public interface Skinning
setStyleName() or
setBackgroundColor(), or you can
skin all
components of the same class at once, by using Canvas.setDefaultProperties()
to change the defaults for the class.
CSSStyleName for more details
about correct
usage.
skin_styles.css)
load_skin.js)
skin_styles.css
load_skin.js
images/
ListGrid/
sort_ascending.gif
...
Tab/
... other directories containing
component or shared media ...
Smart GWT can make use of CSS3 features to render user interface component
details such as rounded corners, gradients and drop-shadows. Prior to the wide adoption
of CSS3 by browsers such UI details could only be achieved by writing out HTML structures
including images.
Using images is a less efficient approach - it leads to a more complex DOM structure and
increased server load to retrieve media.
The most modern Smart GWT skin, Tahoe, will always rely on CSS3 features for certain appearance details. If loaded in a browser with no CSS3 support (such as Internet Explorer 8), developers can expect to see some degredation in appearance (lack of certain drop-shadows, rounded edges becoming square, etc).
Three of Smart GWT's other most commonly used skins, Enterprise, EnterpriseBlue and Graphite will conditionally make use of CSS3 features. These skins have a "CSS3 mode" in which many images required by the skin are replaced with CSS3 settings that appear nearly identical to the image-based appearance.
For these skins, CSS3 mode is automatically used in modern browsers such as
Firefox, Chrome, Safari, IE 9 in standards mode, and IE 10+.
Internet Explorer version 8 and earlier does not have sufficient
CSS support to create a close match to the existing image-based skin, so CSS3 mode is not
enabled by default. If CSS3 mode is manually enabled for IE when not automatically enabled,
this will result in a degraded appearance that is similar across IE6, 7, and 8: rounded
elements
such as tabs will become square, and backgrounds will have lower quality if not disappear.
To override the default decision on whether to use CSS3 support, set the JavaScript global
variable isc_css3Mode before any of the Smart GWT libraries are loaded. For
example:
<script>isc_css3Mode = "on";</script>
Possible settings are:
For more control than the above settings provide, you can create a custom skin based on one
of the above 3 skins and modify load_skin.js - whether CSS3 mode is used is controlled by a
JavaScript variable useCSS3 defined in this file.
Smart GWT also makes use of a CSS technique known as "spriting" to improve performance when rendering certain user interface images. This technique improves performance when rendering a number of small images within an application. Instead of loading a separate image file for each element, this technique involves creating a single composite image file consisting of smaller images sewn together, and using css background-sizing and offset to display the desired portion of this larger image within elements on a page.
This reduces the overall file size for the media as the combined image's size will
typically be significantly less than the sum of the sizes of the smaller images. It also
allows the browser to issue a single HTTP request for the composite image instead of
separate requests for each image element showing parts of this composite image.
For example, the up and down arrow images of a SpinnerItem in
the normal, "Focused", and "Disabled" states can be combined into one image. The file size of
the combined image is typically ~65% smaller than the sum of the file sizes of the 6
constituent images, and a single HTTP request provides media for all 6 states.
Spriting typically results in reduced load times and eliminates noticeable delays in changes of component appearance while the browser downloads a required image. It is natively supported in all browsers.
One consideration when using spriting is how to handle images being rendered at different
sizes on the page. Simply increasing the size of an element using CSS to display a
portion of a larger background image will not change the scale of that image - instead
more of the image will be revealed to the user. This can result in visual glitches,
for example, the user may be able to see other sprited elements from the larger
background image.
If the "native" size of the image sprite is known as well as the desired rendered size
scaling can be achieved. For Smart GWT image attributes that support the special
sprited image URL format, this can be
specified, allowing the image to
be rendered at various sizes.
The Tahoe skin makes use of the sprite-URL capability to ensure that sprited
images appear correctly regardless of the size at which they are being drawn.
The Enterprise, EnterpriseBlue, and Graphite skins
also support spriting of user
interface images, but do so via settings embedded in the css applied to certain elements
instead of using the sprite-URL capability. As such if certain component metrics
(such as the height of a component or padding) are changed, then the image sprites may
no longer work. In this case, spriting can be disabled by setting the JavaScript global
variable isc_spriting to "off" before any of the Smart GWT libraries are loaded.
For example:
<script>isc_spriting = "off";</script>
Possible settings are:
To modify a skin, first create a copy of one of the skins that comes with the Smart GWT SDK, then modify the copy. Full instructions are provided in Chapter 9 of the QuickStart Guide.
