Android .txt resource file editing in Qt



  • Can I add a blank file "Orders.txt" to .qrc resources, and then edit it in application? What will happen after the application restart? Will the text in file remain in the next application startup?

    I mean - I want to create an order database. On the beginning of the file there will be a number of orders actually made. In the next lines will be records. Every record has 3 parts, and every part take one line in the file, so 3 lines are for one record.

    I actually have one version of my application, but it doesn't work. I test it by writing one record to file and then by reading it. When I try to list record fields, I'm getting blank strings.

    Thank you for your help.



  • ORDERPROCEDURES.H:

    #ifndef ORDERPROCEDURES_H
    #define ORDERPROCEDURES_H
    
    #include <QObject>
    #include <QQuickItem>
    #include <QTextStream>
    
    
    struct Order_Details {
         uint16_t order_number;
         char product_number;
         QString name_surname;
         QString email_adress;
    };
    
    
    class OrderProcedures : public QObject
    {
        Q_OBJECT
    public:
        explicit OrderProcedures(QObject *parent = 0);
        Q_INVOKABLE bool UpdateOrdersCount(const QString &filename);
        Q_INVOKABLE Order_Details ReadOneRecord(const QString &filename, uint16_t record_number);
        Q_INVOKABLE bool WriteOneRecord(const QString &filename, Order_Details &details, char tproduct_number);
        Q_INVOKABLE bool ReadAllOrders(const QString &filename);
    
    signals:
    
    public slots:
    private:
        uint16_t order_count = 0;
        Order_Details order_table[sizeof(uint16_t)];
    };
    
    
    
    #endif // ORDERPROCEDURES_H
    

    ORDERPROCEDURES.CPP

    #include "orderprocedures.h"
    
    OrderProcedures::OrderProcedures(QObject *parent) : QObject(parent)
    {
    
    }
    bool OrderProcedures::UpdateOrdersCount(const QString &filename)
    {
        char buffer[2];
        QFile file(filename);
        if (!file.open(QIODevice::ReadOnly))
            return false;
    
        if (!file.getChar(&buffer[0]))  //buffering the file data connected with number of orders
            return false;
        if (!file.getChar(&buffer[1]))
            return false;
    
        memcpy(&order_count, buffer, sizeof(uint16_t)); //setting the current number of orders
    
        file.close();
        return true;
    
    }
    
    Order_Details OrderProcedures::ReadOneRecord(const QString &filename, uint16_t record_number)
    {
        Order_Details detailsoforder;
        detailsoforder.name_surname="";
        detailsoforder.email_adress="";
    
        if(record_number>order_count)   //break if there is no such record
            return detailsoforder;
    
        QFile file(filename);           //break if it is impossible to open file
        if (!file.open(QIODevice::ReadOnly | QIODevice::Text))
            return detailsoforder;
    
        if (!file.canReadLine())        //break if there is nothing in the file
            return detailsoforder;
    
        file.readLine();                //skip first line with numbers
    
    
        for(uint16_t i=0 ; i<record_number ; i++)
        {
            file.readLine();            //skip lines with data that we aren't interested in
            file.readLine();
            file.readLine();
        }
    
        file.getChar(&(detailsoforder.product_number));  //getting the number of order Ist ROW
        file.readLine();                //skipping "\n"
    
        QString nas = file.readLine();  //buffering names and email
        QString ead = file.readLine();
    
        detailsoforder.name_surname.resize(nas.size()-1);   //resizing, throwing away "/n" character
        detailsoforder.email_adress.resize(ead.size()-1);
        for (uint16_t i=0 ; i<nas.size() ; i++)
        {
            detailsoforder.name_surname[i]=nas[i];
        }
        for (uint16_t i=0 ; i<nas.size() ; i++)
        {
            detailsoforder.email_adress[i]=ead[i];
        }
    
        file.close();               //closing the file
        return detailsoforder;
    }
    
    bool OrderProcedures::WriteOneRecord(const QString &filename, Order_Details &details, char tproduct_number)
    {
        char buffer[2];
        QFile file(filename);
        if (!file.open(QIODevice::Append | QIODevice::Text))
            return false;
    
    
        if(order_count<sizeof(uint16_t)-2)
            order_count++;                              //order counter incrementing
        else
            return false;                               //overflow - no more place for records
    
        memcpy(buffer, &order_count, sizeof(uint16_t)); //order counter buffering
    
        QTextStream writer(&file);
    
        file.putChar(tproduct_number);
        file.putChar('\n');
        writer<<details.name_surname<<"\n";             //appending order
        writer<<details.email_adress<<"\n";
        file.close();                                   //closing file
    
    
        if (!file.open(QIODevice::WriteOnly))           //opening again to write on the begginning
            return false;
    
        if (!file.putChar(buffer[0]))                   //updating order counter
        {
            order_count--;
            return false;
        }
        if (!file.putChar(buffer[1]))
        {
            order_count--;
            return false;
        }
        if (!file.putChar('\n'))
        {
            order_count--;
            return false;
        }
    
        file.close();
    
        order_table[order_count-1].name_surname.resize(details.name_surname.size());   //resizing the database record
        order_table[order_count-1].email_adress.resize(details.email_adress.size());
    
        order_table[order_count-1].product_number=tproduct_number;
        order_table[order_count-1].name_surname=details.name_surname;                  //updating the database with the current record
        order_table[order_count-1].email_adress=details.email_adress;
        return true;
    }
    
    bool OrderProcedures::ReadAllOrders(const QString &filename)
    {
        if(!UpdateOrdersCount(filename))
            return false;
    
