Judul : Moving from Scene to Scene
link : Moving from Scene to Scene
Moving from Scene to Scene
Be careful with scenes:
Most animators, and Macromedia as well, don't recommend using scenes except
with long animations. We're discussing it here only because you should know how
to do it.
Let's say our assignment
is to create a Flash version of a PowerPoint presentation. It's for Buzzkill
Industries, a young, edgy company that makes safety equipment. Someone else has
created the slides for the presentation, and it's our job to make sure the
presenter can move from slide to slide. For the purposes of this tutorial,
we'll only deal with the first three slides of the presentation, shown in Figure 3–4.
1.
Open the file chapter3/buzzkill1.fla.
2.
Notice that there are
three scenes—one for each slide. Each scene has one frame action on its last
frame: stop().
3.
Click on the last frame
in the actions layer in each scene, and then open the Actions panel to see the
ActionScript. The only ActionScript you'll see is stop(). This stop method halts the playhead in its tracks. That
is, it stops the Flash movie from playing further.
4.
Go ahead and play with
the movie, using Control 
Test Movie.
Test Movie.
NOTE
Always test your movies with Control Test Movie, since that's the only way you can properly test your
actions.
Test Movie, since that's the only way you can properly test your
actions.
5.
Notice that there's no
way to go beyond the first scene/slide.
6.
Close the window with
the movie playing.
7.
Go to the last frame in
Scene 1 of the movie (frame 60) on the button layer.
8.
Insert Keyframe.
Keyframe.
9.
Window Library.
Library.
10.
Drag the Forward Button
symbol onto the empty button layer. Make sure you're still on frame 60.
Position the button wherever you want.
11.
Click on the button.
12.
Open the Actions panel.
13.
Enter the following
code:
14. on(release)
15. {
16. gotoAndPlay("Scene
2","slide2");
}
17.
Control Test Movie. Once the movie is playing, pressing the button should
send you to the next scene.
Test Movie. Once the movie is playing, pressing the button should
send you to the next scene.
Let's look at this code
in detail. The first thing you see is the on(release); on is what's known as an event handler.
If something happens, like the user pressing down the mouse button or hitting
the keyboard, that's called an event. An event handler is some code that is executed
when an event happens. For buttons in Flash, their event handler is the on(event) function. There are about a dozen events (for a
complete list, see Appendix A, "ActionScript Reference"), but the
only one we're dealing with is release, which is short for "when the user presses
the mouse button and then releases it."
Once the user releases
the mouse button, everything between the curly braces that follow theon(release) is executed. As it happens, there's only one
line of code: gotoAndPlay("Scene
2", "slide2").
As you might have guessed, this command tells the playhead to jump to Scene 2
and start playing from the frame that has the label "slide2". In this case, frame 1 holds the "slide2"label.
Unfortunately, Flash
isn't smart enough to look through all the scenes in your movie and find the
right frame if you've labeled it, so gotoAndPlay("slide2") wouldn't have worked. If you direct Flash to a
frame label that doesn't exist, it'll start playing at frame 1.
Here's another way to do
it:
on(release)
{
gotoAndPlay("Scene 2", 1);
}
In this case, Flash goes
to Scene 2 and starts playing at the first frame. I recommend using frame
labels—it lets you move stuff around without having to keep track of frame
numbers.
NOTE
Labels and actions do
not have to go on their own layers. However, it's a good way to stay organized,
especially as your movies get more and more complex. I recommend doing it, even
if there's only one frame label or only one frame action. I also strongly recommend
always using frame labels—don't use frame numbers. Your ActionScript is less
likely to have bugs down the road if you use frame labels.
Now let's add the two
buttons on the second scene/slide.
1.
Open up Scene 2.
2.
Open up the Library if
it isn't already open.
3.
Go to the last frame in
the movie (40) on the empty button layer.
4.
Insert Keyframe.
Keyframe.
5.
Drag the Backward button
and the Forward button to the stage and place them wherever you like.
6.
Click on the Forward
button.
7.
Open up the Actions
panel if it isn't open.
8.
