3.4 Handling slider change events in flex 3 and flex 4  (Page 7/9)

An Image control

The Flex 3 documentation tells us:

The Image control lets you import JPEG, PNG, GIF, and SWF files at runtime. You can also embed any of these files and SVG files at compile timeby using @Embed(source='filename').

The primary output that is produced by compiling a Flex application is an swf file that can be executed in Flash Player.

The documentation goes on to explain that by using @Embed , you can cause resources such as images to be embedded in the swf file.

The advantage to embedding is that embedding the resource eliminates the requirement to distribute the resource files along with the swf files. Thedisadvantage is that it causes the swf file to be larger.

Import an image

Listing 4 imports an image from the file named myimage.jpg that is located in the src folder of the project tree. This image is embedded in the swf file when the Flex application is compiled.

The id property

Setting the id property on the image to myimg makes it possible to refer to the image in the change-event code in Listing 3.

(Note that there is no requirement to set the value of the id property to be the same as the name of the image file as was done in Listing 4.)

The height property

Setting the height property of the image to 250 pixels in Listing 4 causes the image height to be 250 pixels when it is first displayed as shown inFigure 1.

The end of the application

Listing 4 contains the closing tag for the Application element signaling the end of the Flex 3 application named SliderChangeEvent01 .

The hybrid Flex3-4 project named SliderChangeEvent02

The mxml project code

The mxml code for this project is shown in its entirety in Listing 7.

If you examine this code you will see that:

• It uses a Flex 4 spark s:Application element instead of a Flex 3 mx:Application element.
• It declares the standard set of Flex 4 namespaces.
• It uses a spark s:VGroup element as the container for the following Flex 3 components. (Note that the Flex 3 project in Listing 6 doesn't require another container in addition to the mx:Application container.) :
  • mx:Label
  • mx:Label
  • mx:HSlider
  • mx:Image

Otherwise, the mxml code for this project is the same as the code for the Flex 3 project shown in Listing 6. The mixture of spark and mx componentscauses this to be a hybrid Flex 3-4 project.

Visual appearance of the project

If you run the online version of the project named SliderChangeEvent02 , you should see an initial screen display similar to Figure 7.

Figure

Browser image at startup for the hybrid project.

Compare with the Flex 3 project

By comparing this screen output for the hybrid project with the screen output for the Flex 3 project in Figure 1, you can immediately spot several significantdifferences:

• The background is white instead of gray.
• The labels, the slider, and the image are not centered horizontally in the browser window.
• The appearance of the thumb on the slider is a circle instead of a triangle.