Starting from the name of the component
Given a Smart GWT component that you want to skin, open its JavaDoc:
Button.baseStyle
Img.src
"AutoChildren" and check the reference
for the type of
the AutoChild for settable properties. For example, Window.minimizeButton is an
ImgButton and therefore supports ImgButton.src.
Starting from a running example
Specific browsers offer alternate approaches to quickly discover the images or style names being used for a part of a Smart GWT component's appearance:
Properties that refer to images by URL, such as Img.src and Button.icon, are
specially interpreted in Smart GWT to allow for simpler and more uniform image URLs,
and to allow applications to be restructured more easily.
Unlike the URL used with an HTML <IMG> element, the image URL passed to a Smart GWT
component is not assumed to be relative to the current page. See SCImgURL for a
full explanation of the default application image directory, and the meaning of the "[SKIN]"
prefix.
Default image URLs for Smart GWT components are specified in load_skin.js via
JavaScript, using calls to Class.addProperties() and
Class.changeDefaults(). For example, the load_skin.js file
from the "Enterprise" skin includes the following code to establish the media used by
Window.minimizeButton:
isc.Window.changeDefaults("minimizeButtonDefaults", {
src:"[SKIN]/Window/minimize.png"
});
NOTE: These are JavaScript APIs and hence do not appear in SmartGWT JavaDoc - you may want to refer to the SmartClient Reference available at Isomorphic.com for these specific APIs.
Many Smart GWT components must know some image sizes in advance, in order to allow those components to autosize to data or content.
For example, the ImgTabs used in TabSets are capable of automatically sizing
to a variable length Tab.title. To make
this possible, Smart GWT must know the
sizes of the images used as "endcaps" on each tab in advance.
Like image URLs, image sizes are specified in load_skin.js. The following code
sample establishes the default size of the "endcaps" for tabs, by setting a default value
for ImgTab.capSize:
isc.ImgTab.addProperties({
capSize:4
})
Some components or areas within components, including buttons and the cells within a grid, are "stateful", meaning that they can be in one of a set of states each of which has a distinct visual appearance.
Stateful components switch the CSS styles or image URLs they are using as they transition
from state to state, appending state information as suffixes on the style names or URL.
See Img.src and Button.baseStyle for details and examples.
Smart GWT has built-in logic to manage a series of state transitions, such as:
ImgButton.showRollOver, allow you to control whether the
component will switch CSS style or image URL when the component transitions into a given state.
A StretchImg is Smart GWT component that renders out a
compound image composed of 3
image files: two fixed-size endcaps images and a stretchable center segment. Like stateful
components, the names of each image segment is appended to the image URL as a suffix. See
StretchImg.src for details.
Similar to a StretchImg, an EdgedCanvas provides an
image-based decorative edge
around and/or behind another component, with up to 9 segments (a 3x3 grid). Decorative
edges can be added to any component by setting showEdges:true.
EdgedCanvas is also used to construct dropshadows, which can be enabled on any component via
showShadow:true.
In rare situations, such as trying to share a skin between a SmartClient and Smart GWT application, you may have a SmartClient class that has been defined to hold certain skin settings where there is no corresponding Smart GWT class. For example, you might have a SmartClient subclass of ListGrid called "LedgerGrid" that changes cell styles to appear more like a ledger.
In this case, you can generally use the Smart GWT class that is the nearest superclass of the SmartClient class (ListGrid in this case), then use a call to setScClassName("LedgerGrid") to cause the SmartClient class to be used as the underlying SmartClient class used by the GWT ListGrid instance.
If you're creating a custom skin, you can place JavaScript snippets such as those shown above in your custom skin's load_skin.js file. If you prefer not to create a custom skin for small customizations, you can execute JavaScript via a JSNI method in your Java code. With this latter approach, be sure to change "isc." to "$wnd.isc." wherever it appears, and to call the JSNI method before creating any SmartGWT components.
In most cases, using newer CSS features such as CSS3 prefix attribute selectors or CSS3
pseudo-classes in a skin will just work, provided the browser supports those CSS features.
However, in some cases, Smart GWT needs to be able to extract style information from
CSS style declarations. For this reason, only single class name selectors are officially
supported (e.g. .myButton, .myButtonDown) and @-rules are not supported.