重写代码以避免 NetworkonMainThreadException

Question

我终于让我的登录应用程序与我的在线数据库一起运行。我跟着this 教程。在调试它并让它与我的在线 SQL dB 一起运行时，我通过将 minSDK 设置为“3”来避免 NetworkonMainThreadException 的问题。显然，当我将其恢复到 13+ 时，我再次收到错误消息。那么我怎样才能着手修改这些类以避免异常呢？看来我需要修改的不仅仅是一两个简单的方法，对吗？

除了LoginActivity之外，还有RegisterActivity和DashboardActivity，但是它们和LoginActivity非常相似。

登录活动：

package com.davekelley;

import java.util.HashMap;

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

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;

import library.DatabaseHandler;
import library.UserFunctions;

public class LoginActivity extends Activity {
    Button btnLogin;
    Button btnLinkToRegister;
    EditText inputEmail;
    EditText inputPassword;
    TextView loginErrorMsg;

    // JSON Response node names
    private static String KEY_SUCCESS = "success";
    private static String KEY_ERROR = "error";
    private static String KEY_ERROR_MSG = "error_msg";
    private static String KEY_UID = "uid";
    private static String KEY_NAME = "name";
    private static String KEY_EMAIL = "email";
    private static String KEY_CREATED_AT = "created_at";
    private String re;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.login);

        // Importing all assets like buttons, text fields
        inputEmail = (EditText) findViewById(R.id.loginEmail);
        inputPassword = (EditText) findViewById(R.id.loginPassword);
        btnLogin = (Button) findViewById(R.id.btnLogin);
        btnLinkToRegister = (Button) findViewById(R.id.btnLinkToRegisterScreen);
        loginErrorMsg = (TextView) findViewById(R.id.login_error);

        // Login button Click Event
        btnLogin.setOnClickListener(new View.OnClickListener() {

            public void onClick(View view) {
                String email = inputEmail.getText().toString();
                String password = inputPassword.getText().toString();
                UserFunctions userFunction = new UserFunctions();
                JSONObject json = userFunction.loginUser(email, password);

                // check for login response
                try {
                    if (json.getString(KEY_SUCCESS) != null) {
                        loginErrorMsg.setText("");

                        String res = json.getString(KEY_SUCCESS);
                        re = res;
                        if(Integer.parseInt(res) == 1){
                            // user successfully logged in
                            // Store user details in SQLite Database
                            DatabaseHandler db = new DatabaseHandler(getApplicationContext());
                            JSONObject json_user = json.getJSONObject("user");

                            // Clear all previous data in database
                            userFunction.logoutUser(getApplicationContext());
                            db.addUser(json_user.getString(KEY_NAME), json_user.getString(KEY_EMAIL), json.getString(KEY_UID), json_user.getString(KEY_CREATED_AT));                        

                            // Launch Dashboard Screen
                            Intent dashboard = new Intent(getApplicationContext(), DashboardActivity.class);

                            // Close all views before launching Dashboard
                            dashboard.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
                            startActivity(dashboard);

                            // Close Login Screen
                            finish();
                        }else{
                            // Error in login
                            loginErrorMsg.setText("Incorrect username/password");
                        }
                    }
                } catch (NullPointerException e) {
                    e.printStackTrace();

                    }
                catch (JSONException e) {
                    e.printStackTrace();
                }

            }
        });

        // Link to Register Screen
        btnLinkToRegister.setOnClickListener(new View.OnClickListener() {

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

用户功能：

package library;
import java.util.ArrayList;
import java.util.List;

import org.apache.http.NameValuePair;
import org.apache.http.message.BasicNameValuePair;
import org.json.JSONObject;

import android.content.Context;

public class UserFunctions {

    private JSONParser jsonParser;

    // Testing in localhost using wamp or xampp
    // use http://10.0.2.2/ to connect to your localhost ie http://localhost/
    private static String loginURL = "http://davidjkelley.net/android_api/";
    private static String registerURL = "http://davidjkelley.net/android_api/";

    private static String login_tag = "login";
    private static String register_tag = "register";

    // constructor
    public UserFunctions(){
        jsonParser = new JSONParser();
    }

    /**
     * function make Login Request
     * @param email
     * @param password
     * */
    public JSONObject loginUser(String email, String password){
        // Building Parameters
        List<NameValuePair> params = new ArrayList<NameValuePair>();
        params.add(new BasicNameValuePair("tag", login_tag));
        params.add(new BasicNameValuePair("email", email));
        params.add(new BasicNameValuePair("password", password));
        JSONObject json = jsonParser.getJSONFromUrl(loginURL, params);
        // return json
        // Log.e("JSON", json.toString());
        return json;
    }

    /**
     * function make Login Request
     * @param name
     * @param email
     * @param password
     * */
    public JSONObject registerUser(String name, String email, String password){
        // Building Parameters
        List<NameValuePair> params = new ArrayList<NameValuePair>();
        params.add(new BasicNameValuePair("tag", register_tag));
        params.add(new BasicNameValuePair("name", name));
        params.add(new BasicNameValuePair("email", email));
        params.add(new BasicNameValuePair("password", password));

        // getting JSON Object
        JSONObject json = jsonParser.getJSONFromUrl(registerURL, params);
        // return json
        return json;
    }

