Question

无法找到答案（或者很可能我没有正确询问）。

我的JTextField textfield1启动后，如何将注意力集中在JFrame上？通过焦点我的意思是用户可以立即开始输入，而无需点击JTextField。

我尝试textfield1.setCaretPosition(0)和textfield1.moveCaretPosition(0)，但都没有效果。

点击后，焦点仍然停留在提交按钮上（即使我在点击后调用上面的2）。

Answer 1

在Swing中可以通过多种方式控制焦点，但在您的情况下，最简单的可能就是使用JTextField#requestFocusInWindow

这有点偏离主题，但你可能想看看How to use the a Focus Subsystem

Answer 2

比直接请求关注初始组件更有趣的是自定义FocusTraversalPolicy，它实现了查找/配置默认值的一般机制。基本概念已在其api中可用，具有返回初始/ defaultComponent的方法，f.i。：

public abstract Component getDefaultComponent（Container aContainer）

返回要关注的默认Component。这个组件将是   首先在遍历新的焦点遍历时获得焦点   以aContainer为基础的循环。

默认实现返回循环中的第一个组件，自定义实现可能会查找自定义指示符f.i.客户财产。简单的用法会将该策略设置为在其contentPane中具有标记的框架，如：

// a custom policy checking for the property
FocusTraversalPolicy policy = new LayoutFocusTraversalPolicy() {

    @Override
    public Component getDefaultComponent(Container aContainer) {
        if (aContainer instanceof JComponent) {
            JComponent parent = (JComponent) aContainer;
            if (parent.getClientProperty("defaultFocus") instanceof Component) {
                return (Component) parent.getClientProperty("defaultFocus");
            }
        }
        if (aContainer instanceof RootPaneContainer) {
            RootPaneContainer root = (RootPaneContainer) aContainer;
            JComponent parent = (JComponent) root.getContentPane();
            if (parent.getClientProperty("defaultFocus") instanceof Component) {
                return (Component) parent.getClientProperty("defaultFocus");
            }

        }
        return super.getDefaultComponent(aContainer);
    }

};
JFrame frame = ... // create  and fill
JTextField field = new JTextField(20);
frame.add(field, BorderLayout.SOUTH);
// set the client property 
((JComponent) frame.getContentPane()).putClientProperty("defaultFocus", field);
// set the custom policy
frame.setFocusTraversalPolicy(policy);

更优雅的是默认使用这样的策略 - 可以通过将其安装为KeyboardFocusManager的默认策略来实现。有了这个，使用将简化为

在应用程序生命周期的早期安装自定义默认值
标记初始焦点组件（无需手动设置框架的策略）

代码：

// very early in the application code
initializeDefaultFocusTraversalPolicy();

// default in any frame
JFrame frame = ... // create  and fill
JTextField field = new JTextField(20);
frame.add(field, BorderLayout.SOUTH);
// set the client property 
((JComponent) frame.getContentPane())
    .putClientProperty(DelegatingFocusTraversalPolicy.DEFAULT_FOCUS_KEY, field);

Swing不会是Swing它没有捕获，但是：

框架的默认策略在其实例化时在内部设置 - 因此，在创建框架

并不奇怪。
UIManager对管理器的默认设置有自己的想法，实际上在创建第一个框架时会进行无条件配置（这会覆盖我们自己的默认框架）

出路是创建一个虚拟框架，然后设置策略：

public static void initializeDefaultFocusTraversalPolicy() { // a custom default policy is overwritten by the UIManager the // very first time it sees a top-level container created // it does so unconditionally depending on a flag in LAFState // see UIManager.maybeInitializeFocusPolicy // so we tricks him into doing it for a fake frame new JFrame(); // and set our custom default afterwards FocusTraversalPolicy p = KeyboardFocusManager.getCurrentKeyboardFocusManager() .getDefaultFocusTraversalPolicy(); KeyboardFocusManager.getCurrentKeyboardFocusManager() .setDefaultFocusTraversalPolicy(new CustomFocusTraversalPolicy(p)); } /** * Basically the same custom policy as the ad-hoc above, just with * delegating */ public static class CustomFocusTraversalPolicy extends FocusTraversalPolicy { public static final String DEFAULT_FOCUS_KEY = "defaultFocus"; private FocusTraversalPolicy delegate; public CustomFocusTraversalPolicy(FocusTraversalPolicy delegate) { this.delegate = Contract.asNotNull(delegate, "the delegate must not be null"); } @Override public Component getDefaultComponent(Container container) { if (container instanceof JComponent) { JComponent parent = (JComponent) container; if (parent.getClientProperty(DEFAULT_FOCUS_KEY) instanceof Component) { return (Component) parent.getClientProperty(DEFAULT_FOCUS_KEY); } } if (container instanceof RootPaneContainer) { RootPaneContainer root = (RootPaneContainer) container; JComponent parent = (JComponent) root.getContentPane(); if (parent.getClientProperty(DEFAULT_FOCUS_KEY) instanceof Component) { return (Component) parent.getClientProperty(DEFAULT_FOCUS_KEY); } } return delegate.getDefaultComponent(container); } @Override public Component getComponentAfter(Container aContainer, Component aComponent) { return delegate.getComponentAfter(aContainer, aComponent); } @Override public Component getComponentBefore(Container aContainer, Component aComponent) { return delegate.getComponentBefore(aContainer, aComponent); } @Override public Component getFirstComponent(Container aContainer) { return delegate.getFirstComponent(aContainer); } @Override public Component getLastComponent(Container aContainer) { return delegate.getLastComponent(aContainer); } }

自动将焦点设置在JTextField上

2 个答案: