Problem:

You want to draw a square programmatically using Actionscript's drawing API.

Solution:

1. Create an user interface that allows to user to specify the following attributes for the square: x, y, width, height, line width, line color, and fill color. We will use numeric steppers and color pickers to ensure the attributes are entered in the correct format.

   <mx:HBox width="100%" height="100%">

   <mx:VBox paddingLeft="10">

   <mx:Label text="Box Attributes:" fontWeight="bold"/>
   <mx:Label text="x:"/>
   <mx:NumericStepper id="x_ns" value="50" maximum="{drawing_cvs.width}"/>
   <mx:Label text="y:"/>
   <mx:NumericStepper id="y_ns" value="50" maximum="{drawing_cvs.height}"/>
   <mx:Label text="width:" />
   <mx:NumericStepper id="width_ns" value="50" maximum="{drawing_cvs.width}"/>
   <mx:Label text="height:" />
   <mx:NumericStepper id="height_ns" value="50" maximum="{drawing_cvs.height}"/>
   <mx:Label text="line width:" />
   <mx:NumericStepper id="lineWidth_ns" value="1"/>
   <mx:Label text="line color:" />
   <mx:ColorPicker id="line_cp" selectedColor="#000000"/>
   <mx:Label text="fill color:" />
   <mx:ColorPicker id="fill_cp" selectedColor="#FFFFFF"/>
   <mx:Button label="Draw" click="drawBox()"/>

   </mx:VBox>
   <mx:VBox width="100%" height="100%">

   <mx:Label text="Drawing Area:" fontWeight="bold"/>
   <mx:Canvas id="drawing_cvs" backgroundColor="#FFFFFF" width="500" height="500"/>

   </mx:VBox>

   </mx:HBox>

2. Write the drawBox function that will create a new Shape and empty UIComponent, use the graphics object of the shape to draw a rectangle, and then attach it to our drawing_cvs canvas.
   

   import mx.containers.GridRow;
   import mx.core.UIComponent;
   private function drawBox():void{

   var aBox:Shape = new Shape();
   var c:UIComponent = new UIComponent();

   aBox.graphics.lineStyle(lineWidth_ns.value, line_cp.selectedColor);
   aBox.graphics.beginFill(fill_cp.selectedColor, 1);

   aBox.graphics.drawRect(x_ns.value, y_ns.value, width_ns.value, height_ns.value);
   aBox.graphics.endFill();
   c.addChild(aBox);
   drawing_cvs.addChild(c);

   }

3. Viola!

The source files for this example are attached to this post. On a side note, the UIComponent that holds the Shape could've also been attached to another type of UI element like an image or HTMLControl just to name a couple instead of a Canvas object.