如何在web页面，把元素固定到相对或绝对的位置上去

[山尖美色]

如何在web页面，把元素固定到相对或绝对的位置上去

[wsj]

style="position:absolute"
style="position:relative"

[wsj]

position Attribute | position Property

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Retrieves the type of positioning used for the object.

Syntax

HTML { position : sPosition }
Scripting object.style.position [ = sPosition ]

Possible Values

sPosition String that specifies or receives one of the following values:static Default. Object has no special positioning; it follows the layout rules of HTML.
absolute Object is positioned relative to parent element's position梠r to the body object if its parent element is not positioned梪sing the top and left properties.
relative Object is positioned according to the normal flow, and then offset by the top and left properties.


The property is read/write. The property has a default value of static. The cascading style sheets (CSS) attribute is not inherited.

Expressions can be used in place of the preceding value(s), as of Microsoft?Internet Explorer 5. For more information, see Dynamic Properties.

Remarks

Setting the property to absolute pulls the object out of the "flow" of the document and positions it regardless of the layout of surrounding objects. If other objects already occupy the given position, they do not affect the positioned object, nor does the positioned object affect them. Instead, all objects are drawn at the same place, causing the objects to overlap. This overlap is controlled by using the z-index attribute or property. Absolutely positioned objects do not have margins, but they do have borders and padding.

To enable absolute positioning on an object you must specify at least one of the top, bottom, left, or right properties, in addition to setting the position property to absolute. Otherwise, these positioning properties use their default value of auto, which causes the object to render immediately after the preceding elements, according to the layout rules of HTML.

Setting the property to relative places the object in the natural HTML flow of the document, but offsets the position of the object based on the preceding content. The following syntax shows how to create superscript text by placing the text in a SPAN that is positioned relative to the remaining text in the paragraph.

<P>The superscript in this name
<SPAN STYLE="position:relative;
top:-3px">xyz </SPAN> is "xyz".</P>

Text and objects that follow a relatively positioned object occupy their own space and do not overlap the natural space for the positioned object. In contrast, text and objects that follow an absolutely positioned object occupy what would have been the natural space for the positioned object before it was pulled out of the flow. Placing an absolutely positioned object beyond the viewable area of the window causes a scroll bar to appear. When relatively positioned objects are placed beyond the viewable area, a scroll bar is not shown.

The size of the content determines the size of objects with layout. For example, setting the height and position properties on a DIV object gives it layout. The content of the DIV determines the size. In this case, the content determines the size of the width.

For an overview about how to use dynamic positioning, see Positioning.

See the Applies To section for elements that can be relatively and absolutely positioned.

Example

This examples uses the position property's absolute, static, and relative values to change the position of the text.

<STYLE>
.pitem { position: static }
</STYLE>

<SCRIPT>
function fnAbsolute(){
oSpan.style.position="absolute";
}
function fnRelative(){
oSpan.style.position="relative";
}
function fnStatic(){
oSpan.style.position="static";
}
</SCRIPT>

<P>
<SPAN ID=oSpan CLASS="pitem">
This is a SPAN in a paragraph of text.
</SPAN>

This is a paragraph of text.</P>

<INPUT onclick="fnRelative()" TYPE=button VALUE="Relative">
<INPUT onclick="fnAbsolute()" TYPE=button VALUE="Absolute">
<INPUT onclick="fnStatic()" TYPE=button VALUE="Static">


Applies To


A, ADDRESS, APPLET, B, BDO, BIG, BLOCKQUOTE, BUTTON, CENTER, CITE, CODE, custom, DD, defaults, DFN, DIR, DIV, DL, DT, EM, EMBED, FIELDSET, FONT, FORM, Hn, HR, I, IFRAME, IMG, INPUT type=button, INPUT type=checkbox, INPUT type=file, INPUT type=image, INPUT type=password, INPUT type=radio, INPUT type=reset, INPUT type=submit, INPUT type=text, ISINDEX, KBD, LABEL, LEGEND, LI, LISTING, MARQUEE, MENU, OBJECT, OL, P, PRE, RUBY, runtimeStyle, S, SAMP, SELECT, SMALL, SPAN, STRIKE, STRONG, style, SUB, SUP, TABLE, TD, TEXTAREA, TH, TR, TT, U, UL, VAR, XMP