Question

当我的应用程序加载时，使用netbeans进行加载，第一个JTextField会自动聚焦，而在这个JTextField中，我写了“输入你的用户名”，当用户点击这个字段时它会消失，但当应用程序已加载，此字段为焦点，表示我无法看到“输入您的用户名”，如何在启动时将其取消焦点？

Answer 1

登录最好在模式对话框中完成，但这会带来一些问题，因为在组件可见之后，方法requestFocusInWindow()必须被调用，但是被阻止了对话框是模态的！

此示例使用Rob Camick的RequestFocusListener（如Dialog Focus中所示）在对话框可见后管理焦点。

注意：这是用户执行任何操作之前的显示方式。密码字段默认为焦点。

package test.t100.t001; import java.awt.BorderLayout; import java.awt.GridLayout; import javax.swing.JComponent; import javax.swing.JFrame; import javax.swing.JLabel; import javax.swing.JOptionPane; import javax.swing.JPanel; import javax.swing.JPasswordField; import javax.swing.JTextField; import javax.swing.SwingConstants; import javax.swing.SwingUtilities; import javax.swing.event.AncestorEvent; import javax.swing.event.AncestorListener; public class LoginRequired { LoginRequired() { JFrame f = new JFrame("Login Required"); f.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE); f.setSize(400, 300); f.setResizable(false); f.setLocationByPlatform(true); f.setVisible(true); showLogin(f); } private void showLogin(JFrame frame) { JPanel p = new JPanel(new BorderLayout(5,5)); JPanel labels = new JPanel(new GridLayout(0,1,2,2)); labels.add(new JLabel("User Name", SwingConstants.RIGHT)); labels.add(new JLabel("Password", SwingConstants.RIGHT)); p.add(labels, BorderLayout.WEST); JPanel controls = new JPanel(new GridLayout(0,1,2,2)); JTextField username = new JTextField("Joe Blogs"); controls.add(username); JPasswordField password = new JPasswordField(); password.addAncestorListener(new RequestFocusListener(false)); controls.add(password); p.add(controls, BorderLayout.CENTER); //LayoutManager l = new GroupLayout(p); //p.setLayout(l); JOptionPane.showMessageDialog( frame, p, "Log In", JOptionPane.QUESTION_MESSAGE); } /** * @param args none */ public static void main(String[] args) { SwingUtilities.invokeLater(new Runnable(){ @Override public void run() { new LoginRequired(); } }); } } /** * Convenience class to request focus on a component. * * When the component is added to a realized Window then component will * request focus immediately, since the ancestorAdded event is fired * immediately. * * When the component is added to a non realized Window, then the focus * request will be made once the window is realized, since the * ancestorAdded event will not be fired until then. * * Using the default constructor will cause the listener to be removed * from the component once the AncestorEvent is generated. A second constructor * allows you to specify a boolean value of false to prevent the * AncestorListener from being removed when the event is generated. This will * allow you to reuse the listener each time the event is generated. */ class RequestFocusListener implements AncestorListener { private boolean removeListener; /* * Convenience constructor. The listener is only used once and then it is * removed from the component. */ public RequestFocusListener() { this(true); } /* * Constructor that controls whether this listen can be used once or * multiple times. * * @param removeListener when true this listener is only invoked once * otherwise it can be invoked multiple times. */ public RequestFocusListener(boolean removeListener) { this.removeListener = removeListener; } @Override public void ancestorAdded(AncestorEvent e) { JComponent component = e.getComponent(); component.requestFocusInWindow(); if (removeListener) component.removeAncestorListener( this ); } @Override public void ancestorMoved(AncestorEvent e) {} @Override public void ancestorRemoved(AncestorEvent e) {} }

Answer 2

使用requestFocusInWindow()将注意力设置在其他组件上而不是JTextfield上。

但我建议不要改变原生焦点系统，而是setText(String s) JTextField initComponents()之后的constructor {{1}} （假设是在netbeans中）。

进一步可选阅读：How to Use the Focus Subsystem

Answer 3

我认为将键盘焦点放在用户名字段是正确的行为，假设这是用户首先需要做的事情。而不是清除焦点，为什么不在用户输入内容后才清除？：

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

public class PlaceholderTextField extends JTextField {

    public static void main(final String[] args) {
        final PlaceholderTextField tf = new PlaceholderTextField("");
        tf.setColumns(20);
        tf.setPlaceholder("All your base are belong to us!");
        final Font f = tf.getFont();
        tf.setFont(new Font(f.getName(), f.getStyle(), 30));
        JOptionPane.showMessageDialog(null, tf);
    }

    private String placeholder;

    public PlaceholderTextField() {
    }

    public PlaceholderTextField(
        final Document pDoc,
        final String pText,
        final int pColumns)
    {
        super(pDoc, pText, pColumns);
    }

    public PlaceholderTextField(final int pColumns) {
        super(pColumns);
    }

    public PlaceholderTextField(final String pText) {
        super(pText);
    }

    public PlaceholderTextField(final String pText, final int pColumns) {
        super(pText, pColumns);
    }

    public String getPlaceholder() {
        return placeholder;
    }

    @Override
    protected void paintComponent(final Graphics pG) {
        super.paintComponent(pG);

        if (placeholder.length() == 0 || getText().length() > 0) {
            return;
        }

        final Graphics2D g = (Graphics2D) pG;
        g.setRenderingHint(
            RenderingHints.KEY_ANTIALIASING,
            RenderingHints.VALUE_ANTIALIAS_ON);
        g.setColor(getDisabledTextColor());
        g.drawString(placeholder, getInsets().left, pG.getFontMetrics()
            .getMaxAscent() + getInsets().top);
    }

    public void setPlaceholder(final String s) {
        placeholder = s;
    }

}

如果你真的只想删除焦点，可以选择一些选项：

component.setFocusable(false);
KeyboardFocusManager.getCurrentKeyboardFocusManager().focusNextComponent();
KeyboardFocusManager.getCurrentKeyboardFocusManager().clearGlobalFocusOwner();

Answer 4

textField.setFocusable(false);
textField.setFocusable(true);

当且仅当textField具有焦点时，TAB顺序中的下一个组件将自动获得焦点。效果与TAB印刷机相同。

（未在只有一个可聚焦组件的GUI中进行测试:)）

如何取消焦点JTextField

4 个答案: