Accessing value of lineEdit in .cpp file- [SOLVED]



  • It depends on how you created your wave class in relation to the gui. The documentation lists three possible ways. What you tried would work if you inherited from the generated UI:: file. Usually, you don't do that, but use a member variable called ui (or, something else to match your taste) instead. Eddy assumes you use this approach :-)

    The answer above then gives you a pointer to the line edit itself. Its value can then be accessed using the text() method:

    @
    ui->frequency->text();
    @

    Note that frequency is a member variable of ui that you can access directly. It is not a method:
    @
    //wrong:
    ui->frequency()->text();
    @


  • Moderators

    Andre, you have a wonderfull way of explaining things!

    @ogopa :
    The bottom line is : if you give us some code or more details we can help you without guessing or forecasting every possible way you could have done things.



  • [quote author="Eddy" date="1311867800"]Andre, you have a wonderfull way of explaining things!

    @ogopa :
    The bottom line is : if you give us some code or more details we can help you without guessing or forecasting every possible way you could have done things.[/quote]

    Thanks alot guys. The information helped alot. sorry. here is the code of wave.cpp. i couldn't post the entire code because there is a 6000 character limit. So I posted just a little of it which includes line 369 :
    I used your advice and it worked. However. I am getting a new error:

    ./Wave/wave.cpp:369:34: error: ‘ui’ was not declared in this scope

    I'm not sure what it means. Please help

    line 369:@
    double freq = ui->frequency->text().toDouble();@

    @ static int write_loop(snd_pcm_t *handle,
    signed short *samples,
    snd_pcm_channel_area_t *areas)
    {
    double phase = 0;
    signed short *ptr;
    int err, cptr;

           while (1) {
                  
                   {
    
    • line 369:* double freq = ui->frequency->text().toDouble();
      double ampl = ui->amplitude->text().toDouble();
      const snd_pcm_channel_area_t *areas;
      snd_pcm_uframes_t offset=0;
      int count = period_size;
      double *_phase;
      static double max_phase = 2. * M_PI;
      double phase = _phase;
      double step = max_phase
      freq/(double)rate;
      unsigned char samples[channels];
      int steps[channels];
      unsigned int chn;
      int format_bits = snd_pcm_format_width(format);
      unsigned int maxval = (1 << (format_bits - 1)) - 1;
      int bps = format_bits / 8; /
      bytes per sample */
      int phys_bps = snd_pcm_format_physical_width(format) / 8;
      int big_endian = snd_pcm_format_big_endian(format) == 1;
      int to_unsigned = snd_pcm_format_unsigned(format) == 1;
      int is_float = (format == SND_PCM_FORMAT_FLOAT_LE ||
      format == SND_PCM_FORMAT_FLOAT_BE);
      float amplitude_scale = ampl/8.56;
           /* verify and prepare the contents of areas */
           for (chn = 0; chn < channels; chn++) {
                   if ((areas[chn].first % 8) != 0) {
                           printf("areas[%i].first == %i, aborting...\n", chn, areas[chn].first);
                           exit(EXIT_FAILURE);
                   }
                   samples[chn] = /*(signed short *)*/(((unsigned char *)areas[chn].addr) + (areas[chn].first / 8));
                   if ((areas[chn].step % 16) != 0) {
                            printf("areas[%i].step == %i, aborting...\n", chn, areas[chn].step);
                           exit(EXIT_FAILURE);
                   }
                   steps[chn] = areas[chn].step / 8;
                   samples[chn] += offset * steps[chn];
           }
           /* fill the channel areas */
           while (count-- > 0) {
                   union {
                           float f;
                           int i;
                   } fval;
                   int res, i;
                   if (is_float) {
                           fval.f = amplitude_scale * sin(phase) * maxval;
                           res = fval.i;
                   } else
                           res = amplitude_scale * sin(phase) * maxval;
                   if (to_unsigned)
                           res ^= 1U << (format_bits - 1);
                   for (chn = 0; chn < channels; chn++) {
                           /* Generate data in native endian format */
                           if (big_endian) {
                                   for (i = 0; i < bps; i++)
                                           *(samples[chn] + phys_bps - 1 - i) = (res >> i * 8) & 0xff;
                           } else {
                                   for (i = 0; i < bps; i++)
                                           *(samples[chn] + i) = (res >>  i * 8) & 0xff;
                           }
                           samples[chn] += steps[chn];
                   }
                   phase += step;
                   if (phase >= max_phase)
                           phase -= max_phase;
           }
           *_phase = phase;
    

