英文:
Curious behavior of java.awt.Component, setVisible(), LayoutManager
问题
以下是您提供的代码的翻译部分:
我试图创建一个GUI,并发现了java.awt.Component的一些奇怪行为。我想通过外部事件对java.awt.Component使用`setVisible(true)`/`setVisible(false)`。但只有当要切换的组件在第一次出现时已经可见才起作用。附上我问题的最小复制版。
package test;
import java.awt.Button;
import java.awt.Dimension;
import java.awt.Frame;
import java.awt.Menu;
import java.awt.MenuBar;
import java.awt.MenuItem;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
public final class Test {
public static void main(String[] args) {
Button testButton = new Button("测试按钮");
testButton.setVisible(false); /* 移除此行使代码按预期工作,但为什么? */
Frame mainFrame = new Frame("测试");
mainFrame.setMinimumSize(new Dimension(640, 480));
mainFrame.setVisible(true);
mainFrame.addWindowListener(new WindowAdapter() {
public void windowClosing(WindowEvent event) {
System.exit(0);
}
});
mainFrame.add(testButton);
mainFrame.setMenuBar(new MenuBar());
mainFrame.getMenuBar().add(new Menu("测试"));
mainFrame.getMenuBar().getMenu(0).add(new MenuItem("显示/隐藏 \"测试按钮\""));
mainFrame.getMenuBar().getMenu(0).getItem(0).addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent arg0) {
if(testButton.isVisible()) testButton.setVisible(false);
else testButton.setVisible(true);
System.out.println("testButton.getBounds()" + testButton.getBounds()); /* 编辑:为调试添加了这一行。 */
System.out.println("testButton.isVisible() " + testButton.isVisible());
}
});
}
}
当您移除`testButton.setVisible(false);`这一行时,testButton是可见的,也可以切换其可见状态,否则不行。有人知道为什么吗?也许布局管理器不适用于不可见的组件?
编辑:似乎布局管理器不会为不可见的组件`setBounds(...)`,但为什么?
请注意,以上只是您提供的代码的翻译部分,如有需要,您可以使用这些翻译来处理您的工作。如果您有任何其他问题或需要进一步帮助,请随时提问。
英文:
I was trying to create a GUI and found some curious behavior of java.awt.Component. I wanted to setVisible(true)
/setVisible(false)
an java.awt.Component by an external Event. But this only works when the to be switched Component was already visible in the first place. Attached, I provided a minimal replica of my problem.
package test;
import java.awt.Button;
import java.awt.Dimension;
import java.awt.Frame;
import java.awt.Menu;
import java.awt.MenuBar;
import java.awt.MenuItem;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
public final class Test {
public static void main(String[] args) {
Button testButton = new Button("Test Button");
testButton.setVisible(false); /* Removing this line makes the code to work as intended, but why? */
Frame mainFrame = new Frame("Test");
mainFrame.setMinimumSize(new Dimension(640, 480));
mainFrame.setVisible(true);
mainFrame.addWindowListener(new WindowAdapter() {
public void windowClosing(WindowEvent event) {
System.exit(0);
}
});
mainFrame.add(testButton);
mainFrame.setMenuBar(new MenuBar());
mainFrame.getMenuBar().add(new Menu("Test"));
mainFrame.getMenuBar().getMenu(0).add(new MenuItem("Show/Hide \"Test Button\""));
mainFrame.getMenuBar().getMenu(0).getItem(0).addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent arg0) {
if(testButton.isVisible()) testButton.setVisible(false);
else testButton.setVisible(true);
System.out.println("testButton.getBounds()" + testButton.getBounds()); /* EDIT: Added this line for debugging. */
System.out.println("testButton.isVisible() " + testButton.isVisible());
}
});
}
}
When you remove line testButton.setVisible(false);
, testButton is viewable and also switchable in its state of visibility, otherwise not. Does anyone know why? Maybe the layout-manager doesn't work with invisible components?
EDIT: It seems the layout-manager doesn't setBounds(...)
for invisible components, but why?
答案1
得分: 1
> 或许布局管理器不适用于不可见组件?
是的,这取决于布局管理器的规则。
例如,FlowLayout 和 BoxLayout 在进行布局时会忽略不可见组件。然而,GridLayout 会保留空间。
在使用 Swing 时,更改组件的属性应会自动调用布局管理器。因此,调用 setVisible() 应该会导致新的布局。
然而,如果布局不是自动执行的,你需要使用类似以下的代码:
testButton.getParent().revalidate();
我已经十多年没有使用 AWT 了,但我记得 AWT 不如 Swing 聪明,所以在设置按钮的可见状态后,你需要使用:
testButton.getParent().validate();
至少在你提供的最小重现环境中是有效的。
英文:
> Maybe the layout-manager doesn't work with invisible components?
Correct, it depends on the rules of the layout manager.
For example the FlowLayout and BoxLayout, ignore invisible components when doing the layout. However, a GridLayout will reserve space.
When using Swing changing a property of a component should automatically invoke the layout manager. So invoking setVisible() should cause a new layout.
However, if layout is not done automatically then you would use code like:
testButton.getParent().revalidate();
I haven't used AWT for over a decade now but as I recall AWT is not as smart as Swing so you need to use:
testButton.getParent().validate();
after setting the visible state of the button. At least it works in the MRE you provided.
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