>I want to use:
>SELECT * FROM MyTable WHERE MyField = thisform.MyObject.Text
>in ComboBox.RowSource property but I get error message that Thisform can be used only in methods.
>
>How to solve this?

One way is to use a custom form method to create a cursor for the ComboBox, and then set the ComboBox.RowSource:

* ComboBox.Init( )
DODEFAULT( )

ThisForm.ComboBoxRowSourceSet( This, ThisForm.MyObject.Text )

* Form.ComboBoxRowSourceSet
LPARAMETERS loComboBox, lcText

SELECT SomeColumn FROM MyTable WHERE MyField == lcText INTO CURSOR SomeCursor

WITH loComboBox
  .RowSourceType = 2
  .RowSource = "SomeCursor"

  .Value = SomeCursor.SomeColumn
  .Refresh( )
  * ComboBoxes are tricky, you may need to play around with setting various properties
  * to get it initialized the way you want

ENDWITH