    }
    ptr = samples;
    cptr = period_size;
    while (cptr > 0) {
    err = snd_pcm_writei(handle, ptr, cptr);
    if (err == -EAGAIN)
    continue;
    if (err < 0) {
    if (xrun_recovery(handle, err) < 0) {
    printf("Write error: %s\n", snd_strerror(err));
    exit(EXIT_FAILURE);
    }
    break; /* skip one period */
    }
    ptr += err * channels;
    cptr -= err;
    }
    }
    }
    @


  • Moderators

    if you want to have the value of your lineEdit elsewhere you can use a connect in your constructor :

    After looking into your code I've the impression you want to do that in your write_loop function.
    Here is an example.

    @#include "dialog.h"
    #include "ui_dialog.h"
    #include <QDebug>

    dialog.cpp :

    Dialog::Dialog(QWidget *parent) :
    QDialog(parent),
    ui(new Ui::Dialog)
    {
    ui->setupUi(this);

    connect(ui->lineEdit, SIGNAL(textChanged(QString)), this , SLOT(testFunc(QString)) );
    

    }

    Dialog::~Dialog()
    {
    delete ui;
    }

    void Dialog::testFunc(QString str)
    {
    qDebug() << "teststring : " <<str;
    }@

    dialog.h :

    add in your class :

    @public slots:
    void testFunc(QString str);@

    The above is based on a project generated by QT Creator with a QDialog. In main an instance of this QDialog class is used.

    To understand fully what is happening you could read about "signals and slots":http://doc.qt.nokia.com/4.7/signalsandslots.html. In short : by using the connect Qt always makes sure you get the right value of your LineEdit where you need it.

    PS you can click on the signal and slots tag on the topright of your screen to see more examples, snippets, ... on the forum.



  • [quote author="Eddy" date="1311873669"]if you want to have the value of your lineEdit elsewhere you can use a connect in your constructor :

    After looking into your code I've the impression you want to do that in your write_loop function.
    Here is an example.

    @#include "dialog.h"
    #include "ui_dialog.h"
    #include <QDebug>

    dialog.cpp :

    Dialog::Dialog(QWidget *parent) :
    QDialog(parent),
    ui(new Ui::Dialog)
    {
    ui->setupUi(this);

    connect(ui->lineEdit, SIGNAL(textChanged(QString)), this , SLOT(testFunc(QString)) );
    

    }

    Dialog::~Dialog()
    {
    delete ui;
    }

    void Dialog::testFunc(QString str)
    {
    qDebug() << "teststring : " <<str;
    }@

    dialog.h :

    add in your class :

    @public slots:
    void testFunc(QString str);@

    The above is based on a project generated by QT Creator with a QDialog. In main an instance of this QDialog class is used.

    To understand fully what is happening you could read about "signals and slots":http://doc.qt.nokia.com/4.7/signalsandslots.html. In short : by using the connect Qt always makes sure you get the right value of your LineEdit where you need it.

    PS you can click on the signal and slots tag on the topright of your screen to see more examples, snippets, ... on the forum.[/quote]

    So this is what the first part of my program, wave.cpp looks like(below). I have added the piece of code you gave me. and I also added the lines (directlly below) to the file wave.h. However, I am still getting the same error: ‘ui’ was not declared in this scope, in the same place . I'm not sure whats wrong with it.
    @public slots:
    void testFunc(QString str);
    @

