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Text File  |  1989-07-12  |  3KB  |  71 lines
  1.  
  2. <H3><A ID="SECTION003711100000000000000"><tex2html_anchor_invisible_mark></A> <A ID="ch:before-actions"><tex2html_anchor_mark></A><BR>
  3. Before Actions
  4. </H3><#5031#>
  5.            
  6.       
  7.  
  8.  
  9. <P>
  10. A <#1529#><B>before action</B><#1529#><A ID="1530"><tex2html_anchor_invisible_mark></A><A ID="1531"><tex2html_anchor_invisible_mark></A>
  11. <A ID="1532"><tex2html_anchor_invisible_mark></A> of a <#1533#><TT>contact-display</TT><#1533#> is an action which is called
  12. when an event is dispatched to a contact, but before any other contact input
  13. processing is performed.  Before actions are useful for implementing
  14. various kinds of application-dependent event preprocessing. For example, an
  15. application could define a before action for the <#1534#><TT>contact</TT><#1534#> class that will
  16. record every event in a log file. 
  17.  
  18. <P>
  19. Associated with a <#1535#><TT>contact-display</TT><#1535#> is a list of before actions. 
  20. Each event received by a <#1536#><TT>contact-display</TT><#1536#> is compared with every element of
  21. its before actions list.  If <#1537#><TT>c</TT><#1537#> is the class for which the before
  22. action is defined, and if <#1538#><TT>contact</TT><#1538#> is the contact instance to which the
  23. event has been dispatched, then the before action is called if <#1539#><TT>(typep
  24. contact c)</TT><#1539#> is true.
  25.  
  26. <P>
  27. The following functions control the before actions of a <#1540#><TT>contact-display</TT><#1540#>.
  28.  
  29. <P>
  30. <#4304#><FONT SIZE="+1"><#1541#><B>add-before-action Function, contact-display</B><#1541#></FONT><#4304#> 
  31. <A ID="1542"><tex2html_anchor_invisible_mark></A>
  32. <A ID="1543"><tex2html_anchor_invisible_mark></A>
  33. <DIV class="RIGHT">
  34. <tex2html_image_mark>#tex2html_wrap_inline9980#
  35. </DIV>
  36.  
  37. <P>
  38. <DIV class="RIGHT">
  39. <tex2html_image_mark>#tex2html_wrap_inline9981#
  40. </DIV>
  41.  
  42. <P>
  43. <#4664#>
  44. <#4307#><FONT SIZE="+1"><#1560#><B>delete-before-action Function, contact-display</B><#1560#></FONT><#4307#> 
  45. <A ID="1561"><tex2html_anchor_invisible_mark></A>
  46. <A ID="1562"><tex2html_anchor_invisible_mark></A>
  47. <DIV class="RIGHT">
  48. <tex2html_image_mark>#tex2html_wrap_inline9982#
  49. </DIV><#4664#>
  50.  
  51. <P>
  52. <DIV class="RIGHT">
  53. <tex2html_image_mark>#tex2html_wrap_inline9985#
  54. </DIV>
  55.  
  56. <P>
  57. <#4310#><FONT SIZE="+1"><#1575#><B>before-actions Function, contact-display</B><#1575#></FONT><#4310#> 
  58. <A ID="1576"><tex2html_anchor_invisible_mark></A>
  59. <A ID="1577"><tex2html_anchor_invisible_mark></A>
  60. <DIV class="RIGHT">
  61. <tex2html_image_mark>#tex2html_wrap_inline9986#
  62. </DIV>
  63.  
  64. <P>
  65. <DIV class="RIGHT">
  66. <tex2html_image_mark>#tex2html_wrap_inline9987#
  67. </DIV>
  68.  
  69. <P>
  70.  
  71.  =0 <#5041#>=0 <#5045#>