The CreateWnd method calls CreateParams to initialize the parameters it passes to CreateWindowHandle. Override CreateParams to customize the way a control creates its Windows representation. When overriding CreateParams, always call the inherited method first to set the default values, then make any desired adjustments. 

CreateParams fills in the parameter that is passed as the value of the Params parameter. This data structure holds information needed when telling Windows to create a window handle. The fields of a TCreateParams record become the parameters to a call to the CreateWindowEx API function. 

TWinControl implements CreateParams by setting all the fields of Params to generic base values. A number of the standard controls override CreateParams to change one or more of the default values in Params. 

CreateWindowHandle 

CreateWnd 

AddBiDiModeExStyle