gridbag.html

jsf、swing的官方指南

pane.add(button, c);

button = new JButton("5");
c.ipady = 0;       //reset to default
c.weighty = 1.0;   //request any extra vertical space
c.anchor = GridBagConstraints.PAGE_END; //bottom of space
c.insets = new Insets(10,0,0,0);  //top padding
c.gridx = 1;       //aligned with button 2
c.gridwidth = 2;   //2 columns wide
c.gridy = 2;       //third row
pane.add(button, c);
</pre></blockquote>

<p>
This example uses one <code>GridBagConstraints</code> instance
for all the components the <code>GridBagLayout</code> manages.
Just before each component is added to the container,
the code sets (or resets to default values)
the appropriate instance variables
in the <code>GridBagConstraints</code> object.
It then adds the component to its container,
specifying the <code>GridBagConstraints</code> object
as the second argument to the <code>add</code> method.

<p>

For example,
to make button 4 be extra tall,
the example has this code:

<blockquote><pre>
c.ipady = 40;
</pre></blockquote>

And before setting the constraints of the next component,
the code resets the value of <code>ipady</code>
to the default:

<blockquote><pre>
c.ipady = 0;
</pre></blockquote>

<blockquote><hr><strong>Note:</strong>&nbsp;The Tutorial's examples
used to specify the constraints object
a different way,
which you might see in other programs as well.
Rather than specifying the constraints with the <code>add</code> method,
our examples invoked
the <code>setConstraints</code> method
on the <code>GridBagLayout</code> object. 
For example:

<blockquote><pre>
GridBagLayout gridbag = new GridBagLayout();
pane.setLayout(gridbag);
...
gridbag.setConstraints(button, c);
pane.add(button);
</pre></blockquote>
<hr></blockquote>

Here's a table that shows all the constraints
for each component 
in GridBagLayoutDemo's content pane.
Values that aren't the default
are marked in <b>boldface</b>.
Values that are different from those in the previous table entry
are marked in <i>italics</i>.

<p>
<table>
<tr>
<th align=left> Component
</th>
<th align=left> Constraints
</th>
</tr>
<tr>
<td valign=top>
All components
</td>
<td valign=top>
<pre>
ipadx = 0
<b>fill = GridBagConstraints.HORIZONTAL</b>

</td>
</tr>
<tr>
<td valign=top>
Button 1
</td>
<td valign=top>
<pre>
ipady = 0
<b>weightx = 0.5</b>
weighty = 0.0
gridwidth = 1
anchor = GridBagConstraints.CENTER
insets = new Insets(0,0,0,0)
<b>gridx = 0</b>
<b>gridy = 0</b>

</td>
</tr>
<tr>
<td valign=top>
Button 2
</td>
<td valign=top>
<pre>
<b>weightx = 0.5</b>
<i><b>gridx = 1</b></i>
<b>gridy = 0</b>
</pre>

</td>
</tr>
<tr>
<td valign=top>
Button 3
</td>
<td valign=top>
<pre>
<b>weightx = 0.5</b>
<i><b>gridx = 2</b></i>
<b>gridy = 0</b>
</pre>

</td>
</tr>
<tr>
<td valign=top>
Button 4
</td>
<td valign=top>
<pre>
<i><b>ipady = 40</b></i>
<i>weightx = 0.0</i>
<i><b>gridwidth = 3</b></i>
<i><b>gridx = 0</b></i>
<i><b>gridy = 1</b></i>
</pre>

</td>
</tr>
<tr>
<td valign=top>
Button 5
</td>
<td valign=top>
<pre>
<i>ipady = 0</i>
weightx = 0.0
<i><b>weighty = 1.0</b></i>
<i><b>anchor = GridBagConstraints.SOUTH</b></i>
<i><b>insets = new Insets(10,0,0,0)</b></i>
<i><b>gridwidth = 2</b></i>
<i><b>gridx = 1</b></i>
<i><b>gridy = 2</b></i>
</pre>
</td>
</tr>
</table>

<p>
GridBagLayoutDemo has two components
that span multiple columns
(buttons 4 and 5).
To make button 4 tall,
we added internal padding (<code>ipady</code>) to it.
To put space between buttons 4 and 5,
we used insets to add a minimum of 10 pixels above button 5,
and we made button 5 hug the south
edge of its cell.

<p>
All the components in the <code>pane</code> container
are as wide as possible,
given the cells that they occupy.
The program accomplishes
this by setting the <code>GridBagConstraints</code>
<code>fill</code> instance variable
to <code>GridBagConstraints.HORIZONTAL</code>,
leaving it at that setting for all the components.
If the program didn't specify the fill,
the buttons would be at their natural width, like this:

<p><center><IMG SRC="../../figures/uiswing/layout/GridBagLayoutDemo-nofill.png" WIDTH="253" HEIGHT="161" ALIGN="BOTTOM" ALT="GridBagLayoutDemo with default fill values."></center></p>
<p>

When you enlarge GridBagLayoutDemo's window,
the columns grow proportionately.
This is because
each component in the first row,
where each component is one column wide,
has <code>weightx = 1.0</code>.
The actual value of these components' <code>weightx</code> is unimportant.
What matters is that all the components,
and consequently, all the columns,
have an equal weight
that is greater than 0.
If no component managed by the <code>GridBagLayout</code>
had <code>weightx</code> set,
then when the components' container was made wider,
the components would stay clumped together in the center of the container,
like this:
<p><center><IMG SRC="../../figures/uiswing/layout/GridBagLayoutDemo-noweightx.png" WIDTH="320" HEIGHT="161" ALIGN="BOTTOM" ALT="GridBagLayoutDemo with default weightx values and enlarged by the user."></center></p>
<p>

Note that if you enlarge the window,
the last row is the only one that gets taller.
This is because only button 5 has <code>weighty</code>
greater than zero.



</blockquote>
<h3>
<a name="api">The GridBagLayout API</a>
</h3>
<blockquote>

[PENDING: This section will be changed to use standard API tables.]

<p>
The <code>GridBagLayout</code> and <code>GridBagConstraints</code>
classes each have only one constructor,
with no arguments.
Instead of invoking methods on a <code>GridBagConstraints</code> object,
you manipulate its instance variables,
as described in 
<a href="#gridbagConstraints">Specifying Constraints</a>.
Generally, the only method you invoke on a 
<code>GridBagLayout</code> object
is <code>setConstraints</code>,
as demonstrated in 
<a href="#gridbagExample">The Example Explained</a>.


</blockquote>
<h3>
<a name="eg">Examples that Use GridBagLayout</a>
</h3>
<blockquote>
You can find examples of using <code>GridBagLayout</code>
throughout this tutorial.
The following table lists a few.

<p>

<table>
<tr>
<th align=left> Example
</th>
<th align=left> Where Described
</th>
<th align=left> Notes

</th>
</tr>
<tr>
<td valign=top> <a href="examples/index.html#GridBagLayoutDemo"><code>GridBagLayoutDemo</code></a>
</td>
<td valign=top> This section
</td>
<td valign=top> Uses many features &#151; weights, insets, internal padding,
     horizontal fill, exact cell positioning, multi-column cells,
     and anchoring (component positioning within a cell).

</td>
</tr>
<tr>
<td valign=top> 
<a class="TutorialLink" target="_top" href="../components/examples/index.html#TextSamplerDemo"><code>TextSamplerDemo</code></a></td>
<td valign=top> 
<a class="TutorialLink" target="_top" href="../components/text.html">Using Text Components</a></td>
<td valign=top> Aligns two pairs of labels and text fields, 
     plus adds a label across the full width of the container.

</td>
</tr>
<tr>
<td valign=top> 
<a class="TutorialLink" target="_top" href="../events/examples/index.html#ContainerEventDemo"><code>ContainerEventDemo</code></a></td>
<td valign=top>
<a class="TutorialLink" target="_top" href="../events/containerlistener.html">How to Write a Container Listener</a></td>
<td valign=top> Positions five components within a container,
     using weights, fill, and relative positioning.

</td>
</tr>
</table>


        </blockquote>
        <div class=NavBit>
            <a target=_top href=flow.html>&laquo; Previous</a>
            &bull;
            <a target=_top href=../TOC.html>Trail</a>
            &bull;
            <a target=_top href=grid.html>Next &raquo;</a>
        </div>
    </div>
    <div id=Footer>
<div id=TagNotes>
    Problems with the examples? Try <a target="_blank"
        href=../../information/run-examples.html>Compiling and Running
        the Examples: FAQs</a>.
    <br>
    Complaints? Compliments? Suggestions? <a target="_blank"
        href="http://developer.sun.com/contact/tutorial_feedback.jsp">Give
    us your feedback</a>.
<br><br>
    <a target="_blank" href="../../information/copyright.html">Copyright</a>
    1995-2006 Sun Microsystems, Inc.  All rights reserved.
    <span id=Download>
</span></div> 

    </div>
    <div class=PrintHeaders>
        <b>Previous page:</b> How to Use FlowLayout
        <br><b>Next page:</b> How to Use GridLayout
    </div>
    </body>
</html>