How You Can Pass Parameters Between Frames

When you run a frame with the openframe, callframe, or gotoframe statement, you can pass values to it with a parameter list. The syntax for the parameter list is:

Specifies the name of a variable in the called frame. This variable can be either a field variable or a variable that you declare in the initialize block's parameter list.

Can contain constants, variables, or expressions from the calling frame. OpenROAD transfers the value of this expression to the corresponding variable in the called frame.

The following code example demonstrates opening a frame using the openframe statement. It uses the vlist table field to store information about individual videos. Every time a detail frame is opened for a particular video, the FrameExec for the detail frame is stored in the vlist[ ].details_frame. Before opening a new frame, the code checks to see whether the details frame has already been opened to avoid opening a second instance of it.

The example also illustrates how the calling frame can set an attribute (WindowTitle) of the called frame using the with clause of the openframe statement.

on click view_button =
{
    if (vlist[].details_frame is null) then
        vlist[].details_frame = openframe video_detail(video_info = vlist[])
            with WindowTitle = vlist[].title;
    else
        vlist[].details_frame.BringToFront();
    endif;
}

Any parameter in the called frame that you do not include in the parameter list is set to its default value.

When you pass a simple variable, such as an integer or text string, any changes made to its value in the called frame are not reflected in the calling frame. However, when you pass a 4GL object, such as a table field, you are passing a reference to the object, not the object itself. Therefore, both the called frame and the calling frame have references to the same object, and any changes made to the object by the called frame are reflected in the calling frame as well. For more information about changing the value of a simple variable in both the calling and the called frames, see How You Can Pass Parameters Between an Active Child and Inactive Parent (see How You Can Pass Parameters Between an Active Child and Inactive Parent).