LineEdit.

[Rewo]

Hi,

I want to create simple program. I want to use lineEdit for inserting a 9-digit number. I've set maxLength = 9.

Is there any way to make "if" with checking current length of text in lineEdit ? Unfortunately lineEdit->length() doesn't exist.

When I'm trying to make a QString which will take a value of lineEdit, class isn't looking if QString has length = 9.

I tried something like that:

QString lineeditl;
lineeditl = lineEdit->text(); // i think that line isn't working properly (have no 'if' for reference it)
if(lineeditl.length()==9) {
    label_2->setText("Correct.");
}

QString lineeditl;
lineeditl = lineEdit->text(); // i think that line isn't working properly (have no 'if' for reference it)
if(lineeditl.length()==9) {
    label_2->setText("Correct.");
}

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[ruben.rodrigues]

Hi,

I want to create simple program. I want to use lineEdit for inserting a 9-digit number. I've set maxLength = 9.

Is there any way to make "if" with checking current length of text in lineEdit ? Unfortunately lineEdit->length() doesn't exist.

When I'm trying to make a QString which will take a value of lineEdit, class isn't looking if QString has length = 9.

I tried something like that:

QString lineeditl;
lineeditl = lineEdit->text(); // i think that line isn't working properly (have no 'if' for reference it)
if(lineeditl.length()==9) {
    label_2->setText("Correct.");
}

QString lineeditl;
lineeditl = lineEdit->text(); // i think that line isn't working properly (have no 'if' for reference it)
if(lineeditl.length()==9) {
    label_2->setText("Correct.");
}

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your code looks correct.

are you setting the gui properly?

ui.setupUi(this); //@ the constructor

and I think you should then use ui.lineEdit->text();

Do want to check this as the users types or after pushing a button
if possible place all the code.

[Zlatomir]

Did you connect the textChanged(QString) signal of the lineEdit with a function/slot that sets the QString lineeditl; ?
Or does the lineEdit has the text from the beginning? (not the use entering the text)

Post a compilable example.

[Rewo]

@ruben.rodrigues : Gui setting is good, don't worry about it.

@Zlatomir : I tried to use textChanged(QString) signal, but I don't understand why QString parameter is needed. Unfortunately it's not bool signal. LineEdit is empty at start (hasn't got any value).

[ruben.rodrigues]

can you post the line where you do the connection to the signal textchannged and the function that is called when the text changes?

[Rewo]

I can't, because I don't know how to use textChanged. Imo it should be bool singal, dunno what QString parameter needing does here.

[ruben.rodrigues]

I can't, because I don't know how to use textChanged. Imo it should be bool singal, dunno what QString parameter needing does here.

ah! ok

at the constructor of your gui class you need to write a line like this:

connect(lineEdit, SIGNAL(textChanged()), this , SLOT(checkTextLenght());

define the slot checkTextLenght on your header:

private slots:
void checkTextLenght();

and of course programm the function:

void YourClass::checkTextLenght()
{
your code to check the lenght
QString lineeditl;
lineeditl = lineEdit->text(); // i think that line isn't working properly (have no 'if' for reference it)
if(lineeditl.length()==9) {
label_2->setText("Correct.");
}
}

Let me know how it works and if the syntax doesn't match is because I don't have qt on my pc.

[Zlatomir]

@Zlatomir : I tried to use textChanged(QString) signal, but I don't understand why QString parameter is needed. Unfortunately it's not bool signal. LineEdit is empty at start (hasn't got any value).

The QString parameter it is needed because you need the string.

Right now your QString remains empty...

Create a slot that take a QString parameter, and initialise the lineeditl with that QString, and connect the lineEdit textChanged(QString) with the slot you created (so any time the user change the string you will have the lineeditl updated)

[Rewo]

@ruben.rodrigues

I did it, but nothing changed.

In communicates these lines appeared:

Object::connect: No such signal QLineEdit::textChanged() in mainwindow.cpp:9
Object::connect:  (sender name:   'lineEdit')
Object::connect:  (receiver name: 'MainWindow')

Object::connect: No such signal QLineEdit::textChanged() in mainwindow.cpp:9
Object::connect:  (sender name:   'lineEdit')
Object::connect:  (receiver name: 'MainWindow')

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[Zlatomir]

that is because QLineEdit doesn't have a textChanged( VOID) ... it's a textChanged(QString) or QString&

Post the project...

