Visual Basic Concepts

How Modal and Modeless Forms Behave Out of Process

As mentioned in "Showing Forms from the CoffeeManager Class," modal and modeless forms displayed by an out-of-process component have a different relationship to a client application’s forms than they would if displayed by an in-process component. Running CoffeeWatch will demonstrate this.

Note   This topic is part of a series that walks you through creating a sample ActiveX EXE. It begins with the topic Creating an ActiveX EXE Component.

To demonstrate modal and modeless form behavior with the out-of-process Coffee component

1. Press F5 to run the CoffeeWatch test program.

2. Click Show Modal Form to display a modal form from the Coffee component.

   Depending on your system configuration, the order programs were started, and so on, the modal form may come up in front of CoffeeWatch — or you may see something like this:

   

3. TestForm is not really modal with respect to the CoffeeWatch form. To see this, click anywhere on the CoffeeWatch form. The Component Request Pending dialog box appears, as shown here:

   

   The dialog box appears because CoffeeWatch is waiting on its call to CoffeeMonitor.ShowForm, which is waiting on the modal TestForm. However, if TestForm were truly modal with respect to Form1, clicking on Form1 would generate a system sound indicating that Form1 was disabled.

4. Click Switch To, to bring TestForm to the front.

   Note   Depending on your system configuration and the order in which programs are loaded, the copy of Visual Basic in which Coffee is running may come to the front along with TestForm, obscuring CoffeeWatch.

5. Click on CoffeeWatch again, to bring it to the front and display the Component Request Pending dialog box again.

   Note   If you can’t see CoffeeWatch (the form, not the project), use the task bar (or press ALT+TAB) to bring it to the front.

   In the strict sense of the word, TestForm is modal to CoffeeWatch. That is, you can’t do anything with CoffeeWatch until TestForm is dismissed. However, because the two forms are in different processes, CoffeeWatch can appear on top of TestForm.

6. Click Switch To, to bring TestForm to the front, and then click TestForm’s close box to dismiss the modal form.

7. Click Show Modeless Form to show TestForm as a modeless form.

   TestForm behaves like a modeless form that’s not owned by CoffeeWatch. That is, it doesn’t stay on top of CoffeeWatch. You can verify this by clicking on each of the two forms, to bring them alternately to the front.

   Important   Because TestForm is in a different process from CoffeeWatch, you cannot make CoffeeWatch the owner of TestForm as you would if the forms were in the same process — that is, by passing a reference to CoffeeWatch in the OwnerForm argument of TestForm. For details see "Displaying Forms from Code Components," in "Building Code Components."

8. DO NOT dismiss the modeless TestForm. Instead, close CoffeeWatch by clicking its close box.

   TestForm doesn’t close. (It may be hidden behind the instance of Visual Basic containing the CoffeeWatch project — use the task bar or ALT+TAB to bring it to the front.)

   This illustrates two important points: First, a form displayed by an out-of-process component is not dependent on the client application. Nor is its lifetime limited by the client’s lifetime.

   Second, a loaded form can keep an out-of-process component’s executable from unloading. For details, see "Starting and Ending a Component" in "General Principles of Component Design."

   In its Terminate event, CoffeeMonitor should unload any forms it has shown.

9. Dismiss TestForm by clicking its close box. The Coffee component remains in run mode. To return Coffee to design mode, click the End button, or select End from the Run menu.

   Once you put an ActiveX EXE project in run mode, it remains in run mode. This is convenient for testing, but it’s different from the behavior of the made .exe. The executable for an out-of-process component unloads when the last client releases its last reference to an object provided by the component, as discussed in "Starting and Ending a Component."

   Note   The only way to test the shutdown behavior of an out-of-process component is to test with the made executable.

The lesson to take away from all this is that out-of-process code components are generally not the best way to show forms.

Step by Step

This topic is part of a series that walks you through creating a sample ActiveX EXE.