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Encoding in the QTableView



  • @mrjj I have seen the link about star delegate, but I'm not sure how to edit that for me. Can you write simple code, please?
    And what to do if I have 40 codes that I will need to change?


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    @ro12man3
    hi
    Delegates are a bit involved to code so small samples is not so easy.'
    The main concept for you would to be override
    http://doc.qt.io/qt-5.5/qstyleditemdelegate.html#displayText
    so when view ask how to show data , you can then
    replace the ID with the correct text.

    for 40 codes , you might need a lookup table as pure ifs
    if ( ID == 1000) return "CITY";
    will be a bit verbose :)


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    Hi,

    You should build a hash of your data and use it to map your numbers to your city.



  • @SGaist if I understand you correctly, I need to use QHash, yes?


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  • @mrjj thank you very much! But how integrate that with QTableView?


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    @ro12man3
    well when u create your delegate object
    you also give it a Hash list with the town names.
    so in displayText()
    it can look up in the list the name to use from the number from DB.



  • @mrjj unfortunately, it doesn't work. I read that for solving that problem I need to change TableView to TableWidget and use QTableWidgetItem. How to change the numbers in that variant?


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    @ro12man3 said:

    How to change the numbers in that variant?

    Hi Im not sure what you ask about ?

    QTableWidgetItem is not a variant.



  • @mrjj well... I talk about how to make changing the numbers to text in my tableview(or widget). I wrote

    QHash< int, QString> hash;
     hash.insert(100, "Jackson");
    

    and it doesn't change nothing in the table


  • Lifetime Qt Champion

    Where's that hash located ?
    Did you set your custom QStyledItem delegate on the correct column of your QTableView ?
    Are you sure that the volume contains the correct values ?



  • @SGaist this is the code

    void MainWindow::on_pushButton_clicked() // I click and the quiery result is showing in the qtableview
    {
    QSqlQueryModel * model = new QSqlQueryModel(0);
    QHash< int, QString> hash;
     hash.insert(100, "Jackson");
    model->setQuery("select city-codes from country");
    ui->tableView->setModel(model);
    }
    

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    That hash is destroyed at the end of on_pushButton_clicked



  • @SGaist so what I need to do for the correct changing values in my tableview?
    Where I need to write the QHash function?


  • Lifetime Qt Champion

    Either in your QStyledItemDelegate or as @mrjj suggested pass it to the delegate e.g. at construction time.



  • @SGaist what will be more simple? Cause I don't know how to make that. Sorry about my not big skills in qt


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    In your QStyledItemDelegate, read your file and build the hash with its content. Then in your displayText reimplementation return _hash.value(value.toInt(), tr("Not found"));


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    @ro12man3
    hi
    Starting with models and view are not best intro to Qt.
    They are very powerful but does demand some c++ skills and reading the docs.

    Sometimes code is easier to understand so I made u sample with @SGaist help.

    It has a list of names and if it sees Lars, it replaced it with BANNED.
    For your code, you will use the hash to look up the name from the code.

    https://www.dropbox.com/s/vsiqjrr41jhafqo/myfirstview.zip?dl=0

    the key points to understand is:
    we make a new class to override the default behaviour

    class MyDelegate : public QStyledItemDelegate {
    public:
    MyDelegate(QObject* parent)
    : QStyledItemDelegate(parent) {}
    virtual QString displayText(const QVariant& value, const QLocale& locale) const;
    };

    We set this delegate ONLY to the column we need.

    • ui->tableView->setItemDelegateForColumn(0, new MyDelegate(this));

    the displayText is the key function.:

    QString MyDelegate::displayText(const QVariant& value, const QLocale& locale) const {
    if (value.toString().compare("Lars") == 0) // if found
    return "BANNED";
    else
    return value.toString(); // else just return data unchanged
    }

    Here u will replace the city-code with names using the hash.

    Hope this helps you.



  • @mrjj ohhh thank you! It works!! Thank you very much.

    But I have 40 values that I will need to change(if it will be in quiery result).

    1. I can't write 40 "else if".. "else if"... "else if".... That's unlogic.
    2. I need to write all that values in support *.txt file(or another, the main is a simple format for editing), cause if I will write all that values in the program and then I will need to add new values...That's will be very uncomfortable.

