How do I dynamically generate columns in a WPF DataGrid?

user_155537 0
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I am attempting to display the results of a query in a WPF datagrid. The ItemsSource type I am binding to is IEnumerable<dynamic>. As the fields returned are not determined until runtime I don't know the type of the data until the query is evaluated. Each "row" is returned as an ExpandoObject with dynamic properties representing the fields.

It was my hope that AutoGenerateColumns (like below) would be able to generate columns from an ExpandoObject like it does with a static type but it does not appear to.

<DataGrid AutoGenerateColumns="True" ItemsSource="{Binding Results}"/>

Is there anyway to do this declaratively or do I have to hook in imperatively with some C#?

EDIT

Ok this will get me the correct columns:

// ExpandoObject implements IDictionary<string,object> 
IEnumerable<IDictionary<string, object>> rows = dataGrid1.ItemsSource.OfType<IDictionary<string, object>>();
IEnumerable<string> columns = rows.SelectMany(d => d.Keys).Distinct(StringComparer.OrdinalIgnoreCase);
foreach (string s in columns)
    dataGrid1.Columns.Add(new DataGridTextColumn { Header = s });

So now just need to figure out how to bind the columns to the IDictionary values.

expandoobject dynamic datagrid wpf
4 Answers

Ultimately I needed to do two things:

  1. Generate the columns manually from the list of properties returned by the query
  2. Set up a DataBinding object

After that the built-in data binding kicked in and worked fine and didn't seem to have any issue getting the property values out of the ExpandoObject.

<DataGrid AutoGenerateColumns="False" ItemsSource="{Binding Results}" />

and

// Since there is no guarantee that all the ExpandoObjects have the 
// same set of properties, get the complete list of distinct property names
// - this represents the list of columns
var rows = dataGrid1.ItemsSource.OfType<IDictionary<string, object>>();
var columns = rows.SelectMany(d => d.Keys).Distinct(StringComparer.OrdinalIgnoreCase);

foreach (string text in columns)
{
    // now set up a column and binding for each property
    var column = new DataGridTextColumn 
    {
        Header = text,
        Binding = new Binding(text)
    };

    dataGrid1.Columns.Add(column);
}
user_1555370

The problem here is that the clr will create columns for the ExpandoObject itself - but there is no guarantee that a group of ExpandoObjects share the same properties between each other, no rule for the engine to know which columns need to be created.

Perhaps something like Linq anonymous types would work better for you. I don't know what kind of a datagrid you are using, but binding should should be identical for all of them. Here is a simple example for the telerik datagrid.
link to telerik forums

This isn't actually truly dynamic, the types need to be known at compile time - but this is an easy way of setting something like this at runtime.

If you truly have no idea what kind of fields you will be displaying the problem gets a little more hairy. Possible solutions are:

With dynamic linq you can create anonymous types using a string at runtime - which you can assemble from the results of your query. Example usage from the second link:

var orders = db.Orders.Where("OrderDate > @0", DateTime.Now.AddDays(-30)).Select("new(OrderID, OrderDate)");

In any case, the basic idea is to somehow set the itemgrid to a collection of objects whose shared public properties can be found by reflection.

user_1758230

my answer from Dynamic column binding in Xaml

I've used an approach that follows the pattern of this pseudocode

columns = New DynamicTypeColumnList()
columns.Add(New DynamicTypeColumn("Name", GetType(String)))
dynamicType = DynamicTypeHelper.GetDynamicType(columns)

DynamicTypeHelper.GetDynamicType() generates a type with simple properties. See this post for the details on how to generate such a type

Then to actually use the type, do something like this

Dim rows as List(Of DynamicItem)
Dim row As DynamicItem = CType(Activator.CreateInstance(dynamicType), DynamicItem)
row("Name") = "Foo"
rows.Add(row)
dataGrid.DataContext = rows
user_559480
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