When you place a polymorphic VI on the block diagram, the polymorphic VI defaults to the first instance subVI listed in the SubVIs listbox of the Polymorphic VI dialog box. When you create a control, indicator, or constant from the polymorphic VI terminals, the default instance determines the data type of each object.
The instance of a polymorphic VI changes automatically when you wire an input. For example, if you wire a string constant to the default value input terminal of the Read Key VI, LabVIEW selects the String instance subVI of the polymorphic VI and the value output terminal changes to a string data type. If you select an instance of a polymorphic VI manually, the polymorphic VI does not behave as a polymorphic VI because it accepts only the data types of the instance you specify.
Complete the following steps to select an instance of a polymorphic VI manually.
To revert back to the polymorphic VI accepting all of the handled data types, select Select Type»Automatic from the shortcut menu.