Clear QLineEdit on Click

Shoaib Muhammad

Good day all,

Hope everyone is well.

I am a beginner programmer for QT 5.6 on an embedded platform.

ISSUE #1:
I wanted to do something specific with a QLineEdit object. On selecting the object (kind of like a mouse click), I want the current values to be cleared to be ready for the new values to be typed.

For example, here is my QLineEdit named StrtEdit on my main window:

Enter Value:|         |

Upon entering a value:

Enter Value:|123456789|

And when I click on another QLineEdit the value would still show, but when I click on it again to enter data it should clear previous data and show:

Enter Value:|         |

Having a clear QPushButton makes sense but it's not currently an option due to the space limit of the application.

Basically what I'm looking for is a 'clicked' signal from a QLineEdit.

ISSUE #2:

I could only delete the values of the QLineEdit using the 'backspace' key of a virtual keyboard on the first time I write data to a QLineEdit field. Once I click on something else and return to that input field, I am unable to delete the values using backspace and must use QlineEdit->setText(" "); instead. Why is that?

Thank you for taking the time to read all this. Additional info available upon request.

Kind regards,
Shoaib

jsulm

@Shoaib-Muhammad said in Clear QLineEdit on Click:

Why is that?

I don't know. This should work. Are you doing anything else with this widgets?

Regarding your first issue: you can subclass QLineEdit and overwrite https://doc.qt.io/qt-5/qlineedit.html#mousePressEvent

SGaist

Hi,

Just one thing about that design, you might get trouble with your users. What if they would like to copy the value ? Add a number ? Or more silly what if they accidentally click on it ?

Shoaib Muhammad

@jsulm @SGaist

Hi guys,

Fair point from SGaist. I might not do that anymore then.

On the second issue, let me share some snippets of my code.

header.h

#pragma once

#include <QWidget>
#include <QPainter>
#include <QApplication>
#include <QPushButton>
#include <QLabel>
#include <QIntValidator>
#include <Qt>
#include <QtDebug>
#include <QLineEdit>
#include <QString>
#include <QFont>
#include <QGraphicsScene>
#include <QFocusEvent>



class CGui : public QWidget {
    
  Q_OBJECT

  public:
    CGui(QWidget *parent = 0);

    QLineEdit *StrtEdit;
    QLineEdit *StopEdit;

  private slots:

    void clickProcess();
    void clickDatacap();
    void clearField1();
    void clearField2();


  private:
    QLabel *rltxt;
    QLabel *imtxt;

    QLabel *strttxt;
    QLabel *stoptxt;

  protected:
    void paintEvent(QPaintEvent *e);
    void drawRectangles();
    void drawGraphs();

};

header.cpp

#include "mainheader.h"
#include <stdio.h>

int rlval = 0;
int imval = 0;

/** Empty Arrays and Array Variables**/
int rlarry[100];
int imarry[100];

/** Graph Variables **/
int min_x1 = 80;
int max_x1 = 380;
int min_y1 = 33;
int max_y1 = 369;
int xlength1 = 0;
int ylength1 = 0;
int yspace1 = 0;
int xspace1 = 0;
int ytemp1 = 0;
int xtemp1 = 0;

int min_x2 = 470;
int max_x2 = 735;
int min_y2 = 236;
int max_y2 = 380;
int xlength2 = 0;
int ylength2 = 0;
int yspace2 = 0;
int yspace2b=0;
int xspace2 = 0;
int ytemp2 = 0;
int xtemp2 = 0;
 
QString tex1 = QString("R: %1").arg(rlval);
QString tex2 = QString("I: %1i").arg(imval);


QFont font1("Fantasy", 15, QFont::Black);
QFont font2("Fantasy", 10, QFont::Black);
QFont font3("Fantasy", 20, QFont::Black);
QFont font4("Fantasy", 10, QFont::Black);

CGui::CGui(QWidget *parent)
    : QWidget(parent) {

/***          Create Widgets          ***/
  
  /** Remove Titlebar **/   
  setWindowFlags(Qt::Window | Qt::FramelessWindowHint);
  
