java - 在显示滚动条之前将内容缩小到 minSize

Question

我想要实现的是，JScrollPane 将在内容缩小到最小尺寸后显示滚动条。滚动条显示后，面板应具有最小尺寸。我能实现的最接近的事情是在 jpanel 上实现 Scrollable 并重写 getScrollableTracksViewportHeight 和 getScrollableTracksViewportWidth 方法。

public class EditPanel extends JPanel implements Scrollable {

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

    @Override
    public int getScrollableUnitIncrement(Rectangle visibleRect, int orientation, int direction) {
        return 16;
    }

    @Override
    public int getScrollableBlockIncrement(Rectangle visibleRect, int orientation, int direction) {
        return 16;
    }

    @Override
    public boolean getScrollableTracksViewportWidth() {
        return this.getMinimumSize().width < this.getWidth();
    }

    @Override
    public boolean getScrollableTracksViewportHeight() {
        return this.getMinimumSize().height < this.getHeight();
    }
}

但是，当内容缩小到其最小尺寸以下时，这会导致滚动条闪烁。

如何在滚动条不闪烁的情况下实现这一目标？这是我用来测试这个的代码:

public class Main {
    public static void main(String[] args) {
        JFrame f = new JFrame();
        JScrollPane sp = new JScrollPane();
        EditPanel p = new EditPanel();
        p.setMinimumSize(new Dimension(200, 200));
        p.setPreferredSize(new Dimension(500, 500));
        p.setBackground(Color.white);

        sp.setViewportView(p);
        f.setContentPane(sp);

        f.pack();
        f.setVisible(true);
    }
}

Answer 1

您想要根据视口(viewport)的大小而不是面板的大小进行比较:

@Override
public boolean getScrollableTracksViewportWidth() {
    //return this.getMinimumSize().width < this.getWidth();
    return this.getMinimumSize().width < getParent().getWidth();
}

@Override
public boolean getScrollableTracksViewportHeight() {
    //return this.getMinimumSize().height < this.getHeight();
    return this.getMinimumSize().height < getParent().getHeight();
}

编辑:

when the scrollbars show up, EditPanels size will be preferred size instead of minimum size.

滚动条基于视口(viewport)中组件的首选大小。因此，您还需要动态管理首选大小。也许是这样的:

@Override
public Dimension getPreferredSize()
{
    Dimension preferredSize = super.getPreferredSize();
    Component parent = getParent();

    if (parent == null)
        return preferredSize;

    Dimension parentSize = parent.getSize();
    Dimension minimumSize = getMinimumSize();

    int width = Math.min(preferredSize.width, parentSize.width);
    width = Math.max(width, minimumSize.width);

    int height = Math.min(preferredSize.height, parentSize.height);
    height = Math.max(height, minimumSize.height);

    return new Dimension(width, height);
}