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Windows Controls: Scroll Bars

 

Introduction to Scroll Bars

 

Description

A scrollbar is a control that allows the user to navigate a document in two directions by clicking a button that displays an arrow. The control is equipped with one button at each of its ends. Between the buttons, there is a (long) bar and on the bar, there is sliding object called a thumb:

Scroll Bars

To use a scroll bar, the user can click one of the arrows. This causes the thumb to move towards the button that was clicked. The user can also click and hold the mouse on a button. This causes the thumb to move continuously, as long as the button is held down, towards the button, until the thumb cannot move any farther. The user can also drag the thumb in one direction to move it or click between a button and the thumb. This causes the thumb to move faster than clicking a button. The thumb of a scroll bar can be positioned only along the scroll bar, between the scroll barís button.

Based on their orientation, there are two types of scroll bars: horizontal and vertical. The horizontal scroll bar allows the user to navigate a document left and right. The vertical scroll bar allows navigating up and down.

Based on their relationship with the parent control or owner, there are two types of scroll bars: those that are (automatically) associated with their parent or owner and scroll bar controls that are manually added by the programmer.

Automatically-Added Scroll Bars

To effectively implement their functionality, some controls must be equipped with one or two scroll bars. When the list of items of a list-based control (list boxes, combo boxes, tree views, list views, etc) exceeds the allocated client area of the control, the list should display a scroll bar to give access to the hidden part of their list. This type of automatically added scroll bars is usually positioned on the right side of the control for most Latin-based languages including US English. Here are examples:

Options

These types of scroll bars are automatically added by the operating system to the control that needs it, unless the programmer explicitly prevented their showing.

Scroll Bars Upon Request

Some controls are ready to display a scroll bar upon request, that is, if you want them to. Such controls are the form, the text box, the rich text box, and the panel. When designing one of these controls, you can ask it to display or hide either or both scroll bars as you see fit.

Although they are the most used containers, by default, the form and the panel control don't display scroll bars, even if you add controls that exceed their allocated client area:

Lack of Scroll Bars

If you have controls that exceed the client area of a form or a panel and if you want them to display scroll bars so the user can navigate to the hidden parts of the container, change the value of the form or the panel's AutoScroll Boolean property. By default, this property is set to False. If you set its value to true, the control container would be equipped with one or both of the scroll bars as necessary:

Auto Scroll

The text box and the rich text box controls are equipped with a property called ScrollBars.

Text-Based Applications and Scroll Bars

Because they are always likely to display a long text, the multi-line text box and the rich text box controls are natively ready to display either or both scroll bars. This is easily done using the ScrollBars property. It provides four options as follows:

Value Comments
None No scroll bar will be displayed
This is the default value
Horizontal A horizontal scroll bar will display at the bottom of the control or document
Vertical A vertical scroll bar will display on the right side of the control or document
Both  A horizontal scroll bar will display at the bottom of the control and a vertical scroll bar will display on the right side of the control or document

Thanks to rapid application development (RAD) and object-oriented programming (OOP), you do not have to permanently set the scroll bar(s). You can act in response to the user doing something and decide when to display or hide either or both scroll bars.

 
 
 

The Scroll Bar Control

 

Introduction

Microsoft Windows provides two other types of scroll bars, considered complete controls in their own right. Like all other controls, these ones must be explicitly created; that is, they are not added automatically but they provide most of the same basic functionality as if the operating system's automatically added the scroll bars.

Creating a Scroll Bar Control

To create a scroll bar control, on the Toolbox, you can click either the VScrollBar or the HScrollBar button then click a container. The scroll bar is one of the earliest controls of the Microsoft Windows operating system. Each control is implemented through a class of the same name. The VScrollBar and the HScrollBar classes are based on the ScrollBar class that essentially provides all of their functionalities.