[Rewo]

It's my mainwindow.cpp (nothing else is needed, because rest of project is correct)

#include "mainwindow.h"
#include "ui_mainwindow.h"
#include <QInputDialog>
 
QString lineeditl;
 
MainWindow::MainWindow(QWidget *parent) : QMainWindow(parent)
{
    setupUi(this);
    //connect(pnt,SIGNAL(triggered()),this,SLOT(pnts()));
    connect(lineEdit,SIGNAL(textChanged()),this,SLOT(checkTextLength()));
    //if(lineeditl[0] == '7') { label_2->setText("Plus ?"); }
}
 
void MainWindow::checkTextLength(){
    lineeditl = lineEdit->text();
    if(lineeditl.length()==9) {
        label_2->setText("Correct.");
    }
}
 
MainWindow::~MainWindow()
{
}

#include "mainwindow.h"
#include "ui_mainwindow.h"
#include <QInputDialog>

QString lineeditl;

MainWindow::MainWindow(QWidget *parent) : QMainWindow(parent)
{
    setupUi(this);
    //connect(pnt,SIGNAL(triggered()),this,SLOT(pnts()));
    connect(lineEdit,SIGNAL(textChanged()),this,SLOT(checkTextLength()));
    //if(lineeditl[0] == '7') { label_2->setText("Plus ?"); }
}

void MainWindow::checkTextLength(){
    lineeditl = lineEdit->text();
    if(lineeditl.length()==9) {
        label_2->setText("Correct.");
    }
}

MainWindow::~MainWindow()
{
}

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Every time I'm trying to put QString in textChanged, it gives me information that:

c:\Qt\4.6.2\include/QtGui/../../src/gui/widgets/qlineedit.h:196: error: 'void QLineEdit::textChanged(const QString&)' is protected

c:\Qt\4.6.2\include/QtGui/../../src/gui/widgets/qlineedit.h:196: error: 'void QLineEdit::textChanged(const QString&)' is protected

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[Zlatomir]

create a slot in mainWidow something like:

//...
public slots: 
        void setTextInQString (QString inString) {
                     lineeditl = inString;
}

//...
public slots: 
        void setTextInQString (QString inString) {
                     lineeditl = inString;
}

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And connect the textChanged(QString) with setTextInQString(QString) in mainWindow constructor

And you will need more signals and slots, because it the constructor of mainWidondow the QString will be empty... Only the connections need to be in the constructor!!!

[Rewo]

It's hard to understand.

I did:

mainwindow.h

#ifndef MAINWINDOW_H
#define MAINWINDOW_H
 
#include <QMainWindow>
#include "ui_mainwindow.h"
 
QString lineeditl;
 
class MainWindow : public QMainWindow, Ui::MainWindow {
    Q_OBJECT
public:
    MainWindow(QWidget *parent = 0);
    ~MainWindow();
public slots:
    void setTextInQString (QString inString) {
        lineeditl = inString;
    }
/*protected slots:
    void pnts();
    void checkTextLength();*/
};
 
#endif // MAINWINDOW_H

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>
#include "ui_mainwindow.h"

QString lineeditl;

class MainWindow : public QMainWindow, Ui::MainWindow {
    Q_OBJECT
public:
    MainWindow(QWidget *parent = 0);
    ~MainWindow();
public slots:
    void setTextInQString (QString inString) {
        lineeditl = inString;
    }
/*protected slots:
    void pnts();
    void checkTextLength();*/
};

#endif // MAINWINDOW_H

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mainwindow.cpp

#include "mainwindow.h"
#include "ui_mainwindow.h"
#include <QInputDialog>
 
QString lineeditl;
 
MainWindow::MainWindow(QWidget *parent) : QMainWindow(parent)
{
    setupUi(this);
    //connect(pnt,SIGNAL(triggered()),this,SLOT(pnts()));
    connect(lineEdit,SIGNAL(textChanged()),this,SLOT(checkTextLength()));
    //if(lineeditl[0] == '7') { label_2->setText("Plus ?"); }
    connect(lineEdit,textChanged(QString),this,setTextInQString(QString));
}
 
void MainWindow::checkTextLength(){
    lineeditl = lineEdit->text();
    if(lineeditl.length()==9) {
        label_2->setText("Correct.");
    }
}
 
MainWindow::~MainWindow()
{
}

#include "mainwindow.h"
#include "ui_mainwindow.h"
#include <QInputDialog>

QString lineeditl;

