java - 如何在另一个类中调用我的paintComponent() 方法
问题描述
我正在编写一个 Blackjack 程序,该程序有时会调用 paintComponent() 方法从文件中绘制图像。图片应该出现在 JPanel 中,但如果我尝试调用该方法JPanel-> style2b1.paintComponent(getGraphics())
;
它不起作用(NullPointerException
),但这本身并不让我感到惊讶。我尝试过并且没有给我任何错误的唯一方法就是简单地写:paintComponent(getGraphics())
;
但是图像也没有显示。
就像我之前说的,我尝试了一堆不同的调用,用不同的东西作为参数,但它从来没有给出积极的结果。
我的班级视窗
package com;
import javax.imageio.ImageIO;
import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.io.File;
import java.io.IOException;
public class Windows extends JFrame{
JFrame test = new JFrame();
JLabel text = new JLabel("Welcome to Blackjack 21");
JLabel textAction = new JLabel("");
JLabel textBank = new JLabel("BANK");
JLabel textPlayer = new JLabel("PLAYER");
JPanel style = new JPanel();
JPanel style2 = new JPanel(new BorderLayout());
JPanel style2a = new JPanel(new BorderLayout());
JPanel style2a1 = new JPanel();
JPanel style2a2 = new JPanel();
JPanel style2b = new JPanel(new BorderLayout());
JPanel style2b1 = new JPanel();
JPanel style2b2 = new JPanel();
JPanel style3 = new JPanel();
JButton b1 = new JButton("Stand");
JButton b2 = new JButton("Hit");
JButton b3 = new JButton("Double");
JButton b4 = new JButton("Split");
JButton b5 = new JButton("Insurance");
Font font = new Font("Helvetica", 10, 20);
public Windows(){
style.setBackground(Color.BLACK);
style2.setBackground(Color.DARK_GRAY);
style2a.setBackground(Color.magenta);
style2a1.setBackground(Color.BLACK);
style2a2.setBackground(Color.DARK_GRAY);
style2b.setBackground(Color.magenta);
style2b1.setBackground(Color.DARK_GRAY);
style2b2.setBackground(Color.BLACK);
style3.setBackground(Color.BLACK);
style3.add(b1);
style3.add(b2);
style3.add(b3);
style3.add(b4);
style3.add(b5);
text.setForeground(Color.WHITE);
text.setFont(font);
style.add(text);
textAction.setForeground(Color.WHITE);
textAction.setFont(font);
style2.add(textAction);
textBank.setFont(font);
textBank.setForeground(Color.RED);
style2a1.add(textBank);
textPlayer.setForeground(Color.GREEN);
textPlayer.setFont(font);
style2b2.add(textPlayer);
style2b1.setSize(this.getWidth(), 300);
DrawPicture otaku = new DrawPicture();
b1.addActionListener(new ActionListener() {
@Override
public void actionPerformed(ActionEvent e) {
textAction.setText("You choose to stand. You won't receive any more cards.");
}
});
b2.addActionListener(new ActionListener() {
@Override
public void actionPerformed(ActionEvent e) {
textAction.setText("You choose to hit. You will receive another card");
//This is where I want to call my method
paintComponents(getGraphics());
}
});
b3.addActionListener(new ActionListener() {
@Override
public void actionPerformed(ActionEvent e) {
textAction.setText("You choose to double. You will receive one last card and you have to double your bet");
}
});
b4.addActionListener(new ActionListener() {
@Override
public void actionPerformed(ActionEvent e) {
textAction.setText("You choose to split. Each deck of card will be considered as individual, however you have to double your bet ");
}
});
b5.addActionListener(new ActionListener() {
@Override
public void actionPerformed(ActionEvent e) {
textAction.setText("You choose to raise an insurance. Please double your bet.");
}
});
test.add(style, BorderLayout.PAGE_START);
test.add(style2, BorderLayout.CENTER);
style2.add(style2a, BorderLayout.NORTH);
style2a.add(style2a1, BorderLayout.NORTH);
style2a.add(style2a2, BorderLayout.SOUTH);
style2.add(style2b, BorderLayout.SOUTH);
style2b.add(style2b1, BorderLayout.NORTH);
style2b.add(style2b2, BorderLayout.SOUTH);
test.add(style3, BorderLayout.PAGE_END);
test.setSize(1000, 1000);
test.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
test.setVisible(true);
test.setLocation(500, 0);
test.setResizable(false);
}
}
我的班级画图
package com;
import javax.imageio.ImageIO;
import javax.swing.*;
import java.awt.*;
import java.io.File;
import java.io.IOException;
public class DrawPicture extends JPanel {
File a = new File("C:\\Users\\km\\Pictures\\Cards\\red_back.png");
public void paintComponents(Graphics g){
try {
Image testItOut = ImageIO.read(a);
g.drawImage(testItOut, 50, 300, this);
}catch(IOException e){
e.printStackTrace();
}
}
}
我的目标是能够在 JPanel style2a2 和 JPanel style2b1 中显示许多图片(然后调整它们的大小)。我不知道我是否可以通过 JPanel 放置多个元素,但我还没有想到那么远。
解决方案
在 GUI 的(重新)绘制期间会自动调用一个paintComponent(更好地定义为检测错别字)。@Override
所以他们是事件驱动的,反应的。它不打算被称为直。repaint*
而是在 DrawPicture 变量上或整个 JFrame ( Windows
)上使用 JComponent 的方法之一。
public class DrawPicture extends JPanel {
private Image testItOut;
// Access for setting an other image.
public void setImage(Image testItOut) {
this.testItOut = testItOut;
}
public Image getImage() {
return testItOut;
}
public DrawPicture() {
try {
File a = new File("C:\\Users\\km\\Pictures\\Cards\\red_back.png");
testItOut = ImageIO.read(a);
} catch(IOException e) {
e.printStackTrace();
}
}
@Override
public void paintComponent(Graphics g) {
if (testItOut != null) {
g.drawImage(testItOut, 50, 300, this);
}
}
}
例如:
b5.addActionListener(new ActionListener() {
@Override
public void actionPerformed(ActionEvent e) {
otaku.repaint(50L); // Repaint after 50 ms.
}
});
这可以用 lambdas 缩短为:
b5.addActionListener(e -> {
otaku.repaint(50L); // Repaint after 50 ms.
});
甚至
b5.addActionListener(e -> otaku.repaint(50L));
更现实一点:
b5.addActionListener(e ->
SwingUtilities.invokeLater(() -> {
File imgFile = new File("C:\\Users\\km\\Pictures\\Cards\\green_back.png");
Image img = ImageIO.read(imgFile);
otaku.setImage(img);
otaku.repaint(50L);
}));
invokeLater
actionPerformed
当代码需要更长的时间(在按钮按下期间它不会阻塞)时,使 GUI 表现得更加响应。
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