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SnapLine Class

Note: This class is new in the .NET Framework version 2.0.

Represents the horizontal and vertical line segments that are dynamically created in the user interface (UI) to assist in the design-time layout of controls in a container. This class cannot be inherited.

Namespace: System.Windows.Forms.Design.Behavior
Assembly: System.Design (in

public sealed class SnapLine
public final class SnapLine
public final class SnapLine

The following table lists the common modes that visual design tools support to assist you with positioning and sizing controls on a design surface.




Enables you to freely lay out controls.


Displays a static overlaid grid that assists you in laying out controls.


Displays guide lines that assist you in laying out the container's controls relative to each other. Snaplines originate from controls and their container.

The SnapLine class and related types help support the Snapline mode.

Snaplines are generated dynamically and automatically as a control edge moves near another control or near the boundaries of its container. This can occur when a control is added from the toolbox, or moved or resized by mouse operations or keyboard commands. Controls typically have both horizontal and vertical snaplines defined; for rectangular controls, these typically extend from all four edges.

The SnapLine class uses only a few properties to describe each snapline, as shown in the following table.




Specifies the location and direction of the line with respect to its associated control. Typically, only snaplines of similar types will auto-align to each other.


Specifies the distance in pixels from the origin, which is the upper-left corner of the control, to where the snapline starts.


Specifies the relative importance of the snapline. During any given layout decision point, only the snaplines that are active and have the highest priority are displayed.


Defines custom categories of snaplines. This is an optional string.

IsHorizontal and IsVertical

Indicates whether a snapline has horizontal or vertical orientation, respectively.

The ControlDesigner class stores snaplines for its corresponding control type in the SnapLines property. This base class handling of snaplines will suffice for the majority of controls, as it defines the Left, Right, Top, and Bottom snaplines, which are aligned along the edges of the control. When you are developing a custom control, if this default organization does not suffice, override the SnapLines property of the class derived from ControlDesigner. For example, you may want to align the horizontal snaplines of text-based controls, such as labels, with the top and base lines of the text (instead of the top and bottom edges of the control).

The SnapLineType class cannot be derived from.

There is extensive support for this feature in Visual Studio.

Walkthrough: Arranging Controls on Windows Forms Using Snaplines
Walkthrough: Arranging Controls on Windows Forms Using Snaplines
Walkthrough: Arranging Controls on Windows Forms Using Snaplines
Walkthrough: Arranging Controls on Windows Forms Using Snaplines


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

Windows 98, Windows 2000 SP4, Windows Millennium Edition, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition

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

.NET Framework

Supported in: 2.0