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TCheckBox

 

 

 

TCheckBox represents a check box that can be on (checked) or off (unchecked). A TCheckBox component presents an option for the user. The user can check the box to select the option, or uncheck it to deselect the option.


In some examples we assume a check box has been created and is named "checkbox".

 

TCheckBox checkbox = TCheckBox.Create(form);

 


Properties



 

property TAlign Align;

Determines how the control aligns within its container (parent control).

 

enum TAlign {

  alNone,

  alTop,

  alBottom,

  alLeft,

  alRight,

  alClient,

  alCustom

};

 

Ex. checkbox.Align = alNone;


 

property TLeftRight Alignment;

Determines whether the check box label aligns to the left or right of the tick box. The TLeftRight alignment type may have one of the following values :

 

taLeftJustify   - The check box label is displayed on the left of the check box.

taRightJustify  - This is the default value. The check box label is displayed on the right of the check box.


 

property Bool AlignWithMargins;

Indicates whether a control should be constrained by margins. If AlignWithMargins is true, use the Margins property of the control to govern the spacing relative to other controls that are aligned with this one.


 

property Bool AllowGrayed;

Determines whether check box can be in a "grayed" state. If AllowGrayed is set to true, the check box has three possible states: checked, unchecked, and grayed. If AllowGrayed is set to false, the check box has only two possible states: checked and unchecked.


 

property TAnchors Anchors;

Specifies how the control is anchored to its parent.

 

enum TAnchorKind {

  akLeft,

  akTop,

  akRight,

  akBottom

};

 

Ex. checkbox.Anchors = akLeft + akTop;


 

property String Caption;

Specifies a text string that identifies the control to the user.  It can be the text label of a radio button or the title text in a form. To underline a character in a Caption, include an ampersand (&) before the character.


 

property Bool Checked;

Specifies whether the button control is checked.


 

property TColor Color;

Specifies the background color of the control. The color value can be an hexadecimal or a color constant.


Defined color constants are:

clAqua, clBlack, clBlue, clCream, clDkGray, clFuchsia, clGray, clGreen, clLime, clLtGray, clMaroon, clMedGray, clMoneyGreen, clNavy, clOlive, clPurple, clRed, clSilver, clSkyBlue, clTeal, clWhite, clYellow.

 

Defined system color constants:

clNone                      White on Windows 9x, Black on NT.

clScrollBar                 Current color for the of scroll bar track.

clBackground                Current background color of the Windows desktop

clActiveCaption             Current color of the title bar of the active window

clInactiveCaption           Current color of the title bar of inactive windows

clMenu                      Current background color of menus

clWindow                    Current background color of windows

clWindowFrame               Current color of window frames

clMenuText                  Current color of text on menus

clWindowText                Current color of text in windows

clCaptionText               Current color of the text on the title bar of the active window

clActiveBorder              Current border color of the active window

clInactiveBorder            Current border color of inactive windows

clAppWorkSpace              Current color of the application workspace

clHighlight                 Current background color of selected text

clHightlightText            Current color of selected text

clBtnFace                   Current color of a button face

clBtnShadow                 Current color of a shadow cast by a button

clGrayText                  Current color of text that is dimmed

clBtnText                   Current color of text on a button

clInactiveCaptionText       Current color of the text on the title bar of an inactive window

clBtnHighlight              Current color of the highlighting on a button

cl3DDkShadow                Windows 95 or NT 4.0 only: Dark shadow for three-dimensional display elements

cl3DLight                   Windows 95 or NT 4.0 only: Light color for three-dimensional display elements (for edges facing the light source)

clInfoText                  Windows 95 or NT 4.0 only: Text color for tool tip controls

clInfoBk                    Windows 95 or NT 4.0 only: Background color for tool tip controls

clGradientActiveCaption     Windows 98 or Windows 2000: Right side color in the color gradient of an active window's title bar.

clActiveCaption             specifies the left side color.

clGradientInactiveCaption   Windows 98 or Windows 2000: Right side color in the color gradient of an inactive window's title bar. clInactiveCaption           specifies the left side color.

clDefault                   The default color for the control to which the color is assigned.


Ex. checkbox.Color = 0x0000FF00;

Ex. checkbox.Color = clGreen;


 

property Bool Enabled;

Controls whether the control responds to mouse, keyboard, and timer events.


 

property TFont Font;

Controls the attributes of text written on or in the control. To change to a new font, specify a new TFont object. To modify a font, change the value of the Charset, Color, Height, Name, Pitch, Size, or Style of the TFont object.

 

Ex. checkbox.Font.Size = 12;


 

property int Height;

Specifies the vertical size of the control in pixels.


Ex. checkbox.Height = 16;


 

property String Hint;

Contains the text string that can appear when the user moves the mouse over the control.


 

property int Left;

Specifies the horizontal coordinate of the left edge of a component relative to its parent.


