TDataMember Class Reference

TDataMember provides information about name of data member, its type, and comment field string. It also tries to find the TMethodCall objects responsible for getting/setting a value of it, and gives you pointers to these methods. This gives you a unique possibility to access protected and private (!) data members if only methods for doing that are defined. These methods could either be specified in a comment field, or found out automatically by ROOT: here's an example: suppose you have a class definition: class MyClass{ private:
TDataMember Class Reference
All ROOT classes may have RTTI (run time type identification) support added. The data is stored in so called DICTIONARY (look at TDictionary). Information about a class is stored in TClass. This information may be obtained via the cling api - see class TCling. TClass has a list of TDataMemberobjects providing information about all data members of described class.
As mentioned above - this information are mainly used by contextmenu, but also in Dump() and Inspect() methods and by the THtml class.
Definition at line 33 of file TDataMember.h.
This trick is widely used in ROOT TContextMenu and dialogs for obtaining current values and put them as initial values in dialog fields.
If you don't want to follow the convention of naming used by ROOT you still could benefit from Getter/Setter method support: the solution is to instruct ROOT what the names of these routines are. The way to do it is putting this information in a comment string to a data field in your class declaration:
IntegerValue = "Text Label" EnumValue = "Text Label" "TextValue" = Text Label"
One can specify values as Integers or Enums - when data field is an Integer, Float or Enum type; as texts - for char (more precisely: Option_t).
Float_t fX1; ... public: void SetX1(Float_t x) {fX1 = x;}; Float_t GetX1() {return fX1;}; ... }
Look at the data member name and method names: a data member name has a prefix letter (f) and has a base name X1 . The methods for getting and setting this value have names which consist of string Get/Set and the same base name. This convention of naming data fields and methods which access them allows TDataMember find this methods by itself completely automatically. To make this description conames that are automatically recognized may be also: for data fields: either fXXX or fIsXXX; and for getter function GetXXX() or IsXXX() [where XXX is base name].
As an example of using it let's analyse a few lines which get and set a fEditable field in TCanvas:
TCanvas *c = new TCanvas("c"); // create a canvas TClass *cl = c->IsA(); // get its class description object. TDataMember *dm = cl->GetDataMember("fEditable"); //This is our data member TMethodCall *getter = dm->GetterMethod(c); //find a method that gets value! Long_t l; // declare a storage for this value; getter->Execute(c,"",l); // Get this Value !!!! It will appear in l !!! TMethodCall *setter = dm->SetterMethod(c); setter->Execute(c,"0",); // Set Value 0 !!!
class MyClass{ Int_t mydata; // *OPTIONS={GetMethod="Get";SetMethod="Set"} ... Int_t Get() const { return mydata;}; void Set(Int_t i) {mydata=i;}; }
However, this getting/setting functions are not the only feature of this class. The next point is providing lists of possible settings for the concerned data member. The idea is to have a list of possible options for this data member, with strings identifying them. This is used in dialogs with parameters to set - for details see TMethodArg, TRootContextMenu, TContextMenu. This list not only specifies the allowed value, but also provides strings naming the options. Options are managed via TList of TOptionListItem objects. This list is also created automatically: if a data type is an enum type, the list will have items describing every enum value, and named according to enum name. If type is Bool_t, two options "On" and "Off" with values 0 and 1 are created. For other types you need to instruct ROOT about possible options. The way to do it is the same as in case of specifying getter/setter method: a comment string to a data field in Your header file with class definition. The most general format of this string is:
*OPTIONS={GetMethod="getter";SetMethod="setter";Items=(it1="title1",it2="ti tle2", ... ) }