ca.weblite.codename1.js

Class JavascriptContext

java.lang.Object

ca.weblite.codename1.js.JavascriptContext

public class JavascriptContext
extends java.lang.Object

Represents a Javascript context of a single BrowserComponent. This provides support for executing Javascript in the BrowserComponent, registering Java callbacks to allow Javascript to call Java functions, and returning values from Javascript to Java.

Typically you would obtain a context for a BrowserComponent via its constructor, passing the BrowserComponent to the context.

E.g.

 WebBrowser b = new WebBrowser();
 BrowserComponent bc = (BrowserComponent)b.getInternal();
 JavascriptContext ctx = new JavascriptContext(bc);
 JSObject window = (JSObject)ctx.get("window");
 

Field Summary

Fields

Modifier and Type	Field and Description
static boolean	DEBUG Flag to enable/disable logging to a debug log.

Constructor Summary

Constructors

Constructor and Description
JavascriptContext(com.codename1.ui.BrowserComponent c) Creates a Javascript context for the given BrowserComponent.

Method Summary

Methods

Modifier and Type	Method and Description
java.lang.Object	call(JSObject func, JSObject self, java.lang.Object[] params) Calls a Javascript function (encapsulated in a JSObject) with a specified Javascript Object as the "this" context for the function call.
java.lang.Object	call(java.lang.String jsFunc, JSObject self, java.lang.Object[] params) Calls a Javascript function with the given parameters.
java.lang.Object	get(java.lang.String javascript) Executes a javascript string and returns the result of the execution as an appropriate object value depending on the type of value that was returned.
void	set(java.lang.String key, java.lang.Object value) Sets a Javascript value given a compatible Java object value.
void	setBrowserComponent(com.codename1.ui.BrowserComponent c) Sets the BrowserComponent on which this javascript context runs.

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

DEBUG

public static boolean DEBUG

Flag to enable/disable logging to a debug log.

Constructor Detail

JavascriptContext

public JavascriptContext(com.codename1.ui.BrowserComponent c)

Creates a Javascript context for the given BrowserComponent.

Parameters:

c -

Method Detail

setBrowserComponent

public final void setBrowserComponent(com.codename1.ui.BrowserComponent c)

Sets the BrowserComponent on which this javascript context runs.

Parameters:

c - The BrowserComponent on which the context runs.

get

public java.lang.Object get(java.lang.String javascript)

Executes a javascript string and returns the result of the execution as an appropriate object value depending on the type of value that was returned.

Return value types will depend on the Javascript type returned. The following table shows the mappings:

Javascript Type	Java Return Type
Number	java.lang.Double
String	java.lang.String
Boolean	java.lang.Boolean
Object	JSObject
Function	JSObject
null	null
undefined	null

Example

 //Get the window object
 JSObject window = (JSObject)ctx.get("window");
 
 // Create a new empty Javascript Object
 JSObject newObj = (JSObject)ctx.get("{}");
 
 // Get the current document body contents as a string.
 String html = (String)ctx.get("document.body.innerHTML");
 
 // Get a numerical result
 Double result = (Double)ctx.get("1+2");
 
 // Get a Javascript function object
 JSObject func = (JSObject)ctx.get("function(a,b){ return a+b }");
 
 // Get a boolean result
 Boolean res = (Boolean)ctx.get("1 < 2");
 

Parameters:

javascript - The javascript to be executed.

Returns:

The result of the javascript expression.

set

public void set(java.lang.String key,
       java.lang.Object value)

Sets a Javascript value given a compatible Java object value. This is an abstraction upon javascript to execute key = value.

The key is any Javascript expression whose result can be assigned. The value is a Java object that will be converted into a Javascript object as follows:

Java type	Converted to
Double	Number
Integer	Number
Float	Number
Long	Number
String	String
JSObject	Object by ref
null	null

Hence if you want to set a Javascript string value, you can just pass a Java string into this method and it will be converted.

JSObject "By Ref"

You may notice that if you pass a JSObject as the value parameter, the table above indicates that it is passed by reference. A JSObject merely stores a reference to a Javascript object from a lookup table in the Javascript runtime environment. It is this lookup that is ultimately assigned to the "key" when you pass a JSObject as the value. This has the effect of setting the actual Javascript Object to this value, which is effectively a pass-by-reference scenario.

Examples

 // Set the window.location.href to a new URL
 ctx.set("window.location.href", "http://google.com");
 
 // Create a new JSObject, and set it as a property of another JSObject
 JSObject camera = (JSObject)ctx.get("{}");
 ctx.set("window.camera", camera);
 
 // Set the name of the camera via JSObject.set()
 camera.set("name", "My Camera");
 
 // Get the camera's name via Javascript
 String cameraName = (String)ctx.get("window.camera.name");
     // Should be "My Camera"
 
 // Set the camera name via context.set()
 ctx.set("camera.name", "New name");
 
 String newName = (String)camera.get("name");
     // Should be "New name"
 
 

Parameters:

key - A javascript expression whose result is being assigned the value.

value - The object or value that is being assigned to the Javascript variable on the left.

call

public java.lang.Object call(JSObject func,
                    JSObject self,
                    java.lang.Object[] params)

Calls a Javascript function (encapsulated in a JSObject) with a specified Javascript Object as the "this" context for the function call. Also passes a set of arguments to the method.

This operates almost exactly like the Javascript Function.apply() method.

Note that JSObject also has a couple of call() methods that may be more convenient to use as they will automatically set the "self" parameter to the JSObject callee. This version of the method is handy in cases where you have been passed a function (perhaps as a callback) and you need to execute that function in a particular context.

Example

 // Get the Array.push method as an object
 JSObject push = (JSObject)ctx.get("Array.prototype.push");
 
 // Create a new array
 JSObject colors = (JSObject)ctx.get("['red', 'green', 'blue']");
 
 // "Push" a new color onto the array directly using the JSObject's call()
 // method
 colors.call("push", "purple");
 
 // Alternate method using JavascriptContext.call()
 ctx.call(push, colors, "orange");
 
 // Check size of colors array now
 Double size = (Double)colors.get("length");
     // Should be 5.0
 
 // Get 4th color (should be purple)
 String purple = (String)colors.get(3);
 
 // Get 5th color (should be orange)
 String orange = (String)colors.get(4);
 

Parameters:

func - The Javascript function object that is being called.

self - Javascript Object that should act as "this" for the function call.

params - The parameters that should be passed to the function. These parameters should be passed as Java objects but will be converted into their associated Javascript version.

Returns:

The result of the function call. Javascript results will be automatically converted to their associated Java types.

call

public java.lang.Object call(java.lang.String jsFunc,
                    JSObject self,
                    java.lang.Object[] params)

Calls a Javascript function with the given parameters. This would translate roughly into executing the following javascript: jsFunc.call(self, param1, param1, ..., paramn)

Parameters:

jsFunc - A javascript expression that resolves to a function object that is to be called.

self - The Javascript object that is used as "this" for the method call.

params - Array of the Javascript parameters, as Java objects. These use the same conversions as are described in the docs for set().

Returns:

Returns the return value converted to the corresponding Java object type.