JPanel什么时候绘制（或重绘）其子组件？ [英] When does a JPanel paint (or repaint) its child components?

问题描述

我有一个使用自定义UI委托绘制的JButton（CustomButtonUI扩展了BasicButtonUI）。 CustomButtonUI的paint（）方法绘制带有圆角抗锯齿角的按钮，使外观尽可能平滑。

I've got a JButton which is painted using a custom UI delegate (CustomButtonUI extends BasicButtonUI). The CustomButtonUI's paint() method draws the button with rounded "antialiased" corners, to make the apperance as "smooth" as possible.

不知何故，抗锯齿边缘每次我将鼠标拖到
按钮上时按钮都会消失。这使按钮边缘看起来像素化。但是，一旦我添加了一行代码来重新绘制按钮的父级，即使我将鼠标拖到按钮上，抗锯齿也会启动。

Somehow the "antialiased" edges of the button disappears each time i drag the mouse over the button. This makes the button edges look "pixelized". However, once I add a line of code to repaint the parent of the button, the antialiasing kicks in even when i drag the mouse over the button.

现在，我的问题涉及到这是一个好主意？我会从子组件重绘父组件。我想知道这是否会导致重绘的循环？如果父
尝试重新绘制其子项并且子项尝试重新绘制其父项 - 那么我假设我们正在讨论循环。

Now, my question relates to wether this is a good idea? I do after all repaint the parent component from a child component. I wonder if this lead to a loop of repaints? If the parent tries to repaint its children and the children tries to repaint its parent - then i assume we're talking about a loop.

我已经附上我的代码作为参考。非常欢迎任何评论！

I've attached my code as a reference. Any comments are very welcome!

public class JCustomButtonUI extends BasicButtonUI {

    @Override
    public void installUI(JComponent c) {
        super.installUI(c);

        AbstractButton b = (AbstractButton) c;
        b.setBorderPainted(false);
    }

    @Override
    public void paint(Graphics g, JComponent c) {

        //Cast the Graphics instance to a Graphics2D instance.
        Graphics2D g2d = (Graphics2D) g;
        JButton b = (JButton) c;

        //Repaint parent component to make sure that we get "antialiased"
        //edges.
        b.getParent().repaint();

        //Get the component's height and width.
        int w = (int) g.getClipBounds().getWidth();
        int h = ((int) g.getClipBounds().getHeight());

        //Make sure the button is drawn with "antialiased" edges.
        g2d.setRenderingHint(RenderingHints.KEY_ANTIALIASING, 
            RenderingHints.VALUE_ANTIALIAS_ON);
        g2d.setColor(Color.GRAY);
        g2d.fillRoundRect(0, 0, w, h, w, h);       
    }
}

更新1

为了说明别名和抗锯齿边框，请看下面的两张图片。当我（来自ButtonUI的paint（）方法）手动调用父JPanel的重绘方法时，所有边框都是完全抗锯齿的。但是，当我不手动调用父JPanel的重绘方法时，一旦我将鼠标悬停在按钮上，边框就不再被抗锯齿了。

Update 1

Just to illustrate the alias and antialiased border, please have a look at the below two pictures. When i (from the ButtonUI's paint() method) manually invoke the parent JPanel's repaint method, all borders are perfectly antialiased all the time. However, when i do not manually invoke the parent JPanel's repaint method, then the borders are no longer antialiased once i hoover the mouse over the button.

我已经分享了整个组件，其中包含一个JPanel，一个JSlider和Snipt上的几个JButton。请从 http://snipt.org/wnllg 获取。

I have shared the entire "component" which consists of a JPanel, a JSlider and a couple of JButtons on Snipt. Please get it from http://snipt.org/wnllg.

似乎我设法让它运转起来。我没有在paintComponent（）方法中绘制JPanel的背景，而是创建了一个安装在JPanel上的JCustomPanelUI。我不认为这是解决方案本身，但我没有使用Graphics实例的宽度和高度，而是尝试使用JPanel本身的widht和height。当我使用Graphics实例的宽度和高度时，我不太确定为什么出了问题。我认为Graphics实例的宽度和高度已经根据JPanel组件的尺寸进行了准备。您可以在此处查看最终组件： http://snipt.org/wnlli ，

It seems that i have managed to get it working. Instead of painting the JPanel's background in its paintComponent() method, i created a JCustomPanelUI which i installed on the JPanel. I don't think that was the solution itself, but instead of using width and height from the Graphics instance, I tried using widht and height from the JPanel itself. I'm not quite sure why things go wrong when i use width and height from the Graphics instance. I thought the width and height from the Graphics instance was already "prepared" with regard to dimensions from the JPanel component. You can have a look at the final component here: http://snipt.org/wnlli,

推荐答案

我已将示例简化为抗锯齿，我无法重现该问题。它似乎不依赖于平台。我不确定你为什么使用 getClipBounds（）。

I've reduced the example to just the anti-aliasing, and I am unable to reproduce the problem. It doesn't appear to be platform dependent. I'm not sure why you are using getClipBounds().

附录：

JPanel 背景（渐变）需要闪耀......

The JPanel background (a gradient) needs to shine through…

我更新了示例，使用透明按钮后面的渐变背景;我并排放置了反锯齿（左）和别名（右）的例子。我没有看到意外的行为。

I've update the example to use a gradient background behind a transparent button; I've put anti-aliased (left) and aliased (right) examples side-by-side. I see no unexpected behavior.

import java.awt.Color;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.GradientPaint;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.GridLayout;
import java.awt.RenderingHints;
import javax.swing.JButton;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.plaf.basic.BasicButtonUI;

/** @see http://stackoverflow.com/questions/5169647 */
public class ButtonUITest extends JPanel {

    public ButtonUITest() {
        this.setLayout(new GridLayout(1, 0));
        this.setPreferredSize(new Dimension(640, 480));
        this.add(new CustomButton(true));
        this.add(new CustomButton(false));
    }

    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        int w = this.getWidth();
        int h = this.getHeight();
        Graphics2D g2d = (Graphics2D) g;
        g2d.setPaint(new GradientPaint(0, 0, Color.blue, w, h, Color.red));
        g2d.fillRect(0, 0, w, h);
    }

    private void display() {
        JFrame f = new JFrame("ButtonUITest");
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.add(this);
        f.pack();
        f.setLocationRelativeTo(null);
        f.setVisible(true);
    }

    private static class CustomButton extends JButton {

        public CustomButton(boolean antialiased) {
            this.setOpaque(false);
            this.setUI(new CustomButtonUI(antialiased));
        }
    }

    private static class CustomButtonUI extends BasicButtonUI {

        private boolean antialiased;

        public CustomButtonUI(boolean antialiased) {
            this.antialiased = antialiased;
        }

        @Override
        public void paint(Graphics g, JComponent c) {
            int w = c.getWidth();
            int h = c.getHeight();
            Graphics2D g2d = (Graphics2D) g;
            if (antialiased) {
                g2d.setRenderingHint(
                    RenderingHints.KEY_ANTIALIASING,
                    RenderingHints.VALUE_ANTIALIAS_ON);
            }
            g2d.setColor(Color.LIGHT_GRAY);
            g2d.fillOval(0, 0, w, 2 * h);
        }
    }

    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {

            @Override
            public void run() {
                new ButtonUITest().display();
            }
        });
    }
}

这篇关于JPanel什么时候绘制（或重绘）其子组件？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！