java - Android - 使用另一个 Activity 的变量

Question

我对 Android 很陌生，我想这是一个愚蠢的问题，但我很高兴获得帮助。我在一个 Activity 中有一段代码将数据库设置为 SQLite。在另一个 Activity 中，我想引用此 SQLite 代码，以便将其输入 json 并将其发送到远程服务器。

问题在于它无法识别来自其​​他 Activity 的变量。这是将数据库中的数据创建为字符串的代码。在这个例子中，我想从数据库创建一个ArrayList，但它找不到我开发的集合函数或表名。我是不是错过了什么？这是 ArrayList 的代码:

GpsPage.java

public class PersonsDatabaseHandler extends SQLiteOpenHelper {

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

        //Table names
        private static final TABLE_RECORD = "record";

        //Get all Persons
        public ArrayList<Record> getAllPersons() {
            ArrayList<Record> localList = new ArrayList<Record>();

            String selectQuery = "SELECT * FROM " + TABLE_RECORD;

            SQLiteDatabase db = this.getReadableDatabase();
            Cursor cursor = db.rawQuery(selectQuery, null);

            //Loops through all rows and adds them to the local list
            if(cursor.moveToFirst())
            {
                do {
                    //Get person information
                    Record record = new Record();
                    Record.setpLong(cursor.getString(0));
                    Record.setpLat(cursor.getString(1));
                    Record.setpAcc(cursor.getString(2));
                    Record.setpTime(cursor.getString(3));

                    //Add person to list
                    localList.add(record);
                } while (cursor.moveToNext());
            }

            return localList;
        }
    }

下面是其他两个 java 页面( Activity )的代码，第一个定义记录的获取和设置:

Record.Java

package com.program.android.taskir;


public class Record {

    //private variables
    private int id;
    private double pLong;
    private double pLat;
    private float pAcc;
    private long pTime;

    public Record(){}
    // Empty constructor

    // constructor
    public Record( double pLong, double pLat, float pAcc, long pTime){
        super();
        this.pLong = pLong;
        this.pLat= pLat;
        this.pAcc= pAcc;
        this.pTime= pTime;
    }

    @Override
    public String toString() {
        return "Record [id=" + id + ", Longtitude=" + pLong + ", Latitude=" + pLat + ", Accuracy" + pAcc + ", Time" +pTime
                + "]";
    }


    // getting ID
    public int getID(){
        return this.id;
    }

    // setting id
    public void setID(int id){
        this.id = id;
    }

    // getting pLong
    public double getpLong(){
        return this.pLong;
    }

    // setting pLong
    public void setpLong(double pLong){
        this.pLong = pLong;
    }

    // getting pLat
    public double getpLat(){
        return this.pLat;
    }

    // setting pLat
    public void setpLat(double pLat){
        this.pLat = pLat;
    }

    // getting pAcc
    public float getpAcc(){
        return this.pAcc;
    }

    // setting pAcc
    public void setpAcc(float pAcc){
        this.pAcc = pAcc;
    }

    // getting pTime
    public long getpTime(){
        return this.pTime;
    }

    // setting pTime
    public void setpTime(long pTime){
        this.pTime = pTime;
    }
}

以及创建数据库的 Activity :

MySQLiteHelper.java

package com.program.android.taskir;

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

import java.util.LinkedList;
import java.util.List;

public class MySQLiteHelper extends SQLiteOpenHelper {


    // Database Version
    private static final int DATABASE_VERSION = 1;

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

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

    @Override
    public void onCreate(SQLiteDatabase db) {
        // SQL statement to create record table
        String CREATE_RECORD_TABLE = "CREATE TABLE RECORD ( " +
                "id INTEGER PRIMARY KEY AUTOINCREMENT, " +
                "latitude TEXT NOT NULL, " +
                "longtitude TEXT NOT NULL, " +
                "accuracy TEXT NOT NULL, " +
                "time TEXT NOT NULL )";

        // create books table
        db.execSQL(CREATE_RECORD_TABLE);
    }


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

        // create fresh record table
        this.onCreate(db);
    }

    // Books table name
    private static final String TABLE_RECORD = "record";

