使用JColorChooser绘图

Question

我正在尝试使用颜色选择器来选择要用来绘制的颜色。我可以让它显示颜色选择和绘制在黑色，但我被卡住了。

package sketch;

import java.awt.BorderLayout;
import java.awt.Graphics;
import java.awt.Point;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.event.MouseMotionAdapter;
import java.awt.Color;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JButton;
import javax.swing.JColorChooser;

import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;
/**
*
* @author Brittany
*/
public class Sketch extends JPanel{

/**
 * Keeps track of the last point to draw the next line from.
 */
private Point lastPoint;

/**
 * Constructs a panel, registering listeners for the mouse.
 */
public Sketch() {

 Color drawColor = Color.BLACK;



    // When the mouse button goes down, set the current point
    // to the location at which the mouse was pressed.
    addMouseListener(new MouseAdapter() {
        @Override
        public void mousePressed(MouseEvent e) {
            lastPoint = new Point(e.getX(), e.getY());
        }
    });

    // When the mouse is dragged, draw a line from the old point
    // to the new point and update the value of lastPoint to hold
    // the new current point.
    addMouseMotionListener(new MouseMotionAdapter() {
        @Override
        public void mouseDragged(MouseEvent e) {
            Graphics g = getGraphics();
            g.setColor(drawColor);
            g.drawLine(lastPoint.x, lastPoint.y, e.getX(), e.getY());
            lastPoint = new Point(e.getX(), e.getY());
            g.dispose();
        }
    });
}
/**
 * @param args the command line arguments
 */
public static void main(String[] args) {
    JFrame frame = new JFrame("Simple Sketching Program");
    JButton colorBtn = new JButton("Color");

   colorBtn.addActionListener(new ActionListener(){
       public void actionPerformed(ActionEvent e) {
 Color newColor = JColorChooser.showDialog(frame,"Choose Color",Color.BLACK);
            if(newColor != null){

            }

        }
    });



    frame.getContentPane().add(new Sketch(), BorderLayout.CENTER);
    frame.getContentPane().add(colorBtn, BorderLayout.NORTH);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setSize(400, 300);
    frame.setVisible(true);

}

}

Answer 1

Graphics g = getGraphics();不是自定义绘画的工作方式。getGraphics可以返回null，它只不过是上一次绘制过程的快照，将在下一次绘制过程中替换。

首先看看Performing Custom Painting和Painting in AWT and Swing，了解更多关于绘画的工作原理和你应该如何使用它的细节。

然后，您有两个选择。可以使用BufferedImage作为主绘制曲面，然后将其绘制到组件，也可以跟踪绘制的内容(以及绘制的颜色)，并在每次发生绘制循环时重新生成它。这两种方法各有优缺点，您将根据自己的需要来决定使用哪种方法。

来回答你的问题。您需要某种方法来将新颜色传递给Sketch的一个实例。

我会从在Sketch中创建一个设置器开始，它可以用于其他类来更改颜色……

public Sketch() {

    private Color drawColor = Color.BLACK;

    public void setDrawColor(Color color) {
        if (color == null) {
            drawColor = Color.BLACK;
        } else {
            drawColor = colorl
        }
    }

然后您将使用此方法将新颜色传递给它。

public static void main(String[] args) {
    JFrame frame = new JFrame("Simple Sketching Program");
    JButton colorBtn = new JButton("Color");

    Sketch sketch = new Sketch();

    colorBtn.addActionListener(new ActionListener(){
        public void actionPerformed(ActionEvent e) {
            Color newColor = JColorChooser.showDialog(frame,"Choose Color",Color.BLACK);
            if(newColor != null){
                sketch.setDrawColor(newColor);
            }
        }
    });


    frame.getContentPane().add(new Sketch(), BorderLayout.CENTER);