我有一个JPanel被覆盖的paintComponent. 我想让我在此面板上手动绘制的某些元素具有焦点，以便使用辅助技术的人可以使用键盘使用我的应用程序。
如果您能给我一些建议，那就太棒了。
问问题
359 次
1 回答
4
您可以执行以下操作：
- 将您的元素转换为
JComponents。 - 将
LayoutManager面板的 设置为null。然后，您将所有组件/元素添加到此面板中，您可以使用方法自由移动它们Component.setBounds(...)。 - 在您的面板中添加一个
MouseListener，每次按下鼠标时都会将焦点转移到选定的组件。 - 您可以通过调用面板
Component.getComponentAt(Point)内部的方法来确定按下了哪个组件。MouseListener
简单的例子：
- 制作一个具有向用户显示是否有焦点的标准行为的组件。在我下面这个类的示例代码中
FocusableComponent extends JComponent，如果它有焦点，它会在组件周围绘制一个蓝色矩形（这是在方法内部完成的FocusableComponent.paintComponent(Graphics)）。 - 然后，对于您绘制的每个不同的“元素
FocusableComponent”，子类化并覆盖其paintComponent(Graphics) 方法以绘制元素。确保在那里调用“super.paintComponent(Graphics)”以绘制蓝色矩形（如果它有焦点）。
代码：
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class FocusablePaintComps {
private static abstract class FocusableComponent extends JComponent {
@Override protected void paintComponent(final Graphics g) {
super.paintComponent(g);
if (hasFocus()) {
final Color prevColor = g.getColor();
g.setColor(Color.BLUE);
g.drawRect(0, 0, getWidth() - 1, getHeight() - 1);
g.setColor(prevColor);
}
}
}
private static class FocusableComponent1 extends FocusableComponent {
@Override protected void paintComponent(final Graphics g) {
super.paintComponent(g);
g.fillOval(0, 0, getWidth() - 1, getHeight() - 1);
}
}
private static class FocusableComponent2 extends FocusableComponent {
@Override protected void paintComponent(final Graphics g) {
super.paintComponent(g);
final int w = getWidth(), h = getHeight();
g.fillRect(20, 20, w - 40, h - 40);
g.fillArc(10, 10, w - 1, h - 1, 60, 150);
}
}
private static class YourPanel extends JPanel {
private Component previousFocusedComponent = null;
private YourPanel() {
super(null); //Null LayoutManager. This is important to be able to
//move added components around freelly (with the method setBounds(...)).
addMouseListener(new MouseAdapter() {
@Override
public void mousePressed(final MouseEvent evt) {
final Component src = getComponentAt(evt.getPoint());
if (src instanceof FocusableComponent) {
final FocusableComponent fc = (FocusableComponent) src;
fc.requestFocusInWindow(); //Transfer focus to the pressed component.
if (previousFocusedComponent != null)
previousFocusedComponent.repaint(); //Repaint the last (without focus now).
setComponentZOrder(fc, 0); //Update: To make fc paint over all others as
//the user http://stackoverflow.com/users/131872/camickr commented.
fc.repaint(); //Repaint the new (with focus now).
previousFocusedComponent = fc;
}
else { //If clicked on empty space, or a non-FocusableComponent:
requestFocusInWindow(); //Tranfer focus to somewhere else (e.g. the panel itself).
if (previousFocusedComponent != null) {
previousFocusedComponent.repaint(); //Repaint the last (without focus now).
previousFocusedComponent = null;
}
}
}
});
setPreferredSize(new Dimension(250, 250));
add(new FocusableComponent1(), Color.RED, new Rectangle(10, 10, 200, 20));
add(new FocusableComponent1(), Color.GREEN, new Rectangle(40, 150, 50, 70));
add(new FocusableComponent2(), Color.GRAY, new Rectangle(60, 125, 90, 100));
add(new FocusableComponent2(), Color.MAGENTA, new Rectangle(150, 60, 80, 150));
}
private void add(final FocusableComponent fc, final Color fgColor, final Rectangle bounds) {
fc.setForeground(fgColor);
add(fc);
fc.setBounds(bounds);
}
}
public static void main(final String[] args) {
final JFrame frame = new JFrame("Focused Paint Comps");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.add(new YourPanel());
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
}
截屏：
一些注意事项：
- 焦点转移的顺序相对于
rapaint()内部调用 s的顺序mousePressed(...)决定了哪个组件周围有蓝色矩形，哪个没有。 - 方法
Component.getElementAt(Point)不会“透视”透明/非透明像素。
更新：
注意：此更新是上述解决方案的可选扩展（但可能更符合 java-contract-consistent - 让我说一下）。您只能阅读两种实现中的一种（以下“更新”一种使用RandomLayout，或者上述“预更新”一种使用null LayoutManager）。
按照用户“Andrew Thompson”在评论中的建议，对上述代码进行了更新，该代码使用自定义LayoutManager布局容器中的组件。
与上述代码的唯一区别是，使用自定义的新实例而不是null在LayoutManager构造时设置，而不是为每个组件设置边界，您只需要设置它的大小。 YourPanelLayoutManager
我已将自定义命名LayoutManager为RandomLayout，它会将容器的所有组件放置在随机位置，同时考虑到组件的大小和Insets容器的大小（这通过添加Border的来证明YourPanel）。
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.border.LineBorder;
public class FocusablePaintComps {
private static abstract class FocusableComponent extends JComponent {
@Override protected void paintComponent(final Graphics g) {
super.paintComponent(g);
if (hasFocus()) {
final Color prevColor = g.getColor();
g.setColor(Color.BLUE);
g.drawRect(0, 0, getWidth() - 1, getHeight() - 1);
g.setColor(prevColor);
}
}
}
private static class FocusableComponent1 extends FocusableComponent {
@Override protected void paintComponent(final Graphics g) {
super.paintComponent(g);
g.fillOval(0, 0, getWidth() - 1, getHeight() - 1);
}
}
private static class FocusableComponent2 extends FocusableComponent {
@Override protected void paintComponent(final Graphics g) {
super.paintComponent(g);
final int w = getWidth(), h = getHeight();
g.fillRect(20, 20, w - 40, h - 40);
g.fillArc(10, 10, w - 1, h - 1, 60, 150);
}
}
private static class YourPanel extends JPanel {
private Component previousFocusedComponent = null;
private YourPanel() {
super(new RandomLayout()); //RandomLayout: custom LayoutManager which lays
//out the components in random positions (takes Insets into account).
addMouseListener(new MouseAdapter() {
@Override
public void mousePressed(final MouseEvent evt) {
final Component src = getComponentAt(evt.getPoint());
if (src instanceof FocusableComponent) {
final FocusableComponent fc = (FocusableComponent) src;
fc.requestFocusInWindow(); //Transfer focus to the pressed component.
if (previousFocusedComponent != null)
previousFocusedComponent.repaint(); //Repaint the last (without focus now).
setComponentZOrder(fc, 0); //Update: To make fc paint over all others as
//the user http://stackoverflow.com/users/131872/camickr commented.
fc.repaint(); //Repaint the new (with focus now).
previousFocusedComponent = fc;
}
else { //If clicked on empty space, or a non-FocusableComponent:
requestFocusInWindow(); //Tranfer focus to somewhere else (e.g. the panel itself).
if (previousFocusedComponent != null) {
previousFocusedComponent.repaint(); //Repaint the last (without focus now).
previousFocusedComponent = null;
}
}
}
});
setBorder(new LineBorder(Color.LIGHT_GRAY, 20));
setPreferredSize(new Dimension(300, 250));
add(new FocusableComponent1(), Color.RED, new Dimension(200, 20));
add(new FocusableComponent1(), Color.GREEN, new Dimension(50, 70));
add(new FocusableComponent2(), Color.GRAY, new Dimension(90, 100));
add(new FocusableComponent2(), Color.MAGENTA, new Dimension(80, 150));
}
private void add(final FocusableComponent fc, final Color fgColor, final Dimension size) {
add(fc);
fc.setForeground(fgColor);
fc.setSize(size);
}
}
public static void main(final String[] args) {
final JFrame frame = new JFrame("Focused Paint Comps");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.add(new YourPanel());
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
}
更新的“随机布局”：
以及带有 JavaDoc的自定义LayoutManager本身（可能很大，但希望可以重用）：
import java.awt.Component;
import java.awt.Container;
import java.awt.Dimension;
import java.awt.Insets;
import java.awt.LayoutManager;
import java.awt.Point;
import java.util.Random;
/**
* A {@link java.awt.LayoutManager} which lays out randomly all the {@link java.awt.Component}s
* of its parent, taking into consideration the parent's {@link java.awt.Insets}.
* <p>
* Use {@link #setRandomizeOnce(boolean)} method to determine if the lastly laid-out parent will
* be only laid-out randomly once and not for each {@link #layoutContainer(java.awt.Container)}
* subsequent call for the same parent, or the opposite.
* </p>
*/
public class RandomLayout implements LayoutManager {
/**
* The {@link java.awt.Container} which was lastly laid-out.
*/
private Container lastParent;
/**
* The {@link java.awt.Insets} of {@code lastParent} the last time it was laid-out.
*/
private Insets lastInsets;
/**
* If {@code true} then this {@link java.awt.LayoutManager} keeps track of the
* {@link java.awt.Container}s laid-out to make sure that {@code lastParent} is
* only laid-out once. If the another {@link java.awt.Container} is laid-out, other
* than {@code lastParent}, then its components are laid-out randomly and the
* {@link java.awt.Container} becomes the {@code lastParent}.
*/
private boolean randomizeOnce;
/**
* Normal constructor of {@code RandomLayout} with explicit value for {@code randomizeOnce}.
*
* @param randomizeOnce {@code true} if the lastly laid-out parent will be only laid-out
* randomly once and not for each {@link #layoutContainer(java.awt.Container)} subsequent call
* for the same parent, otherwise {@code false} and each call to
* {@link #layoutContainer(java.awt.Container)} will lay out randomly the {@link java.awt.Container}.
*/
public RandomLayout(final boolean randomizeOnce) {
this.randomizeOnce = randomizeOnce;
}
/**
* Default constructor of {@code RandomLayout} with {@code randomizeOnce} set to {@code true}.
*/
public RandomLayout() {
this(true);
}
/**
* If {@code true} then this {@link java.awt.LayoutManager} keeps track of the
* {@link java.awt.Container}s laid-out to make sure that {@code lastParent} is
* only laid-out once. If the another {@link java.awt.Container} is laid-out, other
* than {@code lastParent}, then its components are laid-out randomly and the
* {@link java.awt.Container} becomes the {@code lastParent}.
*
* @param randomizeOnce {@code true} if the lastly laid-out parent will be only laid-out
* randomly once and not for each {@link #layoutContainer(java.awt.Container)} subsequent call
* for the same parent, otherwise {@code false}.
*/
public void setRandomizeOnce(final boolean randomizeOnce) {
this.randomizeOnce = randomizeOnce;
}
/**
* Tells if the lastly laid-out parent will be only laid-out randomly once and not for each
* {@link #layoutContainer(java.awt.Container)} subsequent call for the same parent, or the
* opposite.
*
* @return {@code true} if the lastly laid-out parent will be only laid-out randomly once and
* not for each {@link #layoutContainer(java.awt.Container)} subsequent call for the same
* parent, otherwise {@code false}.
*/
public boolean isRandomizeOnce() {
return randomizeOnce;
}
/**
* @return The {@link java.awt.Container} which was lastly laid-out.
*/
protected Container getLastParent() {
return lastParent;
}
/**
* @return The {@link java.awt.Insets} of {@code lastParent} the last time it was laid-out.
* @see #getLastParent()
*/
protected Insets getLastInsets() {
return lastInsets;
}
/**
* Adds the specified component with the specified name to the layout.
* @param name The name of the component.
* @param comp The {@link java.awt.Component} to be added.
*/
public void addLayoutComponent(final String name,
final Component comp) {
}
/**
* Removes the specified component from the layout.
* @param comp The {@link java.awt.Component} to be removed.
*/
public void removeLayoutComponent(final Component comp) {
}
/**
* {@inheritDoc}
* @return The preferred size dimensions for the specified {@link java.awt.Container}.
*/
@Override
public Dimension preferredLayoutSize(final Container parent) {
final Dimension prefDim = minimumLayoutSize(parent);
prefDim.width += 2; //+2 to spare.
prefDim.height += 2; //+2 to spare.
return prefDim;
}
/**
* {@inheritDoc}
* @return The minimum size dimensions for the specified {@link java.awt.Container}.
*/
@Override
public Dimension minimumLayoutSize(final Container parent) {
final Dimension minDim = new Dimension();
final int childCnt = parent.getComponentCount();
for (int i=0; i<childCnt; ++i)
applyBigger(minDim, getPreferredSize(parent, parent.getComponent(i)));
final Insets parInsets = parent.getInsets();
minDim.width += (parInsets.left + parInsets.right);
minDim.height += (parInsets.top + parInsets.bottom);
return minDim;
}
/**
* {@inheritDoc}. If the another {@link java.awt.Container} is laid-out, other
* than {@code lastParent}, then its components are laid-out randomly and the
* {@link java.awt.Container} becomes the {@code lastParent}.
*/
@Override
public void layoutContainer(final Container parent) {
if (parent == null)
throw new IllegalArgumentException("Cannot lay out null.");
if (isRandomizeOnce() && lastParent == parent) { //At least take care of insets (if they have changed).
final Insets parentInsets = parent.getInsets();
if (!lastInsets.equals(parentInsets)) {
final int offx = parentInsets.left - lastInsets.left,
offy = parentInsets.top - lastInsets.top;
final int childCnt = parent.getComponentCount();
for (int i=0; i<childCnt; ++i) {
final Component child = parent.getComponent(i);
final Point childLoca = child.getLocation();
childLoca.x += offx;
childLoca.y += offy;
child.setLocation(childLoca);
}
lastInsets = parentInsets;
}
}
else
layoutContainerRandomly(parent);
}
/**
* Explicitly lays out randomly the specified container.
* <p>
* This is equivalent of calling:
* <pre>
* boolean isRand1 = randomLayout.isRandomizeOnce();
* randomLayout.setRandomizeOnce(false);
* randomLayout.layoutContainer(parent);
* randomLayout.setRandomizeOnce(isRand1);
* </pre>
* {@code parent} becomes {@code lastParent}.
* </p>
* @param parent The container to be laid out.
*/
public void layoutContainerRandomly(final Container parent) { //Place each child at a random location for the "new" parent (lastParent != parent).
if (parent == null)
throw new IllegalArgumentException("Cannot lay out null.");
reset();
final Dimension parentSize = parent.getSize();
final Insets parentInsets = parent.getInsets();
final Dimension childSize = new Dimension();
final Point childLoca = new Point();
final Random rand = new Random();
final int childCnt = parent.getComponentCount();
for (int i=0; i<childCnt; ++i) {
final Component child = parent.getComponent(i);
child.getSize(childSize);
childLoca.x = parentInsets.left + 1;
childLoca.y = parentInsets.top + 1;
final int xBound = parentSize.width - parentInsets.left - parentInsets.right - childSize.width,
yBound = parentSize.height - parentInsets.top - parentInsets.bottom - childSize.height;
if (xBound > 0)
childLoca.x += rand.nextInt(xBound);
if (yBound > 0)
childLoca.y += rand.nextInt(yBound);
child.setLocation(childLoca);
}
lastParent = parent;
lastInsets = parentInsets;
}
/**
* Invalidates the tracking of the lastly laid-out {@link java.awt.Container} and its last
* {@link java.awt.Insets}.
* @see #getLastParent()
* @see #getLastInsets()
*/
protected void reset() {
lastParent = null;
lastInsets = null;
}
private static void applyBigger(final Dimension inputOutput,
final Dimension input) {
if (inputOutput != null && input != null) {
inputOutput.width = (int) Math.max(inputOutput.width, input.width);
inputOutput.height = (int) Math.max(inputOutput.height, input.height);
}
}
private static void applyIfBetter(final Dimension inputOutput,
final Dimension input) {
if (inputOutput != null && input != null
&& (input.width > inputOutput.width
|| input.height > inputOutput.height)) {
inputOutput.width = input.width;
inputOutput.height = input.height;
}
}
/**
* Tries to determine the best size for {@code child}.
* @param parnt The parent {@link java.awt.Container} being laid-out.
* @param child The child {@link java.awt.Component} of {@code parnt} being laid-out.
* @return A preferred size for the {@code child} to be laid-out.
*/
protected static Dimension getPreferredSize(final Container parnt,
final Component child) {
final Dimension minDim = new Dimension();
if (child != null) {
applyIfBetter(minDim, child.getMinimumSize());
applyIfBetter(minDim, child.getSize());
applyIfBetter(minDim, child.getPreferredSize());
}
return minDim;
}
}
更新截图：
这是新的屏幕截图（没有大的视觉差异）：
更新注意事项：
请注意，这是我的第一个 custom LayoutManager，但是我已经阅读了文档以及GridLayout示例SpringLayout（因为在我看来，LayoutManager的文档还不够），当然我也对其进行了测试。由于它现在是正确的，我找不到任何问题。当然，任何改进的建议或建议都将受到赞赏。
于 2016-08-28T13:12:08.580 回答