为什么我的NSRuleEditor不显示条件？

Question

我正在尝试使用NSRuleEditor来显示条件。如果我给它一个条件，它就会工作(创建一个静态标签)，但当我给它多个条件时，规则编辑器的每一行都是空的(除了add/remove按钮之外，没有添加任何子视图)。为什么会这样呢？我的代码如下。

struct RuleItem {

    var text: String

    var children: [RuleItem] = []

}

var ruleItems = [
    RuleItem(text: "hello"),
    RuleItem(text: "world", children: [
        RuleItem(text: "child 1"),
        RuleItem(text: "child 2")
    ])
]

// In class conforming to NSRuleEditorDelegate:

func ruleEditor(_ editor: NSRuleEditor, numberOfChildrenForCriterion criterion: Any?, with rowType: NSRuleEditor.RowType) -> Int {
    if let item = criterion as AnyObject as? RuleItem {
        return item.children.count
    } else {
        return ruleItems.count
    }
}

func ruleEditor(_ editor: NSRuleEditor, child index: Int, forCriterion criterion: Any?, with rowType: NSRuleEditor.RowType) -> Any {
    if let item = criterion as AnyObject as? RuleItem {
        return item.children[index]
    } else {
        return ruleItems[index]
    }
}

func ruleEditor(_ editor: NSRuleEditor, displayValueForCriterion criterion: Any, inRow row: Int) -> Any {
    (criterion as AnyObject as! RuleItem).text as NSString
}

Answer 1

我自己解决了这个问题(在几个令人沮丧的小时之后)。

问题是我们从Objective-C协议方法-ruleEditor:child:forCriterion:withRowType返回Swift结构的实例。这些被编译器自动转换为__SwiftValue (一个Objective-C类)的实例。这看起来很好，直到我们在NSRuleEditor.h的顶部阅读到以下内容

树中的每个节点都由一个“条件”表示，它可以是任何对象。当用户从弹出菜单中进行选择时，规则编辑器视图将向其委托查询所选标准的子标准。对条件的唯一限制是，isEqual应将两个条件视为相等:如果它们表示相同的节点，则不能认为它们表示不同的节点。

所以我们的问题似乎是，我们返回的__SwiftValue没有对isEqual:有意义的定义。如果我们使用Objective-C兼容的类而不是Swift结构，一切都会像预期的那样工作。

可以工作的代码：

class RuleItem: NSObject {
    
    init(text: String, children: [RuleItem] = []) {
        self.text = text
        self.children = children
    }
    
    var text: String
    
    var children: [RuleItem] = []
    
}

var ruleItems = [
    RuleItem(text: "hello"),
    RuleItem(text: "world", children: [
        RuleItem(text: "child 1"),
        RuleItem(text: "child 2")
    ])
]

// In class conforming to NSRuleEditorDelegate:

func ruleEditor(_ editor: NSRuleEditor, numberOfChildrenForCriterion criterion: Any?, with rowType: NSRuleEditor.RowType) -> Int {
    if criterion == nil {
        return ruleItems.count
    }
    return (criterion as! RuleItem).children.count
}

func ruleEditor(_ editor: NSRuleEditor, child index: Int, forCriterion criterion: Any?, with rowType: NSRuleEditor.RowType) -> Any {
    if criterion == nil {
        return ruleItems[index]
    }
    return (criterion as! RuleItem).children[index]
}

func ruleEditor(_ editor: NSRuleEditor, displayValueForCriterion criterion: Any, inRow row: Int) -> Any {
    (criterion as! RuleItem).text
}

顺便说一句，NSRuleEditor.h比实际的文档页面更有帮助；帮您自己一个忙，通读一遍。