Java 在已经可见的帧上调用setVisible(true)
问题: 在已经可见的JFrame上调用setVisible(true)做什么?我一直在挖掘的源代码,最终,它归结为,如果框架已经可见,它对框架没有任何影响。为什么它的行为像Java 在已经可见的帧上调用setVisible(true),java,swing,jpanel,awt,repaint,Java,Swing,Jpanel,Awt,Repaint,问题: 在已经可见的JFrame上调用setVisible(true)做什么?我一直在挖掘的源代码,最终,它归结为,如果框架已经可见,它对框架没有任何影响。为什么它的行为像revalidate();重新油漆()?(见下文SSCCE) 动机: 我正在开发一个java应用程序,为此我编写了一个类JImagePanel,它扩展了JPanel,允许用户将图像设置为背景(请参见SSCCE)。我发现在编辑面板的背景后,我在将背景重新绘制到正确的大小时遇到了问题。在浏览互联网后,我发现以下几点很有效: if
revalidate();重新油漆()代码>?(见下文SSCCE)
动机:
我正在开发一个java应用程序,为此我编写了一个类JImagePanel
,它扩展了JPanel
,允许用户将图像设置为背景(请参见SSCCE)。我发现在编辑面板的背景后,我在将背景重新绘制到正确的大小时遇到了问题。在浏览互联网后,我发现以下几点很有效:
if(frame.isVisible()) frame.setVisible(true);
最终,我使用
panel.revalidate();
panel.repaint();
,我认为这是更好的解决方案,但它让我思考setVisible(true)
在已经可见的帧上实际做了什么。在我看来,它不应该起作用,但事实上它确实起作用了
SSCCE
这里有一个例子说明了我的问题。如果没有其他内容,希望您在将来发现这个类非常有用
注意:此文件的更新源可在创建此文件的项目的主页上找到
享受吧
package com.dberm22.utils;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Image;
import java.awt.RenderingHints;
import java.awt.Toolkit;
import java.awt.image.BufferedImage;
import javax.swing.ImageIcon;
import javax.swing.JFrame;
import javax.swing.JPanel;
public class JImagePanel extends JPanel {
private static final long serialVersionUID = 6841876236948317038L;
private Image img = null;
private Position position = Position.CENTER;
public enum Position{
STRETCH,
CENTER,
FIT,
FILL,
NONE;
}
public JImagePanel() {
}
public JImagePanel(String img) {
this(new ImageIcon(img).getImage());
}
public JImagePanel(Image img) {
setBackgroundImage(img);
}
@Override
public void paintComponent(Graphics g)
{
super.paintComponent(g);
Graphics2D g2 = (Graphics2D) g;
g2.setColor(getBackground());
g2.fillRect(0, 0, getWidth(), getHeight());
if (this.position.equals(Position.STRETCH))
{
if(this.img != null) g2.drawImage(img, 0, 0, getWidth(), getHeight(), null);
}
else if (this.position.equals(Position.FILL) || this.position.equals(Position.FIT))
{
if(this.img != null)
{
double scaleFactor = getScaleFactor(new Dimension(img.getWidth(null), img.getHeight(null)), getSize());
int scaleWidth = (int) Math.round(img.getWidth(null) * scaleFactor);
int scaleHeight = (int) Math.round(img.getHeight(null) * scaleFactor);
//Image img_scaled = img.getScaledInstance(scaleWidth, scaleHeight, Image.SCALE_SMOOTH);
g2.drawImage(scaleImage(img, scaleWidth, scaleHeight, getBackground()), (getWidth() - scaleWidth)/2, (getHeight() - scaleHeight)/2, scaleWidth, scaleHeight, null);
}
}
else if (this.position.equals(Position.CENTER)) { if(this.img != null) g2.drawImage(img, (getWidth() - img.getWidth(null))/2, (getHeight() - img.getHeight(null))/2, null); }
}
public void setBackgroundImage(String img)
{
setBackgroundImage(new ImageIcon(img).getImage());
}
public void setBackgroundImage(Image img)
{
