Load Data On Demand
In this demo, the chart loads data as you pan it. Once a data block is loaded, it stays in memory to reduce requests to the server.
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var DemoApp = angular.module('DemoApp', ['dx']);
var HALFDAY = 43200000;
var packetsLock = 0;
DemoApp.controller('DemoController', function DemoController($scope) {
var currentRange = {
startValue: new Date(2017, 3, 1),
length: {
weeks: 2
}
};
Object.defineProperty($scope, 'currentRange', {
get: function() {
return currentRange;
},
set: function(newRange) {
currentRange = newRange;
onVisualRangeChanged();
}
});
$scope.chartOptions = {
dataSource: new DevExpress.data.DataSource({
store: [],
sort: "date",
paginate: false
}),
title: "Temperature in Toronto (2017)",
zoomAndPan: {
argumentAxis: "pan"
},
scrollBar: {
visible: true
},
bindingOptions: {
"argumentAxis.visualRange": "currentRange"
},
argumentAxis: {
argumentType: "datetime",
wholeRange: [new Date(2017, 0, 1), new Date(2017, 11, 31)],
visualRangeUpdateMode: "keep"
},
valueAxis: {
name: "temperature",
allowDecimals: false,
title: {
text: "Temperature, °C",
font: {
color: "#ff950c"
}
},
label: {
font: {
color: "#ff950c"
}
}
},
series: [{
color: "#ff950c",
type: "rangeArea",
argumentField: "date",
rangeValue1Field: "minTemp",
rangeValue2Field: "maxTemp",
name: "Temperature range"
}],
animation: {
enabled: false
},
loadingIndicator: {
backgroundColor: "none",
font: {
size: 14
}
},
legend: {
visible: false
}
};
function onVisualRangeChanged() {
var component = $("#chart").dxChart("instance");
var items = component.getDataSource().items();
var visualRange = $scope.currentRange;
if(!items.length ||
items[0].date - visualRange.startValue >= HALFDAY ||
visualRange.endValue - items[items.length - 1].date >= HALFDAY) {
uploadDataByVisualRange(visualRange, component);
}
}
function uploadDataByVisualRange(visualRange, component) {
var dataSource = component.getDataSource();
var storage = dataSource.items();
var ajaxArgs = {
startVisible: getDateString(visualRange.startValue),
endVisible: getDateString(visualRange.endValue),
startBound: getDateString(storage.length ? storage[0].date : null),
endBound: getDateString(storage.length ?
storage[storage.length - 1].date : null)
};
if(ajaxArgs.startVisible !== ajaxArgs.startBound &&
ajaxArgs.endVisible !== ajaxArgs.endBound && !packetsLock) {
packetsLock++;
component.showLoadingIndicator();
getDataFrame(ajaxArgs)
.then(function(dataFrame) {
packetsLock--;
var componentStorage = dataSource.store();
dataFrame.forEach(function(item) {
componentStorage.insert(item);
});
dataSource.reload();
onVisualRangeChanged();
},
function(reason) {
packetsLock--;
dataSource.reload();
});
}
}
function getDataFrame(args) {
var deferred = $.Deferred();
$.ajax({
url: "https://js.devexpress.com/Demos/WidgetsGallery/data/temperatureData",
dataType: "json",
data: args,
success: function (result) {
deferred.resolve(result.map(function(i) {
return {
date: new Date(i.Date),
minTemp: i.MinTemp,
maxTemp: i.MaxTemp
};
}));
},
error: function () {
deferred.reject("Data Loading Error");
},
timeout: 2000
});
return deferred.promise();
}
function getDateString(dateTime) {
return dateTime ? dateTime.toLocaleDateString("en-US") : "";
}
});
<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml" >
<head>
<title>DevExtreme Demo</title>
<meta http-equiv="X-UA-Compatible" content="IE=edge" />
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<meta name="viewport" content="width=device-width, initial-scale=1.0, maximum-scale=1.0" />
<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.5.1/jquery.min.js"></script>
<script>window.jQuery || document.write(decodeURIComponent('%3Cscript src="js/jquery.min.js"%3E%3C/script%3E'))</script>
<link rel="stylesheet" type="text/css" href="https://cdn3.devexpress.com/jslib/21.1.6/css/dx.common.css" />
<link rel="stylesheet" type="text/css" href="https://cdn3.devexpress.com/jslib/21.1.6/css/dx.light.css" />
<script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.3.16/angular.min.js"></script>
<script>window.angular || document.write(decodeURIComponent('%3Cscript src="js/angular.min.js"%3E%3C/script%3E'))</script>
<script src="https://cdn3.devexpress.com/jslib/21.1.6/js/dx.all.js"></script>
<link rel="stylesheet" type="text/css" href="styles.css" />
<script src="index.js"></script>
</head>
<body class="dx-viewport">
<div class="demo-container" ng-app="DemoApp" ng-controller="DemoController">
<div id="chart" dx-chart="chartOptions"></div>
</div>
</body>
</html>
#chart {
height: 440px;
}