Flash / Flex / ActionScript/Data Type/Variable Declare
Версия от 12:19, 26 мая 2010; (обсуждение)
Содержание
- 1 It is a good practice to initialize your variables to null when you don"t have any other specific value to assign to them
- 2 Once a variable has been declared, you can assign a value to it using a simple assignment statement with an equals sign
- 3 Overriding Variables
- 4 Perform operations using variables
- 5 To declare a variable using strong typing: var variableName:Datatype;
- 6 To declare the data type of a variable, use the colon operator right after the name of the variable.
- 7 Use the this keyword when referring to an instance variable with the same name as a function variable:
- 8 Using Access Controls
- 9 Using Untyped Variables with the Wildcard (*) Data Type
- 10 You can also declare the variable and assign a value, or initialize the variable, all on one line
- 11 You can declare several variables on a single line
It is a good practice to initialize your variables to null when you don"t have any other specific value to assign to them
<source lang="java">
package{
import flash.display.Sprite; public class Main extends Sprite{ public function Main(){ var myVariable:Number = null; trace(myVariable); var sMessage:String = "Welcome!"; trace(sMessage); } }
}
</source>
Once a variable has been declared, you can assign a value to it using a simple assignment statement with an equals sign
<source lang="java">
package{
import flash.display.Sprite; public class Main extends Sprite{ public function Main(){ var myVariable:Number; myVariable = 6; trace(myVariable); } }
}
</source>
Overriding Variables
<source lang="java">
objects defined in more localized scopes will always override objects defined in more global scopes. package{
import flash.display.Sprite; public class Main extends Sprite{ public function Main(){ var myLocal:Local = new Local(); trace(myLocal.a); // Displays: instance trace(myLocal.b); // Displays: instance myLocal.method(); // Displays: function } }
} class Local {
public var a:String = "instance"; public var b:String = "instance"; public function method():void { var a:String = "function"; b = "function"; trace(a); trace(b); }
}
</source>
Perform operations using variables
<source lang="java">
package{
import flash.display.Sprite; public class Main extends Sprite{ public function Main(){ var myVariable:Number = 6; var nPrice:Number = 9.99; trace(myVariable * nPrice); // Displays: 59.94 } }
}
</source>
To declare a variable using strong typing: var variableName:Datatype;
<source lang="java">
package{
import flash.display.Sprite; public class Main extends Sprite{ public function Main(){ var myVariable:Number; trace(myVariable); } }
}
</source>
To declare the data type of a variable, use the colon operator right after the name of the variable.
<source lang="java">
package{
import flash.display.Sprite; public class Main extends Sprite{ public function Main(){ var x:Number; var name:String = "Mims"; x = 42; // No problem x = -13; // No problem x = 3.141; // No problem } }
}
</source>
Use the this keyword when referring to an instance variable with the same name as a function variable:
<source lang="java">
package{
import flash.display.Sprite; public class Main extends Sprite{ var foo; public function Main(){
}public function setFoo (foo:String):void { this.foo = foo;
}
}
}
</source>
Using Access Controls
<source lang="java">
package{
import flash.display.Sprite; public class Main extends Sprite{ private var lunchtime:Date; public function Main(){ } }
}
</source>
Using Untyped Variables with the Wildcard (*) Data Type
<source lang="java">
package{
import flash.display.Sprite; public class Main extends Sprite{ public function Main(){ var x:*; x = 3; trace(x); x = "name"; trace(x); } }
}
</source>
You can also declare the variable and assign a value, or initialize the variable, all on one line
<source lang="java">
package{
import flash.display.Sprite; public class Main extends Sprite{ public function Main(){ var myVariable:Number = 6; trace(myVariable); } }
}
</source>
You can declare several variables on a single line
<source lang="java">
package{
import flash.display.Sprite; public class Main extends Sprite{ public function Main(){ var breakfast:String, lunch:String, dinner:String;
} }
}
</source>