dojo声明构造函数：对象成员引用未定义

Question

我不知道为什么会遇到麻烦，在下面的代码的checkAcceptance方法中引用类成员对象this.treeStore ？

代码段（ 链接到正在运行的jsfiddle示例... ）：

dojo.declare("at.delta.util.FolderConfigurator", null, {
    treeStore: null,
    treeModel: null,
    tree: null,

    constructor: function (/*string*/ jsonData) {
        this.treeStore = new dojo.data.ItemFileWriteStore({
        data: jsonData
        });
        this.treeModel = new dijit.tree.ForestStoreModel({
           store: this.treeStore // this.treeStore available, perfect no problems
        });  
        this.tree = new dijit.Tree({
           model: this.treeModel,
           showRoot: false,
           betweenThreshold: 5,
           dndController: "dijit.tree.dndSource",
           checkAcceptance: function ( /*Object*/ source, /*Array*/ nodes) {
               // Here comes the code for drag acceptance
               var currentNode = dijit.getEnclosingWidget(nodes[0]).item;
               var parentNode = this.treeStore.getValue(currentNode, 'parent'); // typeError: this.treeStore is undefined
               return (parentNode && parentNode.owners !== undefined);
        }
    }, "pnlTree");
  }

});

尝试拖动树的节点会在firefox / firebug控制台上导致以下错误：

TypeError：this.treeStore未定义

任何帮助将不胜感激 ：）

Answer 1

问题在于，checkAcceptance函数内的this关键字的作用域为dijit.Tree小部件，而不是您自己的小部件。 只需添加一个var self = this; 在构造函数范围级别的某个位置，然后在超出范围时使用self而不是this进行引用。

Answer 2

这是因为您的这是指this.tree而不是主要对象。 用这个 -

dojo.declare("at.delta.util.FolderConfigurator", null, {
    treeStore: null,
    treeModel: null,
    tree: null,

    constructor: function (/*string*/ jsonData) {
        var _this = this;
        this.treeStore = new dojo.data.ItemFileWriteStore({
        data: jsonData
        });
        this.treeModel = new dijit.tree.ForestStoreModel({
           store: _this.treeStore // this.treeStore available, perfect no problems
        });  
        this.tree = new dijit.Tree({
           model: _this.treeModel,
           showRoot: false,
           betweenThreshold: 5,
           dndController: "dijit.tree.dndSource",
           checkAcceptance: function ( /*Object*/ source, /*Array*/ nodes) {
               // Here comes the code for drag acceptance
               var currentNode = dijit.getEnclosingWidget(nodes[0]).item;
               var parentNode = _this.treeStore.getValue(currentNode, 'parent'); // typeError: this.treeStore is undefined
               return (parentNode && parentNode.owners !== undefined);
        }
    }, "pnlTree");
  }

});