图形-使用参数（getSize（））在整个窗口中绘制一条线

Question

我需要帮助。我想给drawLine（）方法提供一个参数，该方法是从getSize（）获得的。我想使用getSize（）方法在整个窗口中画一条线。

package PROG2;

import java.awt.*;
import javax.swing.*;

class MyComponent extends JComponent {

    @Override
    public void paintComponent(Graphics g) {
        g.drawLine(100, 100, 200, 200);
    }
}
    
public class Übung1 extends JFrame{

    public static void berechnen() {
        int height = frame.getHeight(); //Here it says it doesn't know "frame" variable but I don't know how to declare it here.
        int width = frame.getWidth();
    }

    public static void main(String[] args){
            JFrame frame = new JFrame("First window");
            berechnen();
            frame.add(new MyComponent());
            frame.setSize(400, 400);
            frame.setVisible(true);
            frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
            Graphics g = frame.getGraphics();

            // int width = frame.getWidth();
            // int height = frame.getHeight();
            System.out.println("Größe:" + frame.getSize());
            //System.out.println(width);
    }
}

Answer 1

正如安德鲁已经说过的，

• 您不想获取JFrame的尺寸或大小，而是想获取JFrame的contentPane中显示的组件，这里是您的MyComponent实例
• 获取这些信息的最佳位置是在绘制线之前，在paintComponent方法内部
• 总是先打电话给super的绘画方法

我还建议：

• 如果您想要不透明的图像，请在JPanel的油漆组件方法中绘制，而不是在JComponent方法中绘制
• 除非绝对需要，否则避免静态方法和字段

请注意，在下面的代码中，红线穿过JPanel的对角线，并继续绘制对角线，即使手动调整JFrame的大小：

import java.awt.BasicStroke;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.RenderingHints;
import java.awt.Stroke;

import javax.swing.*;

public class DrawLine extends JPanel {
    private static final Stroke LINE_STROKE = new BasicStroke(15f);
    private static final Dimension PREF_SIZE = new Dimension(800, 650);

    public DrawLine() {
        setPreferredSize(PREF_SIZE);
    }
    
    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        
        // code to make the line smooth (antialias the line to remove jaggies)
        // and to make the line thick, using a wider "stroke"
        Graphics2D g2 = (Graphics2D) g;
        g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
        g2.setStroke(LINE_STROKE);

        // if we want a red line
        g2.setColor(Color.RED);

        // this is the key code here:
        int width = getWidth();
        int height = getHeight();
        
        // draw along the main diagonal:
        g2.drawLine(0, 0, width, height);
    }
    
    public static void main(String[] args) {
        SwingUtilities.invokeLater(() -> {
            DrawLine mainPanel = new DrawLine();

            JFrame frame = new JFrame("GUI");
            frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
            frame.add(mainPanel);
            frame.pack();
            frame.setLocationRelativeTo(null);
            frame.setVisible(true);
        });
    }

}