    @#include <QtGui>
    #include <QApplication>
    #include <qlineedit.h>
    #include "wave.h"
    #include "ui_wave.h"
    #include <QString>
    #include <QDebug>
    #include <stdio.h>
    #include <cstdio>
    #include <stdlib.h>
    #include <cstdlib>
    #include <string.h>
    #include <cstring>
    #include <sched.h>
    #include <errno.h>
    #include <getopt.h>
    #include <alsa/asoundlib.h>
    #include <sys/time.h>
    #include <sstream>
    #include <string>
    #include <math.h>
    #include <cmath>
    #include <iostream>
    using namespace std;

    static const char device = "plughw:0,0"; / playback device /
    static snd_pcm_format_t format = SND_PCM_FORMAT_S16; /
    sample format /
    static unsigned int rate = 96000; /
    stream rate /
    static unsigned int channels = 128; /
    count of channels /
    static unsigned int buffer_time = 500000; /
    ring buffer length in us /
    static unsigned int period_time = 100000; /
    period time in us /
    //static double freq = 440; /
    sinusoidal wave frequency in Hz /
    static int verbose = 0; /
    verbose flag /
    static int resample = 1; /
    enable alsa-lib resampling /
    static int period_event = 0; /
    produce poll event after each period */
    static snd_pcm_sframes_t buffer_size;
    static snd_pcm_sframes_t period_size;
    static snd_output_t *output = NULL;
    //static double amplitude = 1;

    wave::wave(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::wave)
    {
    ui->setupUi(this);
    connect(ui->frequency, SIGNAL(textChanged(QString)) , this , SLOT(testFunc(QString)));
    }

    wave::~wave()
    {
    delete ui;
    }

    void wave::testFunc(QString str)
    {
    qDebug() << "teststring: "<<str;
    }

    void wave::on_pushButton_clicked()
    {......
    @


  • Moderators

    Hi ogopa,

    Do you use a form wit ui file? And is your class based on it?
    In a previous post you said you got it working. That's why I assumed you did use an ui file.

    The code I showed you is an example on how you can do things, to learn the general principles. You can not just copy it in your code.

    Try it out using a new project based on QWidget, choose QDialog in one of the next steps and try my suggestion to learn things.

    Did you read the signal and slots link I gave you?

    Here is some explanation:
    TestFunc is an example slot compararable to your function. Using the connect you can use the value of the lineEdit in your function.



  • [quote author="Eddy" date="1311879430"]Hi ogopa,

    Do you use a form wit ui file? And is your class based on it?
    In a previous post you said you got it working. That's why I assumed you did use an ui file.

    The code I showed you is an example on how you can do things, to learn the general principles. You can not just copy it in your code.

    Try it out using a new project based on QWidget, choose QDialog in one of the next steps and try my suggestion to learn things.

    Did you read the signal and slots link I gave you?

    Here is some explanation:
    TestFunc is an example slot compararable to your function. Using the connect you can use the value of the lineEdit in your function.

    [/quote]

    Thanks for the help so far. So i've been reading the signals and slots link you sent me and I tried out a simple project with QDialog. I'm still trying to connect the lineEdit to another function, I can't seem to nail it :(. I named the test function write_loop again :p. Below is the cpp file and below that is the header file.

    dialog.cpp
    @#include "dialog.h"
    #include "ui_dialog.h"
    #include <QDialog>
    #include <QDebug>
    #include <iostream>
    using namespace std;

    static double txt;

    dialog::dialog(QWidget *parent) :
    QDialog(parent),
    ui(new Ui::dialog)
    {
    ui->setupUi(this);
    connect(ui->lineEdit, SIGNAL(textChanged(QString)), this , SLOT(write_loop(QString)) );
    }

    dialog::~dialog()
    {
    delete ui;
    }

    void dialog::write_loop(QString str)
    {
    qDebug() << "teststring : " <<str;
    }

    void dialog::on_pushButton_clicked()
    {
    txt = ui->lineEdit->text().toDouble();
    cout<<txt;
    }

    static int write_loop(QString)
    {
    txt = ui->lineEdit->text().toDouble();
    cout<<"I have"<<txt;
    }@

    dialog.h
    @#ifndef DIALOG_H
    #define DIALOG_H

    #include <QDialog>
    #include <QDebug>

    namespace Ui {
    class dialog;
    }

    class dialog : public QDialog
    {
    Q_OBJECT

    public:
    explicit dialog(QWidget *parent = 0);
    ~dialog();
    public slots:
    void write_loop(QString str);

    private slots:
    void on_pushButton_clicked();

    private:
    Ui::dialog *ui;
    };

    #endif // DIALOG_H
    @

    I also tried this, but it didn't work:
    @static int write_loop(QString)
    {
    connect(ui->lineEdit, SIGNAL(textChanged(QString)), this , SLOT(write_loop(QString)) );
    txt = ui->lineEdit->text().toDouble();
    cout<<"I have"<<txt;
    }
    @


  • Moderators

    Have you changed the value of the lineedit to 5 for instance? Then normally you should get
    bq. teststring : 5
    in the application output.

