Java Swing 中的可调整大小的组件 - 《ZetCode 中文系列教程》

可调整大小的组件

原文： http://zetcode.com/tutorials/javaswingtutorial/resizablecomponent/

在 Java Swing 教程的这一部分中，我们将创建一个可调整大小的组件。

可调整大小的组件

在创建图表时，经常使用可调整大小的组件。常见的可调整大小的组件是电子表格应用中的图表。可以将图表移到应用的表格小部件上并调整大小。

为了创建可以在面板上自由拖动的组件，我们使用启用了绝对定位的面板。在我们的示例中，我们将创建一个可以在父窗口上自由移动并调整大小的组件。

当可调整大小的组件具有焦点时，将在其可调整大小的组件的边框上绘制八个小矩形。矩形用作拖动点，我们可以在其中绘制组件并开始调整大小。

ResizableComponentEx.java

package com.zetcode;
import java.awt.Color;
import java.awt.EventQueue;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import javax.swing.JFrame;
import javax.swing.JPanel;
public class ResizableComponentEx extends JFrame {
    private Resizable res;
    public ResizableComponentEx() {
        initUI();
    }
    private void initUI() {
        var pnl = new JPanel(null);
        add(pnl);
        var area = new JPanel();
        area.setBackground(Color.white);
        res = new Resizable(area);
        res.setBounds(50, 50, 200, 150);
        pnl.add(res);
        addMouseListener(new MouseAdapter() {
            @Override
            public void mousePressed(MouseEvent me) {
                requestFocus();
                res.repaint();
            }
        });
        setSize(350, 300);
        setTitle("Resizable component");
        setLocationRelativeTo(null);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    }
    public static void main(String[] args) {
        EventQueue.invokeLater(() -> {
            var ex = new ResizableComponentEx();
            ex.setVisible(true);
        });
    }
}

ResizableComponentEx设置面板和组件。

var pnl = new JPanel(null);

我们对可调整大小的组件使用绝对定位。通过将null提供给JPanel的构造器，我们创建了具有绝对定位的面板。

addMouseListener(new MouseAdapter() {
    @Override
    public void mousePressed(MouseEvent me) {
        requestFocus();
        res.repaint();
    }
});

如果我们在父面板上（即在可调整大小的组件外部）按下，我们将抓住焦点并重新绘制该组件。边框上的矩形将消失。

ResizableBorder.java

package com.zetcode;
import java.awt.Color;
import java.awt.Component;
import java.awt.Cursor;
import java.awt.Graphics;
import java.awt.Insets;
import java.awt.Rectangle;
import java.awt.event.MouseEvent;
import javax.swing.SwingConstants;
import javax.swing.border.Border;
public class ResizableBorder implements Border {
    private int dist = 8;
    int locations[] = {
            SwingConstants.NORTH, SwingConstants.SOUTH, SwingConstants.WEST,
            SwingConstants.EAST, SwingConstants.NORTH_WEST,
            SwingConstants.NORTH_EAST, SwingConstants.SOUTH_WEST,
            SwingConstants.SOUTH_EAST
    };
    int cursors[] = {
            Cursor.N_RESIZE_CURSOR, Cursor.S_RESIZE_CURSOR, Cursor.W_RESIZE_CURSOR,
            Cursor.E_RESIZE_CURSOR, Cursor.NW_RESIZE_CURSOR, Cursor.NE_RESIZE_CURSOR,
            Cursor.SW_RESIZE_CURSOR, Cursor.SE_RESIZE_CURSOR
    };
    public ResizableBorder(int dist) {
        this.dist = dist;
    }
    @Override
    public Insets getBorderInsets(Component component) {
        return new Insets(dist, dist, dist, dist);
    }
    @Override
    public boolean isBorderOpaque() {
        return false;
    }
    @Override
    public void paintBorder(Component component, Graphics g, int x, int y,
                            int w, int h) {
        g.setColor(Color.black);
        g.drawRect(x + dist / 2, y + dist / 2, w - dist, h - dist);
        if (component.hasFocus()) {
            for (int i = 0; i < locations.length; i++) {
                var rect = getRectangle(x, y, w, h, locations[i]);
                g.setColor(Color.WHITE);
                g.fillRect(rect.x, rect.y, rect.width - 1, rect.height - 1);
                g.setColor(Color.BLACK);
                g.drawRect(rect.x, rect.y, rect.width - 1, rect.height - 1);
            }
        }
    }
    private Rectangle getRectangle(int x, int y, int w, int h, int location) {
        switch (location) {
            case SwingConstants.NORTH:
                return new Rectangle(x + w / 2 - dist / 2, y, dist, dist);
            case SwingConstants.SOUTH:
                return new Rectangle(x + w / 2 - dist / 2, y + h - dist, dist, dist);
            case SwingConstants.WEST:
                return new Rectangle(x, y + h / 2 - dist / 2, dist, dist);
            case SwingConstants.EAST:
                return new Rectangle(x + w - dist, y + h / 2 - dist / 2, dist, dist);
            case SwingConstants.NORTH_WEST:
                return new Rectangle(x, y, dist, dist);
            case SwingConstants.NORTH_EAST:
                return new Rectangle(x + w - dist, y, dist, dist);
            case SwingConstants.SOUTH_WEST:
                return new Rectangle(x, y + h - dist, dist, dist);
            case SwingConstants.SOUTH_EAST:
                return new Rectangle(x + w - dist, y + h - dist, dist, dist);
        }
        return null;
    }
    public int getCursor(MouseEvent me) {
        var c = me.getComponent();
        int w = c.getWidth();
        int h = c.getHeight();
        for (int i = 0; i < locations.length; i++) {
            var rect = getRectangle(0, 0, w, h, locations[i]);
            if (rect.contains(me.getPoint())) {
                return cursors[i];
            }
        }
        return Cursor.MOVE_CURSOR;
    }
}