ApplicationPractical Learning: Introducing Scroll Bar Controls

  1. Start a new Windows Application named HTMLBodyTag1
  2. Design the form as follows:
     
    Body Tag Formatter - Form Designer
     
    Control Name Text Other Properties
    GroupBox GroupBox   Body Attributes  
    RadioButton RadioButton rdoBackground Background Checked: True
    TextBox TextBox txtBackground #000000  
    RadioButton RadioButton rdoText Text  
    TextBox TextBox txtText #0000FF  
    RadioButton RadioButton rdoLink Link  
    TextBox TextBox txtLink #FF0000  
    RadioButton RadioButton rdoActiveLink Active Link  
    TextBox TextBox txtActiveLink #008000  
    RadioButton RadioButton rdoVisitedLink Visited Link  
    TextBox TextBox txtVisitedLink #800000  
    Panel Panel pnlPreview   BackColor: White
    BorderStyle: Fixed3D
    VScrollBar VScrollBar scrRed    
    VScrollBar VScrollBar scrGreen    
    VScrollBar VScrollBar scrBlue    
    Label   R  
    Label   G  
    Label   B  
    Panel Panel pnlBody   BackColor: White
    BorderStyle: Fixed3D
    TextBox TextBox txtTextPreview Body tag formatter and colorizer BorderStyle: None
    ForeColor: Blue
    TextAlign: Center
    TextBox TextBox txtLinkPreview Sample text as link BorderStyle: None
    ForeColor: Red
    TextAlign: Center
    TextBox TextBox txtALinkPreview Current active link BorderStyle: None
    ForeColor: Green
    TextAlign: Center
    TextBox TextBox txtVLinkPreview This link has been visited BorderStyle: None
    ForeColor: Maroon
    TextAlign: Center
    GroupBox GroupBox   Color's Values  
    Label Label   Red:  
    TextBox TextBox txtRed 0  
    Label Label   Green:  
    TextBox TextBox txtGreen 0  
    Label Label   Blue:  
    TextBox TextBox txtBlue 0  
    Button Button btnCopy Copy  
    Button Button btnClose Close  
    TextBox TextBox txtResult <body bgcolor="#FFFFFF" text="#0000FF" link="#FF0000" alink="#008000" vlink="#800000">

Characteristics of a Scroll Bar

 

The Minimum and Maximum Positions

When using a scroll bar, the user can navigate from one end of the control to the other end. These are the controlís minimum and maximum values represented respectively by the Minimum and the Maximum properties. For a horizontal scrollbar, the minimum is the far left position that the bar can assume. For a vertical scrollbar, this would be the most top position:

As you can see from this illustration, the minimum value of a vertical scroll bar is on top. This is the way the vertical scroll bar control of the .NET Framework is configured. On a regular application, the minimum of a vertical scroll is in the bottom section of the control.

The maximum would be the opposite. By default, a newly added scrollbar allows scrolling from 0 to 100. To change these values at design time, type a natural number for each field in the Properties window.

ApplicationPractical Learning: Specifying the Minimum and Maximum

  1. On the form, click one of the scroll bars
  2. Press and hold Ctrl
  3. Click the other two scroll bars and release Ctrl
  4. In the Properties window, click Maximum, type 255, and press Enter
  5. Click an unoccupied area of the form to make sure no control is selected

The Value of a Scroll Bar

The primary technique the user applies to a scrollbar is to click one of the arrows at the ends of the control. As the bar slides inside of the control, it assumes an integer position from Minimum to Maximum. At one time, the position that the bar has is the Value property. At design time, you can use the Value property to set the position that the scrollbar would assume when the form opens. If you set the Value to a value less than the Minimum, you would receive an error of Invalid Property Value:

In the same way, if you set the value of Value to a value higher than the Maximum, you would receive an Invalid Property Value error. To programmatically set the position of the bar, assign the desired value, which must be between Minimum and Maximum, to the Value property.

At run time, when the user scrolls the control, you can find the position of the bar by getting the value of the Value property.

The Small Change

When the user clicks an arrow of a scrollbar, the bar slides by one unit. This unit is represented by the SmallChange property and is set to 1 by default. If you want the bar to slide more than one unit, change the value of the SmallChange property to a natural number between Minimum and Maximum. The higher the value, the faster the sliding would occur because the bar would jump by SmallChange units.

