Question

In this part of the QtJambi programming tutorial, we will work with dialogs.

Dialog windows or dialogs are an indispensable part of most modern GUI applications. A dialog is defined as a conversation between two or more persons. In a computer application a dialog is a window which is used to "talk" to the application. A dialog is used to input data, modify data, change the application settings etc. Dialogs are important means of communication between a user and a computer program.

Message boxes

Message boxes are convenient dialogs that provide messages to the user the application. The message consists of text and image data.

package com.zetcode;

import com.trolltech.qt.QSignalEmitter;
import com.trolltech.qt.gui.QApplication;
import com.trolltech.qt.gui.QGridLayout;
import com.trolltech.qt.gui.QMessageBox;
import com.trolltech.qt.gui.QPushButton;
import com.trolltech.qt.gui.QWidget;

/**
 * ZetCode QtJambi tutorial
 *
 * This program demonstrates
 * QMessageBox dialogs
 *
 * @author jan bodnar
 * website zetcode.com
 * last modified March 2009
 */

public class JambiApp extends QWidget {
  
  public JambiApp() {

    setWindowTitle("Message Dialogs");

    initUI();

    resize(220, 90);
    move(400, 300);
    show();
  }
  
  private void initUI() {

    QGridLayout grid = new QGridLayout(this);
    grid.setSpacing(2);

    QPushButton error = new QPushButton("Error", this);
    QPushButton warning = new QPushButton("Warning", this);
    QPushButton question = new QPushButton("Question", this);
    QPushButton information = new QPushButton("Information", this);
    QPushButton about = new QPushButton("About", this);

    grid.addWidget(error, 0, 0);
    grid.addWidget(warning, 0, 1);
    grid.addWidget(question, 1, 0);
    grid.addWidget(information, 1, 1);
    grid.addWidget(about, 2, 0);

    error.clicked.connect(this, "showDialog()");
    warning.clicked.connect(this, "showDialog()");
    question.clicked.connect(this, "showDialog()");
    information.clicked.connect(this, "showDialog()");
    about.clicked.connect(this, "showDialog()");
  }

  private void showDialog() {

    QPushButton button = (QPushButton) QSignalEmitter.signalSender();

    if ("Error".equals(button.text())) {
      QMessageBox.critical(this, "Error", "Error loading file!");
    } else if ("Warning".equals(button.text())) {
      QMessageBox.warning(this, "Warning", "Operation not permitted!");
    } else if ("Question".equals(button.text())) {
      QMessageBox.question(this, "Question", "Are you sure to quit?");
    } else if ("Information".equals(button.text())) {
      QMessageBox.information(this, "Information", "Download completed.");
    } else if ("About".equals(button.text())) {
      QMessageBox.about(this, "About", "ZetCode QtJambi tutorial.");
    }
  }

  public static void main(String[] args) {
    QApplication.initialize(args);
    new JambiApp();
    QApplication.exec();
  }
}

We use the GridLayout manager to set up a grid of five buttons. Each of the buttons shows a different message box.

QPushButton button = (QPushButton) QSignalEmitter.signalSender();

Here we determine, which button called the showDialog() method.

if ("Error".equals(button.text())) {
  QMessageBox.critical(this, "Error", "Error loading file!");
}

In case we pressed the error button, we show the error dialog. We use static methods of the QMessageBox class to show the message boxes.

QInputDialog

The QInputDialog class provides a simple convenience dialog to get a single value from the user. The input value can be a string, a number or an item from a list. A label must be set to tell the user what they should enter.

package com.zetcode;

import com.trolltech.qt.core.Qt;
import com.trolltech.qt.gui.QApplication;
import com.trolltech.qt.gui.QInputDialog;
import com.trolltech.qt.gui.QLineEdit;
import com.trolltech.qt.gui.QPushButton;
import com.trolltech.qt.gui.QWidget;

/**
 * ZetCode QtJambi tutorial
 * 
 * This program shows an input
 * dialog
 *
 * @author jan bodnar
 * website zetcode.com
 * last modified March 2009
 */

public class JambiApp extends QWidget {

  QLineEdit edit;

  public JambiApp() {

    setWindowTitle("Input Dialog");

    initUI();

    move(400, 300);
    show();
  }


  private void initUI() {

    setGeometry(300, 300, 350, 80);

    QPushButton show = new QPushButton("Dialog", this);

    show.clicked.connect(this, "showDialog()");
    show.setFocusPolicy(Qt.FocusPolicy.NoFocus);

    show.move(20, 20);

    edit = new QLineEdit(this);
    edit.move(130, 22);
  }

  private void showDialog() {
    
    String text = QInputDialog.getText(
        this, "Input Dialog", "Enter your name");

    if (text!=null && !text.trim().isEmpty()) {
      edit.setText(text);
    }
  }

  public static void main(String[] args) {
    QApplication.initialize(args);
    new JambiApp();
    QApplication.exec();
  }
}

In the code example, we have a button and a line edit. The button shows an input dialog. We get some text and the text is shown in the line edit widget.

