Macromedia Flash: Symbol Types
Flash offers a way to simplify your work, called symbols. A symbol can be any object or combination of objects, animation, or a Web button. When you create a symbol, the objects (or animation) become one symbol. The difference is that Flash stores the definition of the symbol in the Library. From the library, you can now effortlessly insert multiple copies of the symbol into your movie. Each copy is called an instance.
Besides making your life easier when you want to use a set of objects more than once, symbols have another advantage: They significantly reduce the size of your files. Rather than store each instance you use, Flash stores one definition for the symbol and only refers to the definition each time you display an instance of the symbol. Turning a bunch of objects into a symbol helps reduce file size even when you use the symbol only once, because Flash remembers only one object rather than many. Backgrounds that aren't animated can therefore be combined into one symbol.
You can place symbols inside other symbols. Used this way, symbols are the building blocks for complex graphics and animation. Motion-tweened animation requires symbols, groups, or text, so you often create symbols when preparing to animate.
So, symbols are all-around good guys, and you should use them as much as possible.
Flash makes available three types of symbols. Each type is made up of a group of objects or animation, but each type has a different purpose. Understanding these types is very important to understanding symbols and Flash animation in general.
Using graphic symbols
Graphic symbols are the simplest and most obvious type of symbol. When you create a Flash movie, you create objects on the Stage. Some objects may remain still, such as backgrounds. You animate other objects — after all, what is Flash for? Use graphic symbols for collections of static objects or for animation.
You create graphic symbols to reduce the size of your file and to make it easier to add multiple copies of a graphic to your movie. Symbols are stored in the Library and are available to not only the movie in which you created them but also any other movie. Therefore, using symbols is a good way to store graphic images for use in Flash movies. You don't have to re-create the wheel.
Flash ignores sounds or actions inside graphic symbols. Actions are the key to creating interactive movies. For that reason, turn animation into graphic symbols only when the animation is simple. Graphic symbols are always placed on the main Timeline of the movie.
Using movie clip symbols
A movie clip is like a movie within a movie that you can manipulate by using interactive controls (also called actions, created with ActionScrip). Movie clips are crucial for complex animation and especially interactive animation. A movie clip doesn't take place on the main Timeline; instead, it has its own Timeline. For example, you can go to a movie clip at any time, play it, and then return to where you left off on the Timeline. You can also attach movie clips to buttons.
Flash comes with several components, special movie clips that allow you to add user interface elements — such as radio buttons, check boxes, and scroll bars — to your movies. Choose Window --> Components and drag one of your choices to the Stage. Then choose Window --> Component Parameters to set the parameters of the component. For example, you can insert a list box and then add all the items (called labels on the Component Parameters panel) you want on the list.
Using button symbols
Button symbols create buttons — those little graphics that you click in Web sites to take you to other places on the site or the Internet. In Flash, you can use buttons in the same way, but you can also use buttons to let viewers decide whether they want to see a movie — when they click the button, the movie starts. You can also use advanced scripting to create buttons that control interactive games and other viewer activities. However you want to use buttons, button symbols are the way to start. You can add movie clips and interactive controls to buttons.