Access Cookbook, 2nd Edition [Electronic resources] نسخه متنی

Recipe 9.3 Create a Geographical Map Interface

9.3.1 Problem

You want to display a map and
allow users to click on regions of the map. You want the form to
react based on which region is clicked on. The regions
aren't necessarily rectangular. How can you do this?

9.3.2 Solution

You can accomplish
this task using a combination of bitmaps and transparent command
buttons. Depending on how far from rectangular your shapes are, this
task may be trivial or quite involved. By making the command buttons
transparent, you make the application appear to react directly to
mouse clicks on the map.

Open frmWesternUS in

09-03.MDB (Figure 9-7). This
form has been created with an imported bitmap file as the background.
Above each state's image on the map
there's at least one command button with its
Transparent property set to Yes. Figure 9-8 shows
the form named frmWesternUSDesign, in which the buttons are not
transparent. Here you can see the actual layout of the command
buttons.

Figure 9-7. The finished map form, frmWesternUS, with transparent buttons

Figure 9-8. The same bitmap form with buttons showing

To implement similar functionality in your own forms, follow these
steps:

1. Create a new form. Click anywhere in the
   detail section of the form, and select Insert Object (or use the form
   design toolbox to place an unbound object frame control form on the
   form). Once you release the mouse button, Access displays a dialog
   requesting information about the object. At this point, you can
   create a new object by launching an application such as Microsoft
   Paint, or you can create an object from an existing file. If you
   choose the latter, a Browse button will appear. Click on the Browse
   button to select a file (see Figure 9-9). Choose
   the appropriate image for the background. For the example form, use
   

   USWEST.BMP .

Figure 9-9. Browsing a file from the Insert Object dialog

2. Set the bitmap's
   SizeMode property to Clip. This disallows resizing of the bitmap, as
   you'll be overlaying the bitmap with command
   buttons.

Using Shift and Ctrl plus the arrow keys is helpful in achieving exact placement of the command buttons. Use Shift-arrow to expand and contract the size of a control one pixel at a time; use Ctrl-arrow to move the control one pixel at a time.

3. Overlay each defined area of the bitmap with a command button, naming
   each as desired. Figure 9-8 shows the completed
   process for the sample form. You'll find that for
   odd-shaped regions, you'll need to use multiple
   buttons, as demonstrated for Idaho, Texas, and Nevada on the map.

4. Select all the command buttons (hold
   down the Shift key and click on each). On the properties sheet, set
   the Transparent property to Yes, making the selected controls
   invisible yet active. Figure 9-10 shows the sample
   form in design view; note that you can still see a faint outline of
   each button.

Figure 9-10. The sample map form in design view

5. For each transparent command
   button, call a function, passing it the name that describes the
   defined area (in this example, the name of the selected U.S. state)
   from the button's OnClick event property. For
   example, the OnClick event property for the command button overlaying
   the state of Wyoming calls the

   HandleStateClick
   function, passing it "Wyoming":

   =HandleStateClick("Wyoming")

6. Create the function called in Step 5. This function can be either in
   the form's module (as we have created) or in a
   global module. It's up to you to decide what to do
   with the information passed to the function. In the sample form, the
   name of the state is passed to an unbound text box. The
   

   HandleStateClick function is shown here:

   Private Function HandleStateClick(strState As String)
   Me.txtChosenState = strState
   End Function

9.3.3 Discussion

Because each button has its
Transparent property set to Yes (which is very different from having
its Visible property set to No!), it's still active.
You can click on transparent buttons and they can react to events.
Each transparent button corresponds to some physical region on the
bitmap, so you can have the buttons' Click event
procedures react according to their location on the bitmap. If only
Windows supported irregularly shaped command buttons!

The size of the bitmap is key
to the effectiveness of this technique. If you lay out the buttons
all over the bitmap and then decide to resize it, your
buttons' locations will no longer be correct. Make
sure that you've fixed the size of the bitmap before
you start laying out buttons. Although you can select all the buttons
and resize them as a group, this is not a perfect solution.

Don't spend too much time getting the transparent
buttons placed exactly. On the example form, the
buttons' placement is fairly precise, but that works
only because most of the states in the west are generally rectangular
(you'll notice that there's no
eastern seaboard on the map). Users will typically click in the
center of the region, so covering each pixel on the edge
isn't a serious concern.