 

property TMargins Margins;

Specifies the margins for the control. TMargins help define the relative position between components on a form, and between the edges of the form and the component. For example, when you set a left margin for a component to 10 pixels, the component will not come closer than 10 pixels to the edge of the container, or to another component on the left edge. The number of pixels by which two components are separated is the sum of the pixels of both components.

TMargins have the class members top, bottom, left and right.


Ex. checkbox.Margins.Left = 10;


 

property String Name;

Specifies the name of the component as referenced in code.


 

property TPadding Padding;

Specifies the padding of a control. Padding works similar to margins.

 

Ex. checkbox.Padding.Left = 4;


 

property TWinControl Parent;

Use the Parent property to get or set the parent of this control. The parent of a control is the control that contains the control. For example, if an application includes three radio buttons in a group box, the group box is the parent of the three radio buttons, and the radio buttons are the child controls of the group box.

 

Ex.

TCheckBox checkbox = TCheckBox.Create(groupbox);

checkbox.Parent = groupbox;

checkbox.Left = 8;


 

property Bool ParentColor;

To have a control use the same color as its parent control, set ParentColor to true. If ParentColor is false, the control uses its own Color property.


 

property Bool ParentFont;

Determines where a control looks for its font information.

To have a control use the same font as its parent control, set ParentFont to true. If ParentFont is false, the control uses its own Font property.


 

property TPopupMenu PopupMenu;

Identifies the pop-up menu associated with the control.


 

property Bool ShowHint;

Determines whether the control displays a Help Hint when the mouse pointer rests momentarily on the control.


 

property CheckState State;

Indicates whether the check box is selected, deselected, or grayed. Use State to determine whether the check box is checked (cbChecked), unchecked (cbUnchecked), or grayed (cbGrayed).


Ex. checkbox.State = cbGrayed;


 

property TTabOrder TabOrder;

TabOrder is the order in which child windows are visited when the user presses the Tab key. The control with the TabOrder value of 0 is the control that has the focus when the form first appears.

 

Initially, the tab order is always the order in which the controls were added to the form. The first control added to the form has a TabOrder value of 0, the second is 1, the third is 2, and so on. Change this by changing the TabOrder property.  


 

property Bool TabStop;

Determines if the user can tab to a control.


 

property int Tag;

Stores an integer value as part of a component.


 

property int Top;

Specifies the Y coordinate of the top left corner of a control, relative to its parent or containing control in pixels.


 

property Boolean Visible;

Indicates whether the control is visible.


 

property int Width;

Specifies the horizontal size of the control or form in pixels.


 

property Bool WordWrap;

Specifies whether the button text wraps to fit the width of the control.


Set WordWrap to true to allow the display of multiple lines of text.

 

 


Methods



 

constructor Create(TComponent AOwner) 

Creates and initializes a new TCheckBox object.

 

Ex. TCheckBox checkbox = TCheckBox.Create(groupbox);


 

procedure Free;

Destroys an object and frees its associated memory, if necessary. Visual controls added to a form is automatically destroyed when the form closes.

 

Ex.

TForm form = new TForm(nil);

TCheckBox checkbox = TCheckBox.Create(form);

...

checkbox.Free;


 

procedure Hide;

Hides the control.


 

procedure Show;

Shows the control. Use Show to set the control's Visible property to true.


 


Events



 

OnClick 

Occurs when the user clicks the control.


Ex.

 

TForm form;

TGroupBox group;

TCheckBox check1;

void check1Click(TObject Sender)

{

  // Do some work here

}

 

{

  form = new TForm(nil);  

 

  group = TGroupBox.Create(form);

  group.Parent = form;

 

  check1 = TCheckBox.Create(group);

  check1.Parent = group;

  check1.OnClick = &check1Click;

}


 

OnEnter 

Occurs when a control receives the input focus. Use the OnEnter event handler to cause any special processing to occur when a control becomes active.


Ex.

 

TForm form;

TGroupBox group;

TCheckBox check1;

void check1Enter(TObject Sender)

{

  // Do some work here

}

 

{

  form = new TForm(nil);

 

  group = TGroupBox.Create(form);

  group.Parent = form;

 

  check1 = TCheckBox.Create(group);

  check1.Parent = group;

  check1.OnEnter = &check1Enter;

}


 

OnExit 

Occurs when the input focus shifts away from one control to another. Use the OnExit event handler to provide special processing when the control ceases to be active.


Ex.

 

TForm form;

TGroupBox group;

TCheckBox check1;

void check1Exit(TObject Sender)

{

  // Do some work here

}

 

{

  form = new TForm(nil);

 

  group = TGroupBox.Create(form);

  group.Parent = form;

 

  check1 = TCheckBox.Create(group);

  check1.Parent = group;

  check1.OnExit = &check1Exit;

}


 

OnKeyDown 

Occurs when a user presses any key while the control has focus.

 

(ssShift, ssAlt, ssCtrl, ssLeft, ssRight, ssMiddle, ssDouble) TShiftState;


Ex.

