Matteo Spinelli's

First things first. Have a look at the demo page or, if you don’t have your device at hand, watch the screencast I baked for you.

Please note that the script is in beta phase, I am publishing it to receive feedback and suggestions. In the next few days we should have a stable version.

Update 2009/03/16: We are out of beta, the script is now stable and ready for production (hope so ). In the zip I also included a minified (9kb) version of the script to save some bits of precious bandwidth.

Update 2009/04/19: the script is now compatible with full screen mode apps. It seems that in full screen mode preventDefault() and stopPropagation() placed in touchStart event are not enough to block the propagation of the touch event. Adding preventDefault() to touchMove event solved the problem.

Update 2009/06/18: the script has been updated for OS3.0 compatibility.

Update 2009/07/09: it turned out that Apple is well aware of the webkit refresh bug, fortunately they are kind enough to offer a workaround. All we have to do is to use translate3d instead of translate and all our animations will be fluid as never before! Go get the latest version of the script!

How to use the script

The widget is composed of two parts: the stylesheet and the javascript. No HTML is needed as all the elements are created by the script on the fly. Include both the JS and the CSS into your page and you are ready to spin. You’ll be also surprised to see that the spinning wheel itself is built with just two images, while other three images are needed for the header and buttons. The PNGs altogether are 4.3kb.

The code does not need initialization on window load. You cannot have more than one picker at a time, so the SpinningWheel object is unique and it is created as soon as you include the JS file.

The first thing you need to do is to define the slots with:

SpinningWheel.addSlot(obj values, str styles, str defaultValue)

values is in the form of: { key: value, key2: value, ... }. Keys are the identifiers that won’t be shown in the picker (think of them as the value parameter in the <option value="foo">bar</option> tag). Values are the labels printed on the slots.
styles is a list of space separated predefined styles to be applied to the slot. The available values are:

• right, align text inside the slot to the right;
• readonly, the slot can’t be spun;
• shrink, shrink the slot width to the minimum possible.

The first element of the slot will be selected if no defaultValue is defined.

When all the slots have been created, set the default actions for the cancel and done buttons.

SpinningWheel.setCancelAction( function(){ } );
SpinningWheel.setDoneAction( function() { } );

Finally show the picker:

SpinningWheel.open();

Voila, the Picker View is ready for countless hours of spinning pleasure.

To get the actual selected values call:

var result = SpinningWheel.getSelectedValues();

result.keys will be filled with an array of the selected keys while result.values will hold the list of the selected values (or labels).

Let’s wrap everything together.

function swExample() {
	var numbers = { 0: 0, 1: 1, 2: 2, 3: 3, 4: 4, 5: 5, 6: 6, 7: 7, 8: 8, 9: 9 };
	SpinningWheel.addSlot(numbers, 'right');
	SpinningWheel.addSlot(numbers, 'right');
	SpinningWheel.addSlot({ separator: '.' }, 'readonly shrink');
	SpinningWheel.addSlot(numbers, 'right');
	SpinningWheel.addSlot({ Kg: 'Kg', Lb: 'Lb', St: 'St' }, 'shrink');

	SpinningWheel.setCancelAction(cancel);
	SpinningWheel.setDoneAction(done);

	SpinningWheel.open();
}

function done() {
	var results = SpinningWheel.getSelectedValues();
	alert('values:' + results.values.join(', ') + ' - keys: ' + results.keys.join(', '));
}

function cancel() {
	alert('cancelled!');
}

Look at the demo for more examples.

Create custom styles

I preconfigured for you three styles for the slots, but you can add as many as you need. Say you want a slot with center aligned text. Add the following to the stylesheet:

#sw-slots .sw-center { text-align:center; }

To apply the style create the slot like this:

SpinningWheel.addSlot(values, 'center');

A piece of cake.

By default the slots try to fit their content. Slots with long text will be wider than ones with short text. (Same as the <table /> cell elements). With custom style you can override this behavior. If you have two slots and you want them to be exactly the same width you may add the following style:

#sw-slots .sw-50percent { width:50%; }

and create the slots with:

SpinningWheel.addSlot(values, '50percent');
SpinningWheel.addSlot(values);

You don’t need to apply the style to both slots as the second will fit the remaining space (or the other 50% of the screen width).

Limitations

None that I can tell if not those imposed by the device small CPU. All animations are hardware accelerated, the “birth date” example in the demo creates more than one hundred elements and all animations are pretty fluid.

The script is also compatible with both landscape and portrait mode and you can freely switch from one to the other while the spinning wheel is opened. (That is more than what the native Picker View has to offer).

Note that once closed the spinning wheel is completely inaccessible and all variables will be null or undefined. So basically you can’t programmatically query the SpinningWheel object while it is not visible.

I’m now working on code optimization to reduce memory usage, I hope to release a stable version as soon as possible. The code is now stable, please leave your comments and suggestions.

As always released under MIT license for all your coding needs.

Download the script