The Large Change

There are two main ways the user can scroll faster using scrollbars: by pressing either page buttons or by clicking the scrolling region. The amount covered using this technique is controlled by the LargeChange property. Once again, the user can scroll only between Minimum and Maximum. To find the scrolling amount, the compiler would divide the actual scrolling range (the difference between Maximum and Minimum) by the LargeChange value. When the user clicks in the scrolling region or presses the Page Up or Page Down keys, the bar would jump by LargeChange up to the scrolling amount value. You can also change the LargeChange property programmatically.

ApplicationPractical Learning: Creating Scroll Bar Controls

  1. On the form, click one of the scroll bars
  2. Press and hold Ctrl
  3. Click the other two scroll bars and release Ctrl
  4. In the Properties window, click LargeChange, type 1, and press Enter
     
    Body Tag Formatter - Vertical Scroll Bars
  5. Right-click the form and click View Code
  6. Create a function as follows:
    void ApplyColor()
    {
        // Retrieve the current hexadecimal colors from their Edit controls
        HexBG = txtBackground->Text;
        HexText = txtText->Text;
        HexLink = txtLink->Text;
        HexALink = txtActiveLink->Text;
        HexVLink = txtVisitedLink->Text;
    
        // Get the integral position of each ScrollBar control
        String ^ strRed = Convert::ToString(255 - scrRed->Value);
        String ^ strGreen = Convert::ToString(255 - scrGreen->Value);
        String ^ strBlue = Convert::ToString(255 - scrBlue->Value);
    
        // Display the position of each ScrollBar
        // in its corresponding Edit control
        txtRed->Text = strRed;
        txtGreen->Text = strGreen;
        txtBlue->Text = strBlue;
    
        // Change the color of the Preview panel
        // according to the values of the ScrollBar positions
        pnlPreview->BackColor = Color::FromArgb(255 - scrRed->Value,
                                                255 - scrGreen->Value,
                                                255 - scrBlue->Value);
    
        String ^ FmtRed = (255 - scrRed->Value).ToString("X");
                if( FmtRed->Length == 1)
                    FmtRed = String::Concat("0", FmtRed);
    
                String ^ FmtGreen = (255 - scrGreen->Value).ToString("X");
                if( FmtGreen->Length == 1)
                    FmtGreen = String::Concat("0", FmtGreen);
    
                String ^ FmtBlue = (255 - scrBlue->Value).ToString("X");
                if( FmtBlue->Length == 1)
                    FmtBlue = String::Concat("0", FmtBlue);
    
                // Get the position of each ScrollBar control
                // Create a hexadecimal color starting with #
                // And display the color in the appropriate Edit control
                if( rdoBackground->Checked == true)
                {
                    String ^ BG = "#";
                    BG = String::Concat(BG, FmtRed);
                    BG = String::Concat(BG, FmtGreen);
                    BG = String::Concat(BG, FmtBlue);
    
                    txtBackground->Text = BG;
                    pnlBody->BackColor = pnlPreview->BackColor;
                    txtTextPreview->BackColor = pnlPreview->BackColor;
                    txtLinkPreview->BackColor = pnlPreview->BackColor;
                    txtALinkPreview->BackColor = pnlPreview->BackColor;
                    txtVLinkPreview->BackColor = pnlPreview->BackColor;
    
                    HexBG = txtBackground->Text;
                }
                else if( rdoText->Checked == true)
                {
                    String ^ Txt = "#";
                    Txt = String::Concat(Txt, FmtRed);
                    Txt = String::Concat(Txt, FmtGreen);
                    Txt = String::Concat(Txt, FmtBlue);
    
                    txtText->Text = Txt;
                    txtTextPreview->ForeColor = Color::FromArgb(255 - scrRed->Value,
                                                              255 - scrGreen->Value,
                                                              255 - scrBlue->Value);
                    HexText = txtText->Text;
                }
                else if( rdoLink->Checked == true)
                {
                    String ^ TL = "#";
                    TL = String::Concat(TL, FmtRed);
                    TL = String::Concat(TL, FmtGreen);
                    TL = String::Concat(TL, FmtBlue);
    
                    txtLink->Text = TL;
                    txtLinkPreview->ForeColor = Color::FromArgb(255 - scrRed->Value,
                                                              255 - scrGreen->Value,
                                                              255 - scrBlue->Value);
    
