PRB: Instance of Container Class Uses Parent Form Scalemode

• Microsoft Visual FoxPro for Windows, version 3.0

SYMPTOMS

Objects added to an instance of a Container Class by a program are placed according to the Scalemode property of the parent form. Although a Container Class has no Scalemode property, an instance inherits the parent's Scalemode property from the form on which it is placed. This occurs regardless of the Scale Units selected in the Class page of the Class Info dialog.

RESOLUTION

Here are two techniques you can use to ensure that objects added to the container are properly sized and placed:

• Reset the parent form Scalemode property to a value that allows proper placement of objects. A Scalemode property can be added to the Container Class and although it has no effect, the value of this property can be read and the parent Scalemode set to the proper value. After the objects are placed, the parent Scalemode can be reset to its original value.
• Determine the Scalemode of the parent form, and use the proper values to place the objects for the current parent Scalemode.

STATUS

This behavior is by design.

MORE INFORMATION

A Visual FoxPro form has a Scalemode property that governs how objects programatically placed will be located and sized. There are two Scalemodes, foxels (0) and pixels (3). A container class, when instantiated and placed on a form, has no Scalemode property. The location and size of any objects placed in this container is governed by the Scalemode value of the parent form. The following examples demonstrate two methods you can use to ensure that objects added to containers are properly placed and sized.

Method One - Change the Parent Scalemode to the Desired Setting

1. Create a form called SCALTEST.SCX.

2. Set the Scalemode property to 3 - Pixels.

3. Save and close the form.

4. Create a new class by choosing New from the File menu. Select Class from New dialog box, and click the New File button.

5. Use Container_test as the class name, and select Container from the Based On dialog box. In Store, type SCALMODE.VCX.

6. Choose Class Info from the Class menu. Then set the Scale Units to Foxels, and close the dialog by clicking OK. Save the class.

7. Add a property called Scalemode by choosing New Property from the Class menu. Set the value of this property to 0 (zero).

8. Set the Height and Width properties of the class to 12 and 35.

9. Create the following program to run the form and programmatically add the container and a command button to the Container_test1 object:

   * Start of Scalprog.prg

      #DEFINE nFormScalemodeSet 3            && 0 - Foxels; 3 - Pixels.
      SET CLASSLIB TO scalmode.vcx ADDITIVE
   
      DO FORM scaltest.SCX
      scaltest.SCALEMODE=nFormScalemodeSet   && Sets form scalemode to
                                             && value in #DEFINE statement.
      nOldscalemode=scaltest.SCALEMODE       && Saves form scalemode.
   
      scaltest.ADDOBJECT("Container_test1","Container_test")
   
      * The following line sets the form scalemode to the desired scalemode
      * saved in the scalemode property added to container. Comment this to
      * see the behavior of adding Foxel sized object to Pixel scalemode form.
   
      scaltest.SCALEMODE=scaltest.Container_test1.SCALEMODE
   
      WITH scaltest.Container_test1
         .VISIBLE=.T.
         .ADDOBJECT("cmdcommand1","commandbutton")
         WITH .cmdcommand1        && Appropriate for Foxel scalemode
            .LEFT=7
            .TOP=5
            .HEIGHT=2
            .WIDTH=20
            .VISIBLE=.T.
         ENDWITH
      ENDWITH
      scaltest.SCALEMODE=nOldscalemode     && Resets form scalemode
      RELEASE CLASSLIB scalmode
   
      * End of Scalprog.prg
   
   

Method One Notes

Of the two methods, this is the better choice. The Scalemode property of the Container_test Class serves as a holder for the value. It is to be used to set the parent form scalemode, but has no effect in itself.

Proper placement and sizing of the command button occurs regardless of the form scalemode. If the parent scalemode was not temporarily reset, the command button would appear very small because the scalemode would be pixels.

Temporarily setting the form scalemode does not affect objects already placed on it, but does affect objects placed on it after the change is made.

Method Two - Determine Parent Scalemode and Place Objects Accordingly

1. Create the Form and the Class library as above.

2. Create and run the following program:

   * Start of Scalprg2.prg

   #DEFINE nFormScalemodeSet 0 && Toggle between 0 and 3 to demonstrate. SET CLASSLIB TO scalmode.vcx ADDITIVE

   DO FORM scaltest.SCX scaltest.SCALEMODE = nFormScalemodeSet

   scaltest.ADDOBJECT("Container_test1","Container_test")

   scaltest.CAPTION=STR(nFormScalemodeSet) && Sets caption to scalemode.

   WITH scaltest.Container_test1

         .VISIBLE=.T.
         .ADDOBJECT("cmdcommand1","commandbutton")
         WITH .cmdcommand1
            DO CASE
               CASE scaltest.SCALEMODE=0      && Foxels.
                  .LEFT=7      && Appropriate for Foxel scalemode.
                  .TOP=5
                  .HEIGHT=2
                  .WIDTH=20
               CASE scaltest.SCALEMODE=3      && Pixels.
                  .LEFT=40     && Appropriate for Pixels scalemode.
                  .TOP=80
                  .HEIGHT=34
                  .WIDTH=120
            ENDCASE
            .VISIBLE=.T.
         ENDWITH
      ENDWITH
      RELEASE CLASSLIB scalmode
   
      * End Scalprg2.prg