        QFile file(filename);           //break if it is impossible to open file
        if (!file.open(QIODevice::ReadOnly | QIODevice::Text))
            return false;
    
        if (!file.canReadLine())        //break if there is nothing in the file
            return false;
    
        file.readLine();                //skip first line with numbers
    
        for(uint16_t i =0 ; i<order_count ; i++)
        {
            file.getChar(&(order_table[i].product_number));  //getting the number of order Ist ROW
            file.readLine();                //skipping "\n"
    
            QString nas = file.readLine();  //buffering names and email
            QString ead = file.readLine();
    
            order_table[i].name_surname.resize(nas.size()-1);   //resizing, throwing away "/n" character
            order_table[i].email_adress.resize(ead.size()-1);
    
            for (uint16_t j=0 ; i<nas.size() ; j++)
            {
                order_table[i].name_surname[j]=nas[j];
            }
            for (uint16_t j=0 ; j<nas.size() ; j++)
            {
                order_table[i].email_adress[j]=ead[j];
            }
        }
    
        file.close();
    
        return true;
    }
    
    

    MAIN.CPP:

    #include <QApplication>
    #include <QQmlApplicationEngine>
    #include <orderprocedures.h>
    
    int main(int argc, char *argv[])
    {
        QApplication app(argc, argv);
        OrderProcedures all;
    
        Order_Details detale;
        detale.name_surname.resize(15);
        detale.email_adress.resize(15);
        detale.name_surname="Jan Kowalski";
        detale.email_adress="jk@wp.pl";
        detale.product_number=1;
    
        all.UpdateOrdersCount("Orders.txt");
        all.WriteOneRecord("Orders.txt",detale,'1');
    
        Order_Details detale2 = all.ReadOneRecord("Orders.txt",1);
    
        //QTextStream out(stdout);
        qWarning()<<"llllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllll"<<"\n"; //For me to notice warnings in console
        qWarning()<<detale2.product_number;
        qWarning()<<detale2.name_surname;
        qWarning()<<detale2.email_adress;
    
        QQmlApplicationEngine engine;
        engine.load(QUrl(QStringLiteral("qrc:/main.qml")));
        return app.exec();
    }
    

    AND THE TESTING OUTPUT

    W libandroidtestQML.so: ../androidtestQML/main.cpp:23 (int main(int, char**)): llllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllll
    01-11 08:45:58.307  1418  1455 W libandroidtestQML.so:
    W libandroidtestQML.so: ../androidtestQML/main.cpp:24 (int main(int, char**)):
    W libandroidtestQML.so: ../androidtestQML/main.cpp:25 (int main(int, char**)): ""
    W libandroidtestQML.so: ../androidtestQML/main.cpp:26 (int main(int, char**)): ""

  • Moderators

    I may be wrong but as far as I know on Android you cannot write in the directory where your app is installed (for security reasons). The qrc file is part of your application, so I guess it will not work this way. You should use a directory where your app has write access.



  • I see. So am I able to create a blank file in the application when it starts for the first time and then to edit it when it actually exists in the given location? How should I do it?


  • Moderators

    Check this one on Android:

    QString QStandardPaths::writableLocation(StandardLocation type)
    Call it like this:
    QStandardPaths::writableLocation(QStandardPaths::AppDataLocation);
    

    More here: http://doc.qt.io/qt-5/qstandardpaths.html



  • Thank you a LOT! Especially for Standard Paths. It works :) I've got last small question. I've noticed that I understand file operation modes wrong. Writing in append mode seems easy. As a ReadOnly mode, I understand the mode in which you start reading the file from the beggining. But now I found that WriteOnly mode erases all file and starts writing from the beginning! Is that right? I thought that WriteOnly opens the file with pointer pointing the beginning of file, and so I thought that writing in that mode allows me to replace previously written characters. I want to find the mode that allows me to change the number at the beginning without writing whole file again...



  • Sorry that I've got even more questions :D

    Can I declare structures with QStrings and then resize them inside that structure? Does structure also resize itself then?

    Am I correct that I don't have to resize the QString when I declare:
    QString valuvalue = somekindofcharorstring;
    ?
    It changes its size automatically, am I right?



  • hi,i offer, you can use xml or json for saving your data
    Data storage



  • I'm afraid that it is too big amount of knowledge for such a small project, but I will consider it, thank you :)



  • I think it can be much easier with LocalStorage , it can be done entirely from QML:
    http://qmlbook.github.io/en/ch12/index.html#local-storage-sql

    I think this is the simpler solution to establish saving ability for an app, but you can't access the stored information from outside your app.


  • Moderators

    @monster Use

    QIODevice::WriteOnly | QIODevice::Append
    

    Then the file should not be overwritten.

    You can declare structures containing strings. The size of the struct does not depend on the size of stored strings, because internally QString stores the actual string on the heap and just points to it. On my machine sizeof(StrStruct) is 16 (StrStruct contains two QString members). So it is 2 * sizeof(void*).



  • Thank you all. Everything works fine. I just corrected my old, first example. There were many problems. I can upload example that works, and correctly fills and reads file according to the picked scheme if anybody is interested.


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