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Using the For command to create a loop

From: ActionScript 3.0 in Flash Professional CS5 Essential Training

Video: Using the For command to create a loop

Sometimes you will want to run the same block of code many times, with little variation. For example, let's say you have a slideshow with a hundred images, and you need to load and place all of the thumbnails. It would be very tedious to copy and paste the loading and placing code 100 times. So to save time, and to be more organized, you can use a loop and write the code only once, and have it repeat itself a hundred times. What we're going to do here is use a loop to place the trashcans on the stage.

Using the For command to create a loop

Sometimes you will want to run the same block of code many times, with little variation. For example, let's say you have a slideshow with a hundred images, and you need to load and place all of the thumbnails. It would be very tedious to copy and paste the loading and placing code 100 times. So to save time, and to be more organized, you can use a loop and write the code only once, and have it repeat itself a hundred times. What we're going to do here is use a loop to place the trashcans on the stage.

I'm going to align the trashcans to the Y position of the second trashcan. If you don't have access to the exercise files, just create nine instances of any movie clip and name them can1_mc, can2 _mc, et cetera, all the way through can9_mc. Let's go to the first keyframe of the actions layer and open the Actions panel. Here I've added all these cans to a trashCans array.

Note that these values are not in quotes, because they are referring to instances on the stage. Now let's take a look at writing a loop to modify the position of each of these objects. Type the word 'for' some parentheses and some curly braces. Notice the parentheses and curly braces are becoming common. We use them for functions, for the if statements, switch/case statements, and for this for loop here. So inside of the parentheses, type var space i, lowercase, colon, uint, u-i-n-t.

This is another data type that starts with a lowercase letter. Set that = 0. By the way, uint is a positive integer, so a whole number, 0 and above. Semicolon after that 0; and i, less than. This is going to run nine times, once for each of the trashcans, a semicolon, and then i++.

Let's walk through what this line of code does. These three different sections of the loop specify different things. The first part is called the iterator variable. This is going to be a variable that we'll use inside of the loop. So we declare the variable, just like any other variable. We call it i for iterator, but it could be anything you want. Declare the datatype as a positive integer and set the value = 0.

That's a starting value for the loop. You can set it to any value you want, but most of the time it's going to be zero. The next part refers to how many times the loop will run. The loop will run as long as i < 9. Finally, you explain what will happen after each time the loop runs. i++ means to increment I by 1 or add 1 to it each time the loop runs. So just to see the loop in action, type 'trace' inside of the loop and in the parentheses for the trace statement, just type i. Make sure not to put it in quotes.

So if you test the movie and take a look in the Output window, you'll see the numbers 0 through 8. Let's go back to the code, and that corresponds to an index of the array, or at least we can tell Flash to make that correspond to an index of the array. So what we'll do is erase the trace statement and place the trashcans. To do that, we'll reference the trashcans through the array.

So type trashCans, index i, which means you put i inside of square brackets, so that's referring to a trashcan each time, and then type .y. That refers to the vertical position of the object. And we'll set that = can2_mc.y; so we're aligning each object to the Y position of can2_mc.

So let's test the movie and see the code in action. Now, all the trashcans are aligned. Remember, if you look at the stage, they're not aligned. So you can use a loop to do that. And the great thing about it is it doesn't matter if we have 9 trashcans or 10,000 trashcans; modifying this code is as simple as modifying that number. Finally, if you really want to optimize this code and have it update based on the size of the array, you can change the 9 value to be the length of the array, or how many items are in the array. So change that to trashCans.length.

Again, that refers to the number of items that are inside of the array, which right now is nine. That way if you ever change the array, you won't have to update the for loop. To test the movie again, show that it's working. Now, if I were to click and drag and erase, let's say almost all of the cans inside of the array, so I only have three cans now, if I test the movie, then only the first three cans will be aligned, so I don't have to update the loop. So this is a pretty a simple example, but you can see how a loop can save you so much time.

Using a for loop, you can perform the same block of code on every object in an array and save loads of time building your applications.

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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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