Understanding the ActionScript Language > About built-in objects > Using a built-in object |
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Using a built-in object
Some built-in Flash objects are top-level objects; you can use the methods and properties of a top-level object without creating a new instance of the object. For example, to use the methods and properties of the top-level Math object, you use the name of the built-in object followed by the method or property, as in the following:
area = Math.PI * radius * radius;
Other built-in objects, like the Date object, require you to create a new instance of the object to use its methods and properties. You use the new
operator with a constructor function to create an object. (A constructor function is a function that creates a new instance of an object.) The ActionScript built-in objects are prewritten constructor functions. When you create a new instance of a built-in object, all the properties and methods of that object are copied into the instance. This is similar to dragging a movie clip from the library to the Stage. For example, the following statement creates a new Date object called currentDate
and then calls the getMinutes
method:
currentDate = new Date(); currentMinute = currentDate.getMinutes();
In the following code, the object c
is created from the constructor Color
:
c = new Color(this);
Each object that requires a constructor function has a corresponding new
element in its folder in the Actions panelfor example, new Color
, new Date
, new String
, and so on.
You can also use the object initializer operator ({}
) to create an object of the generic type Object.
To create an object with the new
operator in normal mode:
1 |
Choose Window > Actions to open the Actions panel if it isn't already open. |
2 |
In the Actions toolbox (at the left of the panel), click the Actions folder to open it, then open the Variables folder. |
3 |
Double-click the |
4 |
Enter an identifier in the Variable box; this is the name of the new object. |
5 |
Click in the Value box to place the insertion point. Then browse in the Actions toolbox to the object you want to create, and double-click |
6 |
Select the Expression option next to the Value box. |
If you don't select the Expression option, the entire value will be a string literal. |
To use the object initializer operator ({}
) in normal mode:
1 |
Choose Window > Actions to open the Actions panel if it isn't already open. |
2 |
In the Actions toolbox, click the Actions folder to open it. Click the Variables folder to open it. |
3 |
Double-click the |
4 |
Enter an identifier in the Variable box; this is the name of the new object. |
5 |
Select the Expression option next to the Value box. |
6 |
In the Value box, enter the property name and value pairs separated by a colon inside the object initializer operator ( |
For example, in this statement the property names are radius
and area
and their values are 5 and the value of an expression:
myRadius = 5; myCircle = {radius: myRadius, area:(Math.PI * myRadius * myRadius)};
The parentheses cause the expression inside them to evaluate. The returned value is assigned to the variable area
.
You can also nest array and object initializers, as in this statement:
newObject = {name: "John Smith", projects: ["Flash", "Dreamweaver"]};
For more information on the Actions panel, see Writing Scripts with ActionScript. For detailed information on each object, see its entry in the ActionScript Dictionary.
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