如何使用JButton在JFilechooser中添加图片

Question

JFileChooser不能工作--我在网上发现了一个错误：

btnNewButton.setIcon(new ImageIcon(ImageIO.read(file)));

请帮帮我，我是初学者。它给了我这个错误：

线程“AWT 0”java.lang.IllegalArgumentException中的异常:输入== null！RecordManagementSystem.addRecord$1.actionPerformed(addRecord.java:185) at javax.swing.AbstractButton.fireActionPerformed(Unknown Source) at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source) at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source) at javax.swing.DefaultButtonModel.setPressed(Unknown Source) at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(Unknown Source)( javax.swing.JComponent.processMouseEvent(Unknown源)在java.awt.Component.processEvent(未知源)在java.awt.Container.processEvent(未知源)在java.awt.Component.dispatchEventImpl(未知源)在java.awt.Container.dispatchEventImpl(未知源)在java.awt.Component.dispatchEvent(未知源)在java.awt.LightweightDispatcher.processMouseEvent(Unknown( java.awt.LightweightDispatcher.dispatchEvent(Unknown来源)在java.awt.Container.dispatchEventImpl(未知来源)在java.awt.Window.dispatchEventImpl(未知来源)在java.awt.Component.dispatchEvent(未知来源)在java.awt.EventQueue.dispatchEventImpl(未知来源)在java.awt.EventQueue.access$000(未知来源)在java.awt.EventQueue$1.运行(未知来源)在java.awt.EventQueue$1运行(未知来源)(来源)在java.security.AccessController.doPrivileged(Native方法)在java.security.AccessControlContext$1.doIntersectionPrivilege(Unknown来源)在java.security.AccessControlContext$1.doIntersectionPrivilege(Unknown来源)在java.awt.EventQueue$2.运行(未知来源)在java.awt.EventQueue$2.运行(未知来源)在java.security.AccessController.doPrivileged(Native方法)在java.security.AccessControlContext$1.doIntersectionPrivilege(Unknown来源)在java.awt.EventQueue.dispatchEvent(未知来源)(来源)在java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown来源)在java.awt.EventDispatchThread.pumpEventsForFilter(Unknown来源)在java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown来源)在java.awt.EventDispatchThread.pumpEvents(Unknown来源)在java.awt.EventDispatchThread.pumpEvents(Unknown来源)在java.awt.EventDispatchThread.run(未知来源)

代码：

btnNewButton.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent ae) {
            JFileChooser fc = new JFileChooser();
            File file = fc.getSelectedFile();
            int result = fc.showOpenDialog(null);

            if (result == JFileChooser.APPROVE_OPTION) {              
                try {
                    btnNewButton.setIcon(new ImageIcon(ImageIO.read(file)));
                } catch (IOException e) {
                    JOptionPane.showMessageDialog(null, e);
                }
            }
        }
    });

Answer 1

在选择JFileChooser 之前，您将从获取该文件，因此fc.getSelectedFile()将返回null。

解决方案:在显示JFileChooser之后，在if块JFileChooser中获取文件。

if (result == JFileChooser.APPROVE_OPTION) {              
    try {
        File file = fc.getSelectedFile();  // **** line added ****
        btnNewButton.setIcon(new ImageIcon(ImageIO.read(file)));
    } catch (IOException e) {
        JOptionPane.showMessageDialog(null, e);
    }
}

顺便说一句，我喜欢避免对代码进行过度压缩，以便在出现错误时更容易找到错误。所以我会这样做：

if (result == JFileChooser.APPROVE_OPTION) {              
    try {
        File file = fc.getSelectedFile();
        Image image = ImageIO.read(file);
        Icon icon = new ImageIcon(image);
        btnNewButton.setIcon(icon);
    } catch (IOException e) {
        // log error
    }
}