Source for javax.swing.plaf.ComponentUI

   1: /* ComponentUI.java --
   2:    Copyright (C) 2002, 2003, 2004  Free Software Foundation, Inc.
   3: 
   4: This file is part of GNU Classpath.
   5: 
   6: GNU Classpath is free software; you can redistribute it and/or modify
   7: it under the terms of the GNU General Public License as published by
   8: the Free Software Foundation; either version 2, or (at your option)
   9: any later version.
  10: 
  11: GNU Classpath is distributed in the hope that it will be useful, but
  12: WITHOUT ANY WARRANTY; without even the implied warranty of
  13: MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14: General Public License for more details.
  15: 
  16: You should have received a copy of the GNU General Public License
  17: along with GNU Classpath; see the file COPYING.  If not, write to the
  18: Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
  19: 02110-1301 USA.
  20: 
  21: Linking this library statically or dynamically with other modules is
  22: making a combined work based on this library.  Thus, the terms and
  23: conditions of the GNU General Public License cover the whole
  24: combination.
  25: 
  26: As a special exception, the copyright holders of this library give you
  27: permission to link this library with independent modules to produce an
  28: executable, regardless of the license terms of these independent
  29: modules, and to copy and distribute the resulting executable under
  30: terms of your choice, provided that you also meet, for each linked
  31: independent module, the terms and conditions of the license of that
  32: module.  An independent module is a module which is not derived from
  33: or based on this library.  If you modify this library, you may extend
  34: this exception to your version of the library, but you are not
  35: obligated to do so.  If you do not wish to do so, delete this
  36: exception statement from your version. */
  37: 
  38: 
  39: package javax.swing.plaf;
  40: 
  41: import java.awt.Color;
  42: import java.awt.Dimension;
  43: import java.awt.Graphics;
  44: 
  45: import javax.accessibility.Accessible;
  46: import javax.swing.JComponent;
  47: 
  48: /**
  49:  * The abstract base class for all delegates that provide the
  50:  * pluggable look and feel for Swing components. User applications
  51:  * should not need to access this class; it is internal to Swing
  52:  * and the look-and-feel implementations.
  53:  *
  54:  * <p><img src="doc-files/ComponentUI-1.png" width="700" height="550"
  55:  * alt="[UML diagram illustrating the architecture for pluggable
  56:  * look and feels]" /></p>
  57:  *
  58:  * <p>Components such as {@link javax.swing.JSlider} do not directly
  59:  * implement operations related to the look and feel of the user
  60:  * interface, such as painting or layout. Instead, they use a delegate
  61:  * object for all such tasks. In the case of <code>JSlider</code>, the
  62:  * user interface would be provided by some concrete subclass of
  63:  * {@link javax.swing.plaf.SliderUI}.
  64:  *
  65:  * <p>Soon after its creation, a <code>ComponentUI</code> will be sent
  66:  * an {@link #installUI} message. The <code>ComponentUI</code> will
  67:  * react by setting properties such as the border or the background
  68:  * color of the <code>JComponent</code> for which it provides its
  69:  * services. Soon before the end of its lifecycle, the
  70:  * <code>ComponentUI</code> will receive an {@link #uninstallUI}
  71:  * message, at which time the <code>ComponentUI</code> is expected to
  72:  * undo any changes.</p>
  73:  *
  74:  * <p>Note that the <code>ui</code> of a <code>JComponent</code>
  75:  * changes whenever the user switches between look and feels.  For
  76:  * example, the <code>ui</code> property of a <code>JSlider</code>
  77:  * could change from an instance of <code>MetalSliderUI</code> to an
  78:  * instance of <code>FooSliderUI</code>. This switch can happen at any
  79:  * time, but it will always be performed from inside the Swing thread.</p>
  80:  *
  81:  * @author Sascha Brawer (brawer@dandelis.ch)
  82:  */
  83: public abstract class ComponentUI
  84: {
  85:   /**
  86:    * Constructs a new UI delegate.
  87:    */
  88:   public ComponentUI()
  89:   {
  90:     // Nothing to do here.
  91:   }
  92: 
  93: 
  94:   /**
  95:    * Sets up the specified component so it conforms the the design
  96:    * guidelines of the implemented look and feel. When the look and
  97:    * feel changes, a <code>ComponentUI</code> delegate is created.
  98:    * The delegate object then receives an <code>installUI</code>
  99:    * message.
