READKEY statement

Reads one keystroke from an input source and sets the value of LASTKEY to the keycode of that keystroke. Use the READKEY statement when you want to look at each keystroke a user makes and take some action based on that keystroke.

Note: Does not apply to SpeedScript programming.

Caution: If you are executing the READKEY statement while blocking on a .NET main form, a user action can unconditionally shut down the ABL application. For more information, see the WAIT-FOR statement (.NET and ABL) reference entry.

Syntax


READKEY [ STREAM `stream` \| STREAM-HANDLE `handle` ] [ PAUSE `n` ]

STREAM stream

Specifies the name of a stream. If you do not name a stream, the AVM uses the unnamed stream. See the DEFINE STREAM statement.

STREAM-HANDLE handle

Specifies the handle to a stream. If handle it is not a valid handle to a stream, the AVM generates a run-time error. Note that stream handles are not valid for the unnamed streams. See the chapter on alternate I/O sources in OpenEdge Development: Programming Interfaces for more information on streams and stream handles.

PAUSE n

The READKEY statement waits up to n seconds for a keystroke. If you do not press a key during that amount of time, READKEY ends, and sets the value in LASTKEY to -1.

PAUSE 0 causes READKEY to immediately return a value. If no character is available, READKEY sets the value of LASTKEY to -1. Use this form of READKEY to do polling through UNIX pipes or terminal ports.

Example

In the following procedure, when the user presses a key, the READKEY statement reads the keystroke and stores the character code value of that key (the key code) as the value of LASTKEY. The CHR function converts the character code value into a character value. If the character value is a Y, the AVM deletes the Customer. KEYFUNCTION determines the function of the LASTKEY. If that function is END-ERROR, the AVM exits the block, ending the procedure.

r-readky.p
FOR EACH Customer: DISPLAY Customer.CustNum Customer.Name Customer.Address Customer.City Customer.State WITH 1 DOWN. MESSAGE "If you want to delete this customer, press Y". MESSAGE "Otherwise, press any other key.". READKEY. IF CHR(LASTKEY) = "Y" THEN DELETE Customer. ELSE IF KEYFUNCTION(LASTKEY) = "END-ERROR" THEN LEAVE. END.

r-readky.p

FOR EACH Customer: 
  DISPLAY Customer.CustNum Customer.Name Customer.Address Customer.City  
    Customer.State WITH 1 DOWN. 
  MESSAGE "If you want to delete this customer, press Y". 
  MESSAGE "Otherwise, press any other key.". 
  READKEY. 
  IF CHR(LASTKEY) = "Y" THEN DELETE Customer. 
  ELSE IF KEYFUNCTION(LASTKEY) = "END-ERROR" THEN LEAVE. 
END.

Notes

If you use READKEY, it intercepts any input from the user. Thus no widgets receive the input. To pass the input to a widget, you must use the APPLY statement.

The READKEY function is double-byte enabled. The READKEY function returns values only after the input method places the data in the keyboard buffer. It returns the key code of the most recent key sequence returned from the keyboard buffer. A key sequence is the set of keystrokes necessary to generate one character or function key event in ABL.

If the current input source is a file, then READKEY reads the next character from that file and returns the value of that character (1 to 255) to LASTKEY. READKEY does not translate periods (.) in the file into the ENDKEY value. It does translate end of line into RETURN (13), but it cannot read any special keys, such as function keys.

When the AVM reaches the end of the file, it sets the value of LASTKEY to -2, but does not close the input file. At that point, an APPLY LASTKEY (same as APPLY -2) raises the ENDKEY condition.

If the current input source is a UNIX pipe, any timer you set with the PAUSE option might expire before READKEY can read a character. If so, LASTKEY is set to -1.

If the last key typed is an invalid character sequence, READKEY sets the value of LASTKEY to -1.

READKEY counts to determine whether an UNDO, RETRY should be treated as UNDO, NEXT, and whether UNDO, NEXT should be treated as UNDO, LEAVE . This presents infinite loops.

For more information on monitoring keystrokes, see OpenEdge Development: Programming Interfaces.