    /**
     * Function get Login status
     * */
    public boolean isUserLoggedIn(Context context){
        DatabaseHandler db = new DatabaseHandler(context);
        int count = db.getRowCount();
        if(count > 0){
            // user logged in
            return true;
        }
        return false;
    }

    /**
     * Function to logout user
     * Reset Database
     * */
    public boolean logoutUser(Context context){
        DatabaseHandler db = new DatabaseHandler(context);
        db.resetTables();
        return true;
    }

}

数据库处理程序：

package library;

import java.util.HashMap;

import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;

public class DatabaseHandler extends SQLiteOpenHelper {

    // All Static variables
    // Database Version
    private static final int DATABASE_VERSION = 1;

    // Database Name
    private static final String DATABASE_NAME = "android_api";

    // Login table name
    private static final String TABLE_LOGIN = "login";

    // Login Table Columns names
    private static final String KEY_ID = "id";
    private static final String KEY_NAME = "name";
    private static final String KEY_EMAIL = "email";
    private static final String KEY_UID = "uid";
    private static final String KEY_CREATED_AT = "created_at";

    public DatabaseHandler(Context context) {
        super(context, DATABASE_NAME, null, DATABASE_VERSION);
    }

    // Creating Tables
    @Override
    public void onCreate(SQLiteDatabase db) {
        String CREATE_LOGIN_TABLE = "CREATE TABLE " + TABLE_LOGIN + "("
                + KEY_ID + " INTEGER PRIMARY KEY,"
                + KEY_NAME + " TEXT,"
                + KEY_EMAIL + " TEXT UNIQUE,"
                + KEY_UID + " TEXT,"
                + KEY_CREATED_AT + " TEXT" + ")";
        db.execSQL(CREATE_LOGIN_TABLE);
    }

    // Upgrading database
    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        // Drop older table if existed
        db.execSQL("DROP TABLE IF EXISTS " + TABLE_LOGIN);

        // Create tables again
        onCreate(db);
    }

    /**
     * Storing user details in database
     * */
    public void addUser(String name, String email, String uid, String created_at) {
        SQLiteDatabase db = this.getWritableDatabase();

        ContentValues values = new ContentValues();
        values.put(KEY_NAME, name); // Name
        values.put(KEY_EMAIL, email); // Email
        values.put(KEY_UID, uid); // Email
        values.put(KEY_CREATED_AT, created_at); // Created At

        // Inserting Row
        db.insert(TABLE_LOGIN, null, values);
        db.close(); // Closing database connection
    }

    /**
     * Getting user data from database
     * */
    public HashMap<String, String> getUserDetails(){
        HashMap<String,String> user = new HashMap<String,String>();
        String selectQuery = "SELECT  * FROM " + TABLE_LOGIN;

        SQLiteDatabase db = this.getReadableDatabase();
        Cursor cursor = db.rawQuery(selectQuery, null);
        // Move to first row
        cursor.moveToFirst();
        if(cursor.getCount() > 0){
            user.put("name", cursor.getString(1));
            user.put("email", cursor.getString(2));
            user.put("uid", cursor.getString(3));
            user.put("created_at", cursor.getString(4));
        }
        cursor.close();
        db.close();
        // return user
        return user;
    }

    /**
     * Getting user login status
     * return true if rows are there in table
     * */
    public int getRowCount() {
        String countQuery = "SELECT  * FROM " + TABLE_LOGIN;
        SQLiteDatabase db = this.getReadableDatabase();
        Cursor cursor = db.rawQuery(countQuery, null);
        int rowCount = cursor.getCount();
        db.close();
        cursor.close();

        // return row count
        return rowCount;
    }

    /**
     * Re crate database
     * Delete all tables and create them again
     * */
    public void resetTables(){
        SQLiteDatabase db = this.getWritableDatabase();
        // Delete All Rows
        db.delete(TABLE_LOGIN, null, null);
        db.close();
    }

}

JSON解析器：

package library;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.UnsupportedEncodingException;
import java.util.List;

import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.NameValuePair;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.entity.UrlEncodedFormEntity;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.impl.client.DefaultHttpClient;
import org.json.JSONException;
import org.json.JSONObject;

import android.util.Log;

public class JSONParser {

    static InputStream is = null;
    static JSONObject jObj = null;
    static String json = "";

    // constructor
    public JSONParser() {

    }

    public JSONObject getJSONFromUrl(String url, List<NameValuePair> params) {

        // Making HTTP request
        try {
            // 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();

        } 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");
                Log.v("err", line);
            }
            is.close();
            json = sb.toString();
            //this is the error
            Log.e("JSON", "json");
        } 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;

    }
}

Answer 1

您不应该在主 (UI) 线程上执行任何需要大量时间或不确定时间的操作，例如联网。您将不得不修改您的源代码，因此每个网络活动都在不同的线程上。一个很好的解决方案是使用 AsyncTask。这样，每个查询或您想做的任何事情都会在后台执行，不会阻塞 UI，因此不会产生该异常。这里有详细说明：

http://developer.android.com/reference/android/os/AsyncTask.html

请注意，即使您成功地在 UI 线程上进行联网，您的应用也很可能会死机。