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3009:How to check a ComboBox without OnClick ocurring.

KEYWORDS: checkbox onclick checked BM_SETCHECK AREA: VCL Programming

When you modify the state of a TCheckBox by setting the value
of its Checked property, the OnClick event of that TCheckBox
is fired.  For example, the following code:

CheckBox1.Checked := True;

causes CheckBox1.OnClick to execute.

Sometimes, however, you may want to check or uncheck the
CheckBox in code without firing the OnClick event.  You
can do this by sending a BM_SETCHECK message to the
ComboBox. The WParam of this message can be 1 (meaning
the box should be checked), or 0 (meaning the box should
be unchecked).  The LParam of this message is always 0.

With this in mind, the following procedure accepts as
parameters a TCheckBox called CB and a Boolean parameter
called CheckIt.  When CheckIt is True, the box will be
checked, and when it's False, the box will be unchecked:

procedure CheckNoClick(CB: TCheckBox; CheckIt: Boolean);
begin
  CB.Perform(BM_SETCHECK, Ord(CheckIt), 0);
end;

Using this procedure, the code for checking a TComboBox
called ComboBox1 looks like this:

CheckNoClick(ComboBox1, True);

        TI

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