private SessionManager session;
    private SQLiteHandler db;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_register);

        inputFullName = (EditText) findViewById(R.id.editTextName);
        inputEmail = (EditText) findViewById(R.id.editTextEmail);
        inputPassword = (EditText) findViewById(R.id.editTextPass);
        inputTel_No = (EditText) findViewById(R.id.editTextPhone);
        inputHome_Add = (EditText) findViewById(R.id.editTextPost);
        inputPostcode = (EditText) findViewById(R.id.editTextPostcode);
        inputPostal = (CheckBox) findViewById(R.id.PostalcheckBox);
        btnRegister = (Button) findViewById(R.id.btnRegister);

        // Progress dialog
        pDialog = new ProgressDialog(this);
        pDialog.setCancelable(false);

        // Session manager
        session = new SessionManager(getApplicationContext());

        // SQLite database handler
        db = new SQLiteHandler(getApplicationContext());

        // Check if user is already logged in or not
        if (session.isLoggedIn()) {
            // User is already logged in. Take him to Legal disclaimer activity
            Intent intent = new Intent(RegisterActivity.this,
                    LegalDiscActivity.class);
            startActivity(intent);
            finish();
        }

        // Register Button Click event
        btnRegister.setOnClickListener(new View.OnClickListener() {
            public void onClick(View view) {
                String name = inputFullName.getText().toString();
                String email = inputEmail.getText().toString();
                String password = inputPassword.getText().toString();

                if (!name.isEmpty() && !email.isEmpty() && !password.isEmpty()) {
                    registerUser(name, email, password);
                } else {
                    Toast.makeText(getApplicationContext(),
                            "Please enter your details!", Toast.LENGTH_LONG)
                            .show();
                }
            }
        });

        // Link to Login Screen
        /*btnLinkToLogin.setOnClickListener(new View.OnClickListener() {

            public void onClick(View view) {
                Intent i = new Intent(getApplicationContext(),
                        LoginActivity.class);
                startActivity(i);
                finish();
            }
        });*/

    }

    /**
     * Function to store user in MySQL database will post params(tag, name,
     * email, password) to register url
     * */
    private void registerUser(final String name, final String email,
                              final String password) {
        // Tag used to cancel the request
        String tag_string_req = "req_register";

        pDialog.setMessage("Registering ...");
        showDialog();

        StringRequest strReq = new StringRequest(Method.POST,
                AppConfig.URL_REGISTER, new Response.Listener<String>() {

            @Override
            public void onResponse(String response) {
                Log.d(TAG, "Register Response: " + response.toString());
                hideDialog();

                try {
                    JSONObject jObj = new JSONObject(response);
                    boolean error = jObj.getBoolean("error");
                    if (!error) {
                        // User successfully stored in MySQL
                        // Now store the user in sqlite
                        String uid = jObj.getString("uid");

                        JSONObject user = jObj.getJSONObject("user");
                        String name = user.getString("name");
                        String email = user.getString("email");
                        String created_at = user
                                .getString("created_at");

                        // Inserting row in users table
                        db.addUser(name, email, uid, created_at);

                        // Launch login activity
                        Intent intent = new Intent(
                                RegisterActivity.this,
                                LoginActivity.class);
                        startActivity(intent);
                        finish();
                    } else {

                        // Error occurred in registration. Get the error
                        // message
                        String errorMsg = jObj.getString("error_msg");
                        Toast.makeText(getApplicationContext(),
                                errorMsg, Toast.LENGTH_LONG).show();
                    }
                } catch (JSONException e) {
                    e.printStackTrace();
                }

            }
        }, new Response.ErrorListener() {

            @Override
            public void onErrorResponse(VolleyError error) {
                Log.e(TAG, "Registration Error: " + error.getMessage());
                Toast.makeText(getApplicationContext(),
                        error.getMessage(), Toast.LENGTH_LONG).show();
                hideDialog();
            }
        }) {

            @Override
            protected Map<String, String> getParams() {
                // Posting params to register url
                Map<String, String> params = new HashMap<String, String>();
                params.put("tag", "register");
                params.put("name", name);
                params.put("email", email);
                params.put("password", password);

                return params;
            }

        };

        // Adding request to request queue
        AppController.getInstance().addToRequestQueue(strReq, tag_string_req);
    }

    private void showDialog() {
        if (!pDialog.isShowing())
            pDialog.show();
    }

    private void hideDialog() {
        if (pDialog.isShowing())
            pDialog.dismiss();
    }


    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.menu_register, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }
}

AppController 类

    package com.disclosure_scots.disclosure_scots;

/**
 * Created by Administrator on 09/05/2015.
 */
import android.app.Application;
import android.text.TextUtils;

import com.android.volley.Request;
import com.android.volley.RequestQueue;
import com.android.volley.toolbox.Volley;

public class AppController extends Application {

    public static final String TAG = AppController.class.getSimpleName();

    private RequestQueue mRequestQueue;

    private static AppController mInstance;

    @Override
    public void onCreate() {
        super.onCreate();
        mInstance = this;
    }

    public static synchronized AppController getInstance() {
        return mInstance;
    }

    public RequestQueue getRequestQueue() {
        if (mRequestQueue == null) {
            mRequestQueue = Volley.newRequestQueue(getApplicationContext());
        }

        return mRequestQueue;
    }

    public <T> void addToRequestQueue(Request<T> req, String tag) {
        req.setTag(TextUtils.isEmpty(tag) ? TAG : tag);
        getRequestQueue().add(req);
    }

    public <T> void addToRequestQueue(Request<T> req) {
        req.setTag(TAG);
        getRequestQueue().add(req);
    }

    public void cancelPendingRequests(Object tag) {
        if (mRequestQueue != null) {
            mRequestQueue.cancelAll(tag);
        }
    }
}

我已多次使用它，但无法说明为什么我在复制版本中获取null对象而原始工作正常。 任何帮助表示赞赏。

2 个答案:

答案 0 :(得分：1)

这很可能是因为您没有在清单中注册AppController，因此getInstance返回null。

答案 1 :(得分：1)

你需要在你的清单中添加这一行（可能你错过了这一行，所以它返回空值）

<application
    android:name="(your app package).app.AppController" // <--this line
    android:allowBackup="true"
    android:icon="@mipmap/ic_launcher"
    android:label="@string/app_name"
   ...../>
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