Control from controller whether a javascript code at my asp view will be executed or not

Question

I am developing a system at ASP.NET MVC4. I have a code written at javascript, and which executes when the page starts, to display a graph about the performance of some students.

The code of the graph is the following

<script>
    window.onload = function () {
        var r = Raphael("holder"),
            txtattr = { font: "20px sans-serif" };

        var lines = r.linechart(30, 30, 600, 440,<%= Json.Encode(ViewBag.dates) %>,<%= Json.Encode(ViewBag.Grades)%>, {axisxstep : 6,nostroke: false, axis: "0 0 1 1", symbol: "circle", smooth: false }).hoverColumn(function () {
            this.tags = r.set();
            for (var i = 0, ii = this.y.length; i < ii; i++) {
                this.tags.push(r.tag(this.x, this.y[i], Number(this.values[i]).toFixed(5), 160, 10).insertBefore(this).attr([{ fill: "#fff" }, { fill: this.symbols[i].attr("fill") }]));
            }
        });
</script>

The data of the graph, come from the function of the controller DisplayGraph. The code of the controller is shown below.

public ActionResult DisplayGraph(String InputStudent = "IP11")
{
    var query = (from b in db.gradesPerStudent
                 where b.Student.Equals(InputStudent)
                 orderby b.Date
                 select b);

    ViewBag.ChartEmpty = "No";
    if (query.ToList().Count == 0)
    {
        ViewBag.ChartEmpty = "Yes";
        ViewBag.Title = "No results for Student " + InputStudent;
        ViewBag.dates = null;
        ViewBag.grades = null;
        DateTime aminDate = new DateTime();
        ViewBag.minDate = aminDate.Subtract(new DateTime(1970, 1, 1)).TotalMilliseconds;
        return View();
    }

    DateTime minDate = query.Min(y => y.Date);
    DateTime maxDate = query.Max(y => y.Date);
    var dates = query.Select(x => EntityFunctions.DiffDays(query.Min(y => y.Date), x.Date));
    var grades = query.Select(x => x.grades);
    var datestable = dates.ToArray();
    var gradestable = grades.ToArray();
    List<int?> dateslist = new List<int?>();
    List<double> gradeslist = new List<double>();
    double result = dates.Count() * 1.0 / 70.0;
    int pointStep = (int)Math.Ceiling(result);
    for (int i = 0; i < dates.Count(); i = i + pointStep)
    {
            dateslist.Add(datestable.ElementAt(i));
            gradeslist.Add(gradestable.ElementAt(i));
    }
    ViewBag.dates = dateslist;
    ViewBag.grades = gradeslist;

    ViewBag.minDate = minDate.Subtract(new DateTime(1970, 1, 1)).TotalMilliseconds;

    return View(query.ToList());

}

Now, at when the student is new at a school, I do not want to display a graph, but a message that the student is new, and there are no statistics yet for that student.

So my question is. How do I say from my controller when a javascript should be executed and when not?

Thanks a lot

@ekad Thanks a lot. this is a very nice idea. I think Tim has already updated his answer. — Jim Blum
– Jim Blum, Commented Feb 1, 2014 at 4:57

Tim M. · Accepted Answer · 2014-02-01 04:59:43Z

2

How do I say from my controller when a javascript should be executed and when not?

Via a view model. A view model should contain all the information needed to render the view, and the view should contain your script (or a link to it).

Try to minimize using ViewBag, and prefer strongly-typed models.

Model

public class MyViewModel {
    public bool ShowGraph { get; set; }

    public List<object> Data { get; set; }

    public List<int?> Dates { get; set; }

    public List<double> Grades { get; set; }
}

Controller

public ActionResult Index(){

    var model = new MyViewModel();
    model.ShowGraph = !IsStudentNew();

    // set your other properties here, instead of using the ViewBag

    return View( model );
}

View

@model MyViewModel

@if( Model.ShowGraph ){
    <script>
        // javascript to render graph goes here
    </script>
}else{
    <div>No statistics yet.</div>
}

edited Feb 1, 2014 at 4:59

answered Feb 1, 2014 at 4:36

Tim M.

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2 Comments

Jim Blum Over a year ago

This seems really nice. Thanks. I will try that now. But creating a model is the easiest way? Because my view is also connected with an other model already...

Tim M. Over a year ago

Creating a model is nearly always the correct approach. It looks like query.ToList() is your current model? You can set that value as a property of your new view model (e.g. the Data property).

Simon Whitehead · Accepted Answer · 2014-02-01 04:36:11Z

0

I would just have a GraphText property of your model. Display it over the top of the graph. If there's statistics, then leave this property empty. If there isn't.. give it a value:

public class YourModel {
    public IList<Statistic> StudentStatistics { get; set; }
    public string GraphText {
        get {
            return StudentStatistics.Any() ? "" : "No statistics yet";
        }
    }
}

Then in your view, just render the GraphText property over the top of the graph.

answered Feb 1, 2014 at 4:36

Simon Whitehead

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