  /** Buttons, Labels, and Input **/
  QPushButton *DcapBtn = new QPushButton("DATA CAPTURE", this);
  DcapBtn->setFont(font1);
  DcapBtn->setStyleSheet("background-color:rgb(249,56,34); border:none; color:white;");
  DcapBtn->setGeometry(602, 150, 193, 50);

  QPushButton *PrcBtn = new QPushButton("PROCESS", this);
  PrcBtn->setFont(font1);
  PrcBtn->setStyleSheet("background-color:rgb(65,182,230); border:none; color:white;");
  PrcBtn->setGeometry(405, 150, 193, 50);

  StrtEdit = new QLineEdit("",this);
  StrtEdit->setFont(font2);
  StrtEdit->setAlignment(Qt::AlignLeft);
  StrtEdit->setGeometry(555, 105, 240, 40);

  StopEdit = new QLineEdit("",this);
  StopEdit->setAlignment(Qt::AlignLeft);
  StopEdit->setFont(font2);
  StopEdit->setGeometry(555, 60, 240, 40);

  rltxt = new QLabel(" ", this);
  rltxt->setFont(font3);
  rltxt->setText(tex1);
  rltxt->setStyleSheet("color:white;");
  rltxt->setGeometry(415, 5, 192, 50);
 
  imtxt = new QLabel(" ", this);
  imtxt->setFont(font3);
  imtxt->setText(tex2); 
  imtxt->setStyleSheet("color:white;");
  imtxt->setGeometry(611, 5, 192, 50);

  strttxt = new QLabel("START FREQUENCY:",this);
  strttxt->setFont(font2);
  strttxt->setGeometry(410, 60, 145, 40);
  
  stoptxt = new QLabel("STOP FREQUENCY:",this);
  stoptxt->setFont(font2);
  stoptxt->setGeometry(410, 105, 145, 40);

  /** Plots **/


  /**  Functions **/
  connect(DcapBtn, &QPushButton::clicked, this, &CGui::clickDatacap);
  connect(PrcBtn, &QPushButton::clicked, this, &CGui::clickProcess);
}


void CGui::clickProcess(){
  qDebug() << "Process Button Clicked";
}

void CGui::clickDatacap(){
  qDebug() << "Data Capture Button Clicked";
}

Once again, when I run this code on the target, I could only use backspace the first time I write something on QLineEdit. Once I click somewhere and return to it I could only backspace the new values that I place.

Also, please feel free to correct my coding methods for Qt. I'm sure my code can be improved. Thank you everyone.

Kind regards,
Shoaib

SGaist

Why not use a QFormLayout to build your GUI ?

Shoaib Muhammad

@SGaist said in Clear QLineEdit on Click:

Why not use a QFormLayout to build your GUI ?

I felt like I had more control over the precise positioning of elements in the GUI if I used absolute position instead of QFormLayout.

One issue I had was that the current Qt I was using didn't have QT+= charts in the sdk as well as the target board. I had no way to work around this and so I used QPainter to draw the entire line graph. That we when I decided to use absolute positioning, since the app will be used only on a specific display.

Would it have any effect on the functionality of the design?

Thank you,
Shoaib

aha_1980

Hi @Shoaib-Muhammad,

one thing to note is, that QLineEdit already has a clearButton. But I'm not sure how much that will help you, as the default implementation clears everything. But probably you can detect that and print your prefix again.

Regards

Shoaib Muhammad

@aha_1980 said in Clear QLineEdit on Click:

Hi @Shoaib-Muhammad,

one thing to note is, that QLineEdit already has a clearButton. But I'm not sure how much that will help you, as the default implementation clears everything. But probably you can detect that and print your prefix again.

Regards

Hi aha_1980,

Thank you for this. This works as an alternative. I have read this function somewhere and completely forgot about it.

Thank you everyone for your inputs. I'll mark this thread solved.

Kind regards,
Shoaib