Tables with Variable Numbers of Columns

Support for tables in Designer assumes you know in advance how many columns there will be in your table. Occasionally this will not be the case.  You might want a table that adapts to the number of columns that occur in your data.  In other words, you want a table with rows where a cell is represented by a repeating subform.  And while Designer doesn’t support creating such a table via the table UI, it is possible to create one using a bit of script

The technique involves leverages the fact that tables and rows are really just subforms with special attributes.  So when designing the form, we create:

• A subform to represent the table.  Make it a subform where content flows top-to-bottom.
• Inside the table subform create one or more row subforms.  Make the row subforms flow left-to-right.
• Inside each row subform, create combinations of fields, text and subforms that will be treated as columns.
• It’s best to make the cells growable in width and allow the layout engine to determine best fit.  If you want control over width, leave the columns growable and set the columnWidths attribute on the table subform (see script below)

And then to turn this into a table, add this initialization script to the table subform:

// mark this subform as a table
this.layout = "table";

/** 
 * if needed, we could explicitly set the column widths
 * If left alone, the columns will be auto-sized
 */
//this.columnWidths = "1in 2in 2in 2in 1in";
            

And then for each row in the table, add this initialization script:

// mark this subform as a row
this.layout = "row";
if (this.instanceIndex === 0) {
    // mark the first row as a header
    this.assist.role="TH";
} else {
    // mark each subsequent row as a regular table row
    this.assist.role="TR";
}

Note that setting the role attribute is very important for accessibility — it allows the screen reader to use the table header cells to describe the contents of the table body cells. Here is a sample form that implements this technique — along with sample data for previewing.