[英]Javascript Variable Scope Issue - Error: TypeError: this.graphics is undefined
我知道這個問題已經死了,但是我還是不明白。 我已經閱讀了StackOverFlow自己的“ this”關鍵字說明(以及其中的Mike West文章)以及其他與范圍相關的問題。 我不知道為什么我不明白,所以我向更精明的JavaScript開發人員尋求幫助。
從代碼和注釋中,它應該是相當自我解釋的。 但是它正在查詢ESRI地圖服務,返回圖形並將其放置在地圖上。
但是問題出在showResults
函數中,我將其稱為this.graphics
,這是地圖的graphics屬性(圖形層)。 我知道它現在不在范圍內(花了更多時間弄清楚我想承認的時間),但是如何才能將其放回范圍內以便使用呢? 即使我已經對代碼進行了實質性的更改...
define([
"dojo/_base/declare",
"dojo/on",
"dijit/_WidgetBase",
"dijit/_TemplatedMixin",
"dijit/_WidgetsInTemplateMixin",
"dijit/form/Button",
"dijit/form/Form",
"dijit/form/FilteringSelect",
"dijit/form/ValidationTextBox",
"dojo/_base/array",
"dojo/_base/Color",
"dojo/_base/lang",
"esri/tasks/find",
"dojo/text!./Find/templates/Find.html"
], function(declare, on, _WidgetBase, _TemplatedMixin, _WidgetsInTemplateMixin, Button, Form, FilteringSelect, ValidationTextBox, array, Color, lang, find, FindTemplate) {
//anonymous function to load CSS files required for this module
(function() {
var css = [require.toUrl("gis/dijit/Find/css/Find.css")];
var head = document.getElementsByTagName("head").item(0),
link;
for(var i = 0, il = css.length; i < il; i++) {
link = document.createElement("link");
link.type = "text/css";
link.rel = "stylesheet";
link.href = css[i].toString();
head.appendChild(link);
}
}());
// Query Dijit
return declare([_WidgetBase, _TemplatedMixin, _WidgetsInTemplateMixin], {
widgetsInTemplate: true,
templateString: FindTemplate,
graphics: null,
findTask: null,
findParams: null,
results: [],
serverError: null,
queryLayer: null,
searchText: null,
postCreate: function() {
// Method is used to call a superclass method. It's good practice to assume that you are overriding a method that may
// do something important in a class up the inheritance chain
this.inherited(arguments);
// Create graphics layer and add it to the map
this.graphics = new esri.layers.GraphicsLayer({id:"queryGraphics"});
this.map.addLayer(this.graphics);
// Create find task with url to map service
this.findTask = new esri.tasks.FindTask("arcgis/rest/services/MapServer");
// Create find parameters and define known values
this.findParams = new esri.tasks.FindParameters();
this.findParams.outSpatialReference = this.map.spatialReference;
this.findParams.returnGeometry = true;
this.findParams.layerIds = [1];
this.findParams.searchFields = ["OBJECTID", "Gauge ID", "FV_ID", "FDC_ID", "Flood_Stage", "Flood_Line", "Municipality", "WATERSHED"];
// Listen for Submit button click
on(this.submitButton, 'click', lang.hitch(this, 'execute'));
},
// Submit button click event
execute: function execute() {
// Set the WHERE search text
this.findParams.searchText = dojo.byId("searchText").value;
// Sends a request to the ArcGIS REST map service resource to perform a search based
// on the FindParameters specified in the findParameters argument. On completion, the
// onComplete event is fired and the optional callback function is invoked.
this.findTask.execute(this.findParams, this.showResults, this.showError);
},
// Fires when the find operation is complete and returns an array of FindResult
showResults: function showResults(results) {
this.graphics.clear();
// Build an array of attribute information and add each found graphic to the map
dojo.forEach(results, function(result) {
var symbol;
switch(result.feature.geometry.type) {
case "point":
symbol = new esri.symbol.SimpleMarkerSymbol(esri.symbol.SimpleMarkerSymbol.STYLE_CIRCLE, 10, new esri.symbol.SimpleLineSymbol(esri.symbol.SimpleLineSymbol.STYLE_SOLID, new Color([255, 0, 0]), 1), new Color([255, 0, 0, 1.0]));
break;
case "polyline":
symbol = new esri.symbol.SimpleLineSymbol(esri.symbol.SimpleLineSymbol.STYLE_DASH, new Color([255, 0, 0]), 1);
break;
case "polygon":
symbol = new esri.symbol.SimpleFillSymbol(esri.symbol.SimpleFillSymbol.STYLE_SOLID, new esri.symbol.SimpleLineSymbol(esri.symbol.SimpleLineSymbol.STYLE_DASHDOT, new Color([255, 0, 0]), 2), new Color([255, 255, 0, 0.0]));
break;
default:
symbol = new esri.symbol.SimpleMarkerSymbol(esri.symbol.SimpleMarkerSymbol.STYLE_CIRCLE, 10, new esri.symbol.SimpleLineSymbol(esri.symbol.SimpleLineSymbol.STYLE_SOLID, new Color([255, 0, 0]), 1), new Color([255, 0, 0, 1.0]));
}
var graphic = new esri.Graphic(result.feature.geometry, symbol);
this.graphics.add(graphic);
});
},
// Fires if the find execution fails to complete
showError: function showError(serverError) {
alert("The server encountered an error. Error: " + serverError);
}
});
});
回答后更新:
因此,解決這個問題的不是一個答案,而是兩個答案的結合。 我結合了布法羅的答案
this.findTask.execute(this.findParams, lang.hitch(this, this.showResults), this.showError);
布法羅評論克雷格的回答
dojo.forEach(results, function(result) {
...
}, this);
但克雷格(Craig's)也會在這里工作。 我敢肯定,這與泰米爾人的回答相結合也是可以的。
因此,我將Buffalo標記為答案,但所有這三者對於任何進一步的讀者都是值得關注的。
您可以使用Function.bind (請注意,並非所有瀏覽器都支持它)。
更改:
this.findTask.execute(this.findParams, this.showResults, this.showError);
至:
this.findTask.execute(this.findParams, this.showResults.bind(this), this.showError);
或(如果您擔心Function.bind
瀏覽器支持):
使用closure
和Function.apply
execute: function execute() {
...
...
var self = this;
this.findTask.execute(this.findParams, function() {
self.showResults.apply(self, arguments);
}, this.showError);
}
dojo/_base/lang
的hitch
方法將是您最好的朋友。 我假設findTask
函數所做的是執行一些異步請求,然后使用結果調用第二個參數。
首先,將dojo/_base/lang
添加到您的“依賴關系”列表中。
然后,換行
this.findTask.execute(this.findParams, this.showResults, this.showError);
至
this.findTask.execute(this.findParams, lang.hitch(this,this.showResults), this.showError);
lang#hitch所做的是獲取第一個參數(在本例中為小部件的實例),並使其成為執行第二個參數時的作用域。 在這種情況下,我們希望showResults在當前范圍內執行。
您的問題是以下代碼
dojo.forEach(results, function(result) {
...
this.graphics.add(graphic);
});
執行的函數沒有小部件的范圍。 做了:
dojo.forEach(results, lang.hitch(this, function(result) {
}));
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