javascript - 空 Asp.Net 控件导致 Javascript 对象引用未设置为渲染时对象的实例

Question

总而言之，此代码将 Jquery 自动完成添加到位于 UpdatePanel 内部的 Asp.Net Formview 内的文本框。

除非 InsuranceInsertItemTextBox 为空(当 Formview 处于只读模式时总是出现这种情况)，否则以下代码可以正常工作。我尝试使用 if 语句在控件为空时终止该函数，但这不起作用。如果 Formview 模式设置为只读，我还尝试终止该语句，但这也不起作用。关于处理此错误有什么建议吗？仅供引用:第 33 行(在堆栈跟踪中标识)是 InitAutoCompl 函数内部的 if 语句。如果我删除 if 语句，错误将转到下一行。

        $(document).ready(function () {
            var prm = Sys.WebForms.PageRequestManager.getInstance();
            prm.add_initializeRequest(InitializeRequest);
            prm.add_endRequest(EndRequest);
             InitAutoCompl();  
        });

        function InitializeRequest(sender, args) {
        }

        function EndRequest(sender, args) {                
            InitAutoCompl();
        }    function InitAutoCompl(freeInput) {

                if (!document.getElementById('<%= CaseInformationFormView.FindControl("InsuranceInsertItemTextBox").ClientID %>'))return;
                $('#<%= CaseInformationFormView.FindControl("InsuranceInsertItemTextBox").ClientID %>').autocomplete({
                    source: function(request, response) {
                        $.ajax({
                            url: '<%= Page.ResolveUrl("PacketsForUpload.aspx/GetInsuranceCompanies") %>',
                            data: "{ 'prefix': '" + request.term + "'}",
                            dataType: "json",
                            type: "POST",
                            contentType: "application/json; charset=utf-8",
                            messages: {
                                noResults: '',
                                results: function() {}
                            },
                            success: function(data) {
                                response($.map(data.d, function(item) {
                                    return {
                                        label: item.split("-")[0],
                                        val: item.split("-")[1]
                                    };
                                }));
                            },
                            error: function(response) {
                                alert(response.responseText);
                            },
                            failure: function(response) {
                                alert(response.responseText);
                            }
                        });
                    },
                    change: function(e, ui) {
                        if (!(freeInput || ui.item)) e.target.value = "";
                        Page_ClientValidate();
                    },
                    select: function(e, i) {
                        console.log("i.item", i.item);
                        Page_ClientValidate();
                    },
                    minLength: 3

                });
            };

堆栈跟踪:

[NullReferenceException: Object reference not set to an instance of an object.]
ASP.packetsforupload_aspx.__RenderPacketsHeadContent(HtmlTextWriter __w, Control parameterContainer) in :33
System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children) +268
System.Web.UI.Control.RenderChildren(HtmlTextWriter writer) +8
System.Web.UI.Control.Render(HtmlTextWriter writer) +10
System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter) +57
System.Web.UI.Control.RenderControl(HtmlTextWriter writer, ControlAdapter adapter) +100
System.Web.UI.Control.RenderControl(HtmlTextWriter writer) +25
System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children) +128
System.Web.UI.HtmlControls.HtmlHead.RenderChildren(HtmlTextWriter writer) +21
System.Web.UI.HtmlControls.HtmlContainerControl.Render(HtmlTextWriter writer) +32
System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter) +57
System.Web.UI.Control.RenderControl(HtmlTextWriter writer, ControlAdapter adapter) +100
System.Web.UI.Control.RenderControl(HtmlTextWriter writer) +25
System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children) +128
System.Web.UI.Control.RenderChildren(HtmlTextWriter writer) +8
System.Web.UI.Control.Render(HtmlTextWriter writer) +10
System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter) +57
System.Web.UI.Control.RenderControl(HtmlTextWriter writer, ControlAdapter adapter) +100
System.Web.UI.Control.RenderControl(HtmlTextWriter writer) +25
System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children) +128
System.Web.UI.Control.RenderChildren(HtmlTextWriter writer) +8
System.Web.UI.Page.Render(HtmlTextWriter writer) +29
System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter) +57
System.Web.UI.Control.RenderControl(HtmlTextWriter writer, ControlAdapter adapter) +100
System.Web.UI.Control.RenderControl(HtmlTextWriter writer) +25
System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +1386

编辑:此外，我刚刚发现 return 不会破坏该函数。我通过删除 if 语句并仅在其中放置一个 return 来对此进行测试。错误仍然发生。

Answer 1

如果控件“InsuranceInsertItemTextBox”不是 CaseInformationFormView 的子控件，则 CaseInformationFormView.FindControl("InsuranceInsertItemTextBox") 为 null，并且调用属性 ClientID 将生成 NRE。

您可以通过在获取 ClientID 之前检查控件是否可用来防止这种情况:

function InitAutoCompl(freeInput) {
      $('#<%= CaseInformationFormView.FindControl("InsuranceInsertItemTextBox") != null ?CaseInformationFormView.FindControl("InsuranceInsertItemTextBox").ClientID :  "" %>').autocomplete({
        source: function (request, response) {
          $.ajax({
            url: '<%= Page.ResolveUrl("PacketsForUpload.aspx/GetInsuranceCompanies") %>',
            data: "{ 'prefix': '" + request.term + "'}",
            dataType: "json",
            type: "POST",
            contentType: "application/json; charset=utf-8",
            messages: {
              noResults: '',
              results: function () { }
            },
            success: function (data) {
              response($.map(data.d, function (item) {
                return {
                  label: item.split("-")[0],
                  val: item.split("-")[1]
                };
              }));
            },
            error: function (response) {
              alert(response.responseText);
            },
            failure: function (response) {
              alert(response.responseText);
            }
          });
        },
        change: function (e, ui) {
          if (!(freeInput || ui.item)) e.target.value = "";
          Page_ClientValidate();
        },
        select: function (e, i) {
          console.log("i.item", i.item);
          Page_ClientValidate();
        },
        minLength: 3

      });
    };