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Seminar 4. Using Symbols in a Movie > What’s So Important About Symbols and Ins...

What’s So Important About Symbols and Instances?

To use Macromedia Flash MX to its fullest extent, you have to use symbols and instances of those symbols in your movie’s development. This seminar introduces symbols and how to create instances for your movie’s content. Symbols are your first challenge in Flash. If you use them effectively, your movie will be more interactive and rich, ensuring the end-user a very intuitive and fun Internet experience.

Much of the power of Macromedia Flash MX comes from the use of symbols. A symbol is a reusable object in Flash MX. It can be any graphic, picture file, sound file, button, video clip, or movie clip that you create or import into your movie. Each symbol is a complete description of the item, which includes its size, shape, color, and behavior. When you place a symbol on the Stage, an instance of the symbol is created. You can use as many instances of a symbol in your movie as you need. When the Flash MX file is viewed in a browser, the symbol is downloaded to the browser just once and is reused many times as the Flash MX movie plays. This reduces the file size of the SWF file when the movie is exported.

When you create the symbols to be used in your movie, they are stored in the movie’s library (see Figure 4.1).

Figure 4.1. Each Flash MX file has its own library, which is basically an area for grouping and storing symbols for use in a movie, accessible at any time.

Typical of a public library, the Flash MX library can hold many symbols and can have these symbols grouped in folders to create common classifications for easy access. Open a movie’s library by selecting Window, Library.


Any time you plan to use a movie object more than one time, you should convert it to a symbol.

You also can open libraries from other Macromedia Flash MX movies and use symbols from them. Just as every movie has one color palette, every movie has just one library. When you use a symbol from another movie’s library, that symbol automatically becomes a symbol in your movie’s library. Thus, it becomes an asset of your movie.

Recycling Objects: The Power of Macromedia Flash MX

After a symbol is created, it can be used in the movie as an instance. An instance is really just a copy of the symbol that points to the original symbol. This causes every instance to be very small in memory because it’s a reference or pointer to the symbol that contains all the information on the item’s composition. You can use instances as many times as you need to in a movie, which results in very efficient memory usage because the instance is just an occurrence of the original symbol.


You can modify an instance in its size, color, brightness, and alpha setting. These modifications do not change the linked symbol—just the instance.

Symbol and Instance Basics

To understand this concept of symbols and instances, let’s look at a basic shape, such as a square. Rectangles and squares are often used in a Web site design for background images, buttons, and menu bars. Relating this to a symbol, if you make a rectangular symbol, you can then reuse this symbol by creating instances of it on your Stage. Every time you place an instance of it on the Stage, you are really just placing a pointer to the symbol. Remember: Flash MX is a vector-based application; therefore, Stage objects are translated into a mathematical formula. The instance is a pointer, which means it’s a mathematical translation of x and y coordinates on the Stage that calls the symbol. Instances can be modified in their sizes, locations, and color compositions. So, even though you have a black square symbol, the instance of the symbol can be modified to any color rectangular shape. Figure 4.2 shows an example of using a square symbol in a Web site design.

Figure 4.2. Each rectangle seen on the Stage in this figure is simply a modified instance of the square from the movie’s library.

To add an instance of a symbol to your Stage, you simply click and drag the symbol from the Library onto the Stage. An instance of the symbol appears, which you can then position in the location that you want on the Stage. By doing so, you create a new instance of this symbol, which is linked to the symbol in the library. Therefore, if you change this library symbol, the linked instance also changes.


If you edit a symbol and change any of its attributes, all instances of the symbol will reflect the new attributes but will maintain any modifications that you might have made to the instance. You will learn more about modifying instances later in this seminar.

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