Centering a panel in GWT using the layoutpanel system
On the GWT developer site there is an example showing a panel that is in the middle of a page. Is this possible to have a fixed with panel in the middle of a page using the GWT layoutpanels?
http://code.google.com开发者_Python百科/webtoolkit/doc/latest/DevGuideUiPanels.html#LayoutPanels
There's a good old CSS trick for centering fixed-size, absolute boxes, using automatic CSS layouting (no JavaScript required):
- First center the top left corner of the box by using
top: 50%; left: 50%;
Of course, the box will be too far to the bottom/right now. - Then subtract half of the box's height/width by using margins. (It's fixed-size, so you can calculate "half of the height/width" with pen and paper :-)
Example:
<!doctype html>
<html>
<head>
<style type="text/css">
.box {
position: absolute;
background-color: red;
height: 300px; width: 400px; /* Using "px" here, but you */
/* can also use "em" etc. */
top: 50%; left: 50%;
margin-top: -150px; margin-left: -200px;
}
</style>
</head>
<body>
<div class="box">Box</div>
</body>
</html>
Apply this style to your LayoutPanel - I don't have a full code example for that, but I think it should be possible.
You can achieve the effect with simple css. For example:
<html><head>
<style>
.outer {
position: absolute;
top: 0;
right: 0;
bottom: 0;
left: 0;
background-color: blue;
}
.inner {
position: absolute;
top: 25%;
right: 25%;
bottom: 25%;
left: 25%;
background-color: red;
}
</style>
</head>
<body>
<div class="outer"><div class="inner" /></div>
</body></html>
Once the basic effect is created in plain CSS using absolutely-positioned objects, you can recreate it with the LayoutPanels, since they're essentially a CSS constraint system.
I don't think you can make a fixed-width layer center itself automatically in a LayoutPanel. However, you can insert the layer into the DOM to get its size, and then calculate the proper offsets yourself. You can see how Google does this (not in a LayoutPanel) in the code for DialogBox.center();
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