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Code Query Language (CQL) can be used to write all sorts of code convention. I’ve described some CQL range of usage, and as an illustration I also exposed some CQL rules dedicated to the .NET Framework usage.

We discovered a weird issue in our last NDepend version: to select programmatically a particular row in a Windows Form DataGridView you need to call the setter DataGridView.FirstDisplayedCell. However if the DataGridView height is too small and doesn’t let show any row, then an exception will be raised:

Exception.Type {System.InvalidOperationException}

Exception.Message {No room is available to display rows.}

Exception.StackTrace {

   at System.Windows.Forms.DataGridView.set_FirstDisplayedScrollingRowIndex(Int32 value)

   at System.Windows.Forms.DataGridView.set_FirstDisplayedCell(DataGridViewCell value)

…

IMHO this behavior is so counter-intuitive and prone to error that I would qualify it as a .NET Framework bug. But Microsoft is not willing to fix such behavior in the name of ascendant compatibility. The solution is then to capitalize on your own knowledge database. Typically we included the following CQL rule in our set of rules. It warns as soon as there is a method that doesn’t check the rows available height before setting FirstDisplayedCell.

// <Name>Check height space before setting FirstDisplayedCell of  a DataGridView</Name>

SELECT METHODS WHERE

  IsDirectlyUsing "System.Windows.Forms.DataGridView.set_FirstDisplayedCell(DataGridViewCell)" AND

  !(IsDirectlyUsing "System.Windows.Forms.Control.get_Height()" AND

    IsDirectlyUsing "System.Windows.Forms.DataGridView.get_ColumnHeadersHeight()")

/* The pattern implementation is:

   if ((rowToSelect.State & DataGridViewElementStates.Displayed) == 0) {

      if (this.Height - this.ColumnHeadersHeight > 0) {

         this.FirstDisplayedCell = rowToSelect.Cells[0];

      }

   }

*/

We immediately spotted 3 others risky areas in our code.