全屏显示JFrame，无需修饰

问题描述

我正在Windows机器上使用Java8，该机器是通过IntelliJ的最新社区版本开发的.为了使JFrame全屏显示，我在下面的解决方案中找到了要验证的一种不同行为.

I am using Java8 on Windows machine developing with latest community edition of IntelliJ. To make JFrame full screen I find below solution where I faced one different behavior which I want to get verified.

我从 JFrame全屏获取的解决方案

根据解决方案，我需要在下面三行输入内容，以使JFrame全屏显示:

As per the solution I need to put three below lines to make JFrame full screen:

frame.setExtendedState(JFrame.MAXIMIZED_BOTH);
frame.setUndecorated(true);
frame.setVisible(true);

但是在我的项目中，我创建了一个扩展JFrame的类AppFrame.java.在默认的构造函数中，我设置了一些基本属性，例如font等，重要的是将可见性设置为true.

But in my project I have created a class AppFrame.java that extends JFrame. And in default constructor I set some basic properties like font etc and importantly visibility to true.

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

public class AppFrame extends JFrame {

    AppFrame() {
        Font baseFont = new Font("Dialog", Font.PLAIN, 12);
        setFont(baseFont);
        setLocationRelativeTo(null);
        setBackground(Color.WHITE);
        setForeground(Color.black);
        setLayout(new FlowLayout());
        setVisible(true);
        setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
    }
}

并且在扩展AppFrame的类中，当我尝试放置三行以上(带有或不带有setVisible，这已经来自AppFrame)以最大化它时，出现以下错误:

And in class that extends AppFrame when I try to put above three lines (with or without setVisible, which is already coming from AppFrame) to maximize it get below error:

Exception in thread "main" java.awt.IllegalComponentStateException: The frame is displayable. at java.awt.Frame.setUndecorated(Frame.java:923)

作为解决方案的一部分(我想验证)-实验上我从AppFrame.java中删除了setVisible(true)，并且它起作用了，但这将影响所有扩展AppFrame的类，因此我也删除了frame.setUndecorated(true);从我的班级中放回setVisible在AppFrame中.而且异常消失了.另外，我相信frame.setUndecorated(true);也会删除JFrame的标题栏.

As a part of solution (which I want to verify) - Experimentally I removed setVisible (true) from AppFrame.java and it worked, but this would be gonna impact all classes extending AppFrame, so I removed frame.setUndecorated(true); as well from my class and put back setVisible in AppFrame. And exception is gone. Also frame.setUndecorated(true); I believe removes title bar of JFrame.

此外，以下是JFrame的javadoc的摘录:

Also, below is excerpt from javadoc of JFrame:

如果有人可以验证此行为，那就太好了.

It would be great if someone can verify this behavior.

推荐答案

修改初始化程序以使用参数.AppFrame() {应该更改为AppFrame(boolean undecorated, boolean visible) {，然后在初始化程序中添加setUndecorated(undecorated);和setVisible(visible);

Modify the initializer to use parameters.AppFrame() { should be changed to AppFrame(boolean undecorated, boolean visible) { then in the initializer add setUndecorated(undecorated); and setVisible(visible);

完整的解决方案:

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

public class AppFrame extends JFrame {

    AppFrame(boolean undecorated, boolean visible) {
        Font baseFont = new Font("Dialog", Font.PLAIN, 12);
        setFont(baseFont);
        setLocationRelativeTo(null);
        setBackground(Color.WHITE);
        setForeground(Color.black);
        setLayout(new FlowLayout());
        setExtendedState(JFrame.MAXIMIZED_BOTH);
        setUndecorated(undecorated);
        setVisible(visible);
        setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
    }
}

关于:

这只是说明您必须在调用setVisible(true);之前执行此操作.要确定是否可以安全地呼叫setUndecorated，可以使用if (!isDisplayable()) { ... }

This is just stating that you have to do this before calling setVisible(true);. To determine if you can call setUndecorated safely, you can use if (!isDisplayable()) { ... }

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