在 JPanel 上绘画
我正在编写一个程序，它只是一个简单的形状生成器，我应该有我的主面板 ShapeMakerPanel，以及该面板上的 2 个面板，controlPanel（其中包含用于选择形状和清除形状的按钮等）和绘图区域（实际绘制形状的地方），但无论我做什么，我都无法让油漆显示在绘图区域上。如果我只使用paintComponent并注释掉add(drawingArea)，那么绘图功能就可以工作，但是在底层，我如何在drawingArea Jpanel上绘图。另外，当我绘制形状时，我一次只能有一个，因为每次我开始一个新的形状时，面板都会被擦干净`
super.paintComponent(g);
g.setColor(penColor);
if (p1 != null && p2 != null)
{
if (shapeChoice.getSelectedItem().equals("Line"))
{
Line line = new Line(p1.x, p1.y, p2.x, p2.y);
line.draw(g);
}
}
我知道它的 super.paintComponent(g) 搞乱了我，但没有那个，当我拖动鼠标时，它会绘制数百条线。
如果您想知道 Line 类，我们必须为我们绘制的每个形状创建一个类，draw() 方法仅使用线条的坐标并将它们放入 drawLine() 中。
I'm writing a program that will be just a simple shape maker, I'm supposed to my main panel, ShapeMakerPanel, along with 2 panels on that one, controlPanel(which holds buttons for choosing the shape and clearing it, etc) and drawingArea (where the shapes are actually drawn), but no matter what I do, I can't get the paint to show up on drawingArea. If I just use paintComponent and comment out add(drawingArea) then the drawing stuff works, but on the bottom layer, how can I paint on the drawingArea Jpanel. Also, when I do draw the shapes, I can only have one at a time, because every time I start a new one, the panel is wiped clean`
super.paintComponent(g);
g.setColor(penColor);
if (p1 != null && p2 != null)
{
if (shapeChoice.getSelectedItem().equals("Line"))
{
Line line = new Line(p1.x, p1.y, p2.x, p2.y);
line.draw(g);
}
}
I know its the super.paintComponent(g) messing me up, but without that, as I drag the mouse, it draws hundreds of lines.
If you were wondering about the Line class, we had to make a class for each shape we drew, the draw() method just uses the coordinates of the line and puts them into drawLine().
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不要重写 ShapeMakerPanel 中的paintComponent()；在drawingArea 的类中覆盖它（如果drawingArea 是普通的JPanel，则创建JPanel 的新子类）。一般来说，您需要对要在其上绘制的组件进行子类化。
Don't override paintComponent() in ShapeMakerPanel; override it in drawingArea's class (if drawingArea is a plain JPanel, then create a new subclass of JPanel). In general you need to subclass the component on which you're going to paint.
请参阅自定义绘画方法了解解决此问题的几种方法。
See Custom Painting Approaches for a couple of ways to solve this.