OC中protocol是用weak和assign修饰的弱引用.Swift中protocol功能被增强了,如果使用以下代码就会变成强引用.

protocol TestDelegate
{
    func cellClicked(let index:Int,let data:AnyObject);
}

class Test: NSObject,TestDelegate {

    var b:Test2?;

    func cellClicked(let index:Int,let data:AnyObject)
    {

    }

    static func test()
    {
        var a:Test? = Test();

        a?.b = Test2();

        a?.b?.delegate = a;

        a = nil;
    }

    deinit
    {
        print("test deinit");
    }

}

class Test2:NSObject {
    var delegate:TestDelegate?;

    deinit
    {
        print("Test2 deinit");
    }
}

上述代码,deinit永远不会被调用,因为Test实例被Test2实例强引用了

正确代码如下

protocol TestDelegate:class
{
    func cellClicked(let index:Int,let data:AnyObject)
    {

    }

    static func test()
    {
        var a:Test? = Test();

        a?.b = Test2();

        a?.b?.delegate = a;

        // b = nil;

        a = nil;
    }

    deinit
    {
        print("test deinit");
    }

}

class Test2:NSObject {
    weak var delegate:TestDelegate?;

    deinit
    {
        print("Test2 deinit");
    }
}

把protocol修饰成class,delegate对象用weak修饰.