 100:    *
 101:    * <p>This method should perform the following tasks:</p>
 102:    *
 103:    * <ul>
 104:    * <li>Set visual properties such as borders, fonts, colors, or
 105:    *     icons. However, no change should be performed for those
 106:    *     properties whose values have been directly set by the client
 107:    *     application. To allow the distinction, LookAndFeels are expected
 108:    *     to use values that implement the {@link UIResource} marker
 109:    *     interface, such as {@link BorderUIResource} or {@link
 110:    *     ColorUIResource}.</li>
 111:    * <li>If necessary, install a {@link java.awt.LayoutManager}.</li>
 112:    * <li>Embed custom sub-components. For instance, the UI delegate
 113:    *     for a {@link javax.swing.JSplitPane} might install a special
 114:    *     component for the divider.</li>
 115:    * <li>Register event listeners.</li>
 116:    * <li>Set up properties related to keyborad navigation, such as
 117:    *     mnemonics or focus traversal policies.</li>
 118:    * </ul>
 119:    *
 120:    * @param c the component for which this delegate will provide
 121:    *        services.
 122:    *
 123:    * @see #uninstallUI
 124:    * @see javax.swing.JComponent#setUI
 125:    * @see javax.swing.JComponent#updateUI
 126:    */
 127:   public void installUI(JComponent c)
 128:   {
 129:     // The default implementation does not change any properties.
 130:   }
 131: 
 132: 
 133:   /**
 134:    * Puts the specified component into the state it had before
 135:    * {@link #installUI} was called.
 136:    *
 137:    * @param c the component for which this delegate has provided
 138:    *        services.
 139:    *
 140:    * @see #installUI
 141:    * @see javax.swing.JComponent#setUI
 142:    * @see javax.swing.JComponent#updateUI
 143:    */
 144:   public void uninstallUI(JComponent c)
 145:   {
 146:     // The default implementation does not change any properties.
 147:   }
 148: 
 149: 
 150:   /**
 151:    * Paints the component according to the design guidelines
 152:    * of the look and feel. Most subclasses will want to override
 153:    * this method.
 154:    *
 155:    * @param g the graphics for painting.
 156:    *
 157:    * @param c the component for which this delegate performs
 158:    *          services.
 159:    */
 160:   public void paint(Graphics g, JComponent c)
 161:   {
 162:     // Nothing is done here. This method is meant to be overridden by
 163:     // subclasses.
 164:   }
 165: 
 166: 
 167:   /**
 168:    * Fills the specified component with its background color
 169:    * (unless the <code>opaque</code> property is <code>false</code>)
 170:    * before calling {@link #paint}.
 171:    *
 172:    * <p>It is unlikely that a subclass needs to override this method.
 173:    * The actual rendering should be performed by the {@link #paint}
 174:    * method.
 175:    *
 176:    * @param g the graphics for painting.
 177:    *
 178:    * @param c the component for which this delegate performs
 179:    *          services.
 180:    *
 181:    * @see #paint
 182:    * @see javax.swing.JComponent#paintComponent
 183:    */
 184:   public void update(Graphics g, JComponent c)
 185:   {
 186:     if (c.isOpaque())
 187:       {
 188:         Color oldColor = g.getColor();
 189:         g.setColor(c.getBackground());
 190:         g.fillRect(0, 0, c.getWidth(), c.getHeight());
 191:         g.setColor(oldColor);
 192:       }
 193:     paint(g, c);
 194:   }
 195: 
 196:   /**
 197:    * Determines the preferred size of a component. The default
 198:    * implementation returns <code>null</code>, which means that
 199:    * <code>c</code>&#x2019;s layout manager should be asked to
 200:    * calculate the preferred size.
 201:    *
 202:    * @param c the component for which this delegate performs services.
 203:    *
 204:    * @return the preferred size, or <code>null</code> to indicate that
 205:    *         <code>c</code>&#x2019;s layout manager should be asked
 206:    *         for the preferred size.
 207:    */
 208:   public Dimension getPreferredSize(JComponent c)
 209:   {
 210:     return null;
 211:   }
 212: 
 213: 
 214:   /**
 215:    * Determines the minimum size of a component. The default
 216:    * implementation calls {@link #getPreferredSize}, but subclasses
 217:    * might want to override this.
 218:    *
 219:    * @param c the component for which this delegate performs services.