 

TForm form;

TGroupBox group;

TCheckBox check1;

void check1KeyDown(TObject Sender, WORD &Key, TShiftState Shift)

{

  // Do some work here

  if (Key == VK_F1) {

    // F1 was pressed, lets do something...

 

  }

}

{

  form = new TForm(nil);

 

  group = TGroupBox.Create(form);

  group.Parent = form;

 

  check1 = TCheckBox.Create(group);

  check1.Parent = group;

  check1.OnKeyDown = &check1KeyDown;

}


 

OnKeyPress 

Occurs when a key is pressed.


Ex.

 

TForm form;

TGroupBox group;

TCheckBox check1;

void check1KeyPress(TObject Sender, char &Key)

{

  // Do something

}

 

{

  form = new TForm(nil);

  group = TGroupBox.Create(form);

  group.Parent = form;

 

  check1 = TCheckBox.Create(group);

  check1.Parent = group;

  check1.OnKeyPress = &check1KeyPress;

}


 

OnKeyUp 

Occurs when the user releases a key that has been pressed.


(ssShift, ssAlt, ssCtrl, ssLeft, ssRight, ssMiddle, ssDouble) TShiftState;


Ex.


TForm form;

TGroupBox group;

TCheckBox check1;

void check1KeyUp(TObject Sender, WORD &Key, TShiftState Shift)

{

  // Do some work here

}

 

{

  form = new TForm(nil);

 

  group = TGroupBox.Create(form);

  group.Parent = form;

 

  check1 = TCheckBox.Create(group);

  check1.Parent = group;

  check1.OnKeyUp = &check1KeyUp;

}


 

OnMouseDown 

Occurs when the user presses a mouse button with the mouse pointer over a control.

 

(ssShift, ssAlt, ssCtrl, ssLeft, ssRight, ssMiddle, ssDouble) TShiftState;

 

enum TMouseButton {

  mbLeft,

  mbRight,

  mbMiddle

};

 

Ex.

 

TForm form;

TGroupBox group;

TCheckBox check1;

void check1MouseDown(TObject Sender, TMouseButton Button, TShiftState Shift, int X, int Y)

{

  // Do some work here if left mouse button was pressed

  if (Button == mbLeft) {

    // Left mouse button was pressed. Lets do something...

 

  }

}

 

{

  form = new TForm(nil);

 

  group = TGroupBox.Create(form);

  group.Parent = form;

 

  check1 = TCheckBox.Create(group);

  check1.Parent = group;

  check1.OnMouseDown = &check1MouseDown;

}


 

OnMouseEnter 

Occurs when the user moves the mouse into a control.


Ex.

 

TForm form;

TGroupBox group;

TCheckBox check1;

void check1MouseEnter(TObject Sender)

{

  // Do some work here

}

 

{

  form = new TForm(nil);

 

  group = TGroupBox.Create(form);

  group.Parent = form;

 

  check1 = TCheckBox.Create(group);

  check1.Parent = group;

  check1.OnMouseEnter = &check1MouseEnter;

}


 

OnMouseLeave 

Occurs when the user moves the mouse outside of a control.


Ex.

 

TForm form;

TGroupBox group;

TCheckBox check1;

void check1MouseLeave(TObject Sender)

{

  // Do some work here

}

 

{

  form = new TForm(nil);

 

  group = TGroupBox.Create(form);

  group.Parent = form;

 

  check1 = TCheckBox.Create(group);

  check1.Parent = group;

  check1.OnMouseLeave = &check1MouseLeave;

}


 

OnMouseMove 

Occurs when the user moves the mouse pointer while the mouse pointer is over a control.

 

Ex.

 

int FMouseX,FMouseY;

TForm form;

TGroupBox group;

TCheckBox check1;

void check1MouseMove(TObject Sender, TMouseButton Button, TShiftState Shift, int X, int Y)

{

  // Do some work here

  FMouseX = X;

  FMouseY = Y;

}

 

{

  form = new TForm(nil);

 

  group = TGroupBox.Create(form);

  group.Parent = form;

 

  check1 = TCheckBox.Create(group);

  check1.Parent = group;

  check1.OnMouseMove = &check1MouseMove;

}


 

OnMouseUp 

Occurs when the user releases a mouse button that was pressed with the mouse pointer over a component.


Ex.

 

TForm form;

TGroupBox group;

TCheckBox check1;

void check1MouseUp(TObject Sender, TMouseButton Button, TShiftState Shift, int X, int Y)

{

  // Do some work here

}

 

{

  form = new TForm(nil);

 

  group = TGroupBox.Create(form);

  group.Parent = form;

 

  check1 = TCheckBox.Create(group);

  check1.Parent = group;

  check1.OnMouseUp = &check1MouseUp;

}


 


 


 


 


 


 


 


 

 

 

 

Copyright © 2022 Rickard Johansson