MainWindow::MainWindow(QWidget *parent) : QMainWindow(parent)
{
    setupUi(this);
    //connect(pnt,SIGNAL(triggered()),this,SLOT(pnts()));
    connect(lineEdit,SIGNAL(textChanged()),this,SLOT(checkTextLength()));
    //if(lineeditl[0] == '7') { label_2->setText("Plus ?"); }
    connect(lineEdit,textChanged(QString),this,setTextInQString(QString));
}

void MainWindow::checkTextLength(){
    lineeditl = lineEdit->text();
    if(lineeditl.length()==9) {
        label_2->setText("Correct.");
    }
}

MainWindow::~MainWindow()
{
}

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Of course - doesn't work.

[msrihari]

it should be:

connect(lineEdit,SIGNAL(textChanged(QString)),this ,SLOT(setTextInQString(QString)));

[Rewo]

mainwindow.cpp

#include "mainwindow.h"
#include "ui_mainwindow.h"
#include <QInputDialog>
 
MainWindow::MainWindow(QWidget *parent) : QMainWindow(parent)
{
    setupUi(this);
    //connect(pnt,SIGNAL(triggered()),this,SLOT(pnts()));
    connect(lineEdit,SIGNAL(textChanged()),this,SLOT(checkTextLength()));
    //if(lineeditl[0] == '7') { label_2->setText("Plus ?"); }
    connect(lineEdit,SIGNAL(textChanged(QString)),this,SLOT(setTextInQString(QString)));
    //,,,SLOT(setTextInQString)
}
 
MainWindow::~MainWindow()
{
}
 
void MainWindow::checkTextLength(){
    //lineeditl = lineEdit->text();
    if(lineeditl.length()==9) {
        label_2->setText("Correct.");
    }
}

#include "mainwindow.h"
#include "ui_mainwindow.h"
#include <QInputDialog>

MainWindow::MainWindow(QWidget *parent) : QMainWindow(parent)
{
    setupUi(this);
    //connect(pnt,SIGNAL(triggered()),this,SLOT(pnts()));
    connect(lineEdit,SIGNAL(textChanged()),this,SLOT(checkTextLength()));
    //if(lineeditl[0] == '7') { label_2->setText("Plus ?"); }
    connect(lineEdit,SIGNAL(textChanged(QString)),this,SLOT(setTextInQString(QString)));
    //,,,SLOT(setTextInQString)
}

MainWindow::~MainWindow()
{
}

void MainWindow::checkTextLength(){
    //lineeditl = lineEdit->text();
    if(lineeditl.length()==9) {
        label_2->setText("Correct.");
    }
}

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#ifndef MAINWINDOW_H
#define MAINWINDOW_H
 
#include <QMainWindow>
#include "ui_mainwindow.h"
 
class MainWindow : public QMainWindow, Ui::MainWindow {
    Q_OBJECT
public:
    MainWindow(QWidget *parent = 0);
    ~MainWindow();
public slots:
    void setTextInQString (QString inString) {
        lineeditl = inString;
    }
protected slots:
    /*void pnts();*/
    void checkTextLength();
};
 
#endif // MAINWINDOW_H

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>
#include "ui_mainwindow.h"

class MainWindow : public QMainWindow, Ui::MainWindow {
    Q_OBJECT
public:
    MainWindow(QWidget *parent = 0);
    ~MainWindow();
public slots:
    void setTextInQString (QString inString) {
        lineeditl = inString;
    }
protected slots:
    /*void pnts();*/
    void checkTextLength();
};

#endif // MAINWINDOW_H

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Problem:

QString lineeditl;

QString lineeditl;

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Where should i define it ? There are errors with multiple definition of this var, wherever I'll put that line.

[Zlatomir]

You have gone in another direction... if you directly check the QString returned you won't need the extra QString variable.

I have wrote a little sample project (it's with a QString variable and a Button to check)

and modified for check directly... (so you have both methods now )

Advice: Read more on signals and slots

[Rewo]

This program resolves everything. Thank You very much !

[lyuts]

Hi,

I want to create simple program. I want to use lineEdit for inserting a 9-digit number. I've set maxLength = 9.

Is there any way to make "if" with checking current length of text in lineEdit ? Unfortunately lineEdit->length() doesn't exist.

Why not just use QRegExpValidator? You regex will look like

[0-9]{,9}

[0-9]{,9}

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