ResizableBorder负责绘制组件的边框并确定要使用的光标的类型。

int locations[] = {
    SwingConstants.NORTH, SwingConstants.SOUTH, SwingConstants.WEST,
    SwingConstants.EAST, SwingConstants.NORTH_WEST,
    SwingConstants.NORTH_EAST, SwingConstants.SOUTH_WEST,
    SwingConstants.SOUTH_EAST
};

这些是绘制矩形的位置。这些位置也是抓取点，可以在其中抓取组件并调整其大小。

g.setColor(Color.black);
g.drawRect(x + dist / 2, y + dist / 2, w - dist, h - dist);

在paintBorder()方法中，我们绘制了可调整大小组件的边框。上面的代码绘制了组件的外边界。

if (component.hasFocus()) {
    for (int i = 0; i < locations.length; i++) {
        var rect = getRectangle(x, y, w, h, locations[i]);
        g.setColor(Color.WHITE);
        g.fillRect(rect.x, rect.y, rect.width - 1, rect.height - 1);
        g.setColor(Color.BLACK);
        g.drawRect(rect.x, rect.y, rect.width - 1, rect.height - 1);
    }
}

仅当可调整大小的组件当前具有焦点时才绘制八个矩形。

private Rectangle getRectangle(int x, int y, int w, int h, int location) {
    switch (location) {
        case SwingConstants.NORTH:
            return new Rectangle(x + w / 2 - dist / 2, y, dist, dist);
        case SwingConstants.SOUTH:
            return new Rectangle(x + w / 2 - dist / 2, y + h - dist, dist, dist);
...
}

getRectangle()方法返回矩形的坐标。

public int getCursor(MouseEvent me) {
    var c = me.getComponent();
    int w = c.getWidth();
    int h = c.getHeight();
    for (int i = 0; i < locations.length; i++) {
        var rect = getRectangle(0, 0, w, h, locations[i]);
        if (rect.contains(me.getPoint())) {
            return cursors[i];
        }
    }
    return Cursor.MOVE_CURSOR;
}

