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ScrollBarRenderer Class

Provides methods used to render a scroll bar control with visual styles. This class cannot be inherited.

System.Object
  System.Windows.Forms.ScrollBarRenderer

Namespace:  System.Windows.Forms
Assembly:  System.Windows.Forms (in System.Windows.Forms.dll)

public sealed class ScrollBarRenderer

The ScrollBarRenderer type exposes the following members.

  NameDescription
Public propertyStatic memberIsSupportedGets a value indicating whether the ScrollBarRenderer class can be used to draw a scroll bar with visual styles.
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  NameDescription
Public methodStatic memberDrawArrowButtonDraws a scroll arrow with visual styles.
Public methodStatic memberDrawHorizontalThumbDraws a horizontal scroll box (also known as the thumb) with visual styles.
Public methodStatic memberDrawHorizontalThumbGripDraws a grip on a horizontal scroll box (also known as the thumb) with visual styles.
Public methodStatic memberDrawLeftHorizontalTrackDraws a horizontal scroll bar track with visual styles.
Public methodStatic memberDrawLowerVerticalTrackDraws a vertical scroll bar track with visual styles.
Public methodStatic memberDrawRightHorizontalTrackDraws a horizontal scroll bar track with visual styles.
Public methodStatic memberDrawSizeBoxDraws a scroll bar sizing handle with visual styles.
Public methodStatic memberDrawUpperVerticalTrackDraws a vertical scroll bar track with visual styles.
Public methodStatic memberDrawVerticalThumbDraws a vertical scroll box (also known as the thumb) with visual styles.
Public methodStatic memberDrawVerticalThumbGripDraws a grip on a vertical scroll box (also known as the thumb) with visual styles.
Public methodEquals(Object)Determines whether the specified Object is equal to the current Object. (Inherited from Object.)
Protected methodFinalizeAllows an object to try to free resources and perform other cleanup operations before it is reclaimed by garbage collection. (Inherited from Object.)
Public methodGetHashCodeServes as a hash function for a particular type. (Inherited from Object.)
Public methodStatic memberGetSizeBoxSizeReturns the size of the sizing handle.
Public methodStatic memberGetThumbGripSizeReturns the size of the scroll box grip.
Public methodGetTypeGets the Type of the current instance. (Inherited from Object.)
Protected methodMemberwiseCloneCreates a shallow copy of the current Object. (Inherited from Object.)
Public methodToStringReturns a string that represents the current object. (Inherited from Object.)
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The ScrollBarRenderer class provides a set of static methods that can be used to render a scroll bar control with the current visual style of the operating system. Rendering a control refers to drawing the user interface of a control. This is useful if you are drawing a custom control that should have the appearance of the current visual style. To draw a scroll bar, use a combination of the methods in this class to render each part of the scroll bar.

If visual styles are enabled in the operating system and visual styles are applied to the client area of application windows, the methods of this class will draw the scroll bar with the current visual style. Otherwise, the methods of this class will throw an InvalidOperationException. To determine whether the members of this class can be used, you can check the value of the IsSupported property.

This class wraps the functionality of a System.Windows.Forms.VisualStyles.VisualStyleRenderer that is set to one of the elements exposed by the System.Windows.Forms.VisualStyles.VisualStyleElement.ScrollBar class. For more information, see Rendering Controls with Visual Styles.

Windows XP Home Edition, Windows XP Professional x64 Edition, Windows Server 2003 Platform Note: Visual styles are supported only on these platforms.

The following code example demonstrates how to create a custom control that uses the ScrollBarRenderer methods to draw a scroll bar that responds to mouse clicks.


using System;
using System.Drawing;
using System.Windows.Forms;
using System.Windows.Forms.VisualStyles;

namespace ScrollBarRendererSample
{
    class Form1 : Form
    {
        public Form1()
            : base()
        {
            this.Size = new Size(500, 500);

            CustomScrollBar Bar1 = new CustomScrollBar();
            Bar1.Location = new Point(50, 100);
            Bar1.Size = new Size(200, 20);

            Controls.Add(Bar1);
        }

        [STAThread]
        static void Main()
        {
            // The call to EnableVisualStyles below does not affect whether 
            // ScrollBarRenderer.IsSupported is true; as long as visual styles 
            // are enabled by the operating system, IsSupported is true.
            Application.EnableVisualStyles();
            Application.Run(new Form1());
        }
    }

    public class CustomScrollBar : Control
    {
        private Rectangle clickedBarRectangle;
        private Rectangle thumbRectangle;
        private Rectangle leftArrowRectangle;
        private Rectangle rightArrowRectangle;
        private bool leftArrowClicked = false;
        private bool rightArrowClicked = false;
        private bool leftBarClicked = false;
        private bool rightBarClicked = false;
        private bool thumbClicked = false;
        private ScrollBarState thumbState = ScrollBarState.Normal;
        private ScrollBarArrowButtonState leftButtonState =
            ScrollBarArrowButtonState.LeftNormal;
        private ScrollBarArrowButtonState rightButtonState =
            ScrollBarArrowButtonState.RightNormal;

