Interface Builder, @IBOutlet and protocols for delegate and dataSource in Swift

Can't connect delegate property of CustomView declared as @IBOutlet toViewController in Interface Builder – simply can't establish a connection.

Here's the code

class CustomView: UIView {
     @IBOutlet var delegate: CustomViewDelegate?
}

@objc protocol CustomViewDelegate {
     ...
}


class ViewController: UIViewController, CustomViewDelegate {
     ...
}

@objc is used because of swift protocol, IBOutlet property cannot have non-object type, don't know why protocol CustomViewDelegate: class {} doesn't work.

Anyone else came across something like that?

From the Xcode release notes:

Interface Builder does not support connecting to an outlet in a Swift file when the outlet’s type is a protocol.

Workaround: Declare the outlet's type as AnyObject or NSObject, connect objects to the outlet using Interface Builder, then change the outlet's type back to the protocol.

EDIT: Xcode 9 beta 3 release notes say that this workaround should no longer be necessary.

Adam Waite provides a nice workaround. I however prefer the following solution as it emphasizes the workaround and the extra property can also easily be removed once Xcode gets fixed.

class CustomView: UIView {
    @IBOutlet
    public var delegate: CustomViewDelegate?

    /// Workaround for Xcode bug that prevents you from connecting the delegate in the storyboard.
    /// Remove this extra property once Xcode gets fixed.
    @IBOutlet
    public var ibDelegate: AnyObject? {
        get { return delegate }
        set { delegate = newValue as? CustomViewDelegate }
    }

    func someMethod() {
        // Here we always refer to `delegate`, not `ibDelegate`
        delegate?.onSomethingHappened()
    }
}

@objc protocol CustomViewDelegate {
    ...
}

Hey, is this bug already one and a half years old?

An elegant workaround：

#if TARGET_INTERFACE_BUILDER
@IBOutlet open weak var delegate: AnyObject?
#else
open weak var delegate: CustomViewDelegate?
#endif

See： https://github.com/WenchaoD/FSPagerView/blob/master/Sources/FSPagerView.swift#L88

Another that's not pretty but:

@IBOutlet weak var ibDelegate: NSObject?
@IBOutlet weak var ibDataSource: NSObject?
var delegate: MultipleButtonViewDelegate? { return ibDelegate as? MultipleButtonViewDelegate }
var dataSource: MultipleButtonViewDataSource? { return ibDataSource as? MultipleButtonViewDataSource }

This is an old thread, but I thought I'd point out that as of Xcode 9 beta 3, it is now possible to connect a custom delegate written in swift to interface builder.

According to the release notes

Interface Builder now recognizes outlets, actions, and inspectable properties declared on classes which have a Swift protocol extension. (22201035)

// Can connect this to interface builder now    
class MyViewController: UIViewController {
    @IBOutlet weak var myDelegate: TheNewDelegate?
}

Tom Howard

For me, the reason was the table view was nil at the point I attempted to set it's datasource and delegate. This was due to the designated initializer calling initWithNibName:bundle: which does not guarantee initialized connections. Deferring my delegate and datasource setting to viewDidload worked like a charm.

来源：https://stackoverflow.com/questions/26180268/interface-builder-iboutlet-and-protocols-for-delegate-and-datasource-in-swift

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swift

interface-builder

iboutlet