                    HexLink = txtLink->Text;
                }
                else if( rdoActiveLink->Checked == true)
                {
                    String ^ AL = "#";
                    AL = String::Concat(AL, FmtRed);
                    AL = String::Concat(AL, FmtGreen);
                    AL = String::Concat(AL, FmtBlue);
    
                    txtActiveLink->Text = AL;
                    txtALinkPreview->ForeColor = Color::FromArgb(255 - scrRed->Value,
                                                               255 - scrGreen->Value,
                                                               255 - scrBlue->Value);
    
                    HexALink = txtActiveLink->Text;
                }
                else if( rdoVisitedLink->Checked == true)
                {
                    String ^ VL = "#";
                    VL = String::Concat(VL, FmtRed);
                    VL = String::Concat(VL, FmtGreen);
                    VL = String::Concat(VL, FmtBlue);
    
                    txtVisitedLink->Text = VL;
                    txtVLinkPreview->ForeColor = Color::FromArgb(255 - scrRed->Value,
                                                               255 - scrGreen->Value,
                                                               255 - scrBlue->Value);
    
                    HexVLink = txtVisitedLink->Text;
        }
    
        // Update the contents of the bottom text box
        String ^ BD = "<body bgcolor=\"";
        BD = String::Concat(BD, HexBG);
        BD = String::Concat(BD, "\" text=\"");
        BD = String::Concat(BD, HexText);
        BD = String::Concat(BD, "\" link=\"");
        BD = String::Concat(BD, HexLink);
        BD = String::Concat(BD, "\" alink=\"");
        BD = String::Concat(BD, HexALink);
        BD = String::Concat(BD, "\" vlink=\"");
        BD = String::Concat(BD, HexVLink);
        BD = String::Concat(BD, "\">");
    
        txtResult->Text = BD;
    }
  7. Return to the form and double-click the left scroll bar
  8. Implement its event as follows:
    System::Void scrRed_Scroll(System::Object^  sender,
    		System::Windows::Forms::ScrollEventArgs^  e)
    {
        ApplyColor();
    }
  9. Return to the form and double-click the middle scroll bar
  10. Implement its event as follows:
    System::Void scrGreen_Scroll(System::Object^  sender,
    			 System::Windows::Forms::ScrollEventArgs^  e)
    {
          ApplyColor();
    }
  11. Return to the form  and double-click the right scroll bar
  12. Implement its event as follows:
    System::Void scrBlue_Scroll(System::Object^  sender,
    			    System::Windows::Forms::ScrollEventArgs^  e)
    {
            ApplyColor();
    }
  13. Execute the application to test the form
  14. Close the form and return to your programming environment
  15. When the user clicks a radio button from the Body Attributes group box, we need to display its color on the Preview panel. When a particular button is clicked, we will retrieve the color of its font from the Body text box, translate that color into red, green, and blue values, and then use those values to automatically update the scroll bars and the edit boxes. While we are at it, we also need to update the corresponding text box in the Body Attributes group box. Since this functionality will be used by all radio buttons in the group, we will use a global function to which we can pass two variables.
    When the user clicks a particular radio button, that button is represented by a text box in the lower-left Body section. We need to get the color of that edit box and pass it to our function. Since the clicked radio button has a corresponding text box in the Body Attributes group box, we need to change/update that value with the hexadecimal value of the first argument. Therefore, we will pass a string argument to our function.
    In the Code Editor, just after the closing curly bracket of the scrBlue_Scroll event, create the following member function:
    void ClickOption(System::Drawing::Color Clr, String ^ Result)
    {
    	// These variables will hold the red, green, and blue
    	// values of the passed color
    	int red, green, blue;
    
