麻烦弄清楚如何设置背景图像[重复]

Question

可能重复：
How to set an image as a background for Frame in Swing GUI of java?

我无法弄清楚如何在我的窗口上设置背景图像。我不确定我的代码有什么问题。图片名为 Background.jpg
有谁知道我的代码有什么问题以及如何修复它

//apples code  

import javax.swing.JFrame;
import java.applet.*;
import javax.swing.*;
import java.awt.*;
import java.awt.Graphics;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.imageio.ImageIO;
import javax.swing.JPanel;
import java.awt.*;
import javax.swing.*;

class  Apples{

public static void main(String[] args) {
  gui go = new gui();
  go.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
  go.setSize(200,290);
  go.setVisible(true);



 }
}



 //Gui Code

    import java.awt.FlowLayout;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;
import javax.swing.*;
import java.awt.Color;
import java.awt.Font;
import javax.swing.JFrame;
import javax.swing.JTextArea;

public class gui extends JFrame{
     private JButton A;
     private JButton B;
     private JButton C;
     private JButton D;
     private JButton E;
     private JButton F;
     private JButton G;
     private JButton H;
     private JButton I;
     private JButton J;
     private JButton K;
     private JButton L;
     private JButton M;
     private JButton N;
     private JButton O;
     private JButton P;
     private JButton Q;
     private JButton R;
     private JButton S;
     private JButton T;
     private JButton U;
     private JButton V;
     private JButton W;
     private JButton X;
     private JButton Y;
     private JButton Z;

     public gui(){
        super("APUSH ABCs");
        setLayout(new FlowLayout());

        A = new JButton("A");
        add(A);
        B = new JButton("B");
        add(B);
        C = new JButton("C");
        add(C);
        D = new JButton("D");
        add(D);
        E = new JButton("E");
        add(E);
        F = new JButton("F");
        add(F);
        G = new JButton("G");
        add(G);
        H = new JButton("H");
        add(H);
        I = new JButton("I");
        add(I);
        J = new JButton("J");
        add(J);
        K = new JButton("K");
        add(K);
        L = new JButton("L");
        add(L);
        M = new JButton("M");
        add(M);
        N = new JButton("N");
        add(N);
        O = new JButton("O");
        add(O);
        P = new JButton("P");
        add(P);
        Q = new JButton("Q");
        add(Q);
        R = new JButton("R");
        add(R);
        S = new JButton("S");
        add(S);
        T = new JButton("T");
        add(T);
        U = new JButton("U");
        add(U);
        V = new JButton("V");
        add(V);
        W = new JButton("W");
        add(W);
        X = new JButton("X");
        add(X);
        Y = new JButton("Y");
        add(Y);
        Z = new JButton("Z");
        add(Z);

        HandlerClass handler = new HandlerClass();
        A.addActionListener(handler);
        B.addActionListener(handler);
        C.addActionListener(handler);
        D.addActionListener(handler);
        E.addActionListener(handler);
        F.addActionListener(handler);
        G.addActionListener(handler);
        H.addActionListener(handler);
        I.addActionListener(handler);
        J.addActionListener(handler);
        K.addActionListener(handler);
        L.addActionListener(handler);
        M.addActionListener(handler);
        N.addActionListener(handler);
        O.addActionListener(handler);
        P.addActionListener(handler);
        Q.addActionListener(handler);
        R.addActionListener(handler);
        S.addActionListener(handler);
        T.addActionListener(handler);
        U.addActionListener(handler);
        V.addActionListener(handler);
        W.addActionListener(handler);
        X.addActionListener(handler);
        Y.addActionListener(handler);
        Z.addActionListener(handler);
    }
      private class HandlerClass implements ActionListener{
  public void actionPerformed(ActionEvent event){

     Object button = event.getSource();

     if(button == A){
String text = "asaasas ";
  JTextArea textArea = new JTextArea(text);

  textArea.setColumns(30);
  textArea.setLineWrap( true );
  textArea.setWrapStyleWord( true );
  textArea.setSize(textArea.getPreferredSize().width, 1);
Font font = new Font("Verdana", Font.BOLD, 12);
textArea.setFont(font);
textArea.setForeground(Color.BLUE);
  JOptionPane.showMessageDialog(
   null, textArea, "Appomattox Court House", JOptionPane.PLAIN_MESSAGE);

