you have to know the number of pictures to display for each category beforehand, try this (make sure you change the number of pics in the SELECT list for each category):<script language="javascript">
var nCurPos, nCurCount;
var sCurImgPrefix;function setButtonState()
{
if (nCurPos > 1)
document.all("btnPrev").style.visibility = "visible";
else
document.all("btnPrev").style.visibility = "hidden"; if (nCurPos < nCurCount)
document.all("btnNext").style.visibility = "visible";
else
document.all("btnNext").style.visibility = "hidden";}function getImage(nDir)
{
nCurPos += nDir;
document.all("myimg").src = sCurImgPrefix + nCurPos + ".jpg";
setButtonState();
}function setImage (obj)
{ var nIndex = obj.selectedIndex;
sCurImgPrefix = "图片" + obj.options[nIndex].text; nCurCount = parseInt(obj.options[nIndex].value);
nCurPos = 1; getImage(0);
}
</script>
<body onload="setImage(piclist)">
<select id="piclist" onchange="setImage(this)">
<option value="1">军事</option>
<option value="3">文化</option>
<option value="2">体育</option>
</select><br>
<img id="myimg"><br>
<input type="button" id="btnPrev" value="向前" onclick="getImage(-1)">
<input type="button" id="btnNext" value="向后" onclick="getImage(1)">
</body>
var nCurPos, nCurCount;
var sCurImgPrefix;function setButtonState()
{
if (nCurPos > 1)
document.all("btnPrev").style.visibility = "visible";
else
document.all("btnPrev").style.visibility = "hidden"; if (nCurPos < nCurCount)
document.all("btnNext").style.visibility = "visible";
else
document.all("btnNext").style.visibility = "hidden";}function getImage(nDir)
{
nCurPos += nDir;
document.all("myimg").src = sCurImgPrefix + nCurPos + ".jpg";
setButtonState();
}function setImage (obj)
{ var nIndex = obj.selectedIndex;
sCurImgPrefix = "图片" + obj.options[nIndex].text; nCurCount = parseInt(obj.options[nIndex].value);
nCurPos = 1; getImage(0);
}
</script>
<body onload="setImage(piclist)">
<select id="piclist" onchange="setImage(this)">
<option value="1">军事</option>
<option value="3">文化</option>
<option value="2">体育</option>
</select><br>
<img id="myimg"><br>
<input type="button" id="btnPrev" value="向前" onclick="getImage(-1)">
<input type="button" id="btnNext" value="向后" onclick="getImage(1)">
</body>
解决方案 »
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