CODEWITHSUNDEEP
classdelphidelphi-xe7
user6012107
user6012107

Reputation: 65

Delphi create button with image

I have problem with creating button with Image and Label inside it. Here my code:

Class:

  type
  Folder = class(TButton)
    AName:TLabel;
    AImage:TImage;
    constructor Create(Nme:String;Path:String;Handle:TForm);
  end;

Constructor:

constructor Folder.Create(Nme:String;Path:String;Handle:TForm);
begin
  AImage:=Timage.Create(Self);
  AName:=TLabel.Create(Self);
  AImage.Parent:=Self;
  AName.Parent:=Self;
  AName.Caption:=Nme;
  AImage.Picture.LoadFromFile(Path);
end;`

And event where I create this button:

procedure TForm3.Button1Click(Sender: TObject);
  var Fld:Folder;
  begin
  Fld:=Folder.Create('It','D:\image.bmp',Form3);
  Fld.Parent:=Form3;
  Fld.Width:=100;
  Fld.Height:=100;
end;

But when I'm creating this button it causes acess violation!What I must to do with it?

Upvotes: 1

Views: 3045

Answers (1)

quasoft
quasoft

Reputation: 5438

Problem:

The problem is that you have declared a customized version of constructor, but you are not calling the parent constructor of TButton class.

You need to change the constructor like this:

constructor Folder.Create(Nme: String; Path: String; Handle: TForm);
begin
  inherited Create(Handle);     // <- Add this line
  AImage := TImage.Create(Self);
  AName := TLabel.Create(Self);
  AImage.Parent := Self;
  AName.Parent := Self;
  AName.Caption := Nme;
  AImage.Picture.LoadFromFile(Path);
end;

General advice:

You need to learn how to debug such problems yourself.

Put a breakpoint on line Fld:=Folder.Create('It','D:\image.bmp',Form3); and use Step Over F8 / Trace Into F7 from Run menu to check your code line by line.

You will see that once you reach the line AImage.Parent:=Self; the exception occurs. This is because Self, which points to your Folder object, was not initialized correctly, and is not a proper TButton descendant.

You need to learn how to do that to progress any further with Delphi, and you will very soon be able to solve such problems yourself.

Also if you need to write a custom component for Delphi, invest some time learning more about the way components work and are being used. I would recommend the following guides on component writing:

Also consult a guide on Delphi Coding Style.

At first glance:

  • Class names should begin with T
  • Class fields should begin with F instead of A
  • constructor should be in public section and fields in private or protected
  • You should use spaces around parameters, after variables in declarations and around operators

Upvotes: 9

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