QtJambi dialogs

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.

Information message dialog Warning message dialog Question message dialog Error message dialog About message dialog

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.

Input dialog
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.

QColorDialog
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.

QFontDialog
Figure: QFontDialog

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