我正在创建一个绘图板程序，基本上是 MS Paint 的简化版本。它大部分时间都在工作，但是当我在板上绘图时，当前选定的 UI 元素会显示在绘图区域上。
我尝试了paintComponent，它在我调用super.paintComponent(g) 时起作用（就像以前一样），但它在我绘制下一个对象之前清除了绘图区域。我覆盖了 update 并在其中放置了一个 println 语句，它永远不会被调用。
顶部的按钮是红色的，因为我将底部 JPanel 的背景设置为红色，以查看这些按钮的背景是什么。很明显，它们是底部 JPanel 的一部分。我正在使用 BorderLayout 进行布局。
这是我的代码（删除了一些不相关的位）：
public class JSPaint extends JFrame implements Serializable
{
private static final long serialVersionUID = -8787645153679803322L;
private JFrame mainFrame;
private JPanel bp;
private JButton ...
private DrawingArea da;
public JSPaint()
{
setTitle("JS Paint");
setSize(1024, 768);
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
// Drawing area
da = new DrawingArea();
setLayout(new BorderLayout());
// add the buttons to the panel
buttonPanel();
// Add the drawing area
add(bp, BorderLayout.SOUTH);
bp.setBackground(Color.RED);
add(da, BorderLayout.CENTER);
da.setBackground(Color.BLUE);
setVisible(true);
}
// I put it here too just in case
@Override
public void update(Graphics g)
{
System.out.println("update in JSPaint called.");
paint(g);
}
/*
* Creates the panel for the buttons, creates the buttons and places them on
* the panel
*/
public void buttonPanel()
{
// Create the panel for the buttons to be placed in
bp = new JPanel();
saveButton = new JButton("Save");
loadButton = new JButton("Load");
//more buttons
bp.add(saveButton);
bp.add(loadButton);
//more buttons
// ActionListeners
colorButton.addActionListener(new ActionListener()
{
public void actionPerformed(ActionEvent ae)
{
System.out.println("color");
da.color();
}
});
}
public class DrawingArea extends JPanel
{
private static final long serialVersionUID = -8299084743195098560L;
boolean dragged = false;
@Override
public void update(Graphics g)
{
System.out.println("Update in DrawingArea called");
paint(g);
}
/*
* Draws the selected shape onto the screen and saves it into a Stack.
*
*/
public void draw()
{
this.addMouseMotionListener(new MouseMotionListener()
{
public void mouseDragged(MouseEvent me)
{
dragged = true;
}
public void mouseMoved(MouseEvent me) {}
});
//more listeners...
});
}
/*
* Draws the selected String onto the screen when the mouse is held down.
*
*/
public void brush()
{
this.addMouseMotionListener(new MouseMotionListener()
{
public void mouseDragged(MouseEvent me)
{
// If we are in drawing mode, draw the String. Create a new
// Figure Object and push it onto the Stack
if(activeButton == "brush")
{
startPoint = me.getPoint();
Figure fig = new Figure("String", startPoint, null, currentColor);
// figures.push(calculate(fig));
toPaint.push(calculate(fig));
repaint();
}
}
public void mouseMoved(MouseEvent me) {}
});
}
// more of the same...
public void paint(Graphics g)
{
toSave.addAll(toPaint);
while(!toPaint.isEmpty())
{
Figure f = toPaint.pop();
String t = f.type;
if(f.color != null)
{
g.setColor(f.color);
}
switch(t)
{
case "Rectangle": g.drawRect(f.x1, f.y1, f.width, f.height);
break;
case "Oval": g.drawOval(f.x1, f.y1, f.width, f.height);
break;
case "Line": g.drawLine(f.x1, f.y1, f.x2, f.y2);
break;
case "Clear":
g.fillRect(0, 0, da.getWidth(), da.getHeight());
clearStack(toSave);
break;
case "String": g.drawString(f.toPrint, f.x1, f.y1);
break;
}
}
}
}
private class Figure implements Serializable
{
private static final long serialVersionUID = 4690475365105752994L;
String type, toPrint;
Color color;
Point start;
Point end;
int x1, y1, x2, y2, width, height;
public Figure(String figureType,
Point startPoint, Point endPoint, Color figureColor)
{
type = figureType;
color = figureColor;
start = startPoint;
end = endPoint;
}
// Rect, Oval
public Figure(String figureType, int figureX, int figureY,
int figureWidth, int figureHeight, Color figureColor)
{
type = figureType;
x1 = figureX;
y1 = figureY;
width = figureWidth;
height = figureHeight;
color = figureColor;
}
// more shapes
}
public static void main(String args[])
{
SwingUtilities.invokeLater(new Runnable()
{
public void run()
{
new JSPaint();
}
});
}
}