Sunncity.com - Developer & I.T. Zone

Tutorial - WRITING YOUR FIRST COMPONENT (Part 2)

12 * When to Override?(4/53)
13 * Component "NewComp" (4/54)
14 * Pre-Install the Component to the palette.(4/55)
15 * "Package" in Delphi (4/56-57)
16 * Start a new project and test Component (4/57)
17 * Assign Event Handler by writing code.(4/58)
18 * Indicate Owner property (4/58-59)
19 * Adding Property to an Object (4/66)
20 * Adding Property to a Class (4/71)
21 * Intercept windows messages to redirect interaction to Component when necessary.(4/73)
22 * Override essential methods in maintaining Component status.(4/74)
23 * Adding existing event or create new Event to interact with users's runtime handler.(4/75)

12 * When to Override?(4/53)
Taking Old Component and Override it to create new component makes programmer's life easier.

When override you have to add command inherited always which indicate that this "Object" will start with what it use to do first as we called "default handler". (Already explained in part 1).
If Override without inherited in Create Method it will translate that you are going to create this OBJECT all by yourself. You can manage by writing approximately 1000 lines or more in order to create OBJECT and enabled it to store in memory and save with form or "Resource Stream". (It would be incredibly too much work, unless you are willing to do that).

Create Constructor Method = Call to use at design time if component is drop on form when designing. At the moment we dropped component create method is call.

Destroy Destructor Method = When programmer deletes component that was dropped on form. (If we create owner of our component as "Self" we won't need to FREE it.) You can also write your own code how you want to destroy your component too. (if you dare).

Back to TOP

13 * Component "NewComp" (4/54)

NewComp is a Component, which allow you to drop it on form and enable MOUSE to drag FORM on your screen by clicking anywhere on FORM. Dragging form is done by instant animation. You should consider how you would like to control action on MouseMove, including what you want to modify after you drop your component on form.

Back to TOP

14 * Pre-Install the Component to the palette.(4/55)

If you are a PRO, you can create your component in one long writing program till completion then installs your component to the palette. If you are not a PRO yet, you can gradually create your component and compile to check your mistake. Recommended you do the second option by starting to draw "ICON" for your component first.

Go to MainMenu --->choose TOOLS-->then choose Image Editor.
Choose -->File---> New --->then DCR (Delphi Component Resource)
Then point to --> CONTENT --->click right -->choose NEW-->then choose BITMAP.
Program will ask you to---> indicate size (24x24 for 800x600) (32x32 for 600x480)
Point to -->Bitmap then -->Click right -->choose Rename (Change name to your CLASS, hence name TNEWCOMP)
Then -->press ENTER --> and then double-click TnewComp to draw.
Once -->finish your drawing -->save file in DCR (same path to UNIT program we are using or NewComp.PAS, hence this file will name NewComp.DCR).

You can create your Component with DESIGN TIME, RUNTIME PACKAGE by clicking "CHECKBOX" name Build with Runtime Package when you compile your component.

Back to TOP

15 * "Package" in Delphi (4/56-57)

• Package - Delphi allow you deposit Package or create new package by your own preferred name. Example like I can use JDELPHI Package. Your package will named DPL and DPK and when install in Delphi it will compile only your package.
• Package in DELPHI called Delphi User's Component allows user to add his personal select component. This File names DclUsr30.Dpk in ROOT name Lib. You can put TNewComp in easily. You need to indicate new package to place TNewComp in.

Go to Mainmenu -->Choose Component -->then choose Install Component
Choose -->TAB Into New package to -->create new package--> Fill indetails as below sample

Unit File Name	Put in NewComp.pas (or choose name from disk)
Search path	Delphi will indicate path for package NewComp.pas for you
Package File Name	let just name it here as sample Working Component
Package Description	Reminder for yourself memo of what this package do

Complete fill in details -->clicks OK. Now you have WORKComponent.DPL or already complied Component.
After finish Complied then click --> INSTALL (for the first installation) after install you can just compile as normall
Then Close program window and -->Save Package name WorkComponent. You will see word NEWCOMP show (alone) in package. If you look at component palette, you will see your component.

Back to TOP

16 * Start a new project and test Component(4/57)
We will test compile component as well run program at the same time.

Go to -->MainMenu -->choose File -->choose New Application to start a new program.
Take Component we just created NEWCOMP drop on FORM.

For testing Compile NEWCOMP to change for any correction -->choose FILE -->choose ADD to Project. Take program NEWCOMP.Pas (add) and then compile.
** This is a test method, actually running program DEBUG will already inspect your component.

Back to TOP

17 * Assign Event Handler by writing code (4/58)
Programmer normally use Object Inspector to assign event handler OnClick then do this, OnXXX then do that, but you can not do that with creating COMPONENT. You have to write CODE

Sample of Code Format (Assign Event Handler)

Object Instance.Event := Method;

OR

Sample of Code Format (Method with parameter or signature)

Object Instance.OnXXX := Method;

Since NewComp allow us to drag FORM (animation), then we have to tell FORM that when there is an event of OnMouseDown Mouse Click be prepare to be dragged. How can we do that then? See below!

Back to TOP

18 * Indicate Owner property (4/58-59)
TNewComp has Property type of TComponent name Owner, and an Owner is a TComponent which is higher than Form, therefore we can modify Owner to Form. Writting code below.

FOldForm := TForm(Owner);

FOldForm is an Instance we created with the type of TForm, above sentence declares that FOldfold is the same form we had dropped our component. Then we can manipulate (event) with form as we intend such as OnMouseMove.
FOldForm is in Private section (see only in this component)
FOldForm := TForm(Owner); refer from FROM, so we don't need command Create

OR

Back to our TnewComp include with OnMouseMove and OnMouseDown we are intending to do now.

