c# - Web 部件中的 NullReferenceException

Question

我创建了一个 web 部件，有五种配置:在 usercontrol.ascx 中，我通过以下代码获取值:

namespace tasks_email.tasks_email_webpart
{
    public partial class tasks_email_webpartUserControl : UserControl
    {

        public tasks_email_webpart WebPart { get; set; }

        protected void Page_Load(object sender, EventArgs e)
        {
        }
 protected void btn_send_id_Click(object sender, EventArgs e)
        {

            string subject = " ";
            subject = this.WebPart.SUBJECT as string;
            string emailAddrS = " ";
            emailAddrS = this.WebPart.EMAILADDR as string;
            string checkout_changes = " ";
            checkout_changes = this.WebPart.CHECKOUTLISTSNAMES as string;
            SendCheckout("bo.wang@us.bnpparibas.com", subject, "this is a project test");

但是当我点击按钮时，它说:空引用异常，无论我编辑配置什么东西，变量都无法获取 SUBJECT 值

任何人都可以告诉我如何处理吗？

*我检查了 webpart.cs，我确实是这样写的:

    namespace tasks_email.tasks_email_webpart
{
    [ToolboxItemAttribute(false)]
    public class tasks_email_webpart : Microsoft.SharePoint.WebPartPages.WebPart
    {

        [WebBrowsable(true), Category("Configurations"), Personalizable(PersonalizationScope.Shared), WebDisplayName("Subject")]
        public string SUBJECT { get; set; }

在 ascx 中，我使用以下方法创建了一个按钮:

<asp:Button ID="btn_send_id" runat="server" Text=" Email_changes " 
onclick="btn_send_id_Click" CssClass="Search_Submit" onclientclick="return checkna()" 
    />

错误报告:

[NullReferenceException: Object reference not set to an instance of an object.]
   tasks_email.tasks_email_webpart.tasks_email_webpartUserControl.btn_send_id_Click(Object sender, EventArgs e) +375
   System.Web.UI.WebControls.Button.OnClick(EventArgs e) +114
   System.Web.UI.WebControls.Button.RaisePostBackEvent(String eventArgument) +139
   System.Web.UI.Page.RaisePostBackEvent(IPostBackEventHandler sourceControl, String eventArgument) +28
   System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +2980

Answer 1

当您开发 SP2010 可视化 Web 部件时，您应该始终从 Microsoft.SharePoint.WebPartPages.WebPart 继承，因此您的部件看起来像这样:

[ToolboxItemAttribute(false)]
public class MyWebPart : Microsoft.SharePoint.WebPartPages.WebPart
{

    [Personalizable(), WebBrowsable, Category("GPWF Settings")]
    public string WebClientUrl { get; set; }

}

因为您是从 UserControl 继承的，所以您总是获得对属性的空引用。

所以如果你不先设置你的 Prop ，你应该像这样修改你的代码:

    string subject = this.WebPart.SUBJECT as string;
    string emailAddrS = this.WebPart.EMAILADDR as string;
    string checkout_changes = this.WebPart.CHECKOUTLISTSNAMES as string;