A text filter function is the input filter for the Text object which allows the programmer to monitor (and control), the characters entered into a Text object of TextField object. \
As Concepts says, \
\fs24 Unlike a character filter, which only receives the individual character that's entered, a text filter additionally receives information about the state of the Text object. Based on this information, the text filter can change a number of variables including the content of the entered or existing text and the location of the insertion point.\
\fs28 In this application, different text filter functions are attached to the fieldEditor of the Window depending on which TextField is the firstResponder. (See chapter 9 of Concepts for details on the fieldEditor and on filter functions.) The application implements the text filtering in three different ways.\
For the name TextField, the filter function is set when the field becomes the firstResponder (after a mouse click or a TAb into the field). This works but isn't extremely elegant. Look in the code for the NameTextField class for details.\
For the date TextField, the filter function is set by a custom Cell class when that cell is notified that the field is being edited. This solution is symmetrical and preferred (by me, at least). Again, look in the source for the DateTextField class.\
For the time and social security number TextFields, the filter function is also set by a custom Cell class. However, an abstract Cell class has been implemented, gathering filter-setting functionality in one encapsulated, reusable class. Much better. Read the source.\
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