Question

In this part of the Qyoto C# 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 of the application. The message consists of text and image data.

using System;
using QtCore;
using QtGui;

/**
 * ZetCode Qyoto C# tutorial
 *
 * This program shows
 * QMessageBox dialogs
 *
 * @author Jan Bodnar
 * website zetcode.com
 * last modified October 2012
 */


public class QyotoApp : QWidget 
{
  public QyotoApp() 
  {
    WindowTitle = "Message boxes";

    InitUI();

    Resize(220, 90);
    Move(300, 300);
    Show();
  }

  void InitUI() 
  {    
    QGridLayout grid = new QGridLayout(this);
    grid.Spacing = 2;

    QPushButton error = new QPushButton("Error", this);
    QPushButton warni = new QPushButton("Warning", this);
    QPushButton quest = new QPushButton("Question", this);
    QPushButton infor = new QPushButton("Information", this);
    QPushButton about = new QPushButton("About", this);

    grid.AddWidget(error, 0, 0);
    grid.AddWidget(warni, 0, 1);
    grid.AddWidget(quest, 1, 0);
    grid.AddWidget(infor, 1, 1);
    grid.AddWidget(about, 2, 0);

    error.Clicked += ShowDialog;
    warni.Clicked += ShowDialog;
    quest.Clicked += ShowDialog;
    infor.Clicked += ShowDialog;
    about.Clicked += ShowDialog;        
  }

  [Q_SLOT]
  void ShowDialog() 
  {
    QPushButton btn = (QPushButton) Sender();

    if ("Error".Equals(btn.Text)) 
    {
      QMessageBox.Critical(this, "Error", "Error loading file!");
    } else if ("Warning".Equals(btn.Text)) 
    {
      QMessageBox.Warning(this, "Warning", "Operation not permitted!");
    } else if ("Question".Equals(btn.Text)) 
    {
      QMessageBox.Question(this, "Question", "Are you sure to quit?");
    } else if ("Information".Equals(btn.Text)) 
    {
      QMessageBox.Information(this, "Information", "Download completed.");
    } else if ("About".Equals(btn.Text)) 
    {
      QMessageBox.About(this, "About", "ZetCode Qyoto C# tutorial.");
    } 
  }

  [STAThread]
  public static int Main(String[] args) 
  {
    new QApplication(args);
    new QyotoApp();
    return 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) Sender();

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

if ("Error".Equals(btn.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 from a list. A label must be set to tell the user what they should enter.

using System;
using QtCore;
using QtGui;

/**
 * ZetCode Qyoto C# tutorial
 *
 * This program shows an input
 * dialog.
 *
 * @author Jan Bodnar
 * website zetcode.com
 * last modified October 2012
 */


public class QyotoApp : QWidget 
{
  QLineEdit edit;
  
  public QyotoApp() 
  {
    WindowTitle = "QInputDialog";

    InitUI();

    Resize(300, 150);
    Move(300, 300);
    Show();
  }

  void InitUI() 
  {    
    QPushButton show = new QPushButton("Dialog", this);
    show.Clicked += ShowDialog;

    show.FocusPolicy = Qt.FocusPolicy.NoFocus;
    show.Move(20, 20);

    edit = new QLineEdit(this);
    edit.Move(130, 22);
  }
  
  [Q_SLOT]
  void ShowDialog() 
  {    
    String text = QInputDialog.GetText(
        this, "Input Dialog", "Enter your name");

    if (text!=null && text.Trim() != String.Empty) 
    {
      edit.Text = text;
    }
  }

  [STAThread]
  public static int Main(String[] args) 
  {
    new QApplication(args);
    new QyotoApp();
    return 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() != String.Empty) 
{
  edit.Text = 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.

using System;
using QtCore;
using QtGui;

/**
 * ZetCode Qyoto C# tutorial
 *
 * In this program, we use the
 * QColorDialog to change the colour
 * of a label text.
 *
 * @author Jan Bodnar
 * website zetcode.com
 * last modified October 2012
 */


public class QyotoApp : QWidget 
{
  QLabel label;
  
  public QyotoApp() : base() 
  {
    WindowTitle = "QColorDialog";

    InitUI();

    Resize(250, 200);
    Move(300, 300);
    Show();
  }

  void InitUI() 
  {
    label = new QLabel("ZetCode Qyoto C# tutorial", this);

    QVBoxLayout vbox = new QVBoxLayout(this);
    label.Alignment = AlignmentFlag.AlignCenter;
    vbox.AddWidget(label);
  }  

  protected override void OnMousePressEvent(QMouseEvent arg1) 
  {
    QColor col = QColorDialog.GetColor();

    if (!col.IsValid()) return;

    String style = String.Format("QWidget {{ color: {0} }}", col.Name());
    label.StyleSheet = style;
  }

  [STAThread]
  public static int Main(String[] args) 
  {
    new QApplication(args);
    new QyotoApp();
    return QApplication.Exec();
  }
}

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

protected override void OnMousePressEvent(QMouseEvent arg1) 
{
  ...
}

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

QColor col = QColorDialog.GetColor();

The QColorDialog is being created. The selected colour is stored in the col variable.

if (!color.IsValid()) return;

We do nothing, when the cancel button was pressed.

String style = String.Format("QWidget {{ color: {0} }}", color.Name());
label.SetStyleSheet(style);

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.

using System;
using QtCore;
using QtGui;

/**
 * ZetCode Qyoto C# tutorial
 *
 * In this program, we use the
 * QFontDialog to change the font
 * of a label text.
 *
 * @author Jan Bodnar
 * website zetcode.com
 * last modified October 2012
 */


public class QyotoApp : QWidget 
{  
  QLabel label;
  
  public QyotoApp() : base() 
  {
    WindowTitle = "QFontDialog";

    InitUI();

    Resize(250, 200);
    Move(300, 300);
    Show();
  }

  void InitUI() 
  {
    label = new QLabel("ZetCode Qyoto C# tutorial", this);

    QVBoxLayout vbox = new QVBoxLayout(this);
    label.Alignment = AlignmentFlag.AlignCenter;
    vbox.AddWidget(label);
  }
  
  protected override void OnMousePressEvent(QMouseEvent arg1) 
  {
    bool ok = true;
    QFont font = QFontDialog.GetFont(ref ok);
    if (!ok) return;
    label.Font = font;
  }

  [STAThread]
  public static int Main(String[] args) 
  {
    new QApplication(args);
    new QyotoApp();
    return QApplication.Exec();
  }
}

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

QFont font = QFontDialog.GetFont(ref ok);

The QFontDialog is being created. The boolean ok variable is set, when we press the OK button of the dialog.

if (!ok) return;

We do nothing if we didn't press the OK button.

label.Font = 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 Qyoto C# tutorial, we worked with dialog windows.