     }else if(button == B){
     String text = "Duriing the last days of the Civil War, Robert E. Lee had abandoned the Confederate capital of Richmond and city of Petersburg, hoping to escape with the remnants of his Army of Northern Virginia to meet up with additional Confederate forces in North Carolina and resume fighting. Union Forces cut him off and finally the Continental army had to surrender. The Appomattox Courthouse is the locaiton where General Robert E. Lee of the Confederate Army surrendered his approximately 28,000 troops to Ulysses S. Grant and the Union Army on April 9, 1865, ending the American Civil War. ";
  JTextArea textArea = new JTextArea(text);

  textArea.setColumns(30);
  textArea.setLineWrap( true );
  textArea.setWrapStyleWord( true );
  textArea.setSize(textArea.getPreferredSize().width, 1);
Font font = new Font("Verdana", Font.BOLD, 12);
textArea.setFont(font);
textArea.setForeground(Color.BLUE);
  JOptionPane.showMessageDialog(
   null, textArea, "Appomattox Court House", JOptionPane.PLAIN_MESSAGE);
     } else if(button == C){

String text = "Duriing the last days of the Civil War, Robert E. Lee had abandoned the Confederate capital of Richmond and city of Petersburg, hoping to escape with the remnants of his Army of Northern Virginia to meet up with additional Confederate forces in North Carolina and resume fighting. Union Forces cut him off and finally the Continental army had to surrender. The Appomattox Courthouse is the locaiton where General Robert E. Lee of the Confederate Army surrendered his approximately 28,000 troops to Ulysses S. Grant and the Union Army on April 9, 1865, ending the American Civil War. ";
  JTextArea textArea = new JTextArea(text);

  textArea.setColumns(30);
  textArea.setLineWrap( true );
  textArea.setWrapStyleWord( true );
  textArea.setSize(textArea.getPreferredSize().width, 1);
Font font = new Font("Verdana", Font.BOLD, 12);
textArea.setFont(font);
textArea.setForeground(Color.BLUE);
  JOptionPane.showMessageDialog(
   null, textArea, "Appomattox Court House", JOptionPane.PLAIN_MESSAGE);     
       }

      }
}

Answer 1

这...

public void paint(Graphics g)
{
    // Draws the img to the BackgroundPanel.
    g.drawImage(img, 0, 0, null);
}

从来都不是一个好主意。你没有尊重油漆链。绘制链是一组复杂的方法，可以完成很多重要的工作。

一个更好的主意是使用paintComponent

protected void paintComponent(Graphics g)
{
    super.paintComponent(g);
    // Draws the img to the BackgroundPanel.
    g.drawImage(img, 0, 0, null);
}

您将遇到的另一个问题是您没有让组件有机会监视图像的状态。因为您使用的是Toolkit.getDefaultToolkit().createImage("Background.jpg")，所以方法可能会使用后台线程来加载图像。你需要一些方法来告诉组件图像已经完成加载并准备好绘画......

g.drawImage(img, 0, 0, this);

这将让组件监控图像的状态并根据需要自行更新。

Toolkit#createImage 可能不是加载图像的最佳选择。如果无法加载图片，该方法不会抛出异常。

最好使用ImageIO#read。这不仅会在类无法加载图像时抛出异常，而且保证返回一个完全限定的图像（即，它会阻塞直到图像被实际加载）。

您还没有告诉我们Background.jpg 的位置。图片是否为嵌入式资源。如果图像只是一个文件（在应用程序的执行上下文中），那么您尝试加载文件就可以了，如果它是嵌入式资源（包含在应用程序 Jar 中），那么您需要使用 Class#getResource 代替...

img = ImageIO.read(getClass().getResource("/Background.jpg"));

您没有为BackgroundPanel 指定首选大小。某些布局管理器将无法按照您预期的方式布局此容器。

public Dimension getPreferredSize() {
    return img == null ? super.getPreferredSize() : new Dimension(img.getWidth(this), img.getHeight(this));
}

另外，正如已经开始提到的，不要忘记将面板添加到您的 UI ;)

更新示例

我还注意到您似乎在混合 Swing 和 AWT 组件，这绝不是一个好主意，如果可以避免，那就这样做（Panel 是 AWT/重量级组件）。

public class Apples {

    public static void main(String[] args) {
        new Apples();
    }

    public Apples() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                }

                JFrame frame = new JFrame();
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.setLayout(new BorderLayout());
                frame.add(new BackgroundPanel());
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    public class BackgroundPanel extends JPanel {

        Image img;

        public BackgroundPanel() {
            try {
                img = ImageIO.read(getClass().getResource("/Background.jpg"));
            } catch (IOException ex) {
                ex.printStackTrace();
            }
        }

        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            // Draws the img to the BackgroundPanel.
            if (img != null) {
                g.drawImage(img, 0, 0, null);
            }
        }

        public Dimension getPreferredSize() {
            return img == null ? super.getPreferredSize() : new Dimension(img.getWidth(this), img.getHeight(this));
        }
    }
}