String text = QInputDialog.getText(
    this, "Input Dialog", "Enter your name");

The getText() static method creates the input dialog. The text from the dialog is stored in the text variable.

if (text!=null && !text.trim().isEmpty()) {
  edit.setText(text);
}

Before we update the line edit, we ensure that the text variable is not null and that it is not empty and does not consists only from spaces.

Figure: Input dialog

QColorDialog

The QColorDialog class provides a dialog widget for specifying colors. The color dialog's function is to allow users to choose colors.

package com.zetcode;

import com.trolltech.qt.core.Qt;
import com.trolltech.qt.gui.QApplication;
import com.trolltech.qt.gui.QColor;
import com.trolltech.qt.gui.QColorDialog;
import com.trolltech.qt.gui.QLabel;
import com.trolltech.qt.gui.QMouseEvent;
import com.trolltech.qt.gui.QVBoxLayout;
import com.trolltech.qt.gui.QWidget;
import java.util.Formatter;

/**
 * ZetCode QtJambi tutorial
 *
 * In this program, we use the
 * QColorDialog to change the color
 * of a label text
 *
 * @author jan bodnar
 * website zetcode.com
 * last modified March 2009
 */


public class JambiApp extends QWidget {
  
  QLabel label;

  public JambiApp() {

    setWindowTitle("Color Dialog");

    initUI();

    resize(250, 200);
    move(400, 300);
    show();
  }

  private void initUI() {

    label = new QLabel("ZetCode QtJambi tutorial", this);

    QVBoxLayout vbox = new QVBoxLayout(this);
    label.setAlignment(Qt.AlignmentFlag.AlignCenter);
    vbox.addWidget(label);

  }

  @Override
  public void mousePressEvent(QMouseEvent event) {

    QColor color = QColorDialog.getColor();

    if (!color.isValid()) return;

    Formatter fmt = new Formatter();
    fmt.format("QWidget { color: %s }", color.name());

    label.setStyleSheet(fmt.toString());
  }
  
  
  public static void main(String[] args) {
    QApplication.initialize(args);
    new JambiApp();
    QApplication.exec();
  }
}

We show a some text in the center of the window. By clicking on the area of the window, we show a color dialog. We change the text foreground color to the selected color from the dialog.

@Override
public void mousePressEvent(QMouseEvent event) {
  ...
}

In order to receive mouse press events for our window, we must reimplement the mousePressEvent() method.

QColor color = QColorDialog.getColor();

The QColorDialog is being created. The selected color is stored in the color variable.

Formatter fmt = new Formatter();
fmt.format("QWidget { color: %s }", color.name());

label.setStyleSheet(fmt.toString());

Here we update the foreground color of the label's text.

Figure: QColorDialog

QFontDialog

The QFontDialog class provides a dialog widget for selecting a font.

package com.zetcode;

import com.trolltech.qt.core.Qt;
import com.trolltech.qt.gui.QApplication;
import com.trolltech.qt.gui.QFontDialog;
import com.trolltech.qt.gui.QLabel;
import com.trolltech.qt.gui.QMouseEvent;
import com.trolltech.qt.gui.QVBoxLayout;
import com.trolltech.qt.gui.QWidget;

/**
 * ZetCode QtJambi tutorial
 *
 * In this program, we use the
 * QFontDialog to change the font
 * of a label text
 * 
 * @author jan bodnar
 * website zetcode.com
 * last modified March 2009
 */

public class JambiApp extends QWidget {

  QLabel label;

  public JambiApp() {
    
    setWindowTitle("QFontColor dialog");

    initUI();

    resize(250, 200);
    move(300, 300);
    show();
  }


  private void initUI() {

    label = new QLabel("ZetCode QtJambi tutorial", this);

    QVBoxLayout vbox = new QVBoxLayout(this);
    label.setAlignment(Qt.AlignmentFlag.AlignCenter);
    vbox.addWidget(label);
  }

  @Override
  public void mousePressEvent(QMouseEvent event) {

    QFontDialog.Result result = QFontDialog.getFont();

    if (!result.ok) return;

    label.setFont(result.font);
  }
  
  
  public static void main(String[] args) {
    QApplication.initialize(args);
    new JambiApp();
    QApplication.exec();
  }
}

This example is similar to the previous one. This time, we change the font of the text.

QFontDialog.Result result = QFontDialog.getFont();

The QFontDialog is being created. The dialog returns the QFontDialog.Result class. This class has two fields. The font and the ok field.

if (!result.ok) return;

The boolean ok variable is true if we clicked on the OK button of the dialog. We return from the method if the cancel button was pressed.

label.setFont(result.font);

The font field stores the selected font. We update the label's font to the newly selected font.

Figure: QFontDialog

In this part of the QtJambi tutorial, we worked with dialog windows.