我在C＃中使用xx.Contains时出现错误信息

Question

我在ASP MVC Razor文件中尝试以下代码：

       var topic = ViewData["TopicID"];
        var mustBeReplaced = string.Empty;
        var topicValue = Model.Topic;
        var replaceResult = string.Empty;
        if (topic.Contains(topicValue)) {
            mustBeReplaced = "value=\"" + topicValue + "\"";
            replaceResult = mustBeReplaced + " selected=\"selected\"";
            topic = topic.Replace(mustBeReplaced, replaceResult);             
        }

但是我收到一条错误消息：

object'不包含'Contains'的定义和最佳扩展方法重载

Answer 1

var topic = ViewData["TopicID"];

返回对象。你需要转换为字符串。

Answer 2

试试这个

    var topic = (string)ViewData["TopicID"];
    var mustBeReplaced = string.Empty;
    var topicValue = "11111";
    var replaceResult = string.Empty;
    if (topic.Contains(topicValue))
    {
        mustBeReplaced = "value=\"" + topicValue + "\"";
        replaceResult = mustBeReplaced + " selected=\"selected\"";
        topic = topic.Replace(mustBeReplaced, replaceResult);
    }