WikiD Instructables

Introduction

Android has hundreds of thousands of functions which apps can use. It's not possible for Tasker to present all of those to the user, so Tasker allows the advanced user to directly call those Java functions and work with Java objects themselves.

It does not allow you to 'write Java code'... but the combination of Tasker's logic and flow control with direct access to the Android API is sufficient for most automation purposes.

This page assumes you have a basic familiarity with the Java concepts of objects and classes.

The Java Function Action

Using The Action

Parameters

If you don't enter a value for a parameter, null will be used for that parameter when the function is called.

If you enter the name of a variable array, Tasker will attempt to convert the array values into the type of object (an array or collection) which the function expects.

Other Tasker variables will be replaced in the usual way.

Here can also be entered Java objects, or their fields, either built-in or created by previous calls to Java Function (e.g. wiman or arr[0].length)

Return Values

When a Java function returns a value, it can be placed in either a Tasker variable or a Java object (or ignored).

If it's placed into a Tasker variable, it's converted to a piece of text and the object itself is lost and can no longer be accessed. Note that if the Java object is an array or list, it will be assigned to multiple Tasker variables in the usual way e.g. %val1, %val2...

When the returned value is placed into a Java object, you can access the object at a later time in another Java Function and some other (see later) actions.

Note that return value classes are inferred from the function, so object names can refer to different classes at different times. It's not recommended to reuse names in this way however!

Objects

Creating An Object

New objects of most types can be created by filling in the class name, hitting the function selector and selecting a function called new.

It's worth noting that many classes in the Android API have special static functions for getting a new object of that class called e.g. getInstance or similar.

Arrays (also multidimensional) can be created by adding [] to the class name (or e.g. [][]).

Here's an example of creating a 3x5 string array:

1. Java Function, arr = new String[][]( 3 )
2. For, %rowno, 0:2
3.    Java Function, arr[%rowno] = new String[]( 5 )

Creating an array is also possible natively via the newInstance function in the the class Array.

Object Naming, Local and Global

Analogous to Tasker variables, Java objects are either local to the current task if their name is all lower case, or global (available to any other task) if there are any upper-case characters in the name. All-upper-case names represent final (fixed) global objects which cannot be modified.

There are three important things to remember about global Java objects:

• it's important to delete them once they are no longer needed, because they can take up a lot of memory.
• unlike global Tasker variables, they are lost when Tasker is killed e.g. because the device was restarted
• their names can only contain upper- or lower-case letters or underscore.

Built-in Objects

• Android Context (class Context)
  CONTEXT
  Many funtions in Android require a context object. In tasks running directly as a result of a scene element event, this is the Activity object which is displaying the scene, otherwise it's Tasker's Application context.
• Image Buffer (class Bitmap)
  IBUFFER The object manipulated by functions in Tasker's Image action category.
  

Assigning Values

	String a = "hello";
	String b = a;

Now both a and b refer to the same object.

To achieve that in Tasker, you use the special assignTo function after selecting the object to assign.

	Java Function, a, "hello", assign (or a = "hello".assign())
	Java Function, b, a, assign (or b = a.assign())

Other Actions Supporting Objects

If

Examples:

	If, arr[0][0] eq 45
	If, arr[0].length > 3 
	If, lightlevel Equals null

You cannot make function calls e.g. str.charAt( 5 )

For

The Value parameter in the For action can include Java object references as for If.

	For, %value, arr

Will repeat once for each value in the array arr. This will also work for string lists and simple objects (boolean etc)

Other Topics

Casting

Casting in Tasker is used only to tell Tasker the type of a particular object. That can be useful so that e.g. Tasker can show functions which are appropriate to it.

In the example at the top of the page, the getSystemService function returns an Object:

	Java Function, wiman = CONTEXT.getSystemService( %service )

Since the object could be one of many kinds of managers, Tasker is not able to list the WifiManager functions for easy selection when creating the next Java Function action in the task.

You can tell Tasker the actual type by adding a cast in brackets before the name:

	Java Function, (WifiManager) wiman = CONTEXT.getSystemService( %service )

Constants

• L a long integer e.g. 300L
• F a floating-point number e.g. 45.6D
• D a double-length float e.g. 45.6D
• double quotes indicate a string e.g. "hello", though in many cases Tasker will infer that a string was intended anyway
• single quotes indicate a character e.g. 'x'

Tasker will attempt to convert numbers without affixes to a Java type in the following order: int, long, float, double.

Generic Classes

Create them by selecting their class in the class selector, clicking the function selector and clicking new.

Generic classes mixed with arrays cannot be handled by Tasker, though you can pass such objects around from function to function.

Permissions

For some function calls, Android requires that the calling app have declared a permission otherwise the call will fail. This means that a Java Function call will fail if the permission is not one of the ones pre-declared by Tasker.