    I see the method of the working the function so:
    The function is searching the values(from *.txt file) that has a quiery result. If it will find, then it will change to another every value.

    But...how make that in reality?


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    hi
    it sounds like your best way would to read in
    the text file to a hash.
    and use that hash in displayText
    I agree, using if for 40 values would be nasty :)

    How does your text file look like?



  • @mrjj I didn't create that file, cause I have no idea. Well, every variant will be good. The main is the working code :D

    Do you think that *.txt file should looks so:

    hash.insert("123", "Jack Sparrow");
    hash.insert("134", "Elvis Presley");
    hash.insert("201", "Walter White");
    ........
    

    ?


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    @ro12man3
    Hi
    For me it sounds like you would have a text file with
    1000, NAME1
    1001, NAME2

    so when u see int 1000, u want "NAME" etc.

    So your task is to look at QFile and read in a text file with your format and stuff it into a hash.
    Then use it.



  • @mrjj ok, I understand how to read the file and search the values. I don't understand another thing.
    On example=, the function will read the .txt file and it will find some value. Let it be 2900.
    In txt file it will be looking:
    2900, "Jackson"

    How to convert to "Jackson"? I don't know how to write that in a hash. How the hash will look the "convert value"?


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    @ro12man3
    say
    u define the hash like
    QHash<int, QString> Hash;
    it means we use int as key and get string as result
    so
    QString Name=hash[2900];
    would give us "Jackson" in name;

    please read doc on how it works.
    http://doc.qt.io/qt-5/qhash.html

    so you would read all lines from text file and insert into hash.



  • @mrjj woooow thank you! You are the master! :) I understand, very clever idea!

    I will try that in the morning.


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    well for 40 lookups its more fun that tons of ifs
    if u make a text file with
    ID, NAME
    like
    1000, TOWN
    1001, TOWN2
    1002, TOWN3

    so u need to ( code handwritten fast, not tested. u need to add includes)

    QFile file("c:/mynames.txt");
    if(!file.open(QIODevice::ReadOnly)) {
    QMessageBox::information(0, "error", file.errorString());
    }

    QTextStream in(&file);
    while(!in.atEnd()) {
    QString line = in.readLine(); // get a line from file
    QStringList fields = line.split(","); <<< KEY point. we ask it to split the text at "," to a list
    /// now fields[0] is first part and fields[1] is rest
    // so
    hash[fields[0].toInt()] = fields[1] ; // store name under key
    }

    file.close();



  • @mrjj thank you very much!! I will try that. If I wiil edit this, I will write here the correct code.
    Thank you for your helping!


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    @ro12man3
    You are very welcome.
    One note is that if u read in text lines then
    it will be text so u need to convert to int for the key if you
    define the hash like that.
    QHash<int, QString> Hash;
    something like
    hash[ fields[0].toInt() ]=xxx
    If it gives u grief , let me know as im not 100% sure of syntax as its free writing :)



  • @mrjj Well, I can extract the second field, but it will be all second fields.

    And I have edited the code:

    QString MyDelegate::displayText(const QVariant& value, const QLocale& locale) const {
           QString line;
            QFile file("C:/QT/Test text/1.txt");
            if(!file.open(QIODevice::ReadOnly))
                   qDebug() << "Error opening file";
            QTextStream in(&file);
    
            QHash<int, QString> hash;
    
             while(!in.atEnd()) {
             QString line = in.readLine(); 
             QStringList fields = line.split(","); 
             hash[fields[0].toInt()] = fields[1] ; 
      if (value.toString().compare(fields[0]) == 0)
        return fields[1];
      else
        return value.toString(); 
    }
    }
    

    And it doesn't work. How to solve that?
    It was working when I wrote

     if (value.toString().compare("1000") == 0)
        return "Jackson";
    

    If I write

    QMessageBox::information(this, fields[0], fields[1] );
    

    it is working, but it shows ALL values.


  • Lifetime Qt Champion

    @ro12man3 said:

    And it doesn't work. How to solve that?

