ScrollBar.Scroll Event

Definition

Namespace:

System.Windows.Forms

Assembly:

System.Windows.Forms.dll

Source:

ScrollBar.cs

Occurs when the scroll box has been moved by either a mouse or keyboard action.

C#

public event System.Windows.Forms.ScrollEventHandler? Scroll;

Event Type

ScrollEventHandler

Examples

The following example scrolls an image in a picture box. It uses the Value of the scrollbar to redraw a new part of the image whenever the user scrolls. This code example is part of a larger example provided for the ScrollBar class overview.

Note

For instructions about how to run this example in Visual Studio, see How to: Compile and Run a Complete Windows Forms Code Example Using Visual Studio.

C#

private void HandleScroll(Object sender, ScrollEventArgs e)
{
    //Create a graphics object and draw a portion of the image in the PictureBox.
    Graphics g = pictureBox1.CreateGraphics();

    int xWidth = pictureBox1.Width;
    int yHeight = pictureBox1.Height;

    int x;
    int y;

    if (e.ScrollOrientation == ScrollOrientation.HorizontalScroll)
    {
        x = e.NewValue;
        y = vScrollBar1.Value;
    }
    else //e.ScrollOrientation == ScrollOrientation.VerticalScroll
    {
        y = e.NewValue;
        x = hScrollBar1.Value;
    }

    g.DrawImage(pictureBox1.Image,
      new Rectangle(0, 0, xWidth, yHeight),  //where to draw the image
      new Rectangle(x, y, xWidth, yHeight),  //the portion of the image to draw
      GraphicsUnit.Pixel);

    pictureBox1.Update();
}

The following code example uses the derived class VScrollBar. Event handlers for the Scroll and ValueChanged events are created. This code assumes that a Label and Button have been created on a form and that the button has an event handler for the Click event. When the button is clicked, the Value property of the scroll bar is adjusted in code. The label will display the current value of the Value property and the event that changed it. You will notice that when the scroll value is changed by the button's Click event, only the ValueChanged event is raised. In contrast, when the scroll bar is scrolled manually, the Scroll event is raised immediately after the ValueChanged event.

C#

private void AddMyScrollEventHandlers()
 {
    // Create and initialize a VScrollBar.
    VScrollBar vScrollBar1 = new VScrollBar();
 
    // Add event handlers for the OnScroll and OnValueChanged events.
    vScrollBar1.Scroll += new ScrollEventHandler(
       this.vScrollBar1_Scroll);
    vScrollBar1.ValueChanged += new EventHandler(
       this.vScrollBar1_ValueChanged); 
 }
 
 // Create the ValueChanged event handler.
 private void vScrollBar1_ValueChanged(Object sender, 
                                       EventArgs e)
 {
     // Display the new value in the label.
     label1.Text = "vScrollBar Value:(OnValueChanged Event) " + vScrollBar1.Value.ToString();
 }
 
 // Create the Scroll event handler.
 private void vScrollBar1_Scroll(Object sender, 
                                 ScrollEventArgs e)
 {
     // Display the new value in the label.
     label1.Text = "VScrollBar Value:(OnScroll Event) " + e.NewValue.ToString();
 }
 
 private void button1_Click(Object sender, 
                           EventArgs e)
 {
    // Add 40 to the Value property if it will not exceed the Maximum value.
    if (vScrollBar1.Value + 40 < vScrollBar1.Maximum)
    {
        vScrollBar1.Value = vScrollBar1.Value + 40;
    }
 }

Remarks

For more information about how to handle events, see Handling and Raising Events.

Applies to

See also

• OnScroll(ScrollEventArgs)
• ScrollEventHandler