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There are three event handlers that need to be assigned: onmouseover,
onmousedown and onmouseup. The onmouseover
event handler is simply used to highlight the current suggestion, the onmousedown
is used to select the given suggestion (place the suggestion in the textbox
and hide the dropdown list) and onmouseup is used to just to set
focus back to the textbox after a selection has been made. Since all of these
event handlers occur on the textbox, it's best just to use a single function
for all of them, as seen below:
AutoSuggestControl.prototype.createDropDown = function () {
this.layer = document.createElement("div");
this.layer.className = "suggestions";
this.layer.style.visibility = "hidden";
this.layer.style.width = this.textbox.offsetWidth;
document.body.appendChild(this.layer);
var oThis = this;
this.layer.onmousedown = this.layer.onmouseup
=
this.layer.onmouseover = function (oEvent) {
oEvent = oEvent || window.event;
oTarget = oEvent.target || oEvent.srcElement;
if (oEvent.type ==
"mousedown") {
oThis.textbox.value
= oTarget.firstChild.nodeValue;
oThis.hideSuggestions();
} else if (oEvent.type == "mouseover")
{
oThis.highlightSuggestion(oTarget);
} else {
oThis.textbox.focus();
}
};
};
The first part of this section is the assignment of oThis equal
to the this object. This is necessary so that a reference to the
AutoSuggestControl object is accessible from within the event handler.
Next, a compound assignment occurs, assigning the same function as an event
handler for onmousedown, onmouseup, and onmouseover.
Inside of the function, the first two lines are used to account for the different
event models (DOM and IE). The event object is stored in oEvent
and the target of the event is stored in oTarget (the target will
always be a <div/> containing a suggestion).
If the event being handled is mousedown, then you set the value
of the textbox equal to the text inside of the event target. The text is a text
node, retrieved by the firstNode property, and the actual text
is stored in the nodeValue of the text node. After the suggestion
is placed into the textbox, the dropdown list is hidden.
When the event being handled is mouseover, the event target is
passed into the highlightSuggestion() method to provide the hover
effect. If the event is mouseup, then the focus is set back to
the textbox (this fires immediately after mousedown).
In order to get the full effect of the dropdown list it's imperative that it
appear immediately below the textbox. If the textbox were absolutely positioned,
this wouldn't be much of an issue. In actual practice, textboxes are rarely
absolutely positioned and more often are placed inline, which presents a problem
in aligning the dropdown list. To do so accurately, you must calculate the location
of the textbox using the offsetLeft, offsetTop, and
offsetParent properties.
The offsetLeft and offsetTop properties tell you
how many pixels away from the left and top of the offsetParent
an element is placed. The offsetParent is usually, but not always,
the parent node of the element, so to get the left position of the textbox,
you need to add up the offsetLeft properties of the textbox and
all of its ancestor elements (stopping at <body/>), as seen
below:
AutoSuggestControl.prototype.getLeft = function () {
var oNode = this.textbox;
var iLeft = 0;
while(oNode.tagName != "BODY") {
iLeft += oNode.offsetLeft;
oNode = oNode.offsetParent;
}
return iLeft;
};
The getLeft() method begins by pointing oNode at
the textbox and defining iLeft with an initial value of 0. The
while loop will continue to add oNode.offsetLeft to iLeft
as it traverses up the DOM structure to the <body/> element.
The same algorithm can be used to get the top of the textbox:
AutoSuggestControl.prototype.getTop = function () {
var oNode = this.textbox;
var iTop = 0;
while(oNode.tagName != "BODY") {
iTop += oNode.offsetTop;
oNode = oNode.offsetParent;
}
return iTop;
};
These two methods will be used to place the dropdown list in the correct location.
The next step in this process is to create a method that adds the suggestions
into the dropdown list and then displays it. The showSuggestions()
method accepts an array of suggestions as an argument and then builds up the
DOM necessary to display them. From there, the method positions the dropdown
list and displays it to the user:
AutoSuggestControl.prototype.showSuggestions = function (aSuggestions)
{
var oDiv = null;
this.layer.innerHTML = "";
for (var i=0; i < aSuggestions.length; i++) {
oDiv = document.createElement("div");
oDiv.appendChild(document.createTextNode(aSuggestions[i]));
this.layer.appendChild(oDiv);
}
this.layer.style.left = this.getLeft() + "px";
this.layer.style.top = (this.getTop()+this.textbox.offsetHeight)
+ "px";
this.layer.style.visibility = "visible";
};
The first line simply defines the variable oDiv for later use.
The second line clears the contents of the dropdown list by setting the innerHTML
property to an empty string. Then, the for loop creates a <div/>
and a text node for each suggestion before adding it to the dropdown list layer.
The next section of code starts by setting the left position of the layer using
the getLeft() method. To set the top position, you need to add
the value from getTop() to the height of the textbox (retrieved
by using the offsetHeight property). Lastly, the layer's visibility
is set to "visible" to show it.
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Created: March 27, 2003
Revised: April 08, 2005
URL: http://webreference.com/programming/javascript/ncz/column2/1
