foreach 语句不能对“object”类型的变量进行操作 [重复]

Question

我有 3 个下拉列表 2 具有相同的来源，第 3 个具有选定列表。如果选择的列表不为空，我应该从第一个中删除选择，并在第三个中绑定。第二个是显示原始列表的静态。

但我不知道如何在对象中进行 foreach。

错误：foreach 语句不能对“object”类型的变量进行操作 因为“对象”不包含公共定义 'GetEnumerator'

    public void DataSource(object source, object select, string Value = "UId", string Text = "Text")
    {
        ddlThis.DataSource = source;
        ddlThis.DataTextField = Text;
        ddlThis.DataValueField = Value;
        ddlThis.DataBind();

        ddlThisHidden.DataSource = source;
        ddlThisHidden.DataTextField = Text;
        ddlThisHidden.DataValueField = Value;
        ddlThisHidden.DataBind();

        if (select != null)
        {
            ddlOther.DataSource = select;
            ddlOther.DataTextField = Text;
            ddlOther.DataValueField = Value;
            ddlOther.DataBind();

            foreach (var item in ddlOther.DataSource)
                ddlThis.Items.Remove(item);
        }
    }

第 2 版

    public void DataSource(IList source, IList select, string Value = "UId", string Text = "Text")
    {
        ddlThis.DataSource = source;
        ddlThis.DataTextField = Text;
        ddlThis.DataValueField = Value;
        ddlThis.DataBind();

        ddlThisHidden.DataSource = source;
        ddlThisHidden.DataTextField = Text;
        ddlThisHidden.DataValueField = Value;
        ddlThisHidden.DataBind();

        if (select != null)
        {
            ddlOther.DataSource = source.Cast<object>()
                .Select(x => select.Cast<object>().Any(c=> c.GetType().GetProperty(Value).GetValue(source, null).ToString() == x.GetType().GetProperty(Value).GetValue(source, null).ToString()));
            ddlOther.DataTextField = Text;
            ddlOther.DataValueField = Value;
            ddlOther.DataBind();

            foreach (var item in select)
                ddlThis.Items.Remove(item.ToString());
        }
    }

版本 3 工作！

    public void DataSource(object source, object select, string Value = "UId", string Text = "Text")
    {
        ddlThis.DataSource = source;
        ddlThis.DataTextField = Text;
        ddlThis.DataValueField = Value;
        ddlThis.DataBind();

        ddlThisHidden.DataSource = source;
        ddlThisHidden.DataTextField = Text;
        ddlThisHidden.DataValueField = Value;
        ddlThisHidden.DataBind();

        if (select != null)
        {
            ddlOther.DataSource = ((IEnumerable)source).Cast<dynamic>().ToList().FindAll(x => ((IEnumerable)select).Cast<dynamic>()
                .Any(c => c.GetType().GetProperty(Value).GetValue(c, null) == x.GetType().GetProperty(Value).GetValue(x, null)));

            ddlOther.DataTextField = Text;
            ddlOther.DataValueField = Value;
            ddlOther.DataBind();

            foreach (var item in (dynamic)(ddlOther.DataSource))
                ddlThis.Items.Remove(item.ToString());
        }
    }

Answer 1

如果您不知道对象的确切类型，但您确定无论它是什么，它上面都会有GetEnumerator（比如说，因为它是一个集合或您自己的对象之一，它实现了IEnumerable ) 你可以通过转换为dynamic 来阻止编译器发出错误，如下所示：

foreach (var item in (dynamic)(ddlOther.DataSource)) {
    ...
}

这里的权衡是，如果事实证明 ddlOther.DataSource 没有 GetEnumerator，您将在运行时收到错误，而不是编译时错误。

Answer 2

修改您的代码以检查 IEnumerable 接口。它有一种感觉，潜在的修正是你想要的。

public void DataSource(object source, object select, string Value = "UId", string Text = "Text")
{
    ddlThis.DataSource = source;
    ddlThis.DataTextField = Text;
    ddlThis.DataValueField = Value;
    ddlThis.DataBind();

    ddlThisHidden.DataSource = source;
    ddlThisHidden.DataTextField = Text;
    ddlThisHidden.DataValueField = Value;
    ddlThisHidden.DataBind();

    if (select != null)
    {
        ddlOther.DataSource = select;
        ddlOther.DataTextField = Text;
        ddlOther.DataValueField = Value;
        ddlOther.DataBind();

        if (select is IEnumerable) //check if the object is a list of objects
            foreach (var item in (IEnumerable)ddlOther.DataSource)
                ddlThis.Items.Remove(item);
        else //try to remove the single object
            ddlThis.Items.Remove(select)
    }
}