Use of the Clipboard in Delphi [2]: Assign, Hasformat

Preparatory work:

Place a tpanel on the form; Put a timage on the Tpanel; Another three buttons are required.

This example effect chart:

First edition code:

Unit Unit1; Interface uses Windows, Messages, sysutils, variants, Classes, Graphics, Controls, Forms, Dialogs, Stdctrls, Extctrl
 
S
    Type TFORM1 = Class (Tform) Button1:tbutton;
    Button2:tbutton;
    Button3:tbutton;
    Panel1:tpanel;
    Image1:timage;
    Procedure Button1Click (Sender:tobject);
    Procedure Button2click (Sender:tobject);
  Procedure Button3click (Sender:tobject);
 
End
 
var Form1:tform1;
 
Implementation {$R *.DFM} uses CLIPBRD;
Procedure Tform1.button1click (Sender:tobject);
  Begin Image1.left: = 0;
  Image1.top: = 0;
  Panel1.autosize: = True;
  Image1.autosize: = True;
 
  Image1.Picture.LoadFromFile (' c:\temp\test.bmp '); TButton (Sender).
Caption: = ' import ';
 
End
Procedure Tform1.button2click (Sender:tobject); Begin Clipboard.assign (image1.picture);
  {Put the picture in the Image1 into the clipboard}
 
  {Now can be pasted in the image software, you can try it with a Windows drawing board} TButton (Sender).
Caption: = ' copy ';
 
End
Procedure Tform1.button3click (Sender:tobject); var Bit:tbitmap; {Prepare to use aTbitmap from the Clipboard to end the picture} X,y:integer;
  Begin bit: = Tbitmap.create; Bit.               Assign (Clipboard); {Get from the Clipboard} x: = Panel1.width + panel1.left * 2;
  {X,y is ready to paste position on the form} y: = Panel1.top;              Canvas.draw (x, y, bit); {Paste is to draw out the bit.}
 
  Free; TButton (Sender).
Caption: = ' paste ';
 
End End.

But now the program still has a loophole: if there is nothing in the Clipboard, what to paste? If the Clipboard is not a picture, how do I paste it?

In fact, we only use the Tclipboard.hasformat function to judge the Clipboard is not a picture on the line.