Enter the following
code:
9. on(release)
10. {
11. gotoAndPlay("Scene
3","slide3");
}
12.
Click on the Backward
button.
13.
Enter the following
code:
14. on(release)
15. {
16. gotoAndPlay("Scene
1","slide1");
}
17.
Save the file and
Control Test Movie.
Test Movie.
For the final step,
let's add the last button to the final slide.
1.
Open up Scene 3.
2.
Open up the Library
(Window Library) if it isn't already open.
Library) if it isn't already open.
3.
Go to the last frame in
Scene 3 on the button layer (frame 45).
4.
Drag the Backward button
to the stage and place it wherever you like.
5.
Click on the Backward
button.
6.
Open up the Actions
panel if it isn't open.
7.
Enter the following
code:
8. on(release)
9. {
10. gotoAndPlay("Scene
2","slide2");
}
11.
Control Test Movie!
Test Movie!
Now you can actually
move from scene to scene inside your movie, and you learned something about
buttons and event handlers along the way! Now let's make this a little more
complex: It turns out that, since they are used to using PowerPoint, the
presenters forget that they have to press buttons on the screen to move from scene
to scene. They want to be able to press the space bar and right arrow to move
forward and the left arrow to move back, just as in PowerPoint.
This isn't a problem at
all. All we're doing here is adding events (the user is pressing keys on the
keyboard), so we can modify the buttons we already have to deal with those
events.
1.
Go back to the Forward
Button on frame 60 of Scene 1.
2.
Click on the button and
open its Actions panel.
3.
Add the following code:
4. on(release, keyPress "<space>")
5. {
6. gotoAndPlay("Scene
2", "slide2");
}
7.
Control Test Movie.
Test Movie.
The new event we have
here is keyPress, and part of using keyPress is saying immediately afterwards which key we're
looking for. By using the <> brackets and spelling out space, we've made this code easier to read than if it were keyPress " ".
Now let's add the right
arrow:
1.
Enter the following
code:
2. on(release, keyPress "<space>", keyPress
"<right>")
3. {
4. gotoAndPlay("Scene
2", "slide2");
}
5.
Control Test Movie.
Test Movie.
Whoops! You received an
error. Flash doesn't like to have two of the same events in the same on()statement. Even though our two keyPress events are for different keys, they still count
as the same kind of event. So we have to rewrite our code slightly:
on(release, keyPress
"<space>")
{
gotoAndPlay("Scene 2",
"slide2");
}
on(keyPress
"<right>")
{
gotoAndPlay("Scene 2",
"slide2");
}
Test the movie again to
make sure it's working correctly.
Now that we have the
first button working, getting the others to work won't take much extra effort.
Here's the code for them:
Scene 2 Backward Button
// This button only
needs one function, since only
// one key can be used
to go backwards, as opposed to
// two keys to go
forward.
on(release, keyPress
"<left>")
{
gotoAndPlay("Scene 1",
"slide1");
}
Scene 2 Forward Button
on(release, keyPress
"<space>")
{
gotoAndPlay("Scene 3",
"slide3");
}
on(keyPress
"<right>")
{
gotoAndPlay("Scene 3",
"slide3");
}
Scene 3 Backward Button
on(release, keyPress
"<left>")
{
gotoAndPlay("Scene 2",
"slide2");
}
To see the final movie,
check out buzzkill2.fla.
Comments
Did you notice we
introduced one new element? For the Scene 2 Backward Button, there are a few
lines that start with two slashes. Those two slashes indicate that the rest of
the line is a comment, which Flash completely ignores. Comments are only for
programmers, not for the computer. Using comments appropriately is called documenting your code. Documenting your code is important, since at
some point you'll have to fix your own old code when you might not remember how
it works anymore, or someone else might have to work on your code. Programmers
who document their code well are happy programmers.
on(event)
As a final note, here
are all of the events that the on event handler can recognize:
·
press
·
release
·
releaseOutside
·
rollOver
·
rollOut
·
dragOver
·
dragOut
·
keyPress
These are discussed in
greater detail later in the book and in Appendix A.
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