如何讓設定 FlowLayout 的 JPanel 有 ScrollBar

因為 JDK 的 bug ，設定 FlowLayout 的 JPanel 沒辦法在 JScrollPane 裡面正確呈現出 ScrollBar，因此要自己實作 Scrollable 來達到這個效果。

import java.awt.Component;
import java.awt.Dimension;
import java.awt.FlowLayout;
import java.awt.Rectangle;

import javax.swing.JPanel;
import javax.swing.Scrollable;
import javax.swing.SwingConstants;

public class ScrollableFlowPanel extends JPanel implements Scrollable {
	public void setBounds(int x, int y, int width, int height) {
		super.setBounds(x, y, getParent().getWidth(), height);
	}

public Dimension getPreferredSize() {
		return new Dimension(getWidth(), getPreferredHeight());
	}

public Dimension getPreferredScrollableViewportSize() {
		return super.getPreferredSize();
	}

public int getScrollableUnitIncrement(Rectangle visibleRect,
			int orientation, int direction) {
		int hundredth = (orientation == SwingConstants.VERTICAL ? getParent()
				.getHeight() : getParent().getWidth()) / 100;
		return (hundredth == 0 ? 1 : hundredth);
	}

public int getScrollableBlockIncrement(Rectangle visibleRect,
			int orientation, int direction) {
		return orientation == SwingConstants.VERTICAL ? getParent().getHeight()
				: getParent().getWidth();
	}

public boolean getScrollableTracksViewportWidth() {
		return true;
	}

public boolean getScrollableTracksViewportHeight() {
		return false;
	}

private int getPreferredHeight() {
		int rv = 0;
		for (int k = 0, count = getComponentCount(); k < count; k++) {
			Component comp = getComponent(k);
			Rectangle r = comp.getBounds();
			int height = r.y + r.height;
			if (height > rv)
				rv = height;
		}
		rv += ((FlowLayout) getLayout()).getVgap();
		return rv;
	}
}

測試這問是困擾了我兩天， sun 竟然這麼久都不修復，唉。

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如何讓設定 FlowLayout 的 JPanel 有 ScrollBar