    • You really have to provide more info that that :)
      if you insert qDebug() << "f1=" << fields[0] << "f2=" << fields[1];
      does it read in the data correctly ? this is critical.

    • Also you build the hash
      hash[fields[0].toInt()] = fields[1] ;
      but don't use it. ? You dont use it to look up the text.
      QString CityName = hash[value.toInt()];
      return CityName;

    • Also you mix reading in the file with compare value. that is wrong.
      You should not read it in displayText as it will then read file each time
      it draw that column. that is not so good.
      Make Hash a member of the class. (in .h) and just use it
      in displayText. then u can read it once and use it over and over.

    • Read in the text file in the constructor of the delegate;


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    In addition to what @mrjj wrote: make the hash a member of your delegate.



  • @mrjj said:

    • You really have to provide more info that that :)
      if you insert qDebug() << "f1=" << fields[0] << "f2=" << fields[1];
      does it read in the data correctly ? this is critical.

    Yes, I can extract this values. I tested that in QMessageBox.
    More info... http://rghost.ru/7wFZPWC4v This is the project.
    Download link(http://rghost.ru/download/7wFZPWC4v/ccf2cf56d3bbd353e8db12f377907d858f261e23/ccf2cf56d3bbd353e8db12f377907d858f261e23/myfirstviewEDITED.rar)

    It's not very difficult code structure, I don't know why it's not working.


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    Hi,

    Because it's not buildable as is.

    MyDelegate::MyDelegate(QObject *parent)
        : QStyledItemDelegate(parent)
    {
        QString line;
        QFile file("1.txt");
        if(file.open(QIODevice::ReadOnly)) {
            QTextStream in(&file);
            while(!in.atEnd()) {
                QString line = in.readLine(); // get a line from file
                QStringList fields = line.split(","); // KEY point. we ask it to split the text at "," to a list
                hash[fields[0].toInt()] = fields[1] ; // store name under key
            }
        } else {
            qDebug() << "Error opening file";
        }
    }
    
    // this is the key delegate function!
    QString MyDelegate::displayText(const QVariant& value, const QLocale& locale) const {
         return hash.value(value.toInt());
    }
    

    [edit: code cleanup SGaist]


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    Note that the build problem isn't with the delegate but with the MainWindow missing slot implementation.

    @mrjj :-D



  • @mrjj @SGaist oooohhh guys, thank you!! You are amazing!!!

    It's working. !!!

    The problem is SOLVED! THANK YOU VERY MUCH!!



  • @mrjj @SGaist
    I started to work and I found one bag.
    My table is:
    Roberto
    Jackson
    1002
    1

    And that's my txt file:
    1002,Hello
    1,How are you

    So the result in the table is
    Roberto
    Jackson
    Hello
    How are you

    It's good. Correct work.
    But if I change 1002 to 10--02 then all const values in the table will become like a second value for 10--02. The result will become:
    Hello
    Hello
    Hello
    How are you

    You can see that, just edit in table Maria to 10--02 and add 10--02 to txt file. What is that?


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    @ro12man3 said:

    10--02

    hi
    If you change the first field in file to 10--02
    it it no longer a valid integer.
    Our hash is Int, String
    so that mean use int as key and get back string
    when we read "10--02", and say toInt() we get 0 or something undefined.

    If you need to use a key that is not really a integer. like 10--02, then
    you must change the hash to be Qstring, QString and NOT use toInt() when inserting
    into hash.
    So make sure your text format fits the Hash or strange things will happen :)



  • @mrjj Ok. It was

    // In .h file:
    QHash<int, QString> hash;
    ......
      hash[fields[0].toInt()] = fields[1] ;
    ......
    // In .cpp file:
    QString mapped = hash.value(value.toInt());
    

    After editing it's:

    // In .h file:
    QHash<QString, QString> hash;
    ......
      hash[fields[0]] = fields[1] ;
    ......
    // In .cpp file:
    QString mapped = hash.value(value);
    

    Is it correct?


  • Lifetime Qt Champion

    hi
    yes, seems fine. good work.
    i think you might need
    QString mapped = hash.value(value.toString);
    as value is variant and hash wants string.


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