在Swift中为UIPickerView委派方法

Question

Just getting started in Swift and having trouble calling the delegate methods for a UIPickerView

So far I have added the UIPickerViewDelegate to my class like so:

class ExampleClass: UIViewController, UIPickerViewDelegate

I have also created my UIPickerView and set the delegate for it:

@IBOutlet var year: UIPickerView
year.delegate = self

Now I am just having trouble turning the following into Swift code:

- (NSInteger)numberOfComponentsInPickerView:(UIPickerView *)pickerView

Any help would be appreciated

Answer 1

That's actually a method in the UIPickerViewDataSource protocol, so you'll want to make sure you set your picker view's dataSource property as well: year.dataSource = self . The Swift-native way seems to be to implement protocols in class extensions, like this:

class ExampleClass: UIViewController {
    // properties and methods, etc.
}

extension ExampleClass: UIPickerViewDataSource {
    // two required methods

    func numberOfComponentsInPickerView(pickerView: UIPickerView!) -> Int {
        return 1
    }

    func pickerView(pickerView: UIPickerView!, numberOfRowsInComponent component: Int) -> Int {
        return 5
    }
}

extension ExampleClass: UIPickerViewDelegate {
    // several optional methods:

    // func pickerView(pickerView: UIPickerView!, widthForComponent component: Int) -> CGFloat

    // func pickerView(pickerView: UIPickerView!, rowHeightForComponent component: Int) -> CGFloat

    // func pickerView(pickerView: UIPickerView!, titleForRow row: Int, forComponent component: Int) -> String!

    // func pickerView(pickerView: UIPickerView!, attributedTitleForRow row: Int, forComponent component: Int) -> NSAttributedString!

    // func pickerView(pickerView: UIPickerView!, viewForRow row: Int, forComponent component: Int, reusingView view: UIView!) -> UIView!

    // func pickerView(pickerView: UIPickerView!, didSelectRow row: Int, inComponent component: Int)
}

Answer 2

The delegate isn't responsible for calling that method. Instead it is called by the UIPickerView's data source. These are the two functions called by the UIPickerView data source that you need to implement:

// returns the number of 'columns' to display.
func numberOfComponentsInPickerView(pickerView: UIPickerView!) -> Int

// returns the # of rows in each component..
func pickerView(pickerView: UIPickerView!, numberOfRowsInComponent component: Int) -> Int

To ensure these functions get called, your class should also implement the data source protocol:

class ExampleClass: UIViewController, UIPickerViewDelegate, UIPickerViewDataSource

And your picker's data source should be set:

year.dataSource = self