如果尝试将组件呈现给找不到的dom元素（或找不到dom ID），则会出现该错误。请参阅下面的示例以重现错误，然后注解掉错误的renderTo并取消注解renderTo: Ext.getBody()以解决问题。
看这个FIDDLE

代码SNIPPET

Ext.onReady(function () {
    // Generic fields array to use in both store defs.
    var fields = [{
        name: 'id',
        type: 'string',
        mapping: 'id'
    }, {
        name: 'lab_name',
        type: 'string',
        mapping: 'lab_name'
    }, {
        name: 'lab_address1',
        type: 'string',
        mapping: 'lab_address1'
    }, {
        name: 'lab_address2',
        type: 'string',
        mapping: 'lab_address2'
    }, {
        name: 'lab_poskod',
        type: 'string',
        mapping: 'lab_poskod'
    }, {
        name: 'lab_bandar',
        type: 'string',
        mapping: 'lab_bandar'
    }, {
        name: 'lab_negeri',
        type: 'string',
        mapping: 'lab_negeri'
    }, {
        name: 'lab_tel',
        type: 'string',
        mapping: 'lab_tel'
    }, {
        name: 'lab_fax',
        type: 'string',
        mapping: 'lab_fax'
    }];

    // create the data store
    var gridStore = new Ext.data.JsonStore({
        fields: fields,
        autoLoad: true,
        url: '../industri/layouts/getLab.php'
    });

    // Column Model shortcut array
    var cols = [{
        id: 'name',
        header: "Id",
        width: 10,
        sortable: true,
        dataIndex: 'id'
    }, {
        id: 'name',
        header: "Laboratory Name",
        width: 200,
        sortable: true,
        dataIndex: 'lab_name'
    }, {
        id: 'name',
        header: "Laboratory Name",
        width: 200,
        sortable: true,
        dataIndex: 'lab_address1'
    }];
    // declare the source Grid
    var grid = new Ext.grid.GridPanel({
        ddGroup: 'gridDDGroup',
        store: gridStore,
        columns: cols,
        enableDragDrop: true,
        stripeRows: true,
        autoExpandColumn: 'name',
        width: 325,
        margins: '0 2 0 0',
        region: 'west',
        title: 'Data Grid',
        selModel: new Ext.grid.RowSelectionModel({
            singleSelect: true
        })
    });

    // Declare the text fields.  This could have been done inline, is easier to read
    // for folks learning :)
    var textField1 = new Ext.form.TextField({
        fieldLabel: 'Laboratory Name',
        name: 'lab_name'
    });

    // Setup the form panel
    var formPanel = new Ext.form.FormPanel({
        region: 'center',
        title: 'Generic Form Panel',
        bodyStyle: 'padding: 10px; background-color: #DFE8F6',
        labelWidth: 100,
        margins: '0 0 0 3',
        width: 325,
        items: [textField1]
    });

    var displayPanel = new Ext.Panel({
        width: 650,
        height: 300,
        layout: 'border',

        renderTo:Ext.getBody(),

        padding: 5,

        items: [
            grid,
            formPanel
        ],
        bbar: [
            '->', // Fill
            {
                text: 'Reset Example',
                handler: function () {
                    //refresh source grid
                    //gridStore.loadData();
                    formPanel.getForm().reset();
                }
            }
        ]

    });

    // used to add records to the destination stores
    var blankRecord = Ext.data.Record.create(fields);

    /****
     * Setup Drop Targets
   ***/

    // This will make sure we only drop to the view container
    var formPanelDropTargetEl = formPanel.body.dom;

    var formPanelDropTarget = new Ext.dd.DropTarget(formPanelDropTargetEl, {
        ddGroup: 'gridDDGroup',
        notifyEnter: function (ddSource, e, data) {

            //Add some flare to invite drop.
            formPanel.body.stopFx();
            formPanel.body.highlight();
        },
        notifyDrop: function (ddSource, e, data) {

            // Reference the record (single selection) for readability
            var selectedRecord = ddSource.dragData.selections[0];

            // Load the record into the form
            formPanel.getForm().loadRecord(selectedRecord);

            // Delete record from the grid.  not really required.
            ddSource.grid.store.remove(selectedRecord);

            return (true);
        }
    });

    var tabsNestedLayouts = {
        id: 'tabs-nested-layouts-panel',
        title: 'Industrial Effluent',
        bodyStyle: 'padding:15px;',
        layout: 'fit',
        items: {
            border: false,
            bodyStyle: 'padding:5px;',
            items: displayPanel
        }
    };
});

这意味着您希望具有dom属性的对象未定义。

• 编辑：*

此行生成错误：

formPanel.body.dom

这意味着未渲染formPanel，因为您正在尝试访问其body属性。此属性自以下日期起可用：Ext 4.1.3

我在执行验证的代码中看到了类似的错误。我所做的与直接访问DOM无关，但我仍然遇到类似的情况。上面的答案是不完整的，dom属性在3.x中的一些ui元素上可用。。。
在早期版本的Extjs（3.x）中，属性是mainBody。dom而不是body.dom
直接从3.4中网格的hasRows（）源：

var fc = this.**mainBody.dom**.firstChild;
return fc && fc.nodeType == 1 && fc.className != 'x-grid-empty';