foreach语句不能对'object'类型的变量进行操作

Question

我有3个具有相同来源的下拉列表2,第3个具有所选列表.如果选中的列表不为null,我应该从第一个中删除选定项,并在第三个中绑定.第二个是静态的,显示原始列表.

但我无法弄清楚如何在一个物体中前进.

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

    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);
        }
    }

版本2

    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,但是您确定无论它是什么,它都会GetEnumerator在它上面(例如,因为它是一个集合或您自己的一个对象实现IEnumerable),您可以阻止编译器发出通过强制转换为错误dynamic,如下所示:

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

这里的交易是,如果事实证明ddlOther.DataSource没有GetEnumerator,你将在运行时得到一个错误,而不是编译时错误.