Drag-and-Drop with the YUI: Part-3

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Visual Selection with the Slider Control

So far in this chapter we’ve focused on the functionality provided by the Drag-and-Drop utility. Let’s shift our focus back to the interface controls section of the library and look at one of the components which is related very closely to drag-and-drop—the Slider control.

A slider can be defined using a very minimal set of HTML. All you need are two elements: the slider background and the slider thumb, with the thumb appearing as a child of the background element:

<div id="slider_bg" title="the slider background">
<div id="slider_thumb" title="the slider thumb">
<img src="images/slider_thumb.gif"></div>
</div>

These elements go together to form the basic Slider control, as shown in below:

Learning the Yahoo! User Interface library

The Slider control works as a specific implementation of DragDrop in that the slider thumb can be dragged along the slider background either vertically or horizontally. The DragDrop classes are extended to provide additional properties, methods, and events specific to Slider.

One of the main concepts differentiating Slider from DragDrop is that with a basic slider, the slider thumb is constrained to just one axis of motion, either X or Y depending on whether the Slider is horizontal or vertical respectively.

The Slider is another control that can be animated by including a reference to the Animation control in the head of the page. Including this means that when any part of the slider background is clicked on, the slider thumb will gracefully slide to that point of the background rather than just moving there instantly.

The Constructor and Factory Methods

The constructor for the slider control is always called in conjunction with one of the three factory methods, depending on which type of slider you want to display. To generate a horizontal slider the YAHOO.widget.Slider.getHorizSlider is called, with the appropriate arguments.

To generate a vertical slider, on the other hand, the YAHOO.widget.Slider.getVertSlider would instead be used. There is also another type of slider that can be created—the YAHOO.widget.Slider.getSliderRegion constructor and factory method combination creates a two-dimensional slider, the thumb of which can be moved both vertically and horizontally.

There are a range of arguments used with the different types of slider constructor. The first two arguments are the same for all of them, with the first argument corresponding to the id of the background HTML element and the second corresponding to the id of the thumb element.

The type of slider you are creating denotes what the next two (or four when using the SliderRegion) arguments relate to. With the horizontal slider or region slider the third argument is the number of pixels that the thumb element can move left, but with the horizontal slider it is the number of pixels it can move up. The fourth argument is either the number of pixels which the thumb can move right, or the number of pixels it can move down.

When using the region slider, the fifth and sixth arguments are the number of pixels the thumb element can move up and down, so with this type of slider all four directions must be specified. Alternatively, with either the horizontal or vertical sliders, only two directions need to be accounted for.

The final argument (either argument number five for the horizontal or vertical sliders, or argument number seven for the region slider) is optional and refers to the number of pixels between each tick, also known as the tick size. This is optional because you may not use ticks in your slider, therefore making the Slider control analogue rather than digital.

Class of Two

There are just two classes that make up the Slider control—the YAHOO.widget.Slider class is a subclass of the YAHOO.util.DragDrop class and inherits a whole bunch of its most powerful properties and methods, as well as defining a load more of its own natively.

The YAHOO.widget.SliderThumb class is a subclass of the YAHOO.util.DD class and inherits properties and methods from this class (as well as defining a few of its own natively).

Some of the native properties defined by the Slider class and available for you to use include:

  • animate—a boolean indicating whether the slider thumb should animate. Defaults to true if the Animation utility is included, false if not
  • animationDuration—an integer specifying the duration of the animation in seconds. The default is 0.2
  • backgroundEnabled—a boolean indicating whether the slider thumb should automatically move to the part of the background that is selected when clicked. Defaults to true
  • enableKeys—another boolean which enables the home, end and arrow keys on the visitors keyboard to control the slider. Defaults to true, although the slider control must be clicked once with the mouse before this will work
  • keyIncrement—an integer specifying the number of pixels the slider thumb will move when an arrow key is pressed. Defaults to 25 pixels

A large number of native methods are also defined in the class, but a good deal of them are used internally by the slider control and will therefore never need to be called directly by you in your own code. There are a few of them that you may need at some point however, including:

  • .getThumb()—returns a reference to the slider thumb
  • .getValue()—returns an integer determining the number of pixels the slider thumb has moved from the start position
  • .getXValue()—an integer representing the number of pixels the slider has moved along the X axis from the start position
  • .getYValue()—an integer representing the number of pixels the slider has moved along the Y axis from the start position
  • .onAvailable()—executed when the slider becomes available in the DOM
  • .setRegionValue() and .setValue()—allow you to programmatically set the value of the region slider’s thumb

More often than not, you’ll find the custom events defined by the Slider control to be most beneficial to you in your implementations. You can capture the slider thumb being moved using the change event, or detect the beginning or end of a slider interaction by subscribing to slideStart or slideEnd respectively.

The YAHOO.widget.SliderThumb class is a subclass of the DD class; this is a much smaller class than the one that we have just looked at and all of the properties are private, meaning that you need not take much notice of them. The available methods are similar to those defined by the Slider class, and once again, these are not something that you need to concern yourself with in most basic implementations of the control.

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