Only data views can listen to data grids. To make a data grid 'listen' to the selection of another data grid, the data grid should be placed in a listening data view. The data grid in the listening data view can then be constrained by the current object with a xpath constraint.
Note that MX5 passing the parameters in a different way; the Boolean became real Booleans in widgets
before Mendix 5
if(this.boolpar = 'true') //do something
in the Mendix 5 widget
if(this.boolpar = true) //do something