Tracking Playback and Downloading Progression
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Tracking Playback and Downloading Progression
The number of frames in a movie and the file size of their contents determine the movie's
overall length and size—a fact made evident by looking at the main timeline where these
factors represent the length and size of the entire SWF. The total number of frames in a
movie is a represented by the_totalframes property. If the main timeline has 400 frames
that span several scenes, the following script sets the value of myVariable to 400:
var myVariable:Number = _root._totalframes;
You can use this property in scripts to determine the overall length of the movie (based in
frames).
NOTE
Because it's a read-only property, the value of _totalframes is set automatically by Flash
(based on the number of frames on a timeline). Not only does it not make sense to
attempt to reset this value—it's not even possible!
If you know the value of _totalframes, you can use it in conjunction with other movie
properties to make comparisons during downloading and playback. For example, by
comparing the value of the _currentframe property with the value of the _totalframes
property, you can determine how much longer the movie will play:
var framesLeft:Number = _root._totalframes - _root._currentframe;
message_txt.text = "There are " + framesLeft + " to go.";
Because Flash is based on streaming technology, the process of downloading and
viewing an SWF from a Web site actually occurs one frame at a time. Another property,
_framesloaded, provides the total number of frames that have been downloaded. The
value of this property can be compared to the _totalframes property to provide
information about the progress of the download. In the following exercise, we'll
demonstrate this principle by creating a progress bar (known as a preloader) that shows
the percentage of frames that have been downloaded.
1. Open preloader1.fla in the Lesson16/Assets folder.
This project contains two scenes: Preloader and Content. The Content scene
simply contains several layers of graphics and animation that demonstrate how the
preloader works. The Content scene also contains a frame label named Start that
plays an important role in the end result of the project. All of our work in this
exercise takes place in the Preloader scene, which contains three layers:
Background, Preloader, and Actions. The Background layer contains a square with
a radial gradient. The Actions layer contains a stop() action to prevent the timeline
from moving forward until we instruct it to do so. The Preloader scene contains
two elements—a text label containing the text "now loading…" and a movie clip
instance named preloader_mc, which includes the elements that show the
downloading progress. We'll add script to this instance's timeline, so let's take a
closer look at it.
2. Double-click the preloader_mc movie clip instance to edit it in place.
This movie clip's timeline consists of four layers named according to their
contents. The most important aspects of this timeline are the text field named
info_txt, which resides on the Text layer, and the tweened animation on the
Amount layer. The text field dynamically displays the percentage of frames that
have downloaded. The tweened animation represents a 100-frame progress bar
that begins at 0 percent and ends at 100 percent. Among other things, our script
moves this movie's timeline to the appropriate frame number based on the
percentage of frames that have been downloaded, and the progress bar moves
accordingly.
3. With the Actions panel open, select Frame 1 of the Actions layer and add the
following script:
4.
5. stop();
6.
7. onEnterFrame = function() {
8.
9. var framesLoaded = (Math.ceil (( _parent._framesloaded / _parent._totalframes)
* 100));
10.
11. gotoAndStop (framesLoaded);
12.
13. info_txt.text = framesLoaded + "% completed";
14.
15. if (framesLoaded >= 90) {
16.
17. _root.gotoAndPlay ("Start");
18.
19. }
20.
21. }
22.
The first action prevents the timeline from moving forward until we tell it to do so.
The second line attaches an onEnterFrame event handler to the preloader clip. As a
result, the script within the event handler is executed 24 times a second, which
means that it instantly reacts to the current downloading conditions to display the
most accurate representation of the process.
This script determines a percentage value for the number of frames that have
downloaded. It then rounds up that number and assigns the resulting value to the
framesLoaded variable. Using precedence, the expression employed to do this
work is evaluated in the following manner:
_parent._framesloaded /_parent._totalframes
With this part of the expression, the number of frames on the main timeline that
have loaded is divided by the total number of frames on the main timeline.
NOTE
Because this script is within the preloader movie clip instance and the instance
resides on the main timeline, the use of _parent as the target path is a reference to
the main timeline. This setup allows the preloader clip to be used (and function
properly) without modification in any project.
For demonstration purposes, let's assume that the movie has 735 frames, 259 of
which have loaded. The expression would look like this:
259 / 735
This would result in a value of .3523. The next part of the expression multiplies
that result by 100:
* 100
This would result in a value of 35.23. Finally, using the Math.ceil() method, this
value is rounded up to the next whole number, 36—and thus framesLoaded is
assigned a value of 36. Remember that because this script is executed 24 times per
second, the value of framesLoaded increases as the movie is downloaded.
TIP
The _framesloaded and _totalframes properties used in this script can be replaced
with the getBytesLoaded() and getByteTotals() methods of the MovieClip class if
