189.htm

水木清华的BBS文章

When viewing the source for the VCL units, it's definitely a good idea to <br>
become comfortable with bookmarks in the editor.  That is,  Ctrl+Shift+N, <br>
when N is a number 0-9, to set a bookmark.  Jump to a bookmark using Ctrl+N. <br>
  <br>
2.6. How can I add to the popup menu that is displayed when the right mouse butt <br>
on is clicked on my component? <br>
  <br>
You do this by creating a Component Editor.  One would think that a component ed <br>
itor would be something that is called from the popup menu but it actually contr <br>
ols what appears in the menu or rather the items that your component can add to <br>
the menu. <br>
  <br>
The steps to follow are: <br>
  <br>
1. Create a class that derives from TComponentEditor <br>
2. In your class override the method GetVerbCount, GetVerb, and ExecuteVerb. <br>
3. In your component's Register procedure add a call to RegisterComponentEditor <br>
that associates your component editor with your <br>
  <br>
  <br>
  <br>
 <br>
  <br>
  <br>

  <br>
When viewing the source for the VCL units, it's definitely a good idea to <br>
become comfortable with bookmarks in the editor.  That is,  Ctrl+Shift+N, <br>
when N is a number 0-9, to set a bookmark.  Jump to a bookmark using Ctrl+N. <br>
  <br>
2.6. How can I add to the popup menu that is displayed when the right mouse butt <br>
on is clicked on my component? <br>
  <br>
You do this by creating a Component Editor.  One would think that a component ed <br>
itor would be something that is called from the popup menu but it actually contr <br>
ols what appears in the menu or rather the items that your component can add to <br>
the menu. <br>
  <br>
The steps to follow are: <br>
  <br>
1. Create a class that derives from TComponentEditor <br>
2. In your class override the method GetVerbCount, GetVerb, and ExecuteVerb. <br>
3. In your component's Register procedure add a call to RegisterComponentEditor <br>
that associates your component editor with your <br>
  <br>
  <br>
  <br>
From Ray Konopka <br>
  <br>
When viewing the source for the VCL units, it's definitely a good idea to <br>
become comfortable with bookmarks in the editor.  That is,  Ctrl+Shift+N, <br>
when N is a number 0-9, to set a bookmark.  Jump to a bookmark using Ctrl+N. <br>
  <br>
2.6. How can I add to the popup menu that is displayed when the right mouse butt <br>
on is clicked on my component? <br>
  <br>
You do this by creating a Component Editor.  One would think that a component ed <br>
itor would be something that is called from the popup menu but it actually contr <br>
ols what appears in the menu or rather the items that your component can add to <br>
the menu. <br>
  <br>
The steps to follow are: <br>
  <br>
1. Create a class that derives from TComponentEditor <br>
2. In your class override the method GetVerbCount, GetVerb, and ExecuteVerb. <br>
3. In your component's Register procedure add a call to RegisterComponentEditor <br>
that associates your component editor with your component. <br>
  <br>
This topic is described well in the book "Developing Delphi Components". <br>
  <br>
  <br>
2.7. How come I get I/O 103 in design mode? <br>
  <br>
You probably have WriteLn statements in your code. <br>
  <br>
2.8. Why are my property values not getting saved when I use a component editor? <br>
  <br>
  <br>
I have found that when using a component editor that a component's properties wi <br>
ll not be saved. The property appears to be correct in design mode but when you <br>
run or save the property is set to a different value. <br>
  <br>
It appears that a property editor needs to call <br>
  <br>
 Designer.Modified <br>
  <br>
to let Delphi know that you have changed a property value. <br>
  <br>
------------------------------------------------------------------------ <br>
Section 3 - Using other components within a component <br>
  <br>
3.1. How can I add a scroll bar component to my component and have it work at in <br>
 design mode? <br>
 design mode? <br>
  <br>
You need to define your own scroll bar class that intercepts the CM_DESIGNHITTES <br>
T message. <br>
  <br>
TMyScrollBar = class (TScrollBar) <br>
      Procedure CMDesignHitTest (var Message : TCMDesignHitTest) ; Message CM_DE <br>
SIGNHITTEST ; <br>
    End ; <br>
  <br>
Procedure TMyScrollBar.CMDesignHitTest (var Message : TCMDesignHitTest) ; <br>
  Begin <br>
  Message.Result := 1 ; <br>
  End ; <br>
  <br>
When your component creates one of these scroll bars it needs to use <br>
  <br>
TMyScrollBar.Create (Nil) <br>
  <br>
rather than <br>
  <br>
TMyScrollBar.Create (Self) <br>
  <br>
  <br>
otherwise the scroll bar will display sizing handles when it is click.   This me <br>
ans you need to be sure to explicitly free the scroll bar in your component's de <br>
structor. <br>
  <br>
3.2 How do I create a Windows '95-style scroll bar? <br>
  <br>
You need to set the page size for the scroll bar.   The following code sequence <br>
illustrates this: <br>
  <br>
Procedure SetPageSize (ScrollBar : TScrollBar ; PageSize : Integer) ; <br>
  Var <br>
    ScrollInfo : TScrollInfo ; <br>
  Begin <br>
  ScrollInfo.cbSize := Sizeof (ScrollInfo) ; <br>
  ScrollInfo.fMask := SIF_PAGE ; <br>
  ScrollInfo.nPage := PageSize ; <br>
  SetScrollInfo (ScrollBar.Handle, SB_CTL, ScrollInfo, True) ; <br>
  End ; <br>
  <br>
To retrieve the page size use: <br>
  <br>
Function GetpageSize (ScrollBar : TScrollBar) ; <br>

