MPAndroidChart - How can I best set the X-axis values as strings/dates?

Question

I'm just a bit lost with this MPAndroid chart library .

I began the beginner example here , which recommends creating an array/list of objects with getValueX() and getValueY() methods, which you would then add as entries, like this:

List<Entry> entries = new ArrayList<Entry>(); // entry list    

for(ValueAndDateObject data : valueAndDateArrayList){ 

    // valueAndDateArrayList is the list of my own data 
    //(objects with a String X-value, and a double Y-value)

    entries.add(new Entry(data.getValueX(), data.getValueY())); //error here
 }

There's an error there because Entry only takes (float x, float y). Obviously I can cast the double as a float, but I need the x-axis to have dates not floats. So I did some more searching and found a lot of Github issues about it, but the solutions there I can't seem to understand. Most point to something like this in the docs . The problem I'm having is I don't understand how this gets applied to the Entry(float x, float y) issue. I can't find when/where the docs/solutions say to apply to Entry().

So when I look at the example about creating the formatter and then setting it, I don't get where the entries.add(new Entry()) stuff comes in. Does that technique replace it? Do I somehow pass it in?

For reference, here's my full method, designed after the beginner example mentioned previously.

public void updateUI(final ArrayList<ValueAndDateObject> valueAndDateArrayList){
    List<Entry> entries = new ArrayList<Entry>();



    for(ValueAndDateObject data : valueAndDateArrayList){

    /** for the sake of the example, let's say there's only one 
    *   ValueAndDataObject in the list and getValueX() returns "02-27-2016"
    *   and getValueY() returns 12,345.0
    */

        entries.add(new Entry(data.getValueX(), data.getValueY())); //error obviously 
    }        

    // would I add the formatter somewhere in here? And what would I "add" it to?

    LineDataSet dataSet = new LineDataSet(entries, "Label");
    dataSet.setColor(Color.YELLOW);
    dataSet.setValueTextColor(Color.BLACK);

    LineData lineData = new LineData(dataSet);
    lineChart.setData(lineData);
    lineChart.invalidate();
}

From what I can tell, I'll have to make my own formatter class, which I'll model off of the string[] example in the formatter doc link. My hang up is on the "Setting the formatter" section. Just not sure about how that will change/interact with the Entry(float x, float y) issue.

Answer 1

You simply need to treat your Date as a timestamp when creating the Entry object, eg:

entries.add(new Entry(new Long(data.getDate().getTime()).floatValue(), new Double(data.getValueY()).floatValue()));

In the above, we assume that data.getDate() returns a java.util.Date and that data.getValueY() returns a double .

Then all you have to do in your IAxisValueFormatter is to convert the timestamp representation back to a Date and then into something human readable, like so:

public class DateValueFormatter implements IAxisValueFormatter {

    @Override
    public String getFormattedValue(float value, AxisBase axis) {
        // Simple version. You should use a DateFormatter to specify how you want to textually represent your date.
        return new Date(new Float(value).longValue()).toString();
    }
    // ...
}

UPDATE:

Setting the value formatter:

XAxis xAxis = chart.getXAxis();
xAxis.setValueFormatter(new DateValueFormatter());

UPDATE:

User 'Yasir-Ghunaim' provides a very good step-by-step guide as a response in this thread on github .