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Adding objects to the stage and changing parents with the addChild method

From: ActionScript 3.0 in Flash Professional CS5 Essential Training

Video: Adding objects to the stage and changing parents with the addChild method

Placing objects on the Stage is an essential skill when working with AS3 in Flash Professional. Sometimes, however, you will want to move an object into a different container once you have already placed it in one. For example, here I'm creating a trashcan from the library and placing it on the Stage. I'm adding it as a child object of the Stage. But what if I started creating more of these trashcans? For example, I could copy and paste this code, change the name of can, to can1 and change the position of the can to 677 pixels.

Adding objects to the stage and changing parents with the addChild method

Placing objects on the Stage is an essential skill when working with AS3 in Flash Professional. Sometimes, however, you will want to move an object into a different container once you have already placed it in one. For example, here I'm creating a trashcan from the library and placing it on the Stage. I'm adding it as a child object of the Stage. But what if I started creating more of these trashcans? For example, I could copy and paste this code, change the name of can, to can1 and change the position of the can to 677 pixels.

So I test the movie, and I have two cans. What if I'm going to have many cans, like a hundred cans? It might make sense to start placing them inside of a container. Let's take a look at how to do that. Above all this code, I'm going to create a new variable. I'm going to call this 'container.' I'm going to datatype it to a sprite. Now a sprite might be a new concept to you, but it's actually, fairly simple. Think of a sprite as a movie clip with only one frame. That's all there is to it.

It's a movie clip, but it takes up less memory in the Flash Player. It's also ActionScript only. So, I'm going to create a new sprite here. So container, datatype it to a sprite. Space, equals, space, new, space, Sprite, with a capital S. Some open and close parenthesis and a semicolon. So that creates a new, empty sprite, which is basically like an empty movie clip. So, now what I'll do is I will place the container on the Stage. So I'll use the addChild method.

Remember that if you forget to use the addChild method, you'll never see your object on the Stage. Creating a new instance of an object simply creates it in memory. addChild is what allows you to see the object, so you need to put it in some sort of Timeline. So, I'm going to add the container to the Stage, and then I'm going to set this container's x and y equal to 577 for x, and container.y = 493.

Notice that they are the same coordinates that I used for the original trashcan. Now I'm going to delete the coordinates for the original trashcan, and I'm going to delete the coordinates for can1. Now let's test the movie. So I can't see the sprite container, but it's in this area over here. It's invisible because it's an empty container, with nothing inside of it. I do see the trashcans at the left of the Stage. Now, if I want to put the trashcans inside of the container, all I have to do is have the container be the one that's adding the child, instead of the main Timeline.

So, right before addChild(can), I can type container.addChild(can). So I can do that in both instances. For the second can, which is can1, I'll set its x-position to 100, can1.x =100. Remember these coordinates are going to be relative to the container object. So a 0,0 position will start at the container's x and y position. So test the movie, and there are the trashcans.

The thing that's great about this is when I move the container, I can also move the trashcans. So at the bottom of my code, let's say I want to move the container 100 pixels to the left, I could type container.x -=. This is a shorthand way of subtracting a value from its current position, = 100. So, it's going to take the position of the container and shift it 100 pixels to the left. So test the movie, and you can see the container is all the way over there.

For a more dramatic effect, I'll put in 500. The trashcans are over there. So this is an easy way to stay organized because I can move all of my trashcans at the same pace, because they're in the same container. Now there is one more thing I want to look at. You can actually reparent a child object if you've already added it to the Stage. So let's take this code, container.addChild (can1), and copy and paste it a few lines down. I'm going to temporarily disable the line of code that I pasted by pressing two forward slashes at the beginning of the line.

So, it'll turn gray, and Flash will not process that code. I'm going to erase container.before addChild, and then we'll test the movie. So can1 is 100 pixels from the left edge of the Stage, and it is now a child of the main Timeline, unlike the original can that's a child of the container movie clip, which you can tell because it's at the bottom-right of the Stage. Now if I uncomment this line of code and Flash processes it, you'll see that the can goes from being a child of the main Timeline to being a child of the container.

So test the movie, and now the second can is a child of the container. Notice that we don't see it move from the one place to another because all this code is processed before the frame is drawn. So if you ever need to, you can reparent a child object to another parent by simply calling the new parent's addChild method and passing in the new child object. So to recap, the addChild method allows you to place a display object, or any other visual object, inside of a display object container.

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This video is part of

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  1. 3m 22s
    1. Welcome
      1m 23s
    2. Using the exercise files
      1m 17s
    3. Using the function keys
      42s
  2. 23m 38s
    1. Adjusting preferences for ActionScript fonts, colors, and formatting
      3m 25s
    2. Changing Flash Player and ActionScript versions in the Publish settings
      1m 35s
    3. Reading and solving errors through the Compiler Errors window
      2m 49s
    4. Using the Actions panel buttons to add and remove comments
      2m 33s
    5. Using the Actions panel to format code
      1m 49s
    6. Using the Actions panel Toolbox
      2m 4s
    7. Seldom-used but helpful functions of the Actions panel
      3m 14s
    8. Understanding code hinting
      2m 3s
    9. Reviewing the Code Snippets panel
      3m 7s
    10. Using help
      59s
  3. 45m 50s
    1. Understanding how ActionScript 3.0 code is processed in the Flash Player
      3m 22s
    2. Understanding variables
      4m 56s
    3. Understanding functions
      9m 1s
    4. Understanding events and event listeners
      5m 47s
    5. Working with conditional statements
      9m 49s
    6. Creating arrays and vectors
      6m 50s
    7. Using the For command to create a loop
      6m 5s
  4. 49m 9s
    1. Reviewing the display list
      3m 0s
    2. Understanding instances referenced through ActionScript
      2m 27s
    3. Using dot syntax to modify properties in an instance
      3m 25s
    4. Placing objects at the center of the stage
      4m 2s
    5. Placing objects at the edges of the stage
      5m 53s
    6. Using the methods of an instance
      3m 44s
    7. Accessing the parents, children, and grandchildren of objects
      5m 50s
    8. Creating instances from Library movie clips using ActionScript
      4m 23s
    9. Adding objects to the stage and changing parents with the addChild method
      5m 45s
    10. Removing objects from the stage with the removeChild method
      4m 17s
    11. Using the numChildren property to loop through a container's child objects
      3m 17s
    12. Using the getChildByName method
      3m 6s
  5. 56m 20s
    1. Understanding timelines
      4m 15s
    2. Using common timeline navigation methods
      5m 34s
    3. Using the currentFrame and totalFrames properties
      8m 2s
    4. Controlling the timeline of an instance
      6m 41s
    5. Detecting and navigating frame labels with ActionScript
      7m 57s
    6. Solving problems when timelines and ActionScript animation collide
      4m 16s
    7. Condensing a multi-frame timeline into one frame
      8m 33s
    8. Creating a simple slide presentation app in the timeline
      7m 51s
    9. Using one event handler with multiple buttons
      3m 11s
  6. 36m 5s
    1. Creating a class using Flash templates
      4m 43s
    2. Setting a document class
      6m 51s
    3. Preparing a class to be connected to a symbol
      4m 31s
    4. Using the Symbol Properties menu to connect a symbol to a class
      4m 55s
    5. Resolving problems with instances in a linked class
      7m 53s
    6. Understanding packages
      3m 17s
    7. Working with ActionScript source paths
      3m 55s
  7. 44m 32s
    1. Viewing the finished game
      51s
    2. Viewing the FLA file
      2m 9s
    3. Creating the DragDrop and Map classes
      2m 51s
    4. Linking the draggable class to Library symbols
      2m 47s
    5. Adding drag-and-drop functionality
      3m 38s
    6. Saving and resetting an object's position
      3m 33s
    7. Giving a target drop object to the draggable objects
      13m 16s
    8. Showing a Win screen
      7m 3s
    9. Resetting the game
      8m 24s
  8. 29m 6s
    1. Loading bitmap images from the Library
      4m 6s
    2. Loading bitmap images from external files
      5m 22s
    3. Adding mouse functionality to bitmap images
      3m 31s
    4. Using a loop to load multiple images
      6m 14s
    5. Creating a simple slideshow
      8m 37s
    6. Using Flash Player 10 color management
      1m 16s
  9. 27m 13s
    1. Loading an external SWF
      4m 14s
    2. Running ActionScript code in an external SWF from its parent
      5m 30s
    3. Running parent code in a child SWF
      5m 7s
    4. Creating a timeline-based preloader to load an external SWF file
      5m 3s
    5. Displaying playback progress of a loaded SWF file
      7m 19s
  10. 40m 10s
    1. Creating plain text files
      2m 8s
    2. Loading text from an external text file
      6m 26s
    3. Loading multiple text files
      6m 43s
    4. Rendering simple HTML in a text field
      5m 51s
    5. Creating a scroll bar for a text field
      5m 29s
    6. Scrolling a text field
      4m 59s
    7. Scrolling movie clips and other objects using masks
      5m 42s
    8. Modifying TLF text properties through ActionScript
      2m 52s
  11. 23m 40s
    1. Reviewing XML and E4X syntax
      3m 29s
    2. Loading an XML file
      3m 26s
    3. Using dot syntax to access XML data
      4m 2s
    4. Using XML data to populate a DataGrid component
      7m 4s
    5. Using XML data to load image files
      5m 39s
  12. 23m 33s
    1. Loading audio from the Library
      1m 41s
    2. Loading audio from external files
      3m 41s
    3. Playing, pausing, and stopping sounds
      5m 39s
    4. Muting all audio with the SoundMixer.stopAll method
      1m 28s
    5. Tracking load progress
      2m 38s
    6. Displaying sound position
      5m 5s
    7. Adjusting volume
      3m 21s
  13. 19m 54s
    1. Touring the FLA file
      5m 57s
    2. Controlling video playing and pausing with ActionScript
      1m 56s
    3. Working with ActionScript cue points to add closed captioning
      3m 35s
    4. Displaying video playback position
      3m 44s
    5. Adjusting video volume
      4m 42s
  14. 5m 32s
    1. Using new code snippets for AIR and mobile
      1m 13s
    2. Viewing the new code snippets HUD
      1m 17s
    3. Loading assets with the new ProLoader class
      1m 8s
    4. Understanding Flash Player premium features
      1m 54s
  15. 16s
    1. Goodbye
      16s

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