为什么谓词在递归函数中调用时会误解参数的值 [英] Why is predicate misinterpreting parameters' values when called in recursive function

问题描述

我正在尝试创建一个继承自现有winform TreeView控件的扩展树视图控件。创建了一个  Load（） 在类TreeViewEx中运行
。在此函数中，dataSource在foreach中循环。这个foreach然后调用  Where（） 扩展名
循环dataSource上的方法传递给它一个方法（需要作为参数当前元素）返回谓词。该谓词错误地解释了传递给它的参数值。它似乎使用以前的参数值。

I'm trying to create a extended treeview control inheriting from the existing winform TreeView control. Created a Load() function in the class TreeViewEx. In this function the dataSource is looped in a foreach. This foreach then calls the Where() extension method on the looping dataSource passing to it a methode (which takes as parameter the current element) returning a predicate. This predicate misintepretes the parameter value passed to it. It seems to be using previous parameter values.

最初我认为这种行为是由于我正在迭代  Enumerable   not
a list，所以我将不同的枚举更改为List但没有任何改变。还试图实例化返回的谓词，但没有任何内容。

Initially i thought this behavior was due to the fact that i am iterating through an Enumerable not a list, so i change the different enumerables to List but nothing changed. Also tried to instatiate the returned predicate but nothing.

加载函数：

Load function :

public Func<T, Func<T, bool>> GetChildrenPredicate { get; set; }
.
.
.
public virtual void Load(List<T> dataSource = null)
{
    try
    {
        if (CreateNode == null)
        {
            OnError?.Invoke(this, new ArgumentNullException("CreateNode"));
            return;
        }
        if (GetParentKey == null)
        {
            OnError?.Invoke(this, new ArgumentNullException("GetParentKey"));
            return;
        }
        if (GetChildrenPredicate == null)
        {
            OnError?.Invoke(this, new ArgumentNullException("GetChildrenPredicate"));
            return;
        }

        var finalDataSource = dataSource ?? DataSource;

        TreeNode node = null;
        BeginUpdate();
        foreach (var item in finalDataSource)
        {
            node = CreateNode(item);
            node.Tag = item;

            if (this.Nodes.Find(node.Name, true).Count() == 0)
            {
                var n = this.Nodes.Find(this.GetParentKey(item), true).FirstOrDefault() as TreeNode;

                if (n == null)
                {
                    this.Nodes.Add(node);
                }
                else
                {
                    n.Nodes.Add(node);
                }

                List<T> children = finalDataSource
                                  .ToList()                                   
                                  .Where(this.GetChildrenPredicate(item))
                                  .ToList(); //this.GetChildrenPredicate is
                                //the property func generating the 
                                //predicate set by a different class

                if (children.Count() > 0)
                {
                    // Recursively call this function for all childRows
                    Load(children);
                }

            }
        }
        EndUpdate();
    }
    catch (Exception ex)
    {
        OnError?.Invoke(this, ex);
    }
}

GetChildrenPredicate：

private Func<ORM.DataModels.Menu, bool> GetChildrenPredicate(ORM.DataModels.Menu arg)
{

    return (ORM.DataModels.Menu m) =>
    (m.Lepere == arg.Codmen) ||
    (m.Lepere == null && arg.Codmen == "_" + m.Niveau);
}

推荐答案

好的。我找到了解决方案。其实我没有意识到 每次调用`Load（）`时都会覆盖`finalDataSource`。我只专注于谓词的奇怪行为。只需使用类中定义的全局DataSource属性。

Ok. I found the solution. Actually i did not realized that  `finalDataSource` was overriden on each call of `Load()`. I was only focused on the weird behaviour of the predicate. just had to used the global DataSource property defined in the class.

List<T> children = this.DataSource.Where(this.GetChildrenPredicate(item)); //<= changed local variable finalDataSource to the defined property this.DataSource

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