this.img = img;
Dimension size = new Dimension(img.getWidth(null), img.getHeight(null));
setPreferredSize(size);
setMinimumSize(size);
setMaximumSize(size);
setSize(size);
repaint();
}
public static double getScaleFactor(int iMasterSize, int iTargetSize) {
double dScale = 1;
if (iMasterSize > iTargetSize) {
dScale = (double) iTargetSize / (double) iMasterSize;
} else {
dScale = (double) iTargetSize / (double) iMasterSize;
}
return dScale;
}
public double getScaleFactor(Dimension original, Dimension targetSize) {
double dScale = 1d;
if (original != null && targetSize != null) {
double dScaleWidth = getScaleFactor(original.width, targetSize.width);
double dScaleHeight = getScaleFactor(original.height, targetSize.height);
if (this.position.equals(Position.FIT)) dScale = Math.min(dScaleHeight, dScaleWidth);
else if(this.position.equals(Position.FILL)) dScale = Math.max(dScaleHeight, dScaleWidth);
}
return dScale;
}
public BufferedImage scaleImage(Image img, int width, int height, Color background) {
BufferedImage newImage = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
Graphics2D g = newImage.createGraphics();
try {
g.setRenderingHint(RenderingHints.KEY_INTERPOLATION,
RenderingHints.VALUE_INTERPOLATION_BICUBIC);
g.setBackground(background);
g.clearRect(0, 0, width, height);
g.drawImage(img, 0, 0, width, height, null);
} finally {
g.dispose();
}
return newImage;
}
public void setBackgroundImagePosition(String pos)
{
if("Stretch".equals(pos)) setBackgroundImagePosition(Position.STRETCH);
else if("Center".equals(pos)) setBackgroundImagePosition(Position.CENTER);
else if("Fit".equals(pos)) setBackgroundImagePosition(Position.FIT);
else if("Fill".equals(pos)) setBackgroundImagePosition(Position.FILL);
else if("None".equals(pos)) setBackgroundImagePosition(Position.NONE);
}
public void setBackgroundImagePosition(Position pos)
{
this.position = pos;
repaint();
}
public static void main(String[] args)
{
JFrame frame = new JFrame("JImagePanel Test");
frame.setSize( Toolkit.getDefaultToolkit().getScreenSize());
frame.setPreferredSize( Toolkit.getDefaultToolkit().getScreenSize());
frame.setExtendedState(JFrame.MAXIMIZED_BOTH); //sets appropriate size for frame
JImagePanel panel = new JImagePanel();
frame.add(panel);
frame.setVisible(true);
try {Thread.sleep(2000);} catch (InterruptedException e) {}
panel.setBackgroundImage("C:\\Users\\David\\Pictures\\Wood.jpg");
panel.setBackgroundImagePosition(JImagePanel.Position.STRETCH);
panel.revalidate(); // need to revalidate()
panel.repaint(); //doesnt work by itself
try {Thread.sleep(2000);} catch (InterruptedException e) {}
panel.setBackgroundImage("C:\\Users\\David\\Pictures\\Wood.jpg");
panel.setBackgroundImagePosition(JImagePanel.Position.FIT);
frame.setVisible(true); //also works --why?
