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Managing Layout

At its simplest, you control the layout of your user interface by where you place controls in your forms. The placement choices you make are reflected in the control's Top, Left, Width, and Height properties. You can change these values at runtime to change the position and size of the controls in your forms.

Controls have a number of other properties, however, that allow them to automatically adjust to their contents or containers. This allows you to lay out your forms so that the pieces fit together into a unified whole.

Two properties affect how a control is positioned and sized in relation to its parent. The Align property lets you force a control to fit perfectly within its parent along a specific edge or filling up the entire client area after any other controls have been aligned. When the parent is resized, the controls aligned to it are automatically resized and remain positioned so that they fit against a particular edge.

If you want to keep a control positioned relative to a particular edge of its parent, but don't want it to necessarily touch that edge or be resized so that it always runs along the entire edge, you can use the Anchors property.

If you want to ensure that a control does not grow too big or too small, you can use the Constraints property. Constraints lets you specify the control's maximum height, minimum height, maximum width, and minimum width. Set these to limit the size (in pixels) of the control's height and width. For example, by setting the MinWidth and MinHeight of the constraints on a container object, you can ensure that child objects are always visible.

The value of Constraints propagates through the parent/child hierarchy so that an object's size can be constrained because it contains aligned children that have size constraints. Constraints can also prevent a control from being scaled in a particular dimension when its ChangeScale method is called.

TControl introduces a protected event, OnConstrainedResize, of type TConstrainedResizeEvent:

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    TConstrainedResizeEvent = procedure(Sender: TObject; var MinWidth, MinHeight, MaxWidth, MaxHeight: Integer) of object;

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    void __fastcall (__closure *TConstrainedResizeEvent)(System::TObject* Sender, int &MinWidth, int &MinHeight, int &MaxWidth, int &MaxHeight);

This event allows you to override the size constraints when an attempt is made to resize the control. The values of the constraints are passed as var parameters which can be changed inside the event handler. OnConstrainedResize is published for container objects (TForm, TScrollBox, TControlBar, and TPanel). In addition, component writers can use or publish this event for any descendant of TControl.

Controls that have contents that can change in size have an AutoSize property that causes the control to adjust its size to its font or contained objects.

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