 220:    *
 221:    * @return the minimum size, or <code>null</code> to indicate that
 222:    *         <code>c</code>&#x2019;s layout manager should be asked
 223:    *         to calculate the minimum size.
 224:    */
 225:   public Dimension getMinimumSize(JComponent c)
 226:   {
 227:     return getPreferredSize(c);
 228:   }
 229: 
 230: 
 231:   /**
 232:    * Determines the maximum size of a component. The default
 233:    * implementation calls {@link #getPreferredSize}, but subclasses
 234:    * might want to override this.
 235:    *
 236:    * @param c the component for which this delegate performs services.
 237:    *
 238:    * @return the maximum size, or <code>null</code> to indicate that
 239:    *         <code>c</code>&#x2019;s layout manager should be asked
 240:    *         to calculate the maximum size.
 241:    */
 242:   public Dimension getMaximumSize(JComponent c)
 243:   {
 244:     return getPreferredSize(c);
 245:   }
 246: 
 247: 
 248:   /**
 249:    * Determines whether a click into the component at a specified
 250:    * location is considered as having hit the component. The default
 251:    * implementation checks whether the point falls into the
 252:    * component&#x2019;s bounding rectangle. Some subclasses might want
 253:    * to override this, for example in the case of a rounded button.
 254:    *
 255:    * @param c the component for which this delegate performs services.
 256:    *
 257:    * @param x the x coordinate of the point, relative to the local
 258:    *        coordinate system of the component. Zero would be be
 259:    *        component&#x2019;s left edge, irrespective of the location
 260:    *        inside its parent.
 261:    *
 262:    * @param y the y coordinate of the point, relative to the local
 263:    *        coordinate system of the component. Zero would be be
 264:    *        component&#x2019;s top edge, irrespective of the location
 265:    *        inside its parent.
 266:    */
 267:   public boolean contains(JComponent c, int x, int y)
 268:   {
 269:     /* JComponent.contains calls the ui delegate for hit
 270:      * testing. Therefore, endless mutual recursion would result if we
 271:      * called c.contains(x, y) here.
 272:      *
 273:      * The previous Classpath implementation called the deprecated
 274:      * method java.awt.Component.inside. In the Sun implementation, it
 275:      * can be observed that inside, other than contains, does not call
 276:      * the ui delegate.  But that inside() behaves different to
 277:      * contains() clearly is in violation of the method contract, and
 278:      * it is not something that a good implementation should rely upon
 279:      * -- even if Classpath ends up being forced to replicate this
 280:      * apparent bug of the Sun implementation.
 281:      */
 282:     return (x >= 0) && (x < c.getWidth())
 283:       && (y >= 0) && (y < c.getHeight());
 284:   }
 285: 
 286: 
 287:   /**
 288:    * Creates a delegate object for the specified component.  Users
 289:    * should use the <code>createUI</code> method of a suitable
 290:    * subclass. The implementation of <code>ComponentUI</code>
 291:    * always throws an error.
 292:    *
 293:    * @param c the component for which a UI delegate is requested.
 294:    */
 295:   public static ComponentUI createUI(JComponent c)
 296:   {
 297:     throw new Error(
 298:       "javax.swing.plaf.ComponentUI does not implement createUI; call "
 299:       + "createUI on a subclass.");
 300:   }
 301: 
 302: 
 303:   /**
 304:    * Counts the number of accessible children in the component.  The
 305:    * default implementation delegates the inquiry to the {@link
 306:    * javax.accessibility.AccessibleContext} of <code>c</code>.
 307:    *
 308:    * @param c the component whose accessible children
 309:    *        are to be counted.
 310:    */
 311:   public int getAccessibleChildrenCount(JComponent c)
 312:   {
 313:     return c.getAccessibleContext().getAccessibleChildrenCount();
 314:   }
 315: 
 316: 
 317:   /**
 318:    * Returns the specified accessible child of the component. The
 319:    * default implementation delegates the inquiry to the {@link
 320:    * javax.accessibility.AccessibleContext} of <code>c</code>.
 321:    *
 322:    * @param i the index of the accessible child, starting at zero.
 323:    *
 324:    * @param c the component whose <code>i</code>-th accessible child
 325:    *        is requested.
 326:    */
 327:   public Accessible getAccessibleChild(JComponent c, int i)
 328:   {
 329:     return c.getAccessibleContext().getAccessibleChild(i);
 330:   }
 331: }