  Var <br>
    ScrollInfo : TScrollInfo ; <br>
  Begin <br>
  If HandleAllocated Then <br>
    Begin <br>
    ScrollInfo.cbSize := Sizeof (ScrollInfo) ; <br>
    ScrollInfo.fMask := SIF_PAGE ; <br>
    GetScrollInfo (ScrollBar.Handle, SB_CTL, ScrollInfo) ; <br>
    Result := ScrollInfo.nPage ; <br>
    End ; <br>
  <br>
------------------------------------------------------------------------ <br>
Section 4 - Bound Controls <br>
  <br>
4.1. Where is the documentation for the TDataLink class? <br>
  <br>
The C++Builder documentation contains a description of the TDataLink class. It i <br>
s not in any Delphi documentation so far. For those of you who do not have C++Bu <br>
ilder here is the description that has been in this document for a long time: <br>
  <br>
Properties: <br>
=========== <br>
=========== <br>
  <br>
Property:       Active : Boolean (Read Only) <br>
---------------------------------------- <br>
  <br>
Returns true when the data link is connected to an active datasource. <br>
The ActiveChanged method is called to give notification when the state changes. <br>
  <br>
Property:       ActiveRecord: (Read/Write) <br>
-------------------------------------- <br>
  <br>
This sets or returns the current record within the TDatalink's buffer window.  V <br>
alid values are <br>
0..BufferCount - 1.  There appear to be no range checks so assigning values outs <br>
ide this range produces unpredictable results. <br>
  <br>
Property:       BufferCount: (Read/Write) <br>
------------------------------------- <br>
  <br>
The TDataLink maintains a window of records into the dataset  This property is t <br>
he size of this window and determines the maximum number of row that can be view <br>
 simultaneously.  For most controls you would use a BufferCount of one.  For con <br>
trols such as a data grid this value is the number of visible rows. <br>

  <br>
Property:       DataSet: TDataSet (Read) <br>
------------------------------------ <br>
  <br>
The dataset the TDataLink is attached to.  This is a shortcut to DataSource.Data <br>
Set. <br>
  <br>
Property:       DataSource: TDataSource (Read/Write) <br>
------------------------------------------------ <br>
  <br>
Sets or returns data source control the TDataLink is attached to. <br>
  <br>
Property:       DataSourceFixed: Boolean (Read/WRite) <br>
------------------------------------------------- <br>
  <br>
This property is used to prevent the data source for the TDataLink from being ch <br>
anged.  If this property is set to Trye then assigning a value to the DataSource <br>
 property will result in an exception. <br>
  <br>
Property:       Editing: Boolean (Read Only) <br>
---------------------------------------- <br>
  <br>
  <br>
Returns true if the datalink is in edit mode. <br>
  <br>
Property:       ReadOnly: Boolean (read/Write) <br>
------------------------------------------ <br>
  <br>
This property determines if the TDataLink is read only.  It does not appear to a <br>
ffect the attached datalink <br>
or dataset.  If this property is set to True the datalink will not go into edit <br>
mode. <br>
  <br>
Property:       RecordCount: Integer (Read) <br>
--------------------------------------- <br>
  <br>
The property returns the approximate number of records in the attached dataset. <br>
  <br>
Methods: <br>
======== <br>
  <br>
function Edit: Boolean; <br>
----------------------- <br>
  <br>
Puts the TDatalink's attached dataset into edit mode. <br>

  <br>
Return Value: <br>
        True => Success <br>
        False => Failure <br>
  <br>
procedure UpdateRecord; <br>
----------------------- <br>
  <br>
It appears that this is a function that is intended to be called by other parts <br>
of the data base interface and should not be called directly.  All it does is se <br>
t a flag and call UpdateData (described below). <br>
  <br>
  <br>
Virtual Methods <br>
=============== <br>
  <br>
The mechanism for having the TDataLink object communicate with a component is to <br>
 override these procedures. <br>
  <br>
procedure ActiveChanged <br>
------------------------ <br>
This procedure is called whenever the datasource the TDataLink is attached to be <br>
enever the datasource the TDataLink is attached to be <br>
comes active or inactive.  Use the Active property to determine whether or not t <br>
he link is active. <br>
  <br>
procedure CheckBrowseMode <br>
------------------------- <br>
This method appears to get called before any changes take place to the database. <br>
  <br>
  <br>
procedure DataSetChanged; <br>
------------------------- <br>
This procedure gets called when the following events occur: <br>
  <br>
   o Moving to the start of the dataset <br>
   o Moving to the end of the dataset <br>
   o Inserting or Appending to the dataset <br>
   o Deleting a record from the dataset <br>
   o Canceling the editing of a record <br>
   o Updating a record <br>
  <br>
The non-overridden action for this procedure is to call <br>
  <br>
        RecordChanged (Nil) <br>
        RecordChanged (Nil) <br>
  <br>
procedure DataSetScrolled(Distance: Integer) <br>
-------------------------------------------- <br>
This procedure is called whenever the current record in the dataset changes.  Th <br>
e Distance parameter tells how far the buffer window into the dataset was scroll <br>
ed (This seems to always be in the range -1, 0, 1). <br>
  <br>
Use the ActiveRecord to determine which record within the buffer window is the c <br>
urrent one. <br>
  <br>
It is not possible to force a scroll of the buffer window. <br>
  <br>
procedure FocusControl(Field: TFieldRef) <br>
---------------------------------------- <br>
This appears to get called as a result of Field.FocusControl. <br>
  <br>
procedure EditingChanged <br>
------------------------- <br>
This procedure is called when the editing state of the TDataLink changes.  Use t <br>
he Editing property to determine if the TDataLink is in edit mode or not. <br>
  <br>
procedure LayoutChanged <br>

----------------------- <br>
This procedure is called when the layout of the attached dataset changes (e.g. c <br>
olumn added). <br>
  <br>