Why addPaintListner (swt) does not put the selected image to canvas?

Question

I want to add a image file selected from a directory (by clicking a button goes to the path). When I choose that jpg image it does not appears directly in the canvas where I want to put on it unless and until I minimize and maximize the application window. Below is the code I am using

    //Button browse = new Button(shell, SWT.PUSH);
    //Canvas dogPhoto = new Canvas(shell, SWT.BORDER);
    //  static Image dogImage;

    browse.addSelectionListener(new SelectionAdapter() {
        public void widgetSelected(SelectionEvent event) {
            fileName = new FileDialog(shell).open();
            System.out.println("fileNmae  "+fileName);
            if (fileName != null) {
                dogImage = new Image(display, fileName);
                
                dogPhoto.addPaintListener(new PaintListener() {
                    public void paintControl(PaintEvent event) {
                        //if (dogImage != null)
                        System.out.println("hello in Paint2");
                        {
                            event.gc.drawImage(dogImage, 0, 0);
                        }
                    }
                });
                
            }
            newText = newText + "File Selected - "+fileName;
            textArea.setText(newText);      
            
        }
    });