    What do you have in the application output pane?



  • I don't have an output because when I build or run, it gives me the error:
    ./Dialog/dialog.cpp:41:11: error: ‘ui’ was not declared in this scope


  • Moderators

    To what line number in the above code does that point?



  • [quote author="Eddy" date="1311969905"]To what line number in the above code does that point?[/quote]

    line 37:
    @static int write_loop(QString)
    {
    txt = ui->lineEdit->text().toDouble();......................line 37
    cout<<"I have"<<txt;
    }@


  • Moderators

    Do you know how to use Qt Creator? Do you know how to debug? Please read the Qt Creator manual if you don't. The purpose of this forum is not that we debug for you. You should be able to narrow down the problems yourself.

    So your problem is merely about the static variable. Why do you want to use static? Using the signal slots you can have the value of the lineEdit where you want all the times.

    If you keep only the function with the qDebug line in it then your program should work and you have a solution to your initial problem : using the vale of lineEdit in a function.
    Hint : comment the others out and start from there.



  • [quote author="Eddy" date="1311971610"]Do you know how to use Qt Creator? Do you know how to debug? Please read the Qt Creator manual if you don't. The purpose of this forum is not that we debug for you. You should be able to narrow down the problems yourself.

    So your problem is merely about the static variable. Why do you want to use static? Using the signal slots you can have the value of the lineEdit where you want all the times.

    If you keep only the function with the qDebug line in it then your program should work and you have a solution to your initial problem : using the vale of lineEdit in a function.
    Hint : comment the others out and start from there.[/quote]

    Yayy, I got it, Thanks alot. I now have new errors. All of them are similar:
    wave.cpp:(.text+0x7b3): undefined reference to snd_pcm_hw_params_set_rate_resample' wave.cpp:(.text+0x7c6): undefined reference tosnd_strerror'
    wave.cpp:(.text+0x7f6): undefined reference to snd_pcm_hw_params_set_access' wave.cpp:(.text+0x809): undefined reference tosnd_strerror'
    wave.cpp:(.text+0x83c): undefined reference to `snd_pcm_hw_params_set_format'

    its the same for all others from the alsa sound library. I have included alsa/asoundlib.h, so i'm confused as to why i am getting these errors. Could you please help me.


  • Moderators

    Make sure you're linking the asound library, not just include its header files.


  • Moderators

    bq. Yayy, I got it, Thanks alot. I now have new errors. All of them are similar:

    Glad you made it that far!

    You described your new problem much better. Now it's easier for the forum members to understand your problem and help out.



  • [quote author="mlong" date="1311975549"]Make sure you're linking the asound library, not just include its header files.
    [/quote]

    Hi, I tried searching online for your suggestion as I am not sure how to do this, but I couldn't find anything that could help me. Would you please explain a little more? I'd really appreciate it.


  • Moderators

    What does your .pro file look like?



  • [quote author="mlong" date="1312296267"]What does your .pro file look like?
    [/quote]

    wave.pro

    @#-------------------------------------------------

    Project created by QtCreator 2011-07-26T15:57:33

    #-------------------------------------------------

    QT += core gui

    TARGET = Wave
    TEMPLATE = app

    SOURCES += main.cpp
    wave.cpp

    HEADERS += wave.h

    FORMS += wave.ui@


  • Moderators

    It's not enough to simply include the <alsa/asoundlib.h> header in your code. You also have to tell the linker that you want to use the asound library. Use the LIBS variable in your .pro file to do so. I don't know for sure what the proper library name to use is (off the top of my head.) Probably want to use -Lasound or something like that.

    There are a number of threads that discuss how to include libraries.



  • Thanks alot, I included this line in my wave.pro and it worked:
    @LIBS += -lasound@


  • Moderators

    Good deal! Be sure to change the title of the thread to add [Solved] if everything is working now.


Log in to reply
 

Looks like your connection to Qt Forum was lost, please wait while we try to reconnect.