Type .....TNewComp = Class(TComponent) .....Private .....FOldForm : TForm; .....{private declarations} .....Protected ............Procedure DoFormMouseMove (Sender : TObject; Shift : TShiftState ; X , Y :; Integer); ............Procedure DoFormMouseDown (Sender : TObject; Button : TMouseButton; ............Shift : TShiftState; X , Y : Integer); .....{protected declarations} .....Public ............Constructor Create (AOwner : TComponent); Override ; ............Desstructor Destroy ; Override ; .....{Public declarations} .....Published .....{published declarations} ......End; ........ procedure TNewComp.DoFormMouseMove (Sender : TObject; Shift:TShiftState; X, Y: Integer); begin ............. end; procedure TNewComp.DoFormMouseDown (Sender : TObject; Button : TMouseButton; .................... Shift:TShiftState; X, Y: Integer); begin ............. end;

* You will see Visibility Section of Object the 4P (private, protected, public and published) The story does not end here, please feel free to expand real action into coding now that you know the main concept and how to do it with real programmer's rules.

Back to TOP

19 * Adding Property to an Object(4/66)
Let us assume we have some more useful PROCEDURE to work with such as BreakBill (not just OnMouseMove, OnMOuseDown) so that we can deal with currency and coins. This procedure will be call for use by another programmer.

Var ........B1,B10,B20,B50,B100,B500,B 1000: LongInt; ........Amounted : Extended; Procedure BreakBill (Amount:Extended;var S50,S1,B1,B10,B20,B50,B100,B1000); ........Begin ................... ........End;

* Procedure Name "BreakBill" send variable one-to-one for each type of money, we call for uselike this BreakBill (Money, TB50, TB1, ....)

Now think money start from big bill, medium, small bills down to coin of 50 cents, 25 cents, 10 cents, 5 cents (depend on that currency could be YEN or DONG or POUND). Gradually it will start to get complicate in remember Procedure by names as well it will take up too many memory (resources).

It's better to create CLASS and take this PROCEDURE put it in CLASS

* When you want to use Object we can refer to it with Instance
VAR
..........Bill : TBill; <this indicate Instance name TBill>
* Before using Instance we neeed to Create (Refer olf lesson)
Bill : = TBill.Create ; <create instance name BILL to be used>
Bill . BreakBill (53250.00) ; <Call method BreakBill to break this amount 53250>

Bill . Free ;

Let's assume we have too many Method to remember by name, so we moved Method name BreakBill to be at Protected section instead and adding variable name FAmount to store it's value. Indicating property name "Amount" in Public section. (compare code to POINT 19 above).

 

Type ........TBill = Class (TObject) ........Protected ............FAmount : Extended ; ............FS50,FS1,FB1,FB10,FB20,FB50,FB100,FB1000 : LongInt; ............Procedure BreakBill(Value:Extended); ........Public ............Property Amount : Extrended Read FAmount Write BreakBill; ........End;

This call "Direct Access". We READ FAmount directly in private area. From now you can create function such as "function GetAmount" and READ AMOUNT through function by writting code "Method name SetAmout"

Back to TOP

20 * Adding Property to a Class(4/71)
If we add PROPERTY in Published section by writing adding CODE, we need to "Rebuild Package" to enable that Property to emerge at "Object Inspector" and re-compile your NewComp.

Go to Delphi MainMenu --> Choose --> File|Reopen -->Call your package WorkComponent.DPK and make changes -->double click NewComp to make change.

Assume we want to add property of DRAGGING FORM, we can put this command

You can also indicate this property when design Object Inspector too.

Object Inspector show when designing, so its PROPERTY will be in Published Section. If you are add new property, you won't be able to compile immediately but you will need to Build Component Library (Rebuild Package). Once you had Build it, you will see new property emerge in Object Inspector.

Back to TOP

21 * Intercept windows messages to redirect interaction to Component when necessary.(4/73)
Window signal is call Iteration Cycle. Delphi can detect this signal with Message Handling Method or Method that follow by Message Handling Directive, or special "Constant value" such as WM_CLOSE = close form) or CM_MOUSELEAVE.

Back to TOP

22 * Override essential methods in maintaining Component status.(4/74)
Delphi has many important METHOD for OVERRIDE. If you dislike drawing, then you can override method name PAINT. If you dislike CLICK, you can override method name CLICK.

IMPORTANT METHOD to secure and preserve your component to work normally and effectively as Component are: Notification, Loaded, SetName, SetParent, GetChildren, GetParentComponent, InsertComponent, RemoveComponent, FindComponent, Paint

Back to TOP

23 * Adding existing event or create new Event to interact with users's runtime handler.(4/75)
Existing events are such as TNotifyEvent, TDataChangeEvent, TKeyEvent to interact with users.
There are 2 kind of events.

• Propagated Event (divided into 2 types)
  System Event - such as open and close form, start and close program, or intercept window message, which send from OSM (operating system message).
  User's Generated Event - User activate action such as keyboard or mouseclick.
• Manufacturing Event is an Event design by programmer follow from existing event or programmer creates all new events. It's similar to writing "PROPERTY" and the different would be that Event you create must have TYPE DECLARATION.
  

Type ........TMyOwnEvent = Procedure (Sender :TObject; X, Y: Integer) of Object ; ........Private ............FMyOwnEvent : TMyOwnEvent ; ........Pubished ............Property OnMyOwnEvent :TMyOwnEvent Read FMyOwnEvent Write FMyOwnEvent ;

Back to TOP