}
}
在已可见的JFrame
上调用setVisible(true)
对您有效,因为这最终会在内部调用validate()
,从而重新验证框架中的所有子组件
要了解原因,请参阅组件.setVisible(布尔b)
的实现:
但是show()
方法在Window
中被重写(其中JFrame
是一个子类)。因此,这将调用Window.show()
:
希望这能解释您所看到的行为。假设您正在对imagePanel进行一半的清理:
- 让面板根据需要进行自己的重新验证/喷漆(vs应用程序代码)
- ,从来没有,甚至在面板内部都没有
JFrame frame = new JFrame("JImagePanel Test");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
// frame.setLayout(new FlowLayout()); // just to see the effect of a pref-respecting layout
final JImagePanel panel = new JImagePanel();
frame.add(panel);
final Image[] images = new Image[]{
XTestUtils.loadDefaultImage(), XTestUtils.loadDefaultImage("500by500.png"), null};
Action toggleImage = new AbstractAction("toggle image") {
int index = 0;
@Override
public void actionPerformed(ActionEvent e) {
panel.setBackgroundImage(images[index]);
index = (index +1) % images.length;
}
};
Action togglePosition = new AbstractAction("toggle position") {
int index = 0;
@Override
public void actionPerformed(ActionEvent e) {
panel.setBackgroundImagePosition(Position.values()[index]);
index = (index +1) % Position.values().length;
}
};
frame.add(new JButton(toggleImage), BorderLayout.NORTH);
frame.add(new JButton(togglePosition), BorderLayout.SOUTH);
// size for frame
//frame.setSize(800, 800);
frame.setExtendedState(JFrame.MAXIMIZED_BOTH); //sets appropriate
frame.setVisible(true);
为什么需要重新粉刷面板?您是否添加了一个新组件,或者有其他原因?发布a会有很大帮助。我确信从JFrame中重新验证()和重新绘制(),以刷新所有JComponents树,确保有一个潜在的问题repaint()可以关闭,对于JComponents这正是史前的AWT问题,如果不是基于AWT容器,请确保检查第三方代码,然后,您必须根据您的措辞重新绘制此容器(例如,reDraw()必须以良好的代码实现)。在添加面板之前,听起来您正在调用
revalidate()
。这是要验证的面板布局,因此应调用revalidate();重新油漆()代码>在删除和添加组件完成后。发布指向项目的链接不推荐,我们太懒了,无法浏览整个项目;-)相反,如前所述(尽管现在称为MCVE),将行为提取到SSCCE中。啊,窗口子类覆盖show()。我错过了-谢谢。这并不能回答问题(请参见Grodriguez),但在内部调用revalidate()无疑是对我的类的一种改进,我应该(也将)这样做。扩展测试用例为+1。谢谢你的意见。
public void show() {
if (peer == null) {
addNotify();
}
validate();
[...]
@Override
public Dimension getPreferredSize() {
if (img != null) {
return new Dimension(img.getWidth(this), img.getHeight(this));
}
return super.getPreferredSize();
}
public void setBackgroundImage(Image img) {
this.img = img;
// need to revalidate as our sizing hints might have changed
revalidate();
repaint();
}
public void setBackgroundImagePosition(Position pos) {
this.position = pos;
repaint();
}
JFrame frame = new JFrame("JImagePanel Test");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
// frame.setLayout(new FlowLayout()); // just to see the effect of a pref-respecting layout
final JImagePanel panel = new JImagePanel();
frame.add(panel);
final Image[] images = new Image[]{
XTestUtils.loadDefaultImage(), XTestUtils.loadDefaultImage("500by500.png"), null};
Action toggleImage = new AbstractAction("toggle image") {
int index = 0;
@Override
public void actionPerformed(ActionEvent e) {
panel.setBackgroundImage(images[index]);
index = (index +1) % images.length;
}
};
Action togglePosition = new AbstractAction("toggle position") {
int index = 0;
@Override
public void actionPerformed(ActionEvent e) {
panel.setBackgroundImagePosition(Position.values()[index]);
index = (index +1) % Position.values().length;
}
};
frame.add(new JButton(toggleImage), BorderLayout.NORTH);
frame.add(new JButton(togglePosition), BorderLayout.SOUTH);
// size for frame
//frame.setSize(800, 800);
frame.setExtendedState(JFrame.MAXIMIZED_BOTH); //sets appropriate
frame.setVisible(true);