# Java Swing 中的可调整大小的组件 > 原文： [http://zetcode.com/tutorials/javaswingtutorial/resizablecomponent/](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。 [Tweet](https://twitter.com/share) 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` ```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。 ```java 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。 ```java 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` ```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。 ```java 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。 ```java 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。 ```java 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。 ```java 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。 ```java 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` ```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。 ```java 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。 ```java 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。 ```java @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。 ```java 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。 ```java 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。  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。