    // Books Table Columns names
    private static final String KEY_ID = "id";
    private static final String KEY_LONG = "longtitude";
    private static final String KEY_LAT = "latitude";
    private static final String KEY_ACC = "accuracy";
    private static final String KEY_TIME = "time";

    private static final String[] COLUMNS = {KEY_ID, KEY_LONG, KEY_LAT, KEY_ACC, KEY_TIME};

    public void addRecord(Record record) {
        //for logging
        Log.d("addBook", record.toString());

        // 1. get reference to writable DB
        SQLiteDatabase db = this.getWritableDatabase();

        // 2. create ContentValues to add key "column"/value
        ContentValues values = new ContentValues();
        values.put(KEY_LONG, record.getpLong());
        values.put(KEY_LAT, record.getpLat());
        values.put(KEY_ACC, record.getpAcc());
        values.put(KEY_TIME, record.getpTime());

        // 3. insert
        db.insert(TABLE_RECORD, // table
                null, //nullColumnHack
                values); // key/value -> keys = column names/ values = column values

        // 4. close
        db.close();
    }

    public Record getRecord(int id) {

        // 1. get reference to readable DB
        SQLiteDatabase db = this.getReadableDatabase();

        // 2. build query
        Cursor cursor =
                db.query(TABLE_RECORD, // a. table
                        COLUMNS, // b. column names
                        " id = ?", // c. selections
                        new String[]{String.valueOf(id)}, // d. selections args
                        null, // e. group by
                        null, // f. having
                        null, // g. order by
                        null); // h. limit

        // 3. if we got results get the first one
        if (cursor != null)
            cursor.moveToFirst();

        // 4. build book object
        Record record = new Record();
        record.setID(Integer.parseInt(cursor.getString(0)));
        record.setpLat(cursor.getDouble(1));
        record.setpLong(cursor.getDouble(2));
        record.setpAcc(cursor.getFloat(2));
        record.setpTime(cursor.getLong(2));

        //log
        Log.d("getBook(" + id + ")", record.toString());

        // 5. return book
        return record;
    }

    public List<Record> getAllRecords() {
        List<Record> records = new LinkedList<Record>();

        // 1. build the query
        String query = "SELECT  * FROM " + TABLE_RECORD;

        // 2. get reference to writable DB
        SQLiteDatabase db = this.getWritableDatabase();
        Cursor cursor = db.rawQuery(query, null);

        // 3. go over each row, build book and add it to list
        Record record = null;
        if (cursor.moveToFirst()) {
            do {
                record = new Record();
                record.setID(Integer.parseInt(cursor.getString(0)));
                record.setpLat(cursor.getDouble(1));
                record.setpLong(cursor.getDouble(2));
                record.setpAcc(cursor.getFloat(2));
                record.setpTime(cursor.getLong(2));


                // Add book to books
                records.add(record);
            } while (cursor.moveToNext());
        }

        Log.d("getAllRecords()", record.toString());

        // return books
        return records;
    }

    public int UpdateRecords(Record record) {

        // 1. get reference to writable DB
        SQLiteDatabase db = this.getWritableDatabase();

        // 2. create ContentValues to add key "column"/value
        ContentValues values = new ContentValues();
        values.put("Latitude", record.getpLat()); //
        values.put("Longtitude", record.getpLong());
        values.put("Accuracy", record.getpAcc());
        values.put("Time", record.getpTime());

        // 3. updating row
        int i = db.update(TABLE_RECORD, //table
                values, // column/value
                KEY_ID + " = ?", // selections
                new String[]{String.valueOf(record.getID())}); //selection args

        // 4. close
        db.close();

        return i;

    }

    public void deleteRecords(Record record) {

        // 1. get reference to writable DB
        SQLiteDatabase db = this.getWritableDatabase();

        // 2. delete
        db.delete(TABLE_RECORD, //table name
                KEY_ID + " = ?",  // selections
                new String[]{String.valueOf(record.getID())}); //selections args

        // 3. close
        db.close();

        //log
        Log.d("deleteBook", record.toString());

    }






}

谢谢!

Answer 1

您正在寻找的是一个 bundle 。它用于在 Activity 之间传递数据。看看What is a "bundle" in an Android application您可以了解它是如何完成的。