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You can use the Open File dialog control to open a
picture, but you would have to configure wholly, almost from scratch. To
give you a convenient ways with a ready made object to open pictures, the
VCL provides the Open Picture dialog box. The Open Picture dialog box is
flexible as it spares you the hassle of setting such aspects as the file
filters. Furthermore, unlike the Open file dialog box, the Open Picture
dialog box gives the ability to preview a picture before opening it.
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Creating an Open Picture Dialog Box
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The Open Picture dialog box is an object of type
TOpenPictureDialog. This class is derived from the
TOpenDialog class but it is defined in the ExtDlgs.hpp header file.
To visually add support to open a picture in your
application, in the Dialogs section of the Tool Palette, click
TOpenPictureDialog
and click its container. In the same way, to programmatically create an
Open Picture dialog box, declare a variable of type
TOpenPictureDialog. In the constructor, specify its owner.
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Characteristics of an Open Picture Dialog Box
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Because the TOpenPictureDialog class is derived from
the TOpenDialog class, that's where it gets all its primary functionality.
These include the title for the dialog box (the Title property), the
filter to restrict the types of files (the Filter
property), the default file extension (the DefaultExt
property), the initial directory (the InitialDir
property), and the ability to display the dialog box (the
Execute() method).
There are two main differences between a TOpenDialog
and a TOpenPictureDialog controls. The latter provides an already-made
filter configured for all popular picture types. The biggest visual
difference is that the Open Picture dialog box is equipped with an area
that previews the picture.