    	// Colorize the Preview panel with the passed color
    	pnlPreview->BackColor = Clr;
    
    	// Get the red value of the color of the Preview panel
    	red = 255 - pnlPreview->BackColor.R;
    	// Get the green value of the color of the Preview panel
    	green = 255 - pnlPreview->BackColor.G;
    	// Get the blue value of the color of the Preview panel
    	blue = 255 - pnlPreview->BackColor.B;
    
    	// Now that we have the red, green, and blue values of the color,
    	// Update the scroll bars with the new values
    	scrRed->Value   = red;
    	scrGreen->Value = green;
    	scrBlue->Value  = blue;
    
    	// Update the red, green, and blue values
    	// of the Numeric Values group box
    	txtRed->Text = red.ToString();
    	txtGreen->Text = green.ToString();
    	txtBlue->Text = blue.ToString();
    
    	// Update the string that was passed using
    	// the retrieved red, green, and blue values
    	Result = String::Concat(Result, "#");
    	Result = String::Concat(Result, red.ToString("X"));
    	Result = String::Concat(Result, green.ToString("X"));
    	Result = String::Concat(Result, blue.ToString("X"));
    }
  16. Return to the form
  17. Double-click the Background radio button and implement its event as follows:
    System::Void rdoBackground_CheckedChanged(Object ^ sender, EventArgs ^ e)
    {
                // If the user clicks Background radio button
                // set color of the panel to that of the radio button
                Color BGColor = pnlBody->BackColor;
    
                pnlBody->BackColor = BGColor;
    
                // Call the ClickOption() member function to calculate
                // the hexadecimal value of the color
                ClickOption(pnlBody->BackColor, txtBackground->Text);
                HexBG = txtBackground->Text;
    }
  18. Return to the form
  19. Double-click the Text radio button and implement its event as follows:
    System::Void rdoText_CheckedChanged(Object ^ sender, EventArgs ^ e)
    {
                Color BGColor = pnlBody->BackColor;
                txtTextPreview->BackColor = BGColor;
    
                ClickOption(txtTextPreview->ForeColor, txtText->Text);
                HexText = txtText->Text;   
    }
  20. Return to the form
  21. Double-click the Link radio button and implement its event as follows:
    System::Void rdoLink_CheckedChanged(Object ^ sender, EventArgs ^ e)
    {
                Color BGColor = pnlBody->BackColor;
                txtLinkPreview->BackColor = BGColor;
    
                ClickOption(txtLinkPreview->ForeColor, txtLink->Text);
                HexLink = txtLink->Text; 
    }
  22. Return to the form
  23. Double-click the Active Link radio button and implement its event as follows:
    System::Void rdoActiveLink_CheckedChanged(Object ^ sender, EventArgs ^ e)
    {
                Color BGColor = pnlBody->BackColor;
                txtALinkPreview->BackColor = BGColor;
    
                ClickOption(txtALinkPreview->ForeColor, txtActiveLink->Text);
                HexALink = txtActiveLink->Text;
    }
  24. Return to the form
  25. Double-click the Visited Link radio button and implement its event as follows:
    System::Void rdoVisitedLink_CheckedChanged(Object ^ sender, EventArgs ^ e)
    {
                Color BGColor = pnlBody->BackColor;
                txtVLinkPreview->BackColor = BGColor;
    
                ClickOption(txtVLinkPreview->ForeColor, txtVisitedLink->Text);
                HexVLink = txtVisitedLink->Text;  
    }
  26. Return to the form
  27. Double-click the Copy button and implement it as follows:
    System::Void btnCopy_Click(Object ^ sender, EventArgs ^ e)
    {
                txtResult->SelectAll();
                txtResult->Copy();
    }
  28. Return to the form
  29. Double-click the Close button and implement it as follows:
    System::Void btnClose_Click(Object ^ sender, EventArgs ^ e)
    {
                Close();
    }
  30. Execute the application
     
    Body Tag Formatter
  31. Close the form
 
 
   
 

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