ios - Swift:将对象类型转换为其他对象

Question

我创建了 UIView 的扩展，以在 UIKeyboard 上为 UITextField/UITextView 添加 UIToolbar。

extension UIView {

    public func addDoneOnKeyboardWithTarget (target : AnyObject, action : Selector) {

        //Creating UIToolbar
        var toolbar = UIToolbar()

        //Configuring toolbar
        var items = NSMutableArray()
        var nilButton = IQBarButtonItem(barButtonSystemItem: UIBarButtonSystemItem.FlexibleSpace, target: nil, action: nil)
        items.addObject(nilButton)
        var doneButton = IQBarButtonItem(barButtonSystemItem: UIBarButtonSystemItem.Done, target: target, action: doneAction)
        items.addObject(doneButton)
        toolbar.items = items

        //Now typecasting self to UITextField for compilation purposes because `inputAccessoryView` is readonly for UIView. it's readwrite for UITextField and UITextView both.
        var textField : UITextField = self as UITextField   //Runtime error for UITextView

        //Setting new toolbar as inputAccessoryView
        textField.inputAccessoryView = toolbar
    }
}

它适用于 UITextField，但是当我在 UITextView 上调用上述函数时，它会在类型转换时崩溃。

---

尝试 1: 我试过将其转换为可选

var textField : UITextField? = self as? UITextField
textField?.inputAccessoryView = toolbar

现在它不会在 UITextView 上崩溃，但也不会在其上设置任何 inputAccessoryView。当我试图打印它时。它在控制台上打印 nil。

println(textField?.inputAccessoryView)  //It prints 'nil'

---

尝试 2: 我尝试将其转换为 AnyObject

var textField : AnyObject = self as AnyObject
textField.inputAccessoryView = toolbar  //Compile time error

---

如果我将 UITextField 替换为 UITextView，那么显然它适用于 UITextView 但不适用于 UITextField。

有什么建议吗？

Answer 1

到 1 textview 不是 textfield
到 2 任何对象都没有方法 inputAccessoryView
-->> swift 强制类型安全

所以你不能只是将对象转换成它们不是的东西

但是

来自文档:
"UIResponder 类为输入 View 和输入附属 View 声明了两个属性:
@property (readonly, retain) UIView *inputView;
@property (readonly, retain) UIView *inputAccessoryView;"

但它在那里是只读的

---

所以检查类

    var xy:AnyObject!;

    if(xy.isKindOfClass(UITextField)) {
        var t = xy as UITextField;
        //...
    }
    else if(xy.isKindOfClass(UITextView)) {
        var t = xy as UITextView;
        //...
    }