I'm using a JS Charts library to draw graphs in a WebView of my Android Application. I want to provide the data from the SQLite database. At this moment I'm stuck on how to pass array of data from Java to JavaScript. The JavaScript part expects something like that:
data = new Array([10, 10], [20, 10]);
I know about the addJavaScriptInterface and I managed to pass single values from my Activity to a WebView. It's only the array that gives me trouble. I thought about something like that:
final class ChartDataLoader {
public double[][] getData() {
double[][] data = {{10, 10}, {20, 10}};
return data;
}
}
Note that for now I'm just hard-coding the data, but eventually this will be pulled out from a database. So then I expose this to my JS:
webView.addJavascriptInterface(new ChartDataLoader(), "dataLoader");
And finally try to read it in JavaScript:
<html>
<head>
<script type="text/javascript" src="jscharts.js"></script>
</head>
<body>
<div id="chartcontainer">You should see a chart here.</div>
<script type="text/javascript">
myData = dataLoader.getData();
alert("DataReceived: " + myData.length);
alert("Element 0 : " + myData[0]);
var myChart = new JSChart('chartcontainer', 'line');
myChart.setDataArray(myData);
myChart.draw();
</script>
</body>
</html>
JavaScript fails on those two alert statements stating:
ERROR/Web Console(2455): Uncaught TypeError: Cannot read property 'length' of undefined at file:///android_asset/chart.html:15
Any hints? I saw some code online where other people convert arrays to a String and then recreate it back in JavaScript but that seems like an overkill to me and I was hoping for a better solution. An alternative is to pass an XML file to the chart library, but again, I thought it would be slow to create a new XML every time a user wants to see a graph.
I'm using a JS Charts library to draw graphs in a WebView of my Android Application. I want to provide the data from the SQLite database. At this moment I'm stuck on how to pass array of data from Java to JavaScript. The JavaScript part expects something like that:
data = new Array([10, 10], [20, 10]);
I know about the addJavaScriptInterface and I managed to pass single values from my Activity to a WebView. It's only the array that gives me trouble. I thought about something like that:
final class ChartDataLoader {
public double[][] getData() {
double[][] data = {{10, 10}, {20, 10}};
return data;
}
}
Note that for now I'm just hard-coding the data, but eventually this will be pulled out from a database. So then I expose this to my JS:
webView.addJavascriptInterface(new ChartDataLoader(), "dataLoader");
And finally try to read it in JavaScript:
<html>
<head>
<script type="text/javascript" src="jscharts.js"></script>
</head>
<body>
<div id="chartcontainer">You should see a chart here.</div>
<script type="text/javascript">
myData = dataLoader.getData();
alert("DataReceived: " + myData.length);
alert("Element 0 : " + myData[0]);
var myChart = new JSChart('chartcontainer', 'line');
myChart.setDataArray(myData);
myChart.draw();
</script>
</body>
</html>
JavaScript fails on those two alert statements stating:
ERROR/Web Console(2455): Uncaught TypeError: Cannot read property 'length' of undefined at file:///android_asset/chart.html:15
Any hints? I saw some code online where other people convert arrays to a String and then recreate it back in JavaScript but that seems like an overkill to me and I was hoping for a better solution. An alternative is to pass an XML file to the chart library, but again, I thought it would be slow to create a new XML every time a user wants to see a graph.
Share Improve this question edited Mar 23, 2016 at 8:30 Artem Mostyaev 3,91810 gold badges56 silver badges65 bronze badges asked Dec 2, 2010 at 2:03 MarkMark 411 silver badge3 bronze badges 1- well, yes ... I think you will have to parse the string and recreate the array in JS. But, I do not see, why that would be such a problem? – LambergaR Commented Dec 2, 2010 at 2:27
2 Answers
Reset to default 5Remove the line: alert("DataReceived: " + myData.length);
To fix the most recent error you need to define myData as a var.
What you talk about at the end of your question (converting arrays to string) is JSON. Any context switch is expensive (e.g. Android to web). The serialisation/de-serialisation probably won't slow you down too much.