        // This control does not allow these widths to be altered.
        private int thumbWidth = 15;
        private int arrowWidth = 17;

        // Set the right limit of the thumb's right border.
        private int thumbRightLimitRight = 0;

        // Set the right limit of the thumb's left border.
        private int thumbRightLimitLeft = 0;

        // Set the left limit of thumb's left border.
        private int thumbLeftLimit = 0;

        // Set the distance from the left edge of the thumb to the 
        // cursor tip.
        private int thumbPosition = 0;

        // Set the distance from the left edge of the scroll bar track 
        // to the cursor tip.
        private int trackPosition = 0;

        // This timer draws the moving thumb while the scroll arrows or 
        // track are pressed.
        private Timer progressTimer = new Timer();

        public CustomScrollBar()
            : base()
        {
            this.Location = new Point(10, 10);
            this.Width = 200;
            this.Height = 20;
            this.DoubleBuffered = true;

            SetUpScrollBar();
            progressTimer.Interval = 20;
            progressTimer.Tick += new EventHandler(progressTimer_Tick);
        }

        // Calculate the sizes of the scroll bar elements.
        private void SetUpScrollBar()
        {
            clickedBarRectangle = ClientRectangle;
            thumbRectangle = new Rectangle(
                ClientRectangle.X + ClientRectangle.Width / 2,
                ClientRectangle.Y, thumbWidth,
                ClientRectangle.Height);
            leftArrowRectangle = new Rectangle(
                ClientRectangle.X, ClientRectangle.Y,
                arrowWidth, ClientRectangle.Height);
            rightArrowRectangle = new Rectangle(
                ClientRectangle.Right - arrowWidth,
                ClientRectangle.Y, arrowWidth,
                ClientRectangle.Height);

            // Set the default starting thumb position.
            thumbPosition = thumbWidth / 2;

            // Set the right limit of the thumb's right border.
            thumbRightLimitRight = ClientRectangle.Right - arrowWidth;

            // Set the right limit of the thumb's left border.
            thumbRightLimitLeft = thumbRightLimitRight - thumbWidth;

            // Set the left limit of the thumb's left border.
            thumbLeftLimit = ClientRectangle.X + arrowWidth;
        }

        // Draw the scroll bar in its normal state.
        protected override void OnPaint(PaintEventArgs e)
        {
            base.OnPaint(e);

            // Visual styles are not enabled.
            if (!ScrollBarRenderer.IsSupported)
            {
                this.Parent.Text = "CustomScrollBar Disabled";
                return;
            }

            this.Parent.Text = "CustomScrollBar Enabled";

            // Draw the scroll bar track.
            ScrollBarRenderer.DrawRightHorizontalTrack(e.Graphics,
                ClientRectangle, ScrollBarState.Normal);

            // Draw the thumb and thumb grip in the current state.
            ScrollBarRenderer.DrawHorizontalThumb(e.Graphics,
                thumbRectangle, thumbState);
            ScrollBarRenderer.DrawHorizontalThumbGrip(e.Graphics,
                thumbRectangle, thumbState);

            // Draw the scroll arrows in the current state.
            ScrollBarRenderer.DrawArrowButton(e.Graphics,
                    leftArrowRectangle, leftButtonState);
            ScrollBarRenderer.DrawArrowButton(e.Graphics,
                    rightArrowRectangle, rightButtonState);

            // Draw a highlighted rectangle in the left side of the scroll 
            // bar track if the user has clicked between the left arrow 
            // and thumb.
            if (leftBarClicked)
            {
                clickedBarRectangle.X = thumbLeftLimit;
                clickedBarRectangle.Width = thumbRectangle.X - thumbLeftLimit;
                ScrollBarRenderer.DrawLeftHorizontalTrack(e.Graphics,
                    clickedBarRectangle, ScrollBarState.Pressed);
            }

            // Draw a highlighted rectangle in the right side of the scroll 
            // bar track if the user has clicked between the right arrow 
            // and thumb.
            else if (rightBarClicked)
            {
                clickedBarRectangle.X =
                    thumbRectangle.X + thumbRectangle.Width;
                clickedBarRectangle.Width =
                    thumbRightLimitRight - clickedBarRectangle.X;
                ScrollBarRenderer.DrawRightHorizontalTrack(e.Graphics,
                    clickedBarRectangle, ScrollBarState.Pressed);
            }
        }

        // Handle a mouse click in the scroll bar.
        protected override void OnMouseDown(MouseEventArgs e)
        {
            base.OnMouseDown(e);

            if (!ScrollBarRenderer.IsSupported)
                return;

