c# - 递归引起的 StackOverflowException

Question

我目前正在编写一个程序来帮助编写 Lore。每个 Book 对象都可以是 parent 并有 child 。这意味着每个 child 都可以有 child 等进入无穷大。我正在研究可以使用递归解决此问题的 ToString() 方法，但我不断收到 StackOverflowException。

我知道这是什么意思，但我不确定如何修复它。我是 C# 的新手，但有很多 Java 经验，所以如果您知道我遗漏的技巧或其他内容，请告诉我!

所以我的问题是:如何避免 StackOverflow 异常？问题出在 GetAllChildren()

编辑:

运行测试后，我应该得到这样的结果:

Name: a
Children:
b
c
    d
e

使用来自@lc 的代码。我得到以下输出:

Name: a
Children: No Children   b
c
e
    b
c
e
    b
c
e

这是类:

class Book
{
    private String name;
    private Book[] children;
    private StringBuilder text;
    private Boolean isParent;

    public Book(String name, Book[] children, StringBuilder text, Boolean isParent)
    {
        this.name = name;
        this.children = children;
        this.text = text;
        this.isParent = isParent;
    }

    /**
     * Most likely all possible Constructors
     * */
    public Book(String name, Book[] children) : this(name, children, new StringBuilder("No Text"), true) { }
    public Book(String name, String text) : this(name, new Book[0], new StringBuilder(text), false) { }
    public Book(String name, StringBuilder text) : this(name, new Book[0], text, false) { }
    public Book(String name) : this(name, new Book[0], new StringBuilder("No Text"), false) { }
    public Book(Book[] children, String text) : this("Unnamed Book", children, new StringBuilder(text), true) { }
    public Book(Book[] children, StringBuilder text) : this("Unnamed Book", children, text, true) { }
    public Book(Book[] children) : this("Unnamed Book", children, new StringBuilder("No Text"), true) { }
    public Book(StringBuilder text) : this("Unnamed Book", new Book[0], text, false) { }
    public Book() : this("Unnamed Book", new Book[0], new StringBuilder("No Text"), false) { }

    public String Name
    {
        get { return name; }
        set { name = value; }
    }

    public Book[] Children
    {
        get { return children; }
        set { children = value; }
    }

    /**
     * Will Return the StringBuilder Object of this Text
     * */

    public StringBuilder Text
    {
        get { return text; }
        set { text = value; }
    }

    public Boolean IsParent
    {
        get { return isParent; }
        set { isParent = value; }
    }

    private void GetAllChildren(Book book, StringBuilder sb)
    {
        if (book.isParent)
        {
            GetAllChildren(book, sb);
        }
        else
        {
            sb.Append("\t");
            foreach (Book b in children)
            {
                sb.Append(b.Name + "\n");
            }
        }
    }

    public override String ToString()
    {
        StringBuilder sChildren = new StringBuilder("No Children");
        if (children.Length != 0)
        {
            GetAllChildren(this, sChildren);
        }

        return "Name: " + name + "\n" +
            "Children: " + sChildren.ToString();
    }
}

Answer 1

我想你的意思是:

if (book.isParent)
{
    foreach (var child in book.Children)
        GetAllChildren(child, sb);
}

否则，您只是用相同的参数 (book, sb) 一遍又一遍地调用 GetAllChildren 方法。

---

旁注 - 您仍然有一些问题，因为 GetAllChildren 中的停止条件正在遍历子级，而实际上它不应该(如果它不是父级，则它不应该有子级)。它应该返回它自己的名字。此外，每个 child 还应该在上面的 foreach 循环中附加自己的名字(或者实际上，每本书都应该附加自己的名字)。

旁注 2 - 所写的方法(进行了这些更改)实际上应该是静态的，因为它与任何给定的实例都不相关(这让我想到了下面的建议)。

---

建议 - 我会推荐类似下面的东西(未经测试，需要在格式上做一些工作):

//name changed to reflect what it really does
//also changed to be an instance method (we no longer pass in a Book)
//added listThisBooksName parameter to allow supressing the topmost book's output
private void AppendAllChildren(StringBuilder sb, int level = 0, 
    bool listThisBooksName = false)
{
    if (listThisBooksName)
    {
        //append ourself here

        //first indent however far we need to
        sb.Append(new String('\t', level));

        //now add our name
        sb.Append(this.Name);

        //and a newline (you can strip the last one later if you want)
        sb.Append('\n');
    }

    //forget the "isParent" property, just check if it has any children
    //we don't need Children.Any() because the foreach will just iterate 0 times
    //you might also consider using a List<Book> instead of an array for Children
    if (this.Children != null)
        foreach (var child in this.Children)
            child.AppendAllChildren(sb, level+1, true);
}