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This section discusses problems that you might encounter while using components. If you don't find your problem in this section, consult the following sections:
- Solving Common Problems Using Other Swing Features
- Solving Common Layout Problems
- Solving Common Event-Handling Problems
- Solving Common Painting Problems
Problem: I'm having trouble implementing a model (or some other code that's similar to something already in Java 2 Platform, Standard Edition).
Problem: Whenever the text in my text field updates, the text field's size changes.
- Look at the J2SE source code. It's distributed with the J2SE SDK, and it's a great resource for finding code examples of implementing models, firing events, and the like.
Problem: Certain areas of the content pane look weird when they're repainted.
- You should specify the preferred width of the text field by specifying the number of columns it should have room to display. To do this, you can use either an
int
argument to theJTextField
constructor or thesetColumns
method.
- If you set the content pane, make sure it's opaque. You can do this by invoking
setOpaque(true)
on your content pane. Note that althoughJPanel
s are opaque in most look and feels, that's not true in the GTK+ look and feel, which was introduced in 1.4.2. See Adding Components to the Content Pane for details.- If one or more of your components performs custom painting, make sure you implemented it correctly. See Solving Common Painting Problems for help.
- You might have a thread safety problem. See the next entry.
Problem: My program is exhibiting weird symptoms that sometimes seem to be related to timing.
- Make sure your code is thread-safe. See How to Use Threads for details.
Problem: My modal dialog gets lost behind other windows.
- If the dialog has a null parent component, try setting it to a valid frame or component when you create it.
- See bug # 4255200 for a possible workaround.
Problem: The scroll bar policies don't seem to be working as advertised.
Problem: My scroll pane has no scroll bars.
- Some Swing releases contain bugs in the implementations for the
VERTICAL_SCROLLBAR_AS_NEEDED
and theHORIZONTAL_SCROLLBAR_AS_NEEDED
policies. If feasible for your project, use the most recent release of Swing.- If the scroll pane's client can change size dynamically, the program should set the client's preferred size and then call
revalidate
on the client.- Make sure you specified the policy you intended for the orientation you intended.
Problem: The divider in my split pane don't move!
- If you want a scroll bar to appear all the time, specify either
VERTICAL_SCROLLBAR_ALWAYS
orHORIZONTAL_SCROLLBAR_ALWAYS
for the scroll bar policy as appropriate.- If you want the scroll bars to appear as needed, and you want to force the scroll bars to be needed when the scroll pane is created, you have two choices: either set the preferred size of scroll pane or its container, or implement a scroll-savvy class and return a value smaller than the component's standard preferred size from the
getPreferredScrollableViewportSize
method. Refer to Sizing a Scroll Pane for information.Problem: The
- You need to set the minimum size of at least one of the components in the split pane. Refer to Positioning the Divider and Restricting Its Range for information.
setDividerLocation
method ofJSplitPane
doesn't work.Problem: The borders on nested split panes look too wide.
- The
setDividerLocation(double)
method has no effect if the split pane has no size (typically true if it isn't onscreen yet). You can either usesetDividerLocation(int)
or specify the preferred sizes of the split pane's contained components and the split pane's resize weight instead. Refer to Positioning the Divider and Restricting Its Range for information.Problem: The buttons in my tool bar are too big.
- If you nest split panes, the borders accumulate the border of the inner split panes display next to the border of the outer split pane causing borders that look extra wide. The problem is particularly noticeable when nesting many split panes. The workaround is to set the border to null on any split pane that is placed within another split pane. For information, see bug # 4131528 in the Bug Parade at the Java Developer's Connection.
Problem: The components in my layered pane aren't layered correctly. In fact, the layers seem to be inversed the lower the depth the higher the component.
- Try reducing the margin for the buttons. For example:
button.setMargin(new Insets(0,0,0,0));
- This can happen if you use an
int
instead of anInteger
when adding components to a layered pane. To see what happens, make the following change toLayeredPaneDemo
:
Change this... to this... layeredPane.add(label, new Integer(i));
layeredPane.add(label, i);
Problem: The method call
colorChooser.setPreviewPanel(null)
does not remove the color chooser's preview panel as expected.Problem: I can't make HTML tags work in my labels or buttons or... (See Using HTML in Swing Components for an example.)
- A
null
argument specifies the default preview panel. To remove the preview panel, specify a standard panel with no size, like this:colorChooser.setPreviewPanel(new JPanel());
- Make sure your program is running in a release that supports HTML text in the desired component. The following table shows which releases support HTML in which components.
Java 2 Release Corresponding JFC 1.1 Release Status of HTML support J2SE v 1.2, v 1.2.1 JFC 1.1 (with Swing 1.1) HTML supported in styled text components only. J2SE v 1.2.2 JFC 1.1 (with Swing 1.1.1) HTML support added for JButton
,JLabel
,JMenuItem
,JMenu
,JCheckBoxMenuItem
,JRadioButtonMenuItem
,JTabbedPane
, andJToolTip
.Because table cells and tree nodes use labels to render strings, tables and trees automatically support HTML, as well.
Java 2 v 1.3 none HTML support added for JToggleButton
,JCheckBox
, andJRadioButton
.
- If you can't guarantee that your program will be executed only with a release that supports HTML text in the desired component, don't use that feature!
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