            // When the thumb is clicked, update the distance from the left
            // edge of the thumb to the cursor tip.
            if (thumbRectangle.Contains(e.Location))
            {
                thumbClicked = true;
                thumbPosition = e.Location.X - thumbRectangle.X;
                thumbState = ScrollBarState.Pressed;
            }

            // When the left arrow is clicked, start the timer to scroll 
            // while the arrow is held down.
            else if (leftArrowRectangle.Contains(e.Location))
            {
                leftArrowClicked = true;
                leftButtonState = ScrollBarArrowButtonState.LeftPressed;
                progressTimer.Start();
            }

            // When the right arrow is clicked, start the timer to scroll 
            // while the arrow is held down.
            else if (rightArrowRectangle.Contains(e.Location))
            {
                rightArrowClicked = true;
                rightButtonState = ScrollBarArrowButtonState.RightPressed;
                progressTimer.Start();
            }

            // When the scroll bar is clicked, start the timer to move the
            // thumb while the mouse is held down.
            else
            {
                trackPosition = e.Location.X;

                if (e.Location.X < this.thumbRectangle.X)
                {
                    leftBarClicked = true;
                }
                else
                {
                    rightBarClicked = true;
                }
                progressTimer.Start();
            }

            Invalidate();
        }

        // Draw the track.
        protected override void OnMouseUp(MouseEventArgs e)
        {
            base.OnMouseUp(e);

            if (!ScrollBarRenderer.IsSupported)
                return;

            // Update the thumb position, if the new location is within 
            // the bounds.
            if (thumbClicked)
            {
                thumbClicked = false;
                thumbState = ScrollBarState.Normal;

                if (e.Location.X > (thumbLeftLimit + thumbPosition) &&
                    e.Location.X < (thumbRightLimitLeft + thumbPosition))
                {
                    thumbRectangle.X = e.Location.X - thumbPosition;
                    thumbClicked = false;
                }
            }

            // If one of the four thumb movement areas was clicked, 
            // stop the timer.
            else if (leftArrowClicked)
            {
                leftArrowClicked = false;
                leftButtonState = ScrollBarArrowButtonState.LeftNormal;
                progressTimer.Stop();
            }

            else if (rightArrowClicked)
            {
                rightArrowClicked = false;
                rightButtonState = ScrollBarArrowButtonState.RightNormal;
                progressTimer.Stop();
            }

            else if (leftBarClicked)
            {
                leftBarClicked = false;
                progressTimer.Stop();
            }

            else if (rightBarClicked)
            {
                rightBarClicked = false;
                progressTimer.Stop();
            }

            Invalidate();
        }

        // Track mouse movements if the user clicks on the scroll bar thumb.
        protected override void OnMouseMove(MouseEventArgs e)
        {
            base.OnMouseMove(e);

            if (!ScrollBarRenderer.IsSupported)
                return;

            // Update the thumb position, if the new location is 
            // within the bounds.
            if (thumbClicked)
            {
                // The thumb is all the way to the left.
                if (e.Location.X <= (thumbLeftLimit + thumbPosition))
                {
                    thumbRectangle.X = thumbLeftLimit;
                }

                // The thumb is all the way to the right.
                else if (e.Location.X >= (thumbRightLimitLeft + thumbPosition))
                {
                    thumbRectangle.X = thumbRightLimitLeft;
                }

                // The thumb is between the ends of the track.
                else
                {
                    thumbRectangle.X = e.Location.X - thumbPosition;
                }

                Invalidate();
            }
        }

        // Recalculate the sizes of the scroll bar elements.
        protected override void OnSizeChanged(EventArgs e)
        {
            base.OnSizeChanged(e);
            SetUpScrollBar();
        }

        // Handle the timer tick by updating the thumb position.
        private void progressTimer_Tick(object sender, EventArgs myEventArgs)
        {
            if (!ScrollBarRenderer.IsSupported)
                return;

            // If an arrow is clicked, move the thumb in small increments.
            if (rightArrowClicked && thumbRectangle.X < thumbRightLimitLeft)
            {
                thumbRectangle.X++;
            }
            else if (leftArrowClicked && thumbRectangle.X > thumbLeftLimit)
            {
                thumbRectangle.X--;
            }

            // If the track bar to right of the thumb is clicked, move the 
            // thumb to the right in larger increments until the right edge 
            // of the thumb hits the cursor.
            else if (rightBarClicked &&
                thumbRectangle.X < thumbRightLimitLeft &&
                thumbRectangle.X + thumbRectangle.Width < trackPosition)
            {
                thumbRectangle.X += 3;
            }

            // If the track bar to left of the thumb is clicked, move the 
            // thumb to the left in larger increments until the left edge 
            // of the thumb hits the cursor.
            else if (leftBarClicked &&
                thumbRectangle.X > thumbLeftLimit &&
                thumbRectangle.X > trackPosition)
            {
                thumbRectangle.X -= 3;
            }

            Invalidate();
        }
    }
}


.NET Framework

Supported in: 4, 3.5, 3.0, 2.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

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