getCursor()方法获取相关抓点的光标类型。

Resizable.java

package com.zetcode;
import javax.swing.JComponent;
import javax.swing.event.MouseInputAdapter;
import javax.swing.event.MouseInputListener;
import java.awt.BorderLayout;
import java.awt.Component;
import java.awt.Cursor;
import java.awt.Point;
import java.awt.event.MouseEvent;
public class Resizable extends JComponent {
    public Resizable(Component comp) {
        this(comp, new ResizableBorder(8));
    }
    public Resizable(Component comp, ResizableBorder border) {
        setLayout(new BorderLayout());
        add(comp);
        addMouseListener(resizeListener);
        addMouseMotionListener(resizeListener);
        setBorder(border);
    }
    private void resize() {
        if (getParent() != null) {
            getParent().revalidate();
        }
    }
    MouseInputListener resizeListener = new MouseInputAdapter() {
        @Override
        public void mouseMoved(MouseEvent me) {
            if (hasFocus()) {
                var resizableBorder = (ResizableBorder) getBorder();
                setCursor(Cursor.getPredefinedCursor(resizableBorder.getCursor(me)));
            }
        }
        @Override
        public void mouseExited(MouseEvent mouseEvent) {
            setCursor(Cursor.getDefaultCursor());
        }
        private int cursor;
        private Point startPos = null;
        @Override
        public void mousePressed(MouseEvent me) {
            var resizableBorder = (ResizableBorder) getBorder();
            cursor = resizableBorder.getCursor(me);
            startPos = me.getPoint();
            requestFocus();
            repaint();
        }
        @Override
        public void mouseDragged(MouseEvent me) {
            if (startPos != null) {
                int x = getX();
                int y = getY();
                int w = getWidth();
                int h = getHeight();
                int dx = me.getX() - startPos.x;
                int dy = me.getY() - startPos.y;
                switch (cursor) {
                    case Cursor.N_RESIZE_CURSOR:
                        if (!(h - dy < 50)) {
                            setBounds(x, y + dy, w, h - dy);
                            resize();
                        }
                        break;
                    case Cursor.S_RESIZE_CURSOR:
                        if (!(h + dy < 50)) {
                            setBounds(x, y, w, h + dy);
                            startPos = me.getPoint();
                            resize();
                        }
                        break;
                    case Cursor.W_RESIZE_CURSOR:
                        if (!(w - dx < 50)) {
                            setBounds(x + dx, y, w - dx, h);
                            resize();
                        }
                        break;
                    case Cursor.E_RESIZE_CURSOR:
                        if (!(w + dx < 50)) {
                            setBounds(x, y, w + dx, h);
                            startPos = me.getPoint();
                            resize();
                        }
                        break;
                    case Cursor.NW_RESIZE_CURSOR:
                        if (!(w - dx < 50) && !(h - dy < 50)) {
                            setBounds(x + dx, y + dy, w - dx, h - dy);
                            resize();
                        }
                        break;
                    case Cursor.NE_RESIZE_CURSOR:
                        if (!(w + dx < 50) && !(h - dy < 50)) {
                            setBounds(x, y + dy, w + dx, h - dy);
                            startPos = new Point(me.getX(), startPos.y);
                            resize();
                        }
                        break;
                    case Cursor.SW_RESIZE_CURSOR:
                        if (!(w - dx < 50) && !(h + dy < 50)) {
                            setBounds(x + dx, y, w - dx, h + dy);
                            startPos = new Point(startPos.x, me.getY());
                            resize();
                        }
                        break;
                    case Cursor.SE_RESIZE_CURSOR:
                        if (!(w + dx < 50) && !(h + dy < 50)) {
                            setBounds(x, y, w + dx, h + dy);
                            startPos = me.getPoint();
                            resize();
                        }
                        break;
                    case Cursor.MOVE_CURSOR:
                        var bounds = getBounds();
                        bounds.translate(dx, dy);
                        setBounds(bounds);
                        resize();
                }
                setCursor(Cursor.getPredefinedCursor(cursor));
            }
        }
        @Override
        public void mouseReleased(MouseEvent mouseEvent) {
            startPos = null;
        }
    };
}

Resizable类表示正在调整大小并在窗口上移动的组件。

private void resize() {
    if (getParent() != null) {
        getParent().revalidate();
    }
}

调整组件大小后，将调用resize()方法。 revalidate()方法导致重画组件。

MouseInputListener resizeListener = new MouseInputAdapter() {
    @Override
    public void mouseMoved(MouseEvent me) {
        if (hasFocus()) {
            var border = (ResizableBorder) getBorder();
            setCursor(Cursor.getPredefinedCursor(border.getCursor(me)));
        }
    }
...
}

当我们将光标悬停在抓取点上时，我们将更改光标类型。仅当组件具有焦点时，光标类型才会更改。

@Override
public void mousePressed(MouseEvent me) {
    var resizableBorder = (ResizableBorder) getBorder();
    cursor = resizableBorder.getCursor(me);
    startPos = me.getPoint();
    requestFocus();
    repaint();
}

如果单击可调整大小的组件，则将更改光标，获得拖动的起点，将焦点放在该组件上，然后重新绘制它。

int x = getX();
int y = getY();
int w = getWidth();
int h = getHeight();
int dx = me.getX() - startPos.x;
int dy = me.getY() - startPos.y;

在mouseDragged()方法中，我们确定光标的 x 和 y 坐标以及组件的宽度和高度。我们计算鼠标拖动事件期间的距离。

case Cursor.N_RESIZE_CURSOR:
    if (!(h - dy < 50)) {
        setBounds(x, y + dy, w, h - dy);
        resize();
    }
    break;

对于所有大小调整，我们确保该组件不小于 50px。否则，我们可以将其减小到最终将其隐藏的程度。 setBounds()方法重新定位组件并调整其大小。

Java Swing 中的可调整大小的组件 - 图1

图：可调整大小的组件

在 Java Swing 教程的这一部分中，我们创建了一个可调整大小的组件。