Over a million developers have joined DZone.

Populating a UIPickerView in Swift

DZone 's Guide to

Populating a UIPickerView in Swift

· Java Zone ·
Free Resource

I thought it would be an interesting exercise to add a picker control (which Flex developers will know as a SpinnerList) to my dial based colour picker. The new control has a hard coded list of colours - if one of those colours is selected, it updates the RBG and CMYK dial controls and conversely, when either dial control creates a colour that is a match to the picker, it sets its selected item accordingly.

Rather than extending the UIPickerView, I opted for composition and added an instance my new component, ColorSpinner which is an extended UI control. UIPickerViews require two important properties - a delegate which implements the UIPickerViewDelegate protocol and a data source which implements the UIPickerViewDataSource protocol.

I've made the host component, ColorSpinner, both the data source and the delegate.

Unlike lists in Flex, the UIPickerView doesn't accept a collection, rather it invokes methods on the delegate to get data for particular rows in a data source. So, ColorSpinner has a constant array that contains NamedColor structures:

let colors = [
        NamedColor(name: "Custom", color: UIColor.clearColor()),
        NamedColor(name: "Red", color: UIColor.redColor()),
        NamedColor(name: "Green", color: UIColor.greenColor()),
        NamedColor(name: "Blue", color: UIColor.blueColor()),
...and the UIPickerView invokes pickerView() with the titleForRow parameter to populate itself:

func pickerView(pickerView: UIPickerView!, titleForRow row: Int, forComponent component: Int) -> String
        return colors[row].name
When the user makes a selection, pickerView() with didSelectRow is invoked, and I set the ColorSpinner's currentColor is set. The didSet observer on that property invokes sendActionsForControlEvents() so that the main view controller can respond:

func pickerView(pickerView: UIPickerView!, didSelectRow row: Int, inComponent component: Int)
        currentColor = colors[row].color
That observer is also invoked when the controller sets the spinner's colour when one of the dial based pickers is changed. Then, I loop over the array, find any matches and the the UIPickerView's selected index. This is a simple loop that uses the enumerate keyword:

for (index, namedColor) in enumerate(colors)
                if namedColor.color.description == currentColor.description
                    spinner.selectRow(index, inComponent: 0, animated: true)
The three controls (spinner, RGB dial control and CMYK dial control) all work together really well (although the UI is a bit ropey in portrait format and works best in landscape). The animated transition on the UIPickerView is a nice touch which I'll be looking to add to my dial controls soon.

As always, all the source code is available in my GitHub repository.


Published at DZone with permission of

Opinions expressed by DZone contributors are their own.

{{ parent.title || parent.header.title}}

{{ parent.tldr }}

{{ parent.urlSource.name }}