我正在使用 mouseListener 和 mouseMotionListener 制作一个 gui 程序。我有以下 Line 类
public class Line {
private int x1, x2, y1, y2;
private Color color;
public Line(int x1, int x2, int y1, int y2, Color color)
{
this.x1 = x1;
this.x2 = x2;
this.y1 = y1;
this.y2 = y2;
this.color = color;
}
public void draw(Graphics page)
{
page.drawLine(x1, y1, x2, y2);
page.setColor(color);
}
}
这是我的鼠标释放,我可以在其中获得所需线的最终点。
public void mouseReleased (MouseEvent event)
{ // ending points
moving = false;
Point p2 = event.getPoint();
x2 = p2.x;
y2 = p2.y;
line = new Line(x1,x2,y1,y2,currentColor);
lineList.add(line);
canvas.paintComponent(??????????);
这是应该在数组列表“lineList”中绘制所有这些线的 Canvas 方法。到 Canvas
private class CanvasPanel extends JPanel
{
//this method draws all shapes specified by a user
public void paintComponent(Graphics page)
{
super.paintComponent(page);
setBackground(Color.WHITE);
for(int i = 0; i <lineList.size()-1;i++)
{
line.draw(page);
}
但是我不知道如何将图形对象传递给 Canvas 类以便在 JPanel 上实际绘制线条。假设我的所有其他信息都正确(初始线点、JPanel 设置正确以及按钮设置),我如何传递这些信息才能真正将线条绘制到 Canvas 上。谢谢你!
最佳答案
不,您不想在任何地方传递 Graphics 对象,事实上您也不会从 MouseListener 或 MouseMotionListener 中进行绘制。相反,您可以从这些类中更改字段,调用 repaint(),然后在 PaintComponent 方法中使用字段结果。
事实上,在您的代码中,如果 CanvasPanel 可以访问 lineList,您所需要做的就是在将新行添加到 lineList 集合后对其调用 repaint() 。就是这样。
此外,不要在paintComponent 中设置背景,而是在构造函数中设置背景。此外,您还需要在 Line 的绘制方法中交换方法调用。您需要在绘制线条之前设置颜色。
例如,
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.util.ArrayList;
import java.util.List;
import javax.swing.*;
@SuppressWarnings("serial")
public class Drawing extends JPanel {
public static final Color BG = Color.WHITE;
public static final Color LINE_COLOR = Color.RED;
public static final Color CURRENT_LINE_COLOR = Color.LIGHT_GRAY;
public static final int PREF_W = 800;
public static final int PREF_H = PREF_W;
private List<Line> lineList = new ArrayList<>();
private Line currentLine = null;
private CanvasPanel canvasPanel = new CanvasPanel();
public Drawing() {
MyMouse myMouse = new MyMouse();
canvasPanel.addMouseListener(myMouse);
canvasPanel.addMouseMotionListener(myMouse);
setLayout(new BorderLayout());
add(canvasPanel);
}
private class CanvasPanel extends JPanel {
public CanvasPanel() {
setBackground(BG);
}
public void paintComponent(Graphics page) {
super.paintComponent(page);
// setBackground(Color.WHITE); // !! no, not here
for (Line line : lineList) {
line.draw(page);
}
if (currentLine != null) {
currentLine.draw(page);
}
}
@Override
public Dimension getPreferredSize() {
if (isPreferredSizeSet()) {
return super.getPreferredSize();
}
return new Dimension(PREF_W, PREF_H);
}
}
private class MyMouse extends MouseAdapter {
private int x1;
private int y1;
@Override
public void mousePressed(MouseEvent e) {
if (e.getButton() != MouseEvent.BUTTON1) {
return;
}
x1 = e.getX();
y1 = e.getY();
currentLine = null;
canvasPanel.repaint();
}
@Override
public void mouseReleased(MouseEvent e) {
if (e.getButton() != MouseEvent.BUTTON1) {
return;
}
Line line = createLine(e, LINE_COLOR);
lineList.add(line);
currentLine = null;
canvasPanel.repaint();
}
@Override
public void mouseDragged(MouseEvent e) {
currentLine = createLine(e, CURRENT_LINE_COLOR);
repaint();
}
private Line createLine(MouseEvent e, Color currentColor) {
int x2 = e.getX();
int y2 = e.getY();
return new Line(x1, x2, y1, y2, currentColor);
}
}
private static void createAndShowGui() {
JFrame frame = new JFrame("Drawing");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.getContentPane().add(new Drawing());
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
createAndShowGui();
}
});
}
}
class Line {
private int x1, x2, y1, y2;
private Color color;
public Line(int x1, int x2, int y1, int y2, Color color) {
this.x1 = x1;
this.x2 = x2;
this.y1 = y1;
this.y2 = y2;
this.color = color;
}
public void draw(Graphics page) {
// swap these calls!
page.setColor(color); //!! This first!
page.drawLine(x1, y1, x2, y2); // **Then** this
// !! page.setColor(color);
}
}
关于java - 如何在类和方法之间传递 Graphics 对象来绘制线条,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/35710659/