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VCL Controls: The Labeled Edit Box

 

Introduction

It is by an unavoidable habit that almost every edit control is accompanied by a label. The reason is that, as stated already when reviewing the edit control, a text box has no mechanism of indicating what it is used for. That precision is usually handled by a label. To make it easy, starting with C++ Builder 6, Borland created a control that combines an edit control and its accompanying label: the LabeledEdit control.

To create a LabeledEdit control, click its button LabeledEdit in the Additional tab of the Component Palette and add it to a container of your choice.

 

Characteristics of the Labeled Edit Control

The LabeledEdit control is an object of type TLabeledEdit. This control shares its ancestry with the edit control: their parent is the TCustomEdit class. The TLabeledEdit class itself is derived from the based on the TCustomLabeledEdit class. Based on its ancestry, the LabeledEdit control inherits the same functionality as the edit control.

After adding a LabeledEdit control to your application, you notice that it is accompanied by a label but both are treated as one control. By default, the (accompanying) label is positioned above the edit control. The position of the label is controlled by the LabelPosition property. This property is type TLabelPosition, which is an enumerator. It can have one of four values:

  • lpAbove: (the defualt) Causes the label to be positioned on top of the edit control
  • lpBelow: Causes the label to be positioned under the edit control
  • lpLeft: Positions the label to the left of the edit control
  • lbRight: The label is positioned on the right side of the edit control

If you use a separate label and edit controls in your application, you know that you can decide about the distance between both controls. For a LabeledEdit object, this characteristic is handled by the LabelSpacing property, which is an integer. The default value of this property is 3. In most cases, and especially if you decide to position the label to the left, this value would be too little.

We mentioned that the TLabeledEdit class, on which the LabeledEdit control is based, derived from the TCustomEdit class, which provides functionality only for an edit control. To respect the avoidance of double-inheritance in a VCL control, the LabeledEdit control is equipped with a property called EditLabel. The role of this property is to identify or represent the label part of the LabeledEdit. To support the whole functionality of a label, the EditLabel property is of type TBoundLabel. The TBoundLabel class is derived from the TCustomLabel class, which is the same immediate class of the Label control. Based on this, to perform any label-related operation on a LabeledEdit control, first invoke its EditLabel property and then access any of the properties and characteristics we reviewed for the label control. At design time, the EditLabel property is represented with a + field in the object inspector. As such, you can click the + button:

This allows you to manipulate the label side of the control.

Practical Learning Practical Learning: Using the LabeledEdit Control

  1. Start a new Application with its default form and change the form's BorderStyle to bsDialog
  2. Save the application in a new folder named ColumnChart1
  3. Save the unit as Exercise and the project as ColumnChart
  4. In the Component Palette, click Additional. Click LabeledEdit LabeledEdit and click form
  5. While the new control is still selected, in the Object Inspector, click Name and type ledMonday
  6. Click the + button of the EditLabel field. Under it, click Caption and type Monday
  7. Complete the design of the form as follows:
     
    Control Caption Text EditLabel=>Caption Name
    Label Furniture Sales      
    LabeledEdit     Monday ledMonday
    LabeledEdit     Tuesday ledTuesday
    LabeledEdit     Wednesday ledWednesday
    LabeledEdit     Thursday ledThursday
    LabeledEdit     Friday ledFriday
    Button Generate     btnGenerate
    PaintBox        
  8. Press F12 to access the Code Editor. In the header file (Exercise.h), declare a private variable as
     
    Graphics::TBitmap *DrawingBoard;
  9. Access the source code of the form and initialize the variable in the constructor as follows:
     
    //---------------------------------------------------------------------------
    __fastcall TForm1::TForm1(TComponent* Owner)
        : TForm(Owner)
    {
        DrawingBoard = new Graphics::TBitmap;
        DrawingBoard->Width  = PaintBox1->Width;
        DrawingBoard->Height = PaintBox1->Height;
    }
    //---------------------------------------------------------------------------
  10. Press F12 to display the form. On the form, click the PaintBox1 control to select it
  11. In the Object Inspector, click the Events tab and double-click the right field to OnPaint
  12. Implement its event as follows:
     
    //---------------------------------------------------------------------------
    void __fastcall TForm1::PaintBox1Paint(TObject *Sender)
    {
        PaintBox1->Canvas->Draw(0, 0, DrawingBoard);
    }
    //---------------------------------------------------------------------------
  13. Return to the form and double-click the Generate button
  14. Implement its event as follows:
     
    //---------------------------------------------------------------------------
    void __fastcall TForm1::btnGenerateClick(TObject *Sender)
    {
        this->DrawingBoard->Canvas->Brush->Color = clWhite;
        this->DrawingBoard->Canvas->Brush->Style = bsSolid;
        this->DrawingBoard->Canvas->Pen->Color   = clWhite;
        this->DrawingBoard->Canvas->Rectangle(0, 0, Width, Height);
    
        Invalidate();
    
        int monday    = this->ledMonday->Text.ToInt() / 100;
        int tuesday   = this->ledTuesday->Text.ToInt() / 100;
        int wednesday = this->ledWednesday->Text.ToInt() / 100;
        int thursday  = this->ledThursday->Text.ToInt() / 100;
        int friday    = this->ledFriday->Text.ToInt() / 100;
    
        this->DrawingBoard->Canvas->Brush->Color = clGreen;
        this->DrawingBoard->Canvas->Brush->Style = bsCross;
        this->DrawingBoard->Canvas->Pen->Color   = clBlack;
        this->DrawingBoard->Canvas->Pen->Width = 1;
        this->DrawingBoard->Canvas->Rectangle(ledMonday->Left+20,
                                              PaintBox1->Height-20-monday,
                                              ledMonday->Left+60,
                                              PaintBox1->Height-20);
    
        this->DrawingBoard->Canvas->Brush->Color = clRed;
        this->DrawingBoard->Canvas->Brush->Style = bsBDiagonal;
        this->DrawingBoard->Canvas->Rectangle(ledTuesday->Left+20,
                                              PaintBox1->Height-20-tuesday,
                                              ledTuesday->Left+60,
                                              PaintBox1->Height-20);
    
        this->DrawingBoard->Canvas->Brush->Color = clBlue;
        this->DrawingBoard->Canvas->Brush->Style = bsFDiagonal;
        this->DrawingBoard->Canvas->Rectangle(ledWednesday->Left+20,
                                              PaintBox1->Height-20-wednesday,
                                              ledWednesday->Left+60,
                                              PaintBox1->Height-20);
    
        this->DrawingBoard->Canvas->Brush->Color = clFuchsia;
        this->DrawingBoard->Canvas->Brush->Style = bsDiagCross;
        this->DrawingBoard->Canvas->Rectangle(ledThursday->Left+20,
                                              PaintBox1->Height-20-thursday,
                                              ledThursday->Left+60,
                                              PaintBox1->Height-20);
    
        this->DrawingBoard->Canvas->Brush->Color = clNavy;
        this->DrawingBoard->Canvas->Brush->Style = bsVertical;
        this->DrawingBoard->Canvas->Rectangle(ledFriday->Left+20,
                                              PaintBox1->Height-20-friday,
                                              ledFriday->Left+60,
                                              PaintBox1->Height-20);
    
        this->DrawingBoard->Canvas->Pen->Width = 4;
        this->DrawingBoard->Canvas->MoveTo(PaintBox1->Left+20,
                                           PaintBox1->Height-20);
        this->DrawingBoard->Canvas->LineTo(PaintBox1->Width-5,
                                           PaintBox1->Height-20);
        Invalidate();
    }
    //---------------------------------------------------------------------------
  15. Execute the application and enter some values in the edit boxes before clicking Generate. Here is an example:
     
  16. Close the form and return to your programming environment

 

 
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