Tài liệu Using Shared Objects docx

Take a look at the following example: myObject.data.userName = userName_txt.text; This would save the userName variable and its value, the text in the userName_txt text field in the shar

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Using Shared Objects

An SWF file can save data (variables as well as array, XML, and other data objects) to a user's hard drive using shared objects—similar to but more powerful than the cookies used by Web browsers You can use shared objects to store information generated by the user while viewing your movie (name, last frame visited, music preference, and so on) Shared objects can be used by movies played in a Web browser as well as those turned into stand-alone projectors

You can use shared objects with any of the following (for example):

• XML.load

• XML.sendAndLoad

• LoadVars.load

• LoadVars.sendAndLoad

• LoadVariables

• LoadVariablesNum

• XMLSocket.connect

• Importing a shared library

The following is an example of a script you might use to create a shared object:

var myObject:SharedObject = SharedObject.getLocal("stuff_I_saved");

If the shared object stuff_I_saved already exists on the user's hard drive, its data is loaded instantly into myObject If stuff_I_saved does not yet exist, it's created and still

referenced by myObject In the latter case, myObject would be empty—that is, it would contain no data

NOTE

If used as just mentioned, the getLocal() method will create a shared object if none exists,

or will retrieve data from an existing shared object

As you can see from the previous syntax, the shared object's name is actually

"stuff_I_saved"; however, in ActionScript you can't reference the shared object directly using that name Therefore, a reference to the shared object is created using myObject This means that whenever you reference myObject in a script, you're actually referencing the shared object named "stuff_I_saved"—a tricky concept but essential to understanding how ActionScript deals with shared objects

Data is saved to a shared object using the data property Take a look at the following example:

myObject.data.userName = userName_txt.text;

This would save the userName variable (and its value, the text in the userName_txt text field) in the shared object You can save entire objects as well For example, if you wanted to save an array contained by your project, you would use the following syntax:

myObject.data.savedArray = nameOfArray;

A single shared object can contain multiple bits of data simultaneously:

myObject.data.savedArray = nameOfArrayObject;

myObject.data.savedXML = nameOfXMLObject;

myObject.data.userName = userName_txt.text;

A particular piece of data can be erased from a shared object using null, as in the

following example:

myObject.data.userName = null;

If userName were a piece of data in the shared object, the preceding script would delete

it

You can delete an entire shared object by using the clear() method of the SharedObject class:

myObject.clear();

Extracting data from a shared object is similar to creating data in one:

userName_txt.text = myObject.data.userName;

In the userName_txt text field, the preceding script will display the value of userName in the shared object If this variable doesn't exist in the shared object, the value displayed in the text field will be undefined

When the SWF session ends (that is, the movie is closed or exited), all the information under the data property of your shared object is automatically written to the shared object file, ready to be retrieved using the getLocal() method described earlier You can force a shared object to be written and saved at any time by using the flush() method For

example:

myObject.flush();

This line of ActionScript forces your shared object and all the data it contains to be saved Because myObject references the shared object named "stuff_I_saved", this is the object that will actually be saved

Flash stores all shared objects in a central location on the user's hard drive—the exact location depends on where the movie resides that created the shared objects

On Windows XP, all shared objects are stored in the following general directory:

Documents and Settings\<username>\Application Data\Macromedia\Flash Player\

where <username> is the name of the user who was logged on when the shared object was created

On a Mac, the location is as follows:

System Folder\Preferences\Macromedia\Flash Player\

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Depending on the version of your operating system, the location of shared object files may vary somewhat To locate shared object files on your machine, search for files with

an sol extension

These are both general paths—that is, when a movie creates a shared object, a new subdirectory is created at one of the previously mentioned locations For example, if you were to view a movie at the following URL:

http://www.electrotank.com/fun/games/MiniGolf.swf

any shared object created by this movie would, by default, be saved at the following path

on a Windows machine:

Documents and Settings\<username>\Application Data\Macromedia\Flash

Player\electrotank.com\fun\games\MiniGolf

Notice how this subdirectory's path structure matches that of the URL

Because a movie played locally (such as a projector) doesn't exist at a URL, Flash will save shared objects that it creates to a localhost directory:

Documents and Settings\<username>\Application Data\Macromedia\Flash

Player\localhost

All these directory paths are default paths where shared object data is stored You

actually have a lot of latitude as to where a shared object is stored or retrieved from within the general directory Using the previous example, imagine playing a movie at the following URL:

http://www.electrotank.com/fun/games/MiniGolf.swf

This movie has the following shared object:

myScores = SharedObject.getLocal("scoreData");

This shared object is saved to the following path in Windows XP:

Documents and Settings\<username>\Application Data\Macromedia\Flash

Player\electrotank.com\fun\games\MiniGolf\scoreData.sol

Flash will look for this same location again when the movie is played from that URL; however, the getLocal() method lets you add an optional directory path where the shared object should be saved Assuming the movie at the aforementioned URL has this shared object declaration:

var myScores:SharedObject = SharedObject.getLocal("scoreData", "/fun");

the shared object would be saved to the following path:

Documents and Settings\<username>\Application Data\Macromedia\Flash

Player\electrotank.com\fun\scoreData.sol

Armed with this knowledge, you can create movies at different locations that use the same shared object—useful if you want all the movies on your site to reference a

"master" shared object containing information about the user Simply save a shared

object in the main (/) directory

Be careful when using a single shared object across movies Any one of the shared

objects has the potential of overwriting the data it contains with new data

A single movie can create, save, and load multiple shared objects simultaneously

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You can configure the amount of data that a given URL can store by using the Flash player If you right-click the window of an open SWF and select Settings, you'll see the Local Storage controls You can block any site from storing information on your

machine

In this exercise, you'll create a journal that saves text entries in an array as a shared

object

1 Open journal1.fla in the Lesson11/Assets folder

You will notice one frame with four layers, named according to their contents The stage contains two text fields that will be used to display information The large text field in the center, journalBody_txt, will be used for journal entries The smaller text field at the bottom of the screen, entryNumber_txt, will be used to

display the current journal entry number The Buttons layer contains the Prev, Next, New, and Save buttons, which have instance names of previous_btn,

next_btn, new_btn, and save_btn, respectively

This application will allow you to start a new journal entry, save it, and browse

through the entries you've created

2 With the Actions panel open, select Frame 1 in the Actions layer and then add the following script:

3

4 var myJournal:SharedObject = SharedObject.getLocal("JournalObject");

5

This line of ActionScript creates a reference to the shared object JournalObject This object can be read and modified using the myJournal reference set up here When using myJournal in the following scripts, we're actually working with the

shared object named JournalObject

3 Add the following conditional statement just below the line of script you added in Step 2:

4

5 if (myJournal.data.journal == undefined) {

6

7 myJournal.data.journal = [];

8

9 }

10

This statement looks in the shared object for an array named journal If it doesn't find one (undefined), the action within the statement creates the journal array NOTE

If an array is created, it automatically becomes part of the shared object when the movie is exited or the shared object is saved using the flush() method

The journal array will appear undefined the first time the movie is played Each subsequent time the movie is played, the array will exist and this action will be ignored

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It's a good idea to check for undefined data values in a shared object This allows you to assign default values the first time a movie is played by the user

4 Add the following function definition at the end of the current script:

5

6 function displayEntry(num:Number) {

7

8 var entry:String = myJournal.data.journal[num - 1];

9

10 if (entry != undefined) {

11

12 entryNumber_txt.text = num;

13

14 journalBody_txt.text = entry;

15

16 }

17

18 }

19

This function does two things: it sets the value of two text fields on the stage— entryNumber_txt and journalBody_txt—based on the value of num Then, a

conditional (if) statement is used to specify what should occur if the user has saved

an entry in the journal

As shown in Step 3, when the application is first used (as opposed to reopening it after adding an entry), an array named journal is created on the shared object By default, a new array object always has a length of 1, indicating that it contains a single value at index 0, which is initially a value of undefined The first time the application is used, myJournal.data.journal[0] contains a value of undefined This value doesn't change until the user deliberately saves an entry into that index number

In Step 5, we will script a call to this function:

displayEntry(myJournal.data.journal.length);

The first time the application is used, the length of the journal array will be 1; therefore, the function call will look like this:

displayEntry(1);

The first line in the displayEntry() function that we just defined uses the parameter value passed to it (in this case, 1) to set the value of entry That line of script gets evaluated this way:

entry = myJournal.data.journal[1 - 1]

or, broken down further:

entry = myJournal.data.journal[0]

As already mentioned, if the user has never saved a journal entry at index 0 (such

as the first time the application is used), entry is assigned a value of undefined; otherwise, it will contain the text of the first entry

The conditional (if) statement looks at the value of entry, and performs an action only if the value of entry is not undefined If entry has a value of undefined, the function does nothing and the entryNumber_txt and journalBody_txt text fields will be empty This only occurs when the user has never saved a journal entry After the user has saved at least one entry in the journal, the actions in the

conditional statement are executed

Assume that the user has saved nine entries and then reopens the application In this circumstance, the displayEntry() function we just defined will be called and passed a parameter value of 9:

displayEntry(9)

NOTE

This function call is added and explained a bit more in the next step

As a result, the value of entry, within the function, is assigned a value representing the text of the ninth entry in the journal (which is actually stored in index 8 of the journal array, as explained later in this lesson) This will cause the actions in the conditional statement to execute because entry is no longer undefined The first action displays the value of the number passed to the function in the

entryNumber_txt text field, which in this case is 9 The second action displays the value of entry in the journalBody_txt text field

The reason for subtracting 1 from the value of num, as shown in the first line of the function definition, is that the index (within the journal array) where each entry

is saved is always one less than its actual entry number Therefore, the fifth entry

is saved in index 4, the sixth entry in index 5, and so on The reason is that array indexes begin at 0, but we want our entry numbers to begin with 1; therefore, this conversion keeps them in sync Several of the scripts that follow employ similar

logic

This script is probably the trickiest to understand of the entire project Be sure to

review it several times until you feel comfortable with how it works

5 Add the following function call to the end of the current script:

6

7 displayEntry(myJournal.data.journal.length);

8

Because this function call exists on Frame 1, it's executed as soon as the movie plays The displayEntry() function (which was defined in Step 4) is called and passed a value based on the length value of the journal array in the shared object This will display the final entry that the user made before exiting the movie For example, if the journal array has three entries, the displayEntry() function is passed a value of 3 and the third journal entry is displayed If the journal array has just been created (as described in Step 3), it will contain a single, empty element;

therefore, a length of 1 gets sent to the function

6 Add the following function definition to handle saving data:

7

8 function save() {

9

10 var num:Number = Number(entryNumber_txt.text) - 1;

11

12 myJournal.data.journal[num] = journalBody_txt.text;

13

14 myJournal.data.flush();

15

16 }

17

As mentioned earlier in this lesson, data is automatically saved to a shared object when a movie is exited By using the flush() method, as shown here, you can save data at any time while the movie is playing This function will be called when the Save button is clicked (see Step 11) Let's take a look at how this function works

The first line in the function creates a variable named num The value of this variable is set to the current value displayed in the entryNumber_txt text field, minus 1 The Number() function is used to make sure num contains a numerical