绘制像JComponent绘图板

Question

I have a class Pad_Draw extending JComponent . Constructor is

public Pad_Draw()
{
      this.setDoubleBuffered(true);
      this.setLayout(null);
};

The paintComponent methpod is :

 public void paintComponent( Graphics g )
 {
      graphics2D = (Graphics2D)g;
      graphics2D.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
      graphics2D.setPaint(Color.white);
      graphics2D.fillRect(0, 0, getSize().width, getSize().height);
 }

In a JFrame I am adding this by a ScrollPane:

    JScrollPane Padscroller = new JScrollPane();
    Padscroller.setWheelScrollingEnabled(true);
    Padscroller.setVerticalScrollBarPolicy(ScrollPaneConstants.VERTICAL_SCROLLBAR_ALWAYS);
    Padscroller.setHorizontalScrollBarPolicy(ScrollPaneConstants.HORIZONTAL_SCROLLBAR_ALWAYS);
    Padscroller.setPreferredSize(new Dimension(200, 100));
    Padscroller.setMinimumSize(new Dimension(200, 100));
    Padscroller.setMaximumSize(new Dimension(200, 100));
    Padscroller.setViewportView(drawPad);
    content.add(Padscroller, BorderLayout.CENTER);

But as soon as I add the content in the Frame and set the size of the frame. The drawing pad is taking whole size whatever it needs.

I want my specified size (200,100) to be maintained and I actually want something like Windows Paint application has. I should be able to increase the size by extending a corner. As soon as I extend corner the scrollbar gets activated. Can anyone give me any idea how to achieve it?

Answer 1

The default layout manager for JFrame , BorderLayout does not respect preferred sizes of its components.

You could a layout manager that does, such as BoxLayout , and override getPreferredSize in your Padscroller component:

JScrollPane padScroller = new JScrollPane() {
   @Override
   public Dimension getPreferredSize() {
      return new Dimension(200, 100);
   } 
};

Regarding increasing the size, have a look at using a MouseAdapter and updating this property in the mouseDragged method.