包含HTML文本的JLabel会自动使用可用空间换行。如果将该JLabel添加到JSrollPane中,则必须将preferredSize设置为适当的值,否则它不会换行。在一个使用LayoutManager的JPanel内,所有这些都应该正常工作。
由于我想要一个可调整大小的应用程序窗口,所以我扩展了JScrollPane来跟踪调整大小事件并动态更改与视口宽度同步的大小。基本上它可以工作,但是有时候布局管理器对首选高度的计算是错误的(值太大或太小)。例如,红色边框穿过第一行的可见性表明高度的计算是错误的。
我无法通过单个换行JLabel复现此故障。
import java.awt.Color;
import java.awt.Container;
import java.awt.Dimension;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import java.awt.event.ComponentEvent;
import java.awt.event.ComponentListener;
import javax.swing.BorderFactory;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.SwingUtilities;
public class WrappedLabel implements Runnable {
public static void main( String[] args ){
SwingUtilities.invokeLater( new WrappedLabel() );
}
@Override
public void run(){
final JPanel panel = new JPanel( new GridBagLayout() );
final GridBagConstraints gc = new GridBagConstraints();
gc.fill = GridBagConstraints.BOTH;
gc.weightx = 1.0;
gc.weighty = 1.0;
{
gc.gridx = 0;
gc.gridy = 0;
final JLabel label = new JLabel(
"<html>" + "please add some more text here"
);
label.setBorder( BorderFactory.createLineBorder( Color.RED ) );
panel.add( label, gc );
}
{
gc.gridx = 0;
gc.gridy = 1;
final JLabel label = new JLabel(
"<html>" + "please add some more text here"
);
label.setBorder( BorderFactory.createLineBorder( Color.RED ) );
panel.add( label, gc );
}
final JFrame frame = new JFrame();
frame.add( new ScrollPane( panel ) );
frame.setDefaultCloseOperation( JFrame.DISPOSE_ON_CLOSE );
frame.setSize( 256, 256 );
frame.setVisible( true );
}
private class ScrollPane extends JScrollPane implements ComponentListener {
ScrollPane( Container view ){
super( view );
this.viewport.addComponentListener( this );
}
@Override
public void componentHidden( ComponentEvent ce ){
}
@Override
public void componentMoved( ComponentEvent ce ){
}
/** calculating required height is a 3 step process
* 1. sync width of client and viewport, set height of client to high value
* 2. let GridbagManager calculate required minimum size
* 3. set preferredSize and revalidate
**/
@Override
public void componentResized( ComponentEvent ce ){
assert( this.viewport == ce.getSource() );
final Container view = (Container) this.viewport.getView();
final int width = this.viewport.getExtentSize().width;
view.setPreferredSize( new Dimension( width, Integer.MAX_VALUE ) );
final int height = view.getLayout().preferredLayoutSize( view ).height;
view.setPreferredSize( new Dimension( width, height ) );
view.revalidate();
}
@